Comprehensive Analysis of 13,897 Consecutive Regional Anesthetics at an Ambulatory Surgery Center

Comprehensive Analysis of 13,897 Consecutive Regional Anesthetics at an Ambulatory Surgery Center Abstract Objective The authors investigated a wide range of perioperative outcome measures in the context of a robust regional anesthesia practice. Design Comprehensive review of a prospectively collected six-year database. Setting Freestanding, academic ambulatory surgery center. Subjects There were 13,897 consecutive regional anesthetics in 10,338 patients. Methods We investigated patient satisfaction, postoperative nausea and vomiting (PONV), postoperative pain, catheter analgesia, and complications. Clinical risk factors were examined and presented as odds ratios for multiple outcome analyses including block success, patient satisfaction, PONV, and postoperative neurologic symptoms (PONS). Results Decreased block success was associated with nerve stimulation alone (P < 0.001), obesity (P = 0.001), higher American Society of Anesthesiologists classification (ASA; P = 0.01), lower extremity blocks (P = 0.04), and male sex (P < 0.001). Decreased patient satisfaction was associated with poor catheter analgesia (P < 0.001), complications (P < 0.001), higher ASA (P = 0.001), and younger age (P = 0.008). PONV was associated with postoperative pain (P < 0.005), female sex (P < 0.001), general anesthesia (P < 0.001), younger age (P = 0.001), lack of catheter (P = 0.03), and lack of dexamethasone/clonidine (D + C) adjuncts (P = 0.01). Serious complications and unexpected hospitalizations were rare (<0.2%). D + C adjuncts, lower extremity blocks, clonidine (but not dexamethasone alone), and female sex were associated with PONS (all P < 0.001). Conclusions A regional anesthesia–based practice in ambulatory surgery is an effective means of providing excellent postoperative analgesia and is associated with a low rate of PONV and unexpected admissions. Dexamethasone, clonidine, and their combination when combined with 0.5% ropivacaine may have mixed effects on PONS risk that warrant dose/concentration alterations of these three drugs in the context of off-label perineural adjunct use. Postoperative Pain, Regional Anesthesia, Ambulatory Surgery, Postoperative Nausea and Vomiting, Patient Satisfaction, Postoperative Neurological Symptoms Introduction Effective and safe perioperative pain management is of utmost importance to patients when considering elective surgical procedures [1]. A regional anesthesia and analgesia–based practice has emerged as a means to minimize perioperative pain and opioid side effects while maximizing patient satisfaction; in fact, postoperative nausea and vomiting (PONV) was the leading complaint in one large study, emphasizing the need for techniques that minimize this complication [2]. Although ultrasound-guided regional anesthesia has imparted benefits including reduced procedure times, onset times, failure rates, and local anesthetic systemic toxicity (LAST) rates, risks such as postoperative neurologic symptoms (PONS; persistent sensory block, motor block, and/or dysesthesias beyond 72 hours following block placement or beyond 48 hours after cessation of catheter infusions) [3] and catheter site infection continue to be described in the literature [4–9]. As part of a quality assurance project, we prospectively collected outcome data on all patients at the Nashville Surgery Center over a six-year period from 2008 until 2014 who underwent operations with regional anesthesia alone or combined with general anesthesia. The aim of this study is to assess the value of a robust regional anesthesia practice regarding a range of perioperative outcome measures and to analyze various predictors for specific outcomes. While several studies have previously reported outcomes using large regional anesthesia databases, this analysis is unique in that the data was collected prospectively within 72 hours on 10,338 consecutive patients undergoing 13,897 regional anesthetics at an ambulatory surgery center (ASC) and did not require the voluntary submission from anesthesia providers involved in the case. Methods Study Design and Patients This study is an analysis of a prospectively collected database of patients undergoing regional anesthesia procedures at a single ASC. Beginning in November 2008, study data were collected and managed for practice improvement purposes using Research Electronic Data Capture (REDCap), a secure, web-based application designed to support data capture for current or future research studies [10]. After obtaining approval from the Vanderbilt University Institutional Review Board, the authors conducted a comprehensive review of 13,897 consecutive regional anesthetics at the Nashville Surgery Center from November 2008 through October 2014. Senior residents or fellows under the supervision of a regional anesthesia faculty member performed regional anesthetic blocks, with a minority of blocks performed by a faculty member alone. Combined general with regional anesthesia or regional anesthesia alone was administered based on the preference of the patient, anesthesiologist, and surgeon. Anesthesiologists routinely administered dual therapies for PONV prevention in patients receiving general anesthesia in addition to their regional anesthetic. Ondansetron and dexamethasone (unless dexamethasone was given as an adjunct within the regional anesthetic) were most commonly administered as most patients were considered at at least moderate risk for PONV [11]. Rarely, patients received either initial or repeat regional anesthetics in the Post-Anesthesia Care Unit (PACU) for breakthrough pain. Continuous peripheral nerve block (CPNB) catheters were placed for patients who were expected to require extended analgesia. Catheter confirmation was determined by visualization of either hydrodissection or color doppler surrounding at least 50% of the neural target with local anesthetic bolus through the catheter. Following catheter placement, Mastisol (Eloquest Healthcare, Ferndale, MI) was routinely applied to the skin as well as a LockIt Device (Smiths Medical, Dublin, OH, USA) and Tegaderm (3M, St Paul, MN, USA). Postoperative Period Patients were assessed in the PACU by the anesthesiologist, given written block-specific discharge instructions, and given the anesthesia on-call cell phone number for questions or concerns. Patients who were discharged home with CPNB catheters also received discharge instructions in the PACU with a family member regarding the elastomeric pain pump and catheter care, given instruction on the use of oral analgesics as adjuncts, provided with two catheter information brochures (one specific to our practice and one from the pump manufacturer), and followed with daily phone calls. The majority of patients with CPNB catheters were connected to an On-Q (Halyard Worldwide, Inc.; Alpharetta, GA, USA) elastomeric single-use disposable pump. If necessary, catheter patients could return to the ASC (or the hospital if after hours) for inadequate analgesia or major concerns. Patients and family members were instructed to remove the pain catheter at home when the elastomeric pump was empty, but no later than the fifth postoperative day. Residents and fellows entered the surgical and regional anesthetic information in the REDCap regional anesthesia database on the day of surgery. They added per-patient data based on phone interviews on postoperative day 1 and/or day 2 (POD1 or POD2); in the rare case of a preverbal child, the parent was asked to assess the patient’s status (e.g., pain subjectively scored by parents as none, mild, moderate, or severe), based on the child’s appearance and age-specific language. Any evidence of PONS or other concerns was documented and followed until resolution. At least two attempts were made on different days before patient follow-up was deemed unsuccessful; follow-up on catheters persisted until contact was made. Patients with CPNBs were followed daily until catheters were removed and blocks resolved. Cases were considered complete only after resolution of the regional anesthetic. Day of surgery information included demographics (age, American Society of Anesthesiologists [ASA] classification, sex, body mass index [BMI], date of surgery, surgical procedure), as well as detailed block information: type of block(s); nerve localization method including nerve stimulation (NSTIM) and/or ultrasound guidance (USG); type, concentration, and volume of local anesthetic (based on anesthesiologist’s discretion); adjuncts (dexamethasone and/or clonidine or none) [12] and dose; presence of a catheter; use of general anesthesia; immediate complications; and block success (defined by lack of response to painful intraoperative stimuli when coupled with sedation or lack of significant postoperative pain when coupled with general anesthesia). Postoperative outcome data included any occurrence of nausea with or without vomiting, daily pain scale (none, mild, moderate, severe), patient satisfaction scale (excellent, very good, good, fair, poor), duration of block (based on patient’s perception of block resolution), presence of postoperative neurological symptoms, or other complications. Additional detailed catheter information included quality of analgesia scale (excellent, very good, good, fair, poor), duration of catheter analgesia, and catheter complications. The data was reviewed weekly for completeness and consistency by the same anesthesiologist, including follow-up on each case until resolution of complications or concerns. Data collection for any patient with PONS included review of long-term follow-up by both orthopedics and anesthesiology for a minimum of one year postprocedure. Where additional information was needed, the electronic medical record was reviewed. Statistical Analysis Surgical procedures were divided into seven major categories based on anatomical regions to facilitate comparison between groups (Table 1). Similarly, the regional anesthetics were divided into six major groups based on neural anatomical distribution for comparison purposes (Table 2). Patient demographics, clinical/procedural characteristics, and outcomes were summarized with the mean, standard deviation, range, median, 25th and 75th percentiles for quantitative variables, and counts and percentages for categorical variables. To further analyze block duration based on specific adjuncts, the largest subset of “blocks for elbow-hand procedures” was examined and duration reported (Table 3). Logistic regression was used to examine the associations between clinical risk factors and binary outcomes, including block success, PONV, and PONS. Proportional odds ordinal logistic regression was similarly used to examine ordered categorical outcomes, namely patient satisfaction (five-point scale) and pain on POD1 (four-point scale). Table 1 Demographics (N = 10,338)   Age, y   1–10, No. (%)  27 (0.3)   11–17, No. (%)  827 (8.0)   18 or older, No. (%)  9,484 (91.7)   Mean (±SD)  43.1 (±17.4)  Gender, No. (%)   Female  4,819 (46.6)   Male  5,519 (53.4)  ASA status, No. (%)   I  2,984 (28.9)   II  5,506 (53.2)   III  1,824 (17.7)   IV  24 (0.2)  BMI (N = 7,028)*, No. (%)   <30  4,446 (63.3)   30–40  2,191 (31.2)   >40  391 (5.6)   Mean (±SD)  28.8 (±6.2)  Surgical procedure by regions, No. (%)   Shoulder/clavicle/scapula  1,822 (17.6)   Elbow  793 (7.7)   Distal forearm/wrist/hand  3,498 (33.8)   Knee  2,139 (20.7)   Foot/ankle  2,010 (19.5)   Head/neck/other  56 (0.5)   Chest/abdomen  20 (0.2)    Age, y   1–10, No. (%)  27 (0.3)   11–17, No. (%)  827 (8.0)   18 or older, No. (%)  9,484 (91.7)   Mean (±SD)  43.1 (±17.4)  Gender, No. (%)   Female  4,819 (46.6)   Male  5,519 (53.4)  ASA status, No. (%)   I  2,984 (28.9)   II  5,506 (53.2)   III  1,824 (17.7)   IV  24 (0.2)  BMI (N = 7,028)*, No. (%)   <30  4,446 (63.3)   30–40  2,191 (31.2)   >40  391 (5.6)   Mean (±SD)  28.8 (±6.2)  Surgical procedure by regions, No. (%)   Shoulder/clavicle/scapula  1,822 (17.6)   Elbow  793 (7.7)   Distal forearm/wrist/hand  3,498 (33.8)   Knee  2,139 (20.7)   Foot/ankle  2,010 (19.5)   Head/neck/other  56 (0.5)   Chest/abdomen  20 (0.2)  ASA = American Society of Anesthesiologists; BMI = body mass index. * Adult patients age 18 years or older with complete BMI data. Table 2 Regional anesthetic procedures Regional anesthesia procedures (N = 13,888)*  Blocks for shoulder region  1,836 (13.2)   Interscalene  1,806 (13.0)   Cervical plexus, suprascapular  30 (0.2)  Blocks for elbow-hand region  4,295 (30.9)   Supraclavicular  850 (6.1)   Infraclavicular  1,605 (11.6)   Axillary  1,840 (13.2)  Distal upper extremity blocks†  1,247 (9.0)  Blocks involving lumbar plexus and branches  3,551 (25.6)   Lumbar plexus  653 (4.8)   Femoral  1,459 (10.5)   Saphenous/adductor canal  1,074 (7.7)   Obturator, other  365 (2.6)  Blocks involving sciatic nerve and branches  2,181 (15.7)   Sciatic  155 (1.1)   Popliteal  1,630 (11.7)   Ankle  396 (2.9)  Miscellaneous blocks  778 (5.6)   Spinal or epidural  294 (2.1)   Blocks for head‡  45 (0.3)   Paravertebral/TAP blocks  53 (0.4)   Repeat blocks, intercostobrachial  386 (2.8)  Nerve localization and other end points    Nerve stimulation only (N = 13,897)  1,319 (9.5)   Ultrasound guidance (N = 13,897)  11,128 (80.1)   Success (N = 13,892)  13,524 (97.4)   Combined with general  anesthesia (N = 10,338)§  5,398 (52.2)  Regional anesthesia procedures (N = 13,888)*  Blocks for shoulder region  1,836 (13.2)   Interscalene  1,806 (13.0)   Cervical plexus, suprascapular  30 (0.2)  Blocks for elbow-hand region  4,295 (30.9)   Supraclavicular  850 (6.1)   Infraclavicular  1,605 (11.6)   Axillary  1,840 (13.2)  Distal upper extremity blocks†  1,247 (9.0)  Blocks involving lumbar plexus and branches  3,551 (25.6)   Lumbar plexus  653 (4.8)   Femoral  1,459 (10.5)   Saphenous/adductor canal  1,074 (7.7)   Obturator, other  365 (2.6)  Blocks involving sciatic nerve and branches  2,181 (15.7)   Sciatic  155 (1.1)   Popliteal  1,630 (11.7)   Ankle  396 (2.9)  Miscellaneous blocks  778 (5.6)   Spinal or epidural  294 (2.1)   Blocks for head‡  45 (0.3)   Paravertebral/TAP blocks  53 (0.4)   Repeat blocks, intercostobrachial  386 (2.8)  Nerve localization and other end points    Nerve stimulation only (N = 13,897)  1,319 (9.5)   Ultrasound guidance (N = 13,897)  11,128 (80.1)   Success (N = 13,892)  13,524 (97.4)   Combined with general  anesthesia (N = 10,338)§  5,398 (52.2)  TAP = transversus abdominis plane block. * Type of block, complete data. † Musculocutaneous, elbow, wrist blocks. ‡ Retrobulbar, trigeminal, scalp. § Based on total patients. Table 3 Local anesthetics and adjuncts Local anesthetics and adjuncts used (N = 13,880)*, No. (%)  Local anesthetics used   Ropivacaine  9,872 (71.1)   Mepivacaine  2,359 (17.0)   Bupivacaine  592 (4.3)   Lidocaine  330 (2.4)   Chloroprocaine  186 (1.3)   Mepivacaine/ropivacaine  481 (3.5)   Mepivacaine/bupivacaine  60 (0.4)  Adjuncts used (N = 13,897)†   None  8,856 (63.7)   Clonidine and dexamethasone (C+D)  1,857 (13.4)   Clonidine (C)  1,733 (12.5)   Dexamethasone (D)  1,451 (10.4)  Adjunct doses   Dexamethasone, mg  Median‡ = 4 (2,8)  Mean (SD) = 4.4 (2.7)  Range = 0.25–8.0   Clonidine, ug  Median‡ = 100 (50,100)  Mean (SD) = 79.6 (26.4)  Range§ = 7.5–100  Duration analysis (Blocks for elbow-hand subset using 0.5% ropivacaine)  Adjunct  No.  Dose dex Mean (SD), mg  Dose clonidine Mean (SD), ug  Duration Mean (SD), h  None  1,582  –  –  15.3 (5.5)   C  544  –  96.4 (13.9)  16.5 (6.0)   D  380  6.0 (2.2)  –  20.5 (7.3)  D4 subgrp  134  4  –  17.8 (6.0)  D8 subgrp  159  8  –  22.3 (7.7)   C+D  644  2.2 (0.6)  86.4 (22.4)  23.7 (9.8)  Local anesthetics and adjuncts used (N = 13,880)*, No. (%)  Local anesthetics used   Ropivacaine  9,872 (71.1)   Mepivacaine  2,359 (17.0)   Bupivacaine  592 (4.3)   Lidocaine  330 (2.4)   Chloroprocaine  186 (1.3)   Mepivacaine/ropivacaine  481 (3.5)   Mepivacaine/bupivacaine  60 (0.4)  Adjuncts used (N = 13,897)†   None  8,856 (63.7)   Clonidine and dexamethasone (C+D)  1,857 (13.4)   Clonidine (C)  1,733 (12.5)   Dexamethasone (D)  1,451 (10.4)  Adjunct doses   Dexamethasone, mg  Median‡ = 4 (2,8)  Mean (SD) = 4.4 (2.7)  Range = 0.25–8.0   Clonidine, ug  Median‡ = 100 (50,100)  Mean (SD) = 79.6 (26.4)  Range§ = 7.5–100  Duration analysis (Blocks for elbow-hand subset using 0.5% ropivacaine)  Adjunct  No.  Dose dex Mean (SD), mg  Dose clonidine Mean (SD), ug  Duration Mean (SD), h  None  1,582  –  –  15.3 (5.5)   C  544  –  96.4 (13.9)  16.5 (6.0)   D  380  6.0 (2.2)  –  20.5 (7.3)  D4 subgrp  134  4  –  17.8 (6.0)  D8 subgrp  159  8  –  22.3 (7.7)   C+D  644  2.2 (0.6)  86.4 (22.4)  23.7 (9.8)  * For a given nerve block, our practice uses one or a combination of the following local anesthetics: 0.5% ropivacaine, 1.5% mepivacaine, 0.25–0.5% bupivacaine, 2% lidocaine, 3% chloroprocaine. Rarely, more dilute concentrations were utilized. † None, one, or more of the following additives were added to the local anesthetic: clonidine and/or dexamethasone; epinephrine was added as a vascular marker to any of above combinations at discretion of anesthesiologist in 21% of blocks. ‡ With 25th and 75th percentiles. § Range = 7.5–100, although one block had 200 ug. For each outcome, the set of risk factors considered was prespecified on the basis of expert opinion among the authors as well as a literature review from previous studies regarding predictors of outcomes (e.g., well-established predictors for PONV). The authors applied predictors uniformly across the outcomes analyzed whenever possible (e.g., demographics including age, sex, ASA, BMI > 30, as well as use of either CPNB or USG). However, some predictors were considered to be unique for certain outcomes. For block success, the outcome-specific risk factors included NSTIM/USG, block type, and local anesthetic. The PONV-specific risk factors included general anesthesia, pain rating postoperatively on day of surgery (PO-DOS), and adjuncts. The PONS-specific risk factors included NSTIM/USG, block type, adjuncts, and paresthesia. For patient satisfaction, risk factors included general anesthesia, complications, NSTIM/USG, pain rating on PO-DOS, PONS, block failure, PONV, and block duration. For pain on POD1, risk factors included surgical group, local anesthetics, adjuncts, and block duration. Other possible predictors, such as preoperative opioid use, ethnicity, and duration of surgery, were not available in the database. All prespecified risk factors were analyzed in the model simultaneously using multiple regression. The possibility of nonlinear association between age and outcomes was examined using a flexible nonlinear function (i.e., a restricted cubic spline with knots at the fifth, 35th, 65th, and 95th percentiles for age) [13]. A linear model was used when there was no evidence of nonlinearity using a likelihood ratio test. Multiple imputation using a chained-equations approach was employed to account for the uncertainty due to missing data [14]. The robust sandwich estimator was used to account for correlation introduced by multiple block data between patients [15]. The effects of demographic factors and risk factors are presented using the odds ratios (OR; 95% confidence interval [CI]). For proportional odds logistic regression (POLR), the odds ratio for a given covariate is relevant to every binary grouping of the ordinal outcome (e.g., none/mild vs moderate/severe). Due to the proportional odds feature, the following two example statements are both valid: “The odds of reporting severe nausea were twofold greater among females vs males” and “The odds of reporting moderate or severe nausea were twofold greater among females vs males.” Thus, POLR odds ratios are often summarized using language that applies to any binary grouping of the outcome, for example, “The odds of reporting more intense nausea were twofold larger among females vs males.” All analyses were performed using R version 3.2.1. Tests with P values of less than than 0.05 were considered statistically significant. Results Demographics The demographics of the 10,338 patients are summarized in Table 1. Mean patient age was 43 years (±SD 17.4), while 854 (8.3%) patients were younger than age 18 years. Females comprised 46.6% of the study population. Most patients were ASA I or II status (82.1%), while the remainders were ASA III (17.7%) and ASA IV (0.2%). The mean BMI for adult patients was 28.8 (±SD 6.2), while 36.8% were obese, with BMI greater than 30. Techniques of Regional Anesthetics Table 2 summarizes the types of blocks performed including 7,378 (53%) upper extremity blocks, 3,551 (26%) blocks involving the lumbar plexus (proximal or distal), 2,181 (16%) blocks involving the sciatic nerve (proximal or distal), 294 (2%) central neuraxial blocks (CNB), and 484 (3%) eye, facial, truncal, and repeat blocks. USG was used in the majority of blocks (80%); NSTIM was used in 66% of blocks while 9.5% utilized NSTIM without USG. General anesthesia was combined with regional anesthesia in 52% of the cases. Overall, 97.4% of the blocks were successful. When independent risk factors were analyzed for block success, factors most associated with decreased success were nerve stimulation alone (OR = 0.3, 95% CI = 0.24–0.46, P < 0.001; 93.2% compared with USG 97.8%) and obesity (OR = 0.6, 95% CI = 0.48–0.83, P = 0.001; 95.6% vs 97.8% success with BMI > 30 compared with BMI <30, respectively). Higher ASA classification (OR = 0.7, 95% CI = 0.50–0.91, P = 0.01), lower extremity blocks (OR = 0.8, 95% CI = 0.56–0.99, P = 0.04), and age (50th vs 25th age percentile, OR = 0.8, 95% CI = 0.71–0.99, nonlinear effect, P = 0.05) were also associated with decreased success. Age was associated with block success in a nonlinear fashion such that blocks in patients at the 50th percentile of age were less successful than those for patients at the 25th percentile of age, while there was no significant difference between those at the 50th and 75th percentiles. Female sex was associated with increased success (OR = 1.6, 95% CI = 1.22–2.01, P < 0.001), while use of CPNBs was not a significant factor (Figure 1, odds ratios for block success). Figure 1 View largeDownload slide Odds ratios (95% confidence intervals) of block success. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Age was examined comparing quartiles of age, which had a nonlinear association (P = 0.005). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE blocks: lower vs upper extremity blocks. Pairwise comparisons were conducted between block types (Table 2). Local anesthetics and other block type comparisons were omitted from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; UE = upper extremity; USG = ultrasound guidance. Figure 1 View largeDownload slide Odds ratios (95% confidence intervals) of block success. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Age was examined comparing quartiles of age, which had a nonlinear association (P = 0.005). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE blocks: lower vs upper extremity blocks. Pairwise comparisons were conducted between block types (Table 2). Local anesthetics and other block type comparisons were omitted from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; UE = upper extremity; USG = ultrasound guidance. Anesthesiologists incorporated ropivacaine or mepivacaine in 71% and 17% of blocks, respectively. Lidocaine, bupivacaine, or combinations were used in the remaining 12% of blocks (Table 3). Low-dose chloroprocaine or lidocaine was used for short-acting spinal anesthesia. In order to increase peripheral nerve block (PNB) duration [12,16], dexamethasone, clonidine, or their combination were incorporated as adjuncts in 10%, 13%, and 13%, respectively, with doses in Table 3. Finally, epinephrine was added as a vascular marker in 21% of the blocks. Median (interquartile range) duration of all blocks was 16.0 (12.0–24.0) hours. Within the blocks for elbow-hand subset using 0.5% ropivacaine, mean duration (SD) with no adjunct was 15.3 (5.5) hours, with clonidine 16.5 (6.0), with dexamethasone 20.5 (7.3), and with dexamethasone and clonidine 23.7 (9.8; all pairwise comparisons were significant; P < 0.001). Ropivacaine 0.25% was only rarely used and therefore not further analyzed. Within the dexamethasone only group, the mean dose was 6.0 mg (2.2 mg), while the mean clonidine dose in the clonidine only group was 96.4 ug (13.9 ug). For the combined dexamethasone and clonidine group, the mean doses were 2.2 mg (0.6 mg) and 86.4 ug (22.4 ug), respectively. Patient Satisfaction Regarding patient satisfaction, most (95%) patients reported “very good” or “excellent” satisfaction with a regional-based anesthetic for their operation; 4% rated their overall satisfaction as “good,” while less than 1% rated their satisfaction as either “fair” or “poor” (Table 4). The risk factors associated with lower patient satisfaction (e.g., “fair/poor”) were poor CPNB analgesia (OR ≤ 0.1, 95% CI = 0.02–0.08, P < 0.001), severe pain PO-DOS (OR = 0.2, 95% CI = 0.14–0.29, P < 0.001), moderate pain PO-DOS (OR = 0.3, 95% CI = 0.21–0.33, P < 0.001), PONS (OR =  0.3, 95% CI = 0.21–0.39, P < 0.001), any complications (OR = 0.3, 95% CI = 0.20–0.42, P < 0.001), block failure (OR = 0.4, 95% CI = 0.27–0.60, P < 0.001), mild pain PO-DOS (OR = 0.5, 95% CI = 0.43–0.56, P < 0.001), catheter complications (OR = 0.6, 95% CI = 0.47–0.88, P = 0.005), PONV (OR = 0.7, 95% CI = 0.61–0.82, P < 0.001), and higher ASA classification (OR = 0.8, 95% CI = 0.69–0.91, P = 0.001). Averaging across all patients, postoperative pain was significantly associated with poor patient satisfaction. Patient satisfaction was progressively worse with increasing postoperative pain severity. Older age was associated with higher patient satisfaction (OR = 1.1, 95% CI = 1.03–1.24, P = 0.008). General anesthesia, sex, BMI, nerve localization technique, and block duration were not significant risk factors. (Figure 2, odds ratios for higher patient satisfaction). Table 4 Patient satisfaction, PONV, and block complications Patient satisfaction (N = 8896), No. (%)   Excellent  6725 (75.6)   Very good  1746 (19.6)   Good  325 (3.7)   Fair  74 (0.8)   Poor  26 (0.3)  PONV (N = 9001), No. (%)   Nausea  1079 (12.0)   Vomiting  286 (3.2)  Complications (N = 8995), No. (%, 95% CI)   None  8,661 (96.3)   PONS*  208 (2.3, 2.0–2.6)   Falls†  25 (0.3, 0.2–0.4)   Epidural spread‡  24 (0.3, 0.2–0.4)   Unexpected hospital admission  pain  21 (0.2, 0.2–0.4)   Pulmonary§  20 (0.2, 0.1–0.3)   Cardiac¶  13 (0.1, 0.1–0.2)   Headache‖  8 (0.1, 0.0–0.2)   Back Pain‖|  4 (<0.1, 0.0–0.1)   Death within 72 h**  2 (<0.1, 0.0–0.1)   Seizures††  1 (<0.1, 0.0–0.1)   Other Minor‡‡  11 (0.1, 0.1–0.2)  Patient satisfaction (N = 8896), No. (%)   Excellent  6725 (75.6)   Very good  1746 (19.6)   Good  325 (3.7)   Fair  74 (0.8)   Poor  26 (0.3)  PONV (N = 9001), No. (%)   Nausea  1079 (12.0)   Vomiting  286 (3.2)  Complications (N = 8995), No. (%, 95% CI)   None  8,661 (96.3)   PONS*  208 (2.3, 2.0–2.6)   Falls†  25 (0.3, 0.2–0.4)   Epidural spread‡  24 (0.3, 0.2–0.4)   Unexpected hospital admission  pain  21 (0.2, 0.2–0.4)   Pulmonary§  20 (0.2, 0.1–0.3)   Cardiac¶  13 (0.1, 0.1–0.2)   Headache‖  8 (0.1, 0.0–0.2)   Back Pain‖|  4 (<0.1, 0.0–0.1)   Death within 72 h**  2 (<0.1, 0.0–0.1)   Seizures††  1 (<0.1, 0.0–0.1)   Other Minor‡‡  11 (0.1, 0.1–0.2)  PONS= postoperative neurological symptoms; PONV = postoperative nausea and vomiting. * See Table 6, PONS defined as neurological symptoms > 72 hours’ duration. † All falls occurred following knee or foot/ankle surgery usually involving either a femoral or popliteal block. Three falls occurred after spinal or epidural block. ‡ Primarily during lumbar plexus blocks. § Symptomatic hemidiaphragmatic paresis (no pneumothorax events). ¶ Includes significant Bezold-Jarisch reflex, syncope, hypotension, myocardial ischemia, or new chest pain within 72 hours. ‖ Six headaches related to spinal/epidurals (2% PDPH rate). ‖| All related to spinal, epidural, or lumbar plexus block. ** Two deaths during this time period. Neither death directly related to the regional anesthetic. See text for details. †† Partial seizure in the Post-Anesthesia Care Unit postoperatively three hours postblock, associated with vasovagal episode, not felt secondary to local anesthetic systemic toxicity. ‡‡ Other events include pain at needle entry site, intravascular local anesthetic injection without symptoms, intolerance to block procedure, hoarseness. Figure 2 View largeDownload slide Odds ratios (95% confidence intervals) for high patient satisfaction. ORs were calculated using a proportional odds logistical regression. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile. Obesity: BMI  > 30 vs < 30. Higher ASA status: III/IV vs I/II. Catheter failure (poor/fair analgesia) vs single injection. NSTIM vs USG (±NSTIM). Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Postoperative neurologic symptoms. The effect of block duration and nonlinear age effect was omitted from the figure for nonsignificance and clarity. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS = postoperative neurological symptoms; PONV = postoperative nausea and vomiting; UE = upper extremity; USG = ultrasound guidance. Figure 2 View largeDownload slide Odds ratios (95% confidence intervals) for high patient satisfaction. ORs were calculated using a proportional odds logistical regression. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile. Obesity: BMI  > 30 vs < 30. Higher ASA status: III/IV vs I/II. Catheter failure (poor/fair analgesia) vs single injection. NSTIM vs USG (±NSTIM). Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Postoperative neurologic symptoms. The effect of block duration and nonlinear age effect was omitted from the figure for nonsignificance and clarity. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS = postoperative neurological symptoms; PONV = postoperative nausea and vomiting; UE = upper extremity; USG = ultrasound guidance. Postoperative Nausea and Vomiting Twelve percent of patients experienced postoperative nausea while 3.2% experienced postoperative vomiting within the first 24 hours following surgery (Table 4). Independent risk factors for PONV were PO-DOS pain (OR = 2.5, 95% CI = 1.60–3.90, P < 0.001; OR = 1.5, 95% CI = 1.07–1.96, P = 0.02; OR = 1.3, 95% CI = 1.08–1.52, P = 0.005, for severe, moderate, and mild pain respectively), female sex (OR = 1.8, 95% CI = 1.55–2.05, P < 0.001), and general anesthesia (OR = 1.3, 95% CI = 1.12–1.50, P < 0.001), while CPNB (OR = 0.8, 95% CI = 0.64–0.97, P = 0.03), older age (OR = 0.8, 95% CI = 0.73–0.93, P = 0.001), and dexamethasone/clonidine adjunct (OR = 0.7, 95% CI = 0.59–0.93, P = 0.01) were less likely to be associated with PONV. BMI, ASA classification, and adjuncts of dexamethasone or clonidine alone were not significant risk factors (Figure 3, ORs for postoperative nausea and vomiting). Figure 3 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative nausea and vomiting. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile of age. (Nonlinear age effect was also examined and removed for lack of evidence.) Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. ASA = American Society of Anesthesiologists classification; OR = odds ratio; PONV = postoperative nausea and vomiting. Figure 3 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative nausea and vomiting. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile of age. (Nonlinear age effect was also examined and removed for lack of evidence.) Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. ASA = American Society of Anesthesiologists classification; OR = odds ratio; PONV = postoperative nausea and vomiting. Postoperative Pain Most patients, 94%, reported “none to mild” pain on the day of surgery, while 33% and 24% reported “moderate to severe” pain on postoperative day 1 and day 2, respectively (Figure 4, postoperative pain chart). Risk factors associated with less pain on POD1 were general anesthesia (OR = 0.8, 95% CI = 0.67–0.84, P < 0.001) and older age, 75th compared with 50th percentile (OR = 0.9, 95% CI = 0.80–0.91, P < 0.001). In addition, compared with distal upper extremity procedures, chest and abdomen procedures (OR =  0.5, 95% CI = 0.26–0.93, P = 0.03), thigh and knee procedures (OR =  0.6, 95% CI = 0.48–0.65, P < 0.001), and foot and ankle procedures (OR =  0.7, 95% CI = 0.58–0.75, P < 0.001) were also associated with less pain. Risk factors associated with more pain were female sex (OR =  1.3, 95% CI = 1.17–1.40, P < 0.001) and higher ASA (OR =  1.3, 95% CI = 1.14–1.44, P < 0001). Figure 4 View largeDownload slide The distribution of postoperative pain scores on day of surgery, postoperative day 1, postoperative day 2, and postoperative day 3 on a four-point scale (none, mild, moderate, severe). DOS = day of surgery; POD = postoperative day. Figure 4 View largeDownload slide The distribution of postoperative pain scores on day of surgery, postoperative day 1, postoperative day 2, and postoperative day 3 on a four-point scale (none, mild, moderate, severe). DOS = day of surgery; POD = postoperative day. Complications Table 4 summarizes reported side effects and complications that may be related to anesthesia. Serious complications were rare: 13 patients (0.1%) had significant hypotension and/or bradycardia; 20 patients (0.2%) had significant respiratory complaints primarily following interscalene blocks due to hemidiaphragmatic paresis (no clinically evident pneumothoraces); 21 patients (0.2%) required unexpected hospital admission due to severe postoperative pain; 25 patients (0.3%) with either femoral, popliteal, or CNB blocks fell postoperatively; one patient (0.01%) had a partial seizure in the PACU; and two patients died in the postoperative period. (One patient with obesity, opioid tolerance, anxiety, and chronic osteomyelitis had an accidental drug overdose involving both opioids and benzodiazepines at home on the day of surgery after meeting PACU discharge criteria. The other patient had significant comorbidities including morbidly obesity [BMI = 48], history of remote cocaine abuse, obstructive sleep apnea [OSA] on continuous positive airway pressure [CPAP], and opioid tolerance on preoperative oxycodone, hydromorphone, cyclobenzaprine, and gabapentin. After an uneventful shoulder operation with combined general anesthesia and an interscalene catheter, the patient met PACU discharge criteria but died on POD2 from unclear etiology.) Catheter Information In addition to single injection blocks, 1,261 indwelling pain catheters were utilized in 1,228 patients (11.9%) at the discretion of the anesthesiologist. Catheter-related information is reported in Table 5. Based on telephone-reported pain information, catheter analgesia was adequate in 93.3% of patients (60.3% “excellent,” 24.5% “very good,” 8.5% “good”), while 6.7% rated their analgesia as “poor” or “fair.” Catheters remained in place 48 to 96 hours in 72% of patients, longer than 96 hours in 18% of patients, and less than 48 hours in 10% of patients. Seventy-four percent of patients had no concerns or complications from their catheters. Leaking around the catheter (17%), catheter dislodgement (3.7%), and need for catheter manipulation by an anesthesiologist (2.3%) were the primary catheter complications, while mechanical pump/clamp issues (0.9%), allergic skin reactions (0.8%), and infections (0.3%) rarely occurred. In the middle of the study period, a medical grade adhesive (Surgiseal, Adhezion BioMedical, LLC, Wyomissing, PA, USA) was increasingly used at catheter insertion sites, yet there was insufficient evidence of an impact on leakage rate. All patients with skin reactions or infections (two deep and two superficial) cleared completely with treatment. Table 6 PONS Overview (N = 8987)*, No. (%) or No. (range)   PONS (>72 h duration)      208 (2.3)   Sensory deficits only      194 (93)†   Sensory and motor deficits      14 (7)†   Dysesthesias present      43 (21)†   Tourniquet time > 120 min      1 (0.7)†  Onset of symptoms, d   <7      190 (93)   7–14      4 (2)   >14      10 (5)  Duration, mo   <4      131 (77)   4–6      14 (8)   7–18      14 (8)   >18      12 (7)   Lost to follow-up      37 (18)  Potentially related to block‡   Improbable      29 (14)   Possible      112 (55)   Probable      64 (31)  Subset: duration > 6 mo and “probably related to anesthesia” (N = 12)   Age, y  42.5 (21–75)  NSTIM  11 (92)   Female sex  5 (42)  USG  8 (67)   ASA  2.1  Volume, mL  33 (25–50)   BMI  26.6 (21–35)  Adjunct¶     Diabetes  0   None  3 (25)   Preop numbness  1 (8)   Dexamethasone, 8 mg  3 (25)   Tourniquet time, min  0–82   C+D‖  6 (50)   Blocks    CPNB  2 (17)    Upper extremity  4 (33)  Gen anesthesia  7 (58)    Lower extremity§  8 (67)  Dysesthesia  7 (58)   0.5% ropivacaine  12 (100)  Weakness  4 (33)  Overview (N = 8987)*, No. (%) or No. (range)   PONS (>72 h duration)      208 (2.3)   Sensory deficits only      194 (93)†   Sensory and motor deficits      14 (7)†   Dysesthesias present      43 (21)†   Tourniquet time > 120 min      1 (0.7)†  Onset of symptoms, d   <7      190 (93)   7–14      4 (2)   >14      10 (5)  Duration, mo   <4      131 (77)   4–6      14 (8)   7–18      14 (8)   >18      12 (7)   Lost to follow-up      37 (18)  Potentially related to block‡   Improbable      29 (14)   Possible      112 (55)   Probable      64 (31)  Subset: duration > 6 mo and “probably related to anesthesia” (N = 12)   Age, y  42.5 (21–75)  NSTIM  11 (92)   Female sex  5 (42)  USG  8 (67)   ASA  2.1  Volume, mL  33 (25–50)   BMI  26.6 (21–35)  Adjunct¶     Diabetes  0   None  3 (25)   Preop numbness  1 (8)   Dexamethasone, 8 mg  3 (25)   Tourniquet time, min  0–82   C+D‖  6 (50)   Blocks    CPNB  2 (17)    Upper extremity  4 (33)  Gen anesthesia  7 (58)    Lower extremity§  8 (67)  Dysesthesia  7 (58)   0.5% ropivacaine  12 (100)  Weakness  4 (33)  PONS = postoperative neurological symptoms. * Patients who were available for follow-up regarding possible residual block. † % of PONS population (N = 208). ‡ Based on authors’ review of each case including targeted history and physical as well as neurological consultations and studies, if available. § Including six popliteal blocks. ¶ Epinephrine was used as a vascular marker in five (42%) cases. ‖ Clonidine dose: mean 100 ug + dexamethasone dose: mean 2.8 mg. Postoperative Neurologic Sequelae Postoperative neurologic symptoms (PONS), defined as neurological symptoms lasting more than 72 hours after the nerve block, were diagnosed in 208 patients (2.3%) in our study population, of whom 14 (7% of those with PONS diagnosis) complained of motor function involvement. Table 6 summarizes PONS information including symptoms, onset, duration, and possible relation to block, as well as a subset analysis of prolonged PONS cases that were “probably related to anesthesia.” Tourniquet ischemia was not a major contributor as only one patient had a tourniquet time beyond 120 minutes and most tourniquets were simply ankle Esmarch wraps. While 190 (93%) patients complained of persistent sensory deficits within seven days following surgery, 10 patients (5% of PONS patients) did not complain of symptoms until at least two weeks following surgery despite reported return of full motor and sensory function during the primary postoperative follow-up phone calls. Duration of symptoms varied substantially, with 85% resolution within six months and 93% resolution within 18 months. Table 5 Catheter information Catheter types (N = 1261)*, No. (%)   Popliteal sciatic  699 (55.4)   Interscalene  430 (34.1)   Supra/infraclavicular  64 (5.0)   Infragluteal sciatic  20 (1.6)   Other†  48 (3.9)  Catheter analgesia (N = 1215)   Excellent  733 (60.3)   Very good  298 (24.5)   Good  103 (8.5)   Fair  36 (3.0)   Poor  45 (3.7)  Issues, complications   None  911 (74.1)   Leaking, overall‡  212 (17.3)   Dislodgement‡  45 (3.7)   Catheter needing  manipulation/replacement  28 (2.3)   Mechanical pump/catheter  issue (usually not infusing)  11 (0.9)   Skin reaction, allergic  10 (0.8)   Pulled prematurely  7 (0.6)   Infection  4 (2 superficial, 2 deep) (0.3)  Catheter types (N = 1261)*, No. (%)   Popliteal sciatic  699 (55.4)   Interscalene  430 (34.1)   Supra/infraclavicular  64 (5.0)   Infragluteal sciatic  20 (1.6)   Other†  48 (3.9)  Catheter analgesia (N = 1215)   Excellent  733 (60.3)   Very good  298 (24.5)   Good  103 (8.5)   Fair  36 (3.0)   Poor  45 (3.7)  Issues, complications   None  911 (74.1)   Leaking, overall‡  212 (17.3)   Dislodgement‡  45 (3.7)   Catheter needing  manipulation/replacement  28 (2.3)   Mechanical pump/catheter  issue (usually not infusing)  11 (0.9)   Skin reaction, allergic  10 (0.8)   Pulled prematurely  7 (0.6)   Infection  4 (2 superficial, 2 deep) (0.3)  * Total catheters in 1,228 patients (some with multiple continuous peripheral nerve blocks). † Other locations include saphenous/adductor canal, cervical plexus, femoral, dual catheter combinations, other. ‡ Cyano-acrylate adhesive applied at the catheter insertion site decreased leaking during second half of study period (P = 0.48 when adjusted for age, gender, body mass index, American Society of Anesthesiologists classification, and ultrasound guidance/nerve stimulation). Of the patients who had PONS more than six months (26 patients), 12 patients had neurologic sequelae that were determined to be “probably related to anesthesia.” Although a statistical analysis of 12 patients was not possible, we performed a detailed chart review to elucidate any possible patterns within this subset of patients (Table 6). Eight (66.7%) received lower extremity blocks including six popliteal blocks. Both nerve stimulation (with no stimulation below 0.3 mA prior to injection) and ultrasound were utilized in most cases. All blocks incorporated ropivacaine 0.5% with median volume of 33.7 mL, and six (50%) blocks included both clonidine (mean 100 ug) and dexamethasone (mean 2.8 mg). General anesthesia was used in conjunction with regional anesthesia in seven (58%) patients. Of the four patients with motor involvement, all were male, half received upper extremity blocks, and half received general anesthesia. Two of these four patients had dexamethasone only (8 mg), while one patient had dexamethasone 4 mg and clonidine 100 ug. Regarding risk factors for PONS, there was no consistent pattern related to age, sex, ASA status, BMI, specific anesthesia providers, diabetes, or tourniquet within the subset analysis. When risk factors were analyzed within the entire PONS group (N = 208), there was no evidence of an association between PONS and obesity, ASA classification, use of ultrasound vs nerve stimulation, presence of paresthesia during the block, or pain catheters. Significant risk factors for PONS were the combination of clonidine and dexamethasone (OR= 5.6, 95% CI = 3.84–8.20, P < 0.001), lower extremity blocks (primarily femoral and popliteal blocks; OR=3.9, 95% CI = 2.78–5.42, P < 0.001), clonidine (OR=2.2, 95% CI = 1.40–3.43, P < 0.001), and female sex (OR=1.9, 95% CI = 1.38–2.56, P < 0.001). Risk factors associated with reduced PONS were older age (OR=0.6, 95% CI = 0.47–0.76, P < 0.001, nonlinear effect) and dexamethasone alone (OR=0.1, 95% CI = 0.01–0.70, P = 0.02) (Figure 5). Figure 5 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative neurologic symptoms. Calculations were based on logistical regression analysis with robust sandwich standard error estimates. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: Quartiles of age had a nonlinear association (P < 0.001). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE Blocks compared upper extremity blocks vs lower extremity blocks. Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. Pairwise comparisons were conducted between block types (Table 2). Other block type comparisons and paresthesia during block were eliminated from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS= postoperative neurological symptoms; UE = upper extremity; USG = ultrasound guidance. Figure 5 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative neurologic symptoms. Calculations were based on logistical regression analysis with robust sandwich standard error estimates. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: Quartiles of age had a nonlinear association (P < 0.001). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE Blocks compared upper extremity blocks vs lower extremity blocks. Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. Pairwise comparisons were conducted between block types (Table 2). Other block type comparisons and paresthesia during block were eliminated from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS= postoperative neurological symptoms; UE = upper extremity; USG = ultrasound guidance. Discussion This large comprehensive database study using prospectively collected and audited data corroborates previous evidence that a regional anesthesia-based practice provides excellent postoperative analgesia, with a high rate of both success (97.4%) and patient satisfaction (98.9%) [17,18]. Significant complications were rare; in fact, no patient experienced major symptoms of LAST or pneumothorax. However, even with USG, the concern for PONS remains, particularly when using combined dexamethasone and clonidine or administering lower extremity blocks. Success We demonstrated that a high degree of success and safety could be achieved even in a busy, primarily orthopedic, ambulatory surgery center that involves teaching residents and fellows. Our overall block success rate of 97.4% compares favorably to other studies involving regional anesthetics in academic medical centers, while our observed tendency for decreased success rates with nerve stimulation alone compared with USG as well as with obesity reinforces the findings of previous publications [19,20]. Female sex as an independent risk factor for increased success (OR = 1.6, P < 0.001) is a new finding, which could be further examined in future research. Duration Based on the analysis using “blocks for elbow-hand procedures,” adding clonidine, dexamethasone, or both significantly increased block duration by 1.2 hours (P < 0.001), 5.2 hours (P < 0.001), and 8.4 hours (P < 0.001), respectively. Combinations of low-dose adjuncts (“multimodal peripheral nerve blocks”) together with local anesthetics have been reported to substantially increase duration compared with single adjuncts with local anesthetics in orthopedic patients [21]. PNBs with dexamethasone demonstrated large variance with an interquartile range of 15 to 24 hours. Unlike previous investigations [22,23], the prolonged duration effect with dexamethasone was dose dependent in our study, with 4 mg increasing duration by 2.5 hours and 8 mg increasing duration seven hours. Increased durations from clonidine and dexamethasone are postulated to be the results of hyperpolarization of cyclic nucleotide–gated channels and inhibition of nociceptive C-fiber transmission, respectively [16]. Postoperative Pain On the day of surgery, 94% of our patients noted “none” or “mild” postoperative pain. Excellent pain control persisted in 67% and 76% of patients through POD1 and POD2, respectively, and only 0.2% of patients required unexpected hospital admissions due to severe pain. These findings are quite favorable compared with prior studies, including a review of 5,703 ambulatory surgical patients done by McGrath et al. [24] in 2004 in which they found that 47% of ambulatory orthopedic patients with both regional and general anesthesia had “moderate” to “severe” pain, with a 1.4% rate of unplanned visits to a physician for poor pain control. Other studies have shown that 25% to 40% of ambulatory patients report moderate to severe pain, with orthopedic patients reporting the greatest pain [25,26]. Previous authors reported that unexpected admissions after ambulatory surgery, frequently due to severe pain, range from 0.28% to 1.42% [27,28]. Increased postoperative pain has been associated with obesity, opioid tolerance, prolonged surgical duration, general anesthesia, and high PACU pain scores [24,25,26]. While direct comparisons are difficult between studies due to varying methodology and types of surgery, we attribute our lower pain scores primarily to the use of long-acting local anesthetic blocks, aggressive CPNB use when appropriate, and minimizing the use of general anesthesia and/or opioid administration. Our results demonstrated that lower pain scores and fewer unexpected admissions may be possible with a robust regional anesthesia program. Patient Satisfaction Patient satisfaction scores in our study were high, with 98.9% reporting good, very good, or excellent satisfaction, similar to other studies [29]. Our study reveals new independent risk factors for poor patient satisfaction, namely poor analgesia from CPNB (OR < 0.1, P < 0.001) and any complications from regional anesthesia including PONS (OR = 0.3, P < 0.001), while confirming that severe postoperative pain (OR = 0.2, P < 0.001) and PONV (OR = 0.7, P < 0.001) lead to diminished patient satisfaction [30]. Our patient satisfaction scores did not differ significantly from previous studies with patients under general anesthesia [30], which is probably a result of overall patient satisfaction being multifactorial, involving administrative, psychological, logistical, and socioeconomic stressors, as well as clinical performance. Postoperative Nausea and Vomiting For an ambulatory surgery orthopedic population, we observed a low PONV rate (12% nausea, 3.2% vomiting) compared with historical norms. In our population, as in other studies, PONV was most associated with the level of postoperative pain, as well as female sex and presence of general anesthesia [31]. Odom-Forren et al. [32] and Gan et al. [33] recently reported postoperative nausea and vomiting as high as 57% and 19%, respectively, for outpatient surgery performed with general anesthesia. Similar to our results, Lin et al. [34] previously published a PONV rate of 5% to 12% when regional anesthesia was used alone for various orthopedic procedures compared with 32% to 62% with general anesthesia alone. Block Complications Compared with previous studies regarding regional anesthesia involving primarily nerve stimulation [8], our rate of LAST was significantly reduced, with no patient presenting major signs or symptoms consistent with LAST. Our LAST outcome is consistent with more recent publications that reported that the incidence of LAST in a predominately USG-based practice was much less than previously described. Orebaugh et al. [6] in their 2012 study reported no cases of LAST in a consecutive series of 9,238 USG blocks compared with six LAST events in 5,436 NSTIM-only blocks (1.1/1,000). Likewise, Barrington et al. [35] demonstrated the benefit of USG blocks, reporting a LAST rate of 0.59 per 1,000 blocks utilizing ultrasound guidance vs a rate of 2.1 per 1,000 blocks using nerve stimulation. With ultrasound guidance, the ability to visualize the needle in relation to vessels, to use lower local anesthetic dosages, and to use a mobile needle technique may have significantly reduced this complication. Similarly, we report no clinically evident cases of pneumothorax in 856 supraclavicular and 49 patients with multiple paravertebral blocks, which is less than the previously established rates of pleural injury [36]. Again, with the advent of USG regional anesthesia, other authors have also reported a precipitous decline in pneumothorax with the use of ultrasound [7,37]. However, we did find an incidence of a 0.2% rate of other symptomatic pulmonary complications, primarily involving symptomatic hemidiaphragmatic paresis with interscalene blocks. Regarding the two postoperative deaths, perioperative opioids combined with other sedatives, obesity, and OSA significantly elevated their risk of postoperative respiratory depression secondary to greater opioid requirements, opioid-induced central sleep apnea, and decreased pharyngeal patency and muscle tone [38,39]. Anesthesiologists should be active participants in deciding whether surgery is most appropriately performed in an ambulatory surgery center vs a hospital with possible admission for observation in high-risk patients [40]. Our overall PONS rate of 2.3% is consistent with previously published studies, some of which publish much higher rates. We agree with the “theory of Hebl” that PONS is most likely multifactorial and may be difficult to ascertain exact etiologies in most clinical situations [7,41]. Most of the PONS in this study was transient in nature, resolving within weeks to months; however, 12 (7% of all PONS) cases that were “probably related to anesthesia” lasted beyond six months. The detailed chart review of these 12 patients did not reveal a consistent pattern relating to demographics, diabetes, or nerve localization technique. While popliteal blocks constituted 11.5% of all blocks in this study, six (50%) of these more severe PONS cases had popliteal blocks. As in other studies, USG did not reduce PONS compared with nerve stimulation alone [7,8]. Previous investigators demonstrated little difference between the regional anesthesia technique and the incidence of PONS, with rates between 0.3 per 1,000 and 2.1 per 1,000 depending on how and when the patient was asked about persistent neurological symptoms [7,8,42]. In fact, our rate of PONS lasting beyond 18 months was 13.3 per 10,000, which is higher than most previously published studies, with rates of 2.7 to 9 per 10,000 [6,7,8]. The off-label use of clonidine and/or dexamethasone as adjuncts in regional anesthesia has not previously been associated with PONS [23], yet in our study, the combination of clonidine and dexamethasone and, to a lesser extent, clonidine alone in blocks with 0.5% ropivacaine were independent risk factors for PONS, consistent with a study by Williams et al. analyzing the effect of ropivacaine with or without combination adjuncts on rat sensory neurons [43]. Our results suggest that dexamethasone may be paradoxical, providing some PONS protection at lower doses while increasing concern for PONS at higher doses (based on our subset review). Although previous clinical studies are reassuring regarding dexamethasone or clonidine in PNBs [16,23], the studies were not powered to analyze PONS, and only one study reported clinical results with the combination of dexamethasone and clonidine [21]. The data suggest a potential benefit to using lower concentrations of local anesthetics when a block is combined with general anesthesia and minimizing the dose of adjuncts (e.g., dexamethasone, clonidine) in order to reduce the risk of PONS. In addition, the combination of dexamethasone and clonidine adjuncts, especially in lower extremity blocks, should be used cautiously until further delineation by future clinical trials. Falls occurred in 25 patients (0.28%). Most patients had femoral or popliteal blocks, although three patients had CNBs and 56% of patients were obese (mean BMI = 33). Falls occurred as late as the postoperative day 3. Of the 25 patients with falls, 18 patients (72%) did not seek medical attention, four patients were evaluated and released without sequelae, and three patients (12%) were treated for complications (one facial laceration and two wrist fractures). Fall prevention remains a critical element of any robust ambulatory regional anesthesia program. Catheter Outcome Finally, our CPNB outcomes demonstrated the ability for continuous ambulatory regional analgesia to provide very good analgesia in most patients for an extended period of time with minimal complications. The quality of catheter analgesia was rated as either very good or excellent in 85% of the patients, with an additional 9% rating their analgesia as “good.” Seventeen percent of patients noted leaking symptoms around their catheter site, which is consistent with other studies [44]. While skin reactions have been previously reported with benzoin [45], 10 (0.8%) patients had allergic reactions to one or a combination of our adhesives. There were four (0.3%) cases of infection, two deep and two superficial. One deep infection occurred in a patient on chronic steroids for systemic lupus erythematosus in addition to a concurrent enoxaparin bridge for history of thrombosis. The catheter was removed on postoperative day 5, at which time a local infection was noted. Subsequent work-up with imaging noted a local soft tissue abscess on POD7, yet the patient refused care until POD10. At this time, surgical irrigation and debridement were performed in addition to administration of intravenous antibiotics. The infection ultimately resolved with no subsequent sequelae. Even though most catheters remained in place longer than most studies, our 0.3% rate of significant infection is consistent with previous studies on catheter-related infections [9,44]. Limitations Several important limitations must be considered when interpreting the results of this study. As in all observational studies, specific risk factors for observed associations may not be causal if there was an unmeasured variable accounting for the difference (e.g., preoperative opioid tolerance). However, we feel that this comprehensive analysis reflects an accurate representation of an actual ambulatory surgical anesthesia practice. Reporting of block duration, patient pain scores, satisfaction, and neurologic symptoms was often done only by phone, not by direct examination, and may be affected by reporting bias, the method with which questions were asked, and variations in expectation management. Assessment tools for postoperative pain and patient satisfaction may differ from other studies’ assessment tools, thereby making direct comparisons difficult. No controls were undertaken regarding the perioperative oral and intravenous pain management strategy, which was left to the discretion of the supervising anesthesia and surgical teams. Postoperative opioid or multimodal oral medications were not tracked. Conclusions This study provides further evidence that utilization of regional-based anesthesia for mainly orthopedic, ambulatory procedures is a safe and effective means of providing excellent postoperative analgesia and is associated with a low rate of PONV and unexpected admissions. In our data set involving ropivacaine 0.5%, the combination of dexamethasone (doses most commonly exceeding 2 mg) and clonidine (median dose 100 ug), as well as clonidine alone, may be associated with a higher risk of PONS, especially in lower extremity blocks. However, these adjuncts incur associated benefits including a lower PONV risk and a longer analgesic duration. Further research is needed to delineate patient-specific comorbidities and/or adjuvant-associated postoperative neurologic symptoms. Future adjunct research specifically involving combined ropivacaine, clonidine, and dexamethasone should entail doses/concentrations that are less than those reported herein. Acknowledgments The authors would like to acknowledge the assistance of the following individuals: Jonathan P. Wanderer, MD, MPhil, Assistant Professor, Departments of Anesthesiology and Biomedical Informatics, Vanderbilt University School of Medicine, Nashville, Tennessee (assisted with data collection); Damon R. 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Comprehensive Analysis of 13,897 Consecutive Regional Anesthetics at an Ambulatory Surgery Center

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© 2017 American Academy of Pain Medicine. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com
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Abstract

Abstract Objective The authors investigated a wide range of perioperative outcome measures in the context of a robust regional anesthesia practice. Design Comprehensive review of a prospectively collected six-year database. Setting Freestanding, academic ambulatory surgery center. Subjects There were 13,897 consecutive regional anesthetics in 10,338 patients. Methods We investigated patient satisfaction, postoperative nausea and vomiting (PONV), postoperative pain, catheter analgesia, and complications. Clinical risk factors were examined and presented as odds ratios for multiple outcome analyses including block success, patient satisfaction, PONV, and postoperative neurologic symptoms (PONS). Results Decreased block success was associated with nerve stimulation alone (P < 0.001), obesity (P = 0.001), higher American Society of Anesthesiologists classification (ASA; P = 0.01), lower extremity blocks (P = 0.04), and male sex (P < 0.001). Decreased patient satisfaction was associated with poor catheter analgesia (P < 0.001), complications (P < 0.001), higher ASA (P = 0.001), and younger age (P = 0.008). PONV was associated with postoperative pain (P < 0.005), female sex (P < 0.001), general anesthesia (P < 0.001), younger age (P = 0.001), lack of catheter (P = 0.03), and lack of dexamethasone/clonidine (D + C) adjuncts (P = 0.01). Serious complications and unexpected hospitalizations were rare (<0.2%). D + C adjuncts, lower extremity blocks, clonidine (but not dexamethasone alone), and female sex were associated with PONS (all P < 0.001). Conclusions A regional anesthesia–based practice in ambulatory surgery is an effective means of providing excellent postoperative analgesia and is associated with a low rate of PONV and unexpected admissions. Dexamethasone, clonidine, and their combination when combined with 0.5% ropivacaine may have mixed effects on PONS risk that warrant dose/concentration alterations of these three drugs in the context of off-label perineural adjunct use. Postoperative Pain, Regional Anesthesia, Ambulatory Surgery, Postoperative Nausea and Vomiting, Patient Satisfaction, Postoperative Neurological Symptoms Introduction Effective and safe perioperative pain management is of utmost importance to patients when considering elective surgical procedures [1]. A regional anesthesia and analgesia–based practice has emerged as a means to minimize perioperative pain and opioid side effects while maximizing patient satisfaction; in fact, postoperative nausea and vomiting (PONV) was the leading complaint in one large study, emphasizing the need for techniques that minimize this complication [2]. Although ultrasound-guided regional anesthesia has imparted benefits including reduced procedure times, onset times, failure rates, and local anesthetic systemic toxicity (LAST) rates, risks such as postoperative neurologic symptoms (PONS; persistent sensory block, motor block, and/or dysesthesias beyond 72 hours following block placement or beyond 48 hours after cessation of catheter infusions) [3] and catheter site infection continue to be described in the literature [4–9]. As part of a quality assurance project, we prospectively collected outcome data on all patients at the Nashville Surgery Center over a six-year period from 2008 until 2014 who underwent operations with regional anesthesia alone or combined with general anesthesia. The aim of this study is to assess the value of a robust regional anesthesia practice regarding a range of perioperative outcome measures and to analyze various predictors for specific outcomes. While several studies have previously reported outcomes using large regional anesthesia databases, this analysis is unique in that the data was collected prospectively within 72 hours on 10,338 consecutive patients undergoing 13,897 regional anesthetics at an ambulatory surgery center (ASC) and did not require the voluntary submission from anesthesia providers involved in the case. Methods Study Design and Patients This study is an analysis of a prospectively collected database of patients undergoing regional anesthesia procedures at a single ASC. Beginning in November 2008, study data were collected and managed for practice improvement purposes using Research Electronic Data Capture (REDCap), a secure, web-based application designed to support data capture for current or future research studies [10]. After obtaining approval from the Vanderbilt University Institutional Review Board, the authors conducted a comprehensive review of 13,897 consecutive regional anesthetics at the Nashville Surgery Center from November 2008 through October 2014. Senior residents or fellows under the supervision of a regional anesthesia faculty member performed regional anesthetic blocks, with a minority of blocks performed by a faculty member alone. Combined general with regional anesthesia or regional anesthesia alone was administered based on the preference of the patient, anesthesiologist, and surgeon. Anesthesiologists routinely administered dual therapies for PONV prevention in patients receiving general anesthesia in addition to their regional anesthetic. Ondansetron and dexamethasone (unless dexamethasone was given as an adjunct within the regional anesthetic) were most commonly administered as most patients were considered at at least moderate risk for PONV [11]. Rarely, patients received either initial or repeat regional anesthetics in the Post-Anesthesia Care Unit (PACU) for breakthrough pain. Continuous peripheral nerve block (CPNB) catheters were placed for patients who were expected to require extended analgesia. Catheter confirmation was determined by visualization of either hydrodissection or color doppler surrounding at least 50% of the neural target with local anesthetic bolus through the catheter. Following catheter placement, Mastisol (Eloquest Healthcare, Ferndale, MI) was routinely applied to the skin as well as a LockIt Device (Smiths Medical, Dublin, OH, USA) and Tegaderm (3M, St Paul, MN, USA). Postoperative Period Patients were assessed in the PACU by the anesthesiologist, given written block-specific discharge instructions, and given the anesthesia on-call cell phone number for questions or concerns. Patients who were discharged home with CPNB catheters also received discharge instructions in the PACU with a family member regarding the elastomeric pain pump and catheter care, given instruction on the use of oral analgesics as adjuncts, provided with two catheter information brochures (one specific to our practice and one from the pump manufacturer), and followed with daily phone calls. The majority of patients with CPNB catheters were connected to an On-Q (Halyard Worldwide, Inc.; Alpharetta, GA, USA) elastomeric single-use disposable pump. If necessary, catheter patients could return to the ASC (or the hospital if after hours) for inadequate analgesia or major concerns. Patients and family members were instructed to remove the pain catheter at home when the elastomeric pump was empty, but no later than the fifth postoperative day. Residents and fellows entered the surgical and regional anesthetic information in the REDCap regional anesthesia database on the day of surgery. They added per-patient data based on phone interviews on postoperative day 1 and/or day 2 (POD1 or POD2); in the rare case of a preverbal child, the parent was asked to assess the patient’s status (e.g., pain subjectively scored by parents as none, mild, moderate, or severe), based on the child’s appearance and age-specific language. Any evidence of PONS or other concerns was documented and followed until resolution. At least two attempts were made on different days before patient follow-up was deemed unsuccessful; follow-up on catheters persisted until contact was made. Patients with CPNBs were followed daily until catheters were removed and blocks resolved. Cases were considered complete only after resolution of the regional anesthetic. Day of surgery information included demographics (age, American Society of Anesthesiologists [ASA] classification, sex, body mass index [BMI], date of surgery, surgical procedure), as well as detailed block information: type of block(s); nerve localization method including nerve stimulation (NSTIM) and/or ultrasound guidance (USG); type, concentration, and volume of local anesthetic (based on anesthesiologist’s discretion); adjuncts (dexamethasone and/or clonidine or none) [12] and dose; presence of a catheter; use of general anesthesia; immediate complications; and block success (defined by lack of response to painful intraoperative stimuli when coupled with sedation or lack of significant postoperative pain when coupled with general anesthesia). Postoperative outcome data included any occurrence of nausea with or without vomiting, daily pain scale (none, mild, moderate, severe), patient satisfaction scale (excellent, very good, good, fair, poor), duration of block (based on patient’s perception of block resolution), presence of postoperative neurological symptoms, or other complications. Additional detailed catheter information included quality of analgesia scale (excellent, very good, good, fair, poor), duration of catheter analgesia, and catheter complications. The data was reviewed weekly for completeness and consistency by the same anesthesiologist, including follow-up on each case until resolution of complications or concerns. Data collection for any patient with PONS included review of long-term follow-up by both orthopedics and anesthesiology for a minimum of one year postprocedure. Where additional information was needed, the electronic medical record was reviewed. Statistical Analysis Surgical procedures were divided into seven major categories based on anatomical regions to facilitate comparison between groups (Table 1). Similarly, the regional anesthetics were divided into six major groups based on neural anatomical distribution for comparison purposes (Table 2). Patient demographics, clinical/procedural characteristics, and outcomes were summarized with the mean, standard deviation, range, median, 25th and 75th percentiles for quantitative variables, and counts and percentages for categorical variables. To further analyze block duration based on specific adjuncts, the largest subset of “blocks for elbow-hand procedures” was examined and duration reported (Table 3). Logistic regression was used to examine the associations between clinical risk factors and binary outcomes, including block success, PONV, and PONS. Proportional odds ordinal logistic regression was similarly used to examine ordered categorical outcomes, namely patient satisfaction (five-point scale) and pain on POD1 (four-point scale). Table 1 Demographics (N = 10,338)   Age, y   1–10, No. (%)  27 (0.3)   11–17, No. (%)  827 (8.0)   18 or older, No. (%)  9,484 (91.7)   Mean (±SD)  43.1 (±17.4)  Gender, No. (%)   Female  4,819 (46.6)   Male  5,519 (53.4)  ASA status, No. (%)   I  2,984 (28.9)   II  5,506 (53.2)   III  1,824 (17.7)   IV  24 (0.2)  BMI (N = 7,028)*, No. (%)   <30  4,446 (63.3)   30–40  2,191 (31.2)   >40  391 (5.6)   Mean (±SD)  28.8 (±6.2)  Surgical procedure by regions, No. (%)   Shoulder/clavicle/scapula  1,822 (17.6)   Elbow  793 (7.7)   Distal forearm/wrist/hand  3,498 (33.8)   Knee  2,139 (20.7)   Foot/ankle  2,010 (19.5)   Head/neck/other  56 (0.5)   Chest/abdomen  20 (0.2)    Age, y   1–10, No. (%)  27 (0.3)   11–17, No. (%)  827 (8.0)   18 or older, No. (%)  9,484 (91.7)   Mean (±SD)  43.1 (±17.4)  Gender, No. (%)   Female  4,819 (46.6)   Male  5,519 (53.4)  ASA status, No. (%)   I  2,984 (28.9)   II  5,506 (53.2)   III  1,824 (17.7)   IV  24 (0.2)  BMI (N = 7,028)*, No. (%)   <30  4,446 (63.3)   30–40  2,191 (31.2)   >40  391 (5.6)   Mean (±SD)  28.8 (±6.2)  Surgical procedure by regions, No. (%)   Shoulder/clavicle/scapula  1,822 (17.6)   Elbow  793 (7.7)   Distal forearm/wrist/hand  3,498 (33.8)   Knee  2,139 (20.7)   Foot/ankle  2,010 (19.5)   Head/neck/other  56 (0.5)   Chest/abdomen  20 (0.2)  ASA = American Society of Anesthesiologists; BMI = body mass index. * Adult patients age 18 years or older with complete BMI data. Table 2 Regional anesthetic procedures Regional anesthesia procedures (N = 13,888)*  Blocks for shoulder region  1,836 (13.2)   Interscalene  1,806 (13.0)   Cervical plexus, suprascapular  30 (0.2)  Blocks for elbow-hand region  4,295 (30.9)   Supraclavicular  850 (6.1)   Infraclavicular  1,605 (11.6)   Axillary  1,840 (13.2)  Distal upper extremity blocks†  1,247 (9.0)  Blocks involving lumbar plexus and branches  3,551 (25.6)   Lumbar plexus  653 (4.8)   Femoral  1,459 (10.5)   Saphenous/adductor canal  1,074 (7.7)   Obturator, other  365 (2.6)  Blocks involving sciatic nerve and branches  2,181 (15.7)   Sciatic  155 (1.1)   Popliteal  1,630 (11.7)   Ankle  396 (2.9)  Miscellaneous blocks  778 (5.6)   Spinal or epidural  294 (2.1)   Blocks for head‡  45 (0.3)   Paravertebral/TAP blocks  53 (0.4)   Repeat blocks, intercostobrachial  386 (2.8)  Nerve localization and other end points    Nerve stimulation only (N = 13,897)  1,319 (9.5)   Ultrasound guidance (N = 13,897)  11,128 (80.1)   Success (N = 13,892)  13,524 (97.4)   Combined with general  anesthesia (N = 10,338)§  5,398 (52.2)  Regional anesthesia procedures (N = 13,888)*  Blocks for shoulder region  1,836 (13.2)   Interscalene  1,806 (13.0)   Cervical plexus, suprascapular  30 (0.2)  Blocks for elbow-hand region  4,295 (30.9)   Supraclavicular  850 (6.1)   Infraclavicular  1,605 (11.6)   Axillary  1,840 (13.2)  Distal upper extremity blocks†  1,247 (9.0)  Blocks involving lumbar plexus and branches  3,551 (25.6)   Lumbar plexus  653 (4.8)   Femoral  1,459 (10.5)   Saphenous/adductor canal  1,074 (7.7)   Obturator, other  365 (2.6)  Blocks involving sciatic nerve and branches  2,181 (15.7)   Sciatic  155 (1.1)   Popliteal  1,630 (11.7)   Ankle  396 (2.9)  Miscellaneous blocks  778 (5.6)   Spinal or epidural  294 (2.1)   Blocks for head‡  45 (0.3)   Paravertebral/TAP blocks  53 (0.4)   Repeat blocks, intercostobrachial  386 (2.8)  Nerve localization and other end points    Nerve stimulation only (N = 13,897)  1,319 (9.5)   Ultrasound guidance (N = 13,897)  11,128 (80.1)   Success (N = 13,892)  13,524 (97.4)   Combined with general  anesthesia (N = 10,338)§  5,398 (52.2)  TAP = transversus abdominis plane block. * Type of block, complete data. † Musculocutaneous, elbow, wrist blocks. ‡ Retrobulbar, trigeminal, scalp. § Based on total patients. Table 3 Local anesthetics and adjuncts Local anesthetics and adjuncts used (N = 13,880)*, No. (%)  Local anesthetics used   Ropivacaine  9,872 (71.1)   Mepivacaine  2,359 (17.0)   Bupivacaine  592 (4.3)   Lidocaine  330 (2.4)   Chloroprocaine  186 (1.3)   Mepivacaine/ropivacaine  481 (3.5)   Mepivacaine/bupivacaine  60 (0.4)  Adjuncts used (N = 13,897)†   None  8,856 (63.7)   Clonidine and dexamethasone (C+D)  1,857 (13.4)   Clonidine (C)  1,733 (12.5)   Dexamethasone (D)  1,451 (10.4)  Adjunct doses   Dexamethasone, mg  Median‡ = 4 (2,8)  Mean (SD) = 4.4 (2.7)  Range = 0.25–8.0   Clonidine, ug  Median‡ = 100 (50,100)  Mean (SD) = 79.6 (26.4)  Range§ = 7.5–100  Duration analysis (Blocks for elbow-hand subset using 0.5% ropivacaine)  Adjunct  No.  Dose dex Mean (SD), mg  Dose clonidine Mean (SD), ug  Duration Mean (SD), h  None  1,582  –  –  15.3 (5.5)   C  544  –  96.4 (13.9)  16.5 (6.0)   D  380  6.0 (2.2)  –  20.5 (7.3)  D4 subgrp  134  4  –  17.8 (6.0)  D8 subgrp  159  8  –  22.3 (7.7)   C+D  644  2.2 (0.6)  86.4 (22.4)  23.7 (9.8)  Local anesthetics and adjuncts used (N = 13,880)*, No. (%)  Local anesthetics used   Ropivacaine  9,872 (71.1)   Mepivacaine  2,359 (17.0)   Bupivacaine  592 (4.3)   Lidocaine  330 (2.4)   Chloroprocaine  186 (1.3)   Mepivacaine/ropivacaine  481 (3.5)   Mepivacaine/bupivacaine  60 (0.4)  Adjuncts used (N = 13,897)†   None  8,856 (63.7)   Clonidine and dexamethasone (C+D)  1,857 (13.4)   Clonidine (C)  1,733 (12.5)   Dexamethasone (D)  1,451 (10.4)  Adjunct doses   Dexamethasone, mg  Median‡ = 4 (2,8)  Mean (SD) = 4.4 (2.7)  Range = 0.25–8.0   Clonidine, ug  Median‡ = 100 (50,100)  Mean (SD) = 79.6 (26.4)  Range§ = 7.5–100  Duration analysis (Blocks for elbow-hand subset using 0.5% ropivacaine)  Adjunct  No.  Dose dex Mean (SD), mg  Dose clonidine Mean (SD), ug  Duration Mean (SD), h  None  1,582  –  –  15.3 (5.5)   C  544  –  96.4 (13.9)  16.5 (6.0)   D  380  6.0 (2.2)  –  20.5 (7.3)  D4 subgrp  134  4  –  17.8 (6.0)  D8 subgrp  159  8  –  22.3 (7.7)   C+D  644  2.2 (0.6)  86.4 (22.4)  23.7 (9.8)  * For a given nerve block, our practice uses one or a combination of the following local anesthetics: 0.5% ropivacaine, 1.5% mepivacaine, 0.25–0.5% bupivacaine, 2% lidocaine, 3% chloroprocaine. Rarely, more dilute concentrations were utilized. † None, one, or more of the following additives were added to the local anesthetic: clonidine and/or dexamethasone; epinephrine was added as a vascular marker to any of above combinations at discretion of anesthesiologist in 21% of blocks. ‡ With 25th and 75th percentiles. § Range = 7.5–100, although one block had 200 ug. For each outcome, the set of risk factors considered was prespecified on the basis of expert opinion among the authors as well as a literature review from previous studies regarding predictors of outcomes (e.g., well-established predictors for PONV). The authors applied predictors uniformly across the outcomes analyzed whenever possible (e.g., demographics including age, sex, ASA, BMI > 30, as well as use of either CPNB or USG). However, some predictors were considered to be unique for certain outcomes. For block success, the outcome-specific risk factors included NSTIM/USG, block type, and local anesthetic. The PONV-specific risk factors included general anesthesia, pain rating postoperatively on day of surgery (PO-DOS), and adjuncts. The PONS-specific risk factors included NSTIM/USG, block type, adjuncts, and paresthesia. For patient satisfaction, risk factors included general anesthesia, complications, NSTIM/USG, pain rating on PO-DOS, PONS, block failure, PONV, and block duration. For pain on POD1, risk factors included surgical group, local anesthetics, adjuncts, and block duration. Other possible predictors, such as preoperative opioid use, ethnicity, and duration of surgery, were not available in the database. All prespecified risk factors were analyzed in the model simultaneously using multiple regression. The possibility of nonlinear association between age and outcomes was examined using a flexible nonlinear function (i.e., a restricted cubic spline with knots at the fifth, 35th, 65th, and 95th percentiles for age) [13]. A linear model was used when there was no evidence of nonlinearity using a likelihood ratio test. Multiple imputation using a chained-equations approach was employed to account for the uncertainty due to missing data [14]. The robust sandwich estimator was used to account for correlation introduced by multiple block data between patients [15]. The effects of demographic factors and risk factors are presented using the odds ratios (OR; 95% confidence interval [CI]). For proportional odds logistic regression (POLR), the odds ratio for a given covariate is relevant to every binary grouping of the ordinal outcome (e.g., none/mild vs moderate/severe). Due to the proportional odds feature, the following two example statements are both valid: “The odds of reporting severe nausea were twofold greater among females vs males” and “The odds of reporting moderate or severe nausea were twofold greater among females vs males.” Thus, POLR odds ratios are often summarized using language that applies to any binary grouping of the outcome, for example, “The odds of reporting more intense nausea were twofold larger among females vs males.” All analyses were performed using R version 3.2.1. Tests with P values of less than than 0.05 were considered statistically significant. Results Demographics The demographics of the 10,338 patients are summarized in Table 1. Mean patient age was 43 years (±SD 17.4), while 854 (8.3%) patients were younger than age 18 years. Females comprised 46.6% of the study population. Most patients were ASA I or II status (82.1%), while the remainders were ASA III (17.7%) and ASA IV (0.2%). The mean BMI for adult patients was 28.8 (±SD 6.2), while 36.8% were obese, with BMI greater than 30. Techniques of Regional Anesthetics Table 2 summarizes the types of blocks performed including 7,378 (53%) upper extremity blocks, 3,551 (26%) blocks involving the lumbar plexus (proximal or distal), 2,181 (16%) blocks involving the sciatic nerve (proximal or distal), 294 (2%) central neuraxial blocks (CNB), and 484 (3%) eye, facial, truncal, and repeat blocks. USG was used in the majority of blocks (80%); NSTIM was used in 66% of blocks while 9.5% utilized NSTIM without USG. General anesthesia was combined with regional anesthesia in 52% of the cases. Overall, 97.4% of the blocks were successful. When independent risk factors were analyzed for block success, factors most associated with decreased success were nerve stimulation alone (OR = 0.3, 95% CI = 0.24–0.46, P < 0.001; 93.2% compared with USG 97.8%) and obesity (OR = 0.6, 95% CI = 0.48–0.83, P = 0.001; 95.6% vs 97.8% success with BMI > 30 compared with BMI <30, respectively). Higher ASA classification (OR = 0.7, 95% CI = 0.50–0.91, P = 0.01), lower extremity blocks (OR = 0.8, 95% CI = 0.56–0.99, P = 0.04), and age (50th vs 25th age percentile, OR = 0.8, 95% CI = 0.71–0.99, nonlinear effect, P = 0.05) were also associated with decreased success. Age was associated with block success in a nonlinear fashion such that blocks in patients at the 50th percentile of age were less successful than those for patients at the 25th percentile of age, while there was no significant difference between those at the 50th and 75th percentiles. Female sex was associated with increased success (OR = 1.6, 95% CI = 1.22–2.01, P < 0.001), while use of CPNBs was not a significant factor (Figure 1, odds ratios for block success). Figure 1 View largeDownload slide Odds ratios (95% confidence intervals) of block success. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Age was examined comparing quartiles of age, which had a nonlinear association (P = 0.005). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE blocks: lower vs upper extremity blocks. Pairwise comparisons were conducted between block types (Table 2). Local anesthetics and other block type comparisons were omitted from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; UE = upper extremity; USG = ultrasound guidance. Figure 1 View largeDownload slide Odds ratios (95% confidence intervals) of block success. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Age was examined comparing quartiles of age, which had a nonlinear association (P = 0.005). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE blocks: lower vs upper extremity blocks. Pairwise comparisons were conducted between block types (Table 2). Local anesthetics and other block type comparisons were omitted from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; UE = upper extremity; USG = ultrasound guidance. Anesthesiologists incorporated ropivacaine or mepivacaine in 71% and 17% of blocks, respectively. Lidocaine, bupivacaine, or combinations were used in the remaining 12% of blocks (Table 3). Low-dose chloroprocaine or lidocaine was used for short-acting spinal anesthesia. In order to increase peripheral nerve block (PNB) duration [12,16], dexamethasone, clonidine, or their combination were incorporated as adjuncts in 10%, 13%, and 13%, respectively, with doses in Table 3. Finally, epinephrine was added as a vascular marker in 21% of the blocks. Median (interquartile range) duration of all blocks was 16.0 (12.0–24.0) hours. Within the blocks for elbow-hand subset using 0.5% ropivacaine, mean duration (SD) with no adjunct was 15.3 (5.5) hours, with clonidine 16.5 (6.0), with dexamethasone 20.5 (7.3), and with dexamethasone and clonidine 23.7 (9.8; all pairwise comparisons were significant; P < 0.001). Ropivacaine 0.25% was only rarely used and therefore not further analyzed. Within the dexamethasone only group, the mean dose was 6.0 mg (2.2 mg), while the mean clonidine dose in the clonidine only group was 96.4 ug (13.9 ug). For the combined dexamethasone and clonidine group, the mean doses were 2.2 mg (0.6 mg) and 86.4 ug (22.4 ug), respectively. Patient Satisfaction Regarding patient satisfaction, most (95%) patients reported “very good” or “excellent” satisfaction with a regional-based anesthetic for their operation; 4% rated their overall satisfaction as “good,” while less than 1% rated their satisfaction as either “fair” or “poor” (Table 4). The risk factors associated with lower patient satisfaction (e.g., “fair/poor”) were poor CPNB analgesia (OR ≤ 0.1, 95% CI = 0.02–0.08, P < 0.001), severe pain PO-DOS (OR = 0.2, 95% CI = 0.14–0.29, P < 0.001), moderate pain PO-DOS (OR = 0.3, 95% CI = 0.21–0.33, P < 0.001), PONS (OR =  0.3, 95% CI = 0.21–0.39, P < 0.001), any complications (OR = 0.3, 95% CI = 0.20–0.42, P < 0.001), block failure (OR = 0.4, 95% CI = 0.27–0.60, P < 0.001), mild pain PO-DOS (OR = 0.5, 95% CI = 0.43–0.56, P < 0.001), catheter complications (OR = 0.6, 95% CI = 0.47–0.88, P = 0.005), PONV (OR = 0.7, 95% CI = 0.61–0.82, P < 0.001), and higher ASA classification (OR = 0.8, 95% CI = 0.69–0.91, P = 0.001). Averaging across all patients, postoperative pain was significantly associated with poor patient satisfaction. Patient satisfaction was progressively worse with increasing postoperative pain severity. Older age was associated with higher patient satisfaction (OR = 1.1, 95% CI = 1.03–1.24, P = 0.008). General anesthesia, sex, BMI, nerve localization technique, and block duration were not significant risk factors. (Figure 2, odds ratios for higher patient satisfaction). Table 4 Patient satisfaction, PONV, and block complications Patient satisfaction (N = 8896), No. (%)   Excellent  6725 (75.6)   Very good  1746 (19.6)   Good  325 (3.7)   Fair  74 (0.8)   Poor  26 (0.3)  PONV (N = 9001), No. (%)   Nausea  1079 (12.0)   Vomiting  286 (3.2)  Complications (N = 8995), No. (%, 95% CI)   None  8,661 (96.3)   PONS*  208 (2.3, 2.0–2.6)   Falls†  25 (0.3, 0.2–0.4)   Epidural spread‡  24 (0.3, 0.2–0.4)   Unexpected hospital admission  pain  21 (0.2, 0.2–0.4)   Pulmonary§  20 (0.2, 0.1–0.3)   Cardiac¶  13 (0.1, 0.1–0.2)   Headache‖  8 (0.1, 0.0–0.2)   Back Pain‖|  4 (<0.1, 0.0–0.1)   Death within 72 h**  2 (<0.1, 0.0–0.1)   Seizures††  1 (<0.1, 0.0–0.1)   Other Minor‡‡  11 (0.1, 0.1–0.2)  Patient satisfaction (N = 8896), No. (%)   Excellent  6725 (75.6)   Very good  1746 (19.6)   Good  325 (3.7)   Fair  74 (0.8)   Poor  26 (0.3)  PONV (N = 9001), No. (%)   Nausea  1079 (12.0)   Vomiting  286 (3.2)  Complications (N = 8995), No. (%, 95% CI)   None  8,661 (96.3)   PONS*  208 (2.3, 2.0–2.6)   Falls†  25 (0.3, 0.2–0.4)   Epidural spread‡  24 (0.3, 0.2–0.4)   Unexpected hospital admission  pain  21 (0.2, 0.2–0.4)   Pulmonary§  20 (0.2, 0.1–0.3)   Cardiac¶  13 (0.1, 0.1–0.2)   Headache‖  8 (0.1, 0.0–0.2)   Back Pain‖|  4 (<0.1, 0.0–0.1)   Death within 72 h**  2 (<0.1, 0.0–0.1)   Seizures††  1 (<0.1, 0.0–0.1)   Other Minor‡‡  11 (0.1, 0.1–0.2)  PONS= postoperative neurological symptoms; PONV = postoperative nausea and vomiting. * See Table 6, PONS defined as neurological symptoms > 72 hours’ duration. † All falls occurred following knee or foot/ankle surgery usually involving either a femoral or popliteal block. Three falls occurred after spinal or epidural block. ‡ Primarily during lumbar plexus blocks. § Symptomatic hemidiaphragmatic paresis (no pneumothorax events). ¶ Includes significant Bezold-Jarisch reflex, syncope, hypotension, myocardial ischemia, or new chest pain within 72 hours. ‖ Six headaches related to spinal/epidurals (2% PDPH rate). ‖| All related to spinal, epidural, or lumbar plexus block. ** Two deaths during this time period. Neither death directly related to the regional anesthetic. See text for details. †† Partial seizure in the Post-Anesthesia Care Unit postoperatively three hours postblock, associated with vasovagal episode, not felt secondary to local anesthetic systemic toxicity. ‡‡ Other events include pain at needle entry site, intravascular local anesthetic injection without symptoms, intolerance to block procedure, hoarseness. Figure 2 View largeDownload slide Odds ratios (95% confidence intervals) for high patient satisfaction. ORs were calculated using a proportional odds logistical regression. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile. Obesity: BMI  > 30 vs < 30. Higher ASA status: III/IV vs I/II. Catheter failure (poor/fair analgesia) vs single injection. NSTIM vs USG (±NSTIM). Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Postoperative neurologic symptoms. The effect of block duration and nonlinear age effect was omitted from the figure for nonsignificance and clarity. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS = postoperative neurological symptoms; PONV = postoperative nausea and vomiting; UE = upper extremity; USG = ultrasound guidance. Figure 2 View largeDownload slide Odds ratios (95% confidence intervals) for high patient satisfaction. ORs were calculated using a proportional odds logistical regression. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile. Obesity: BMI  > 30 vs < 30. Higher ASA status: III/IV vs I/II. Catheter failure (poor/fair analgesia) vs single injection. NSTIM vs USG (±NSTIM). Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Postoperative neurologic symptoms. The effect of block duration and nonlinear age effect was omitted from the figure for nonsignificance and clarity. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS = postoperative neurological symptoms; PONV = postoperative nausea and vomiting; UE = upper extremity; USG = ultrasound guidance. Postoperative Nausea and Vomiting Twelve percent of patients experienced postoperative nausea while 3.2% experienced postoperative vomiting within the first 24 hours following surgery (Table 4). Independent risk factors for PONV were PO-DOS pain (OR = 2.5, 95% CI = 1.60–3.90, P < 0.001; OR = 1.5, 95% CI = 1.07–1.96, P = 0.02; OR = 1.3, 95% CI = 1.08–1.52, P = 0.005, for severe, moderate, and mild pain respectively), female sex (OR = 1.8, 95% CI = 1.55–2.05, P < 0.001), and general anesthesia (OR = 1.3, 95% CI = 1.12–1.50, P < 0.001), while CPNB (OR = 0.8, 95% CI = 0.64–0.97, P = 0.03), older age (OR = 0.8, 95% CI = 0.73–0.93, P = 0.001), and dexamethasone/clonidine adjunct (OR = 0.7, 95% CI = 0.59–0.93, P = 0.01) were less likely to be associated with PONV. BMI, ASA classification, and adjuncts of dexamethasone or clonidine alone were not significant risk factors (Figure 3, ORs for postoperative nausea and vomiting). Figure 3 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative nausea and vomiting. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile of age. (Nonlinear age effect was also examined and removed for lack of evidence.) Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. ASA = American Society of Anesthesiologists classification; OR = odds ratio; PONV = postoperative nausea and vomiting. Figure 3 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative nausea and vomiting. Calculations were based on logistical regression analysis. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: 75th percentile vs 25th percentile of age. (Nonlinear age effect was also examined and removed for lack of evidence.) Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. Combined vs regional: regional + general vs regional + sedation. Mild pain vs no pain postoperatively on day of surgery (PO-DOS). Moderate pain vs no pain (PO-DOS). Severe pain vs no pain (PO-DOS). Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. ASA = American Society of Anesthesiologists classification; OR = odds ratio; PONV = postoperative nausea and vomiting. Postoperative Pain Most patients, 94%, reported “none to mild” pain on the day of surgery, while 33% and 24% reported “moderate to severe” pain on postoperative day 1 and day 2, respectively (Figure 4, postoperative pain chart). Risk factors associated with less pain on POD1 were general anesthesia (OR = 0.8, 95% CI = 0.67–0.84, P < 0.001) and older age, 75th compared with 50th percentile (OR = 0.9, 95% CI = 0.80–0.91, P < 0.001). In addition, compared with distal upper extremity procedures, chest and abdomen procedures (OR =  0.5, 95% CI = 0.26–0.93, P = 0.03), thigh and knee procedures (OR =  0.6, 95% CI = 0.48–0.65, P < 0.001), and foot and ankle procedures (OR =  0.7, 95% CI = 0.58–0.75, P < 0.001) were also associated with less pain. Risk factors associated with more pain were female sex (OR =  1.3, 95% CI = 1.17–1.40, P < 0.001) and higher ASA (OR =  1.3, 95% CI = 1.14–1.44, P < 0001). Figure 4 View largeDownload slide The distribution of postoperative pain scores on day of surgery, postoperative day 1, postoperative day 2, and postoperative day 3 on a four-point scale (none, mild, moderate, severe). DOS = day of surgery; POD = postoperative day. Figure 4 View largeDownload slide The distribution of postoperative pain scores on day of surgery, postoperative day 1, postoperative day 2, and postoperative day 3 on a four-point scale (none, mild, moderate, severe). DOS = day of surgery; POD = postoperative day. Complications Table 4 summarizes reported side effects and complications that may be related to anesthesia. Serious complications were rare: 13 patients (0.1%) had significant hypotension and/or bradycardia; 20 patients (0.2%) had significant respiratory complaints primarily following interscalene blocks due to hemidiaphragmatic paresis (no clinically evident pneumothoraces); 21 patients (0.2%) required unexpected hospital admission due to severe postoperative pain; 25 patients (0.3%) with either femoral, popliteal, or CNB blocks fell postoperatively; one patient (0.01%) had a partial seizure in the PACU; and two patients died in the postoperative period. (One patient with obesity, opioid tolerance, anxiety, and chronic osteomyelitis had an accidental drug overdose involving both opioids and benzodiazepines at home on the day of surgery after meeting PACU discharge criteria. The other patient had significant comorbidities including morbidly obesity [BMI = 48], history of remote cocaine abuse, obstructive sleep apnea [OSA] on continuous positive airway pressure [CPAP], and opioid tolerance on preoperative oxycodone, hydromorphone, cyclobenzaprine, and gabapentin. After an uneventful shoulder operation with combined general anesthesia and an interscalene catheter, the patient met PACU discharge criteria but died on POD2 from unclear etiology.) Catheter Information In addition to single injection blocks, 1,261 indwelling pain catheters were utilized in 1,228 patients (11.9%) at the discretion of the anesthesiologist. Catheter-related information is reported in Table 5. Based on telephone-reported pain information, catheter analgesia was adequate in 93.3% of patients (60.3% “excellent,” 24.5% “very good,” 8.5% “good”), while 6.7% rated their analgesia as “poor” or “fair.” Catheters remained in place 48 to 96 hours in 72% of patients, longer than 96 hours in 18% of patients, and less than 48 hours in 10% of patients. Seventy-four percent of patients had no concerns or complications from their catheters. Leaking around the catheter (17%), catheter dislodgement (3.7%), and need for catheter manipulation by an anesthesiologist (2.3%) were the primary catheter complications, while mechanical pump/clamp issues (0.9%), allergic skin reactions (0.8%), and infections (0.3%) rarely occurred. In the middle of the study period, a medical grade adhesive (Surgiseal, Adhezion BioMedical, LLC, Wyomissing, PA, USA) was increasingly used at catheter insertion sites, yet there was insufficient evidence of an impact on leakage rate. All patients with skin reactions or infections (two deep and two superficial) cleared completely with treatment. Table 6 PONS Overview (N = 8987)*, No. (%) or No. (range)   PONS (>72 h duration)      208 (2.3)   Sensory deficits only      194 (93)†   Sensory and motor deficits      14 (7)†   Dysesthesias present      43 (21)†   Tourniquet time > 120 min      1 (0.7)†  Onset of symptoms, d   <7      190 (93)   7–14      4 (2)   >14      10 (5)  Duration, mo   <4      131 (77)   4–6      14 (8)   7–18      14 (8)   >18      12 (7)   Lost to follow-up      37 (18)  Potentially related to block‡   Improbable      29 (14)   Possible      112 (55)   Probable      64 (31)  Subset: duration > 6 mo and “probably related to anesthesia” (N = 12)   Age, y  42.5 (21–75)  NSTIM  11 (92)   Female sex  5 (42)  USG  8 (67)   ASA  2.1  Volume, mL  33 (25–50)   BMI  26.6 (21–35)  Adjunct¶     Diabetes  0   None  3 (25)   Preop numbness  1 (8)   Dexamethasone, 8 mg  3 (25)   Tourniquet time, min  0–82   C+D‖  6 (50)   Blocks    CPNB  2 (17)    Upper extremity  4 (33)  Gen anesthesia  7 (58)    Lower extremity§  8 (67)  Dysesthesia  7 (58)   0.5% ropivacaine  12 (100)  Weakness  4 (33)  Overview (N = 8987)*, No. (%) or No. (range)   PONS (>72 h duration)      208 (2.3)   Sensory deficits only      194 (93)†   Sensory and motor deficits      14 (7)†   Dysesthesias present      43 (21)†   Tourniquet time > 120 min      1 (0.7)†  Onset of symptoms, d   <7      190 (93)   7–14      4 (2)   >14      10 (5)  Duration, mo   <4      131 (77)   4–6      14 (8)   7–18      14 (8)   >18      12 (7)   Lost to follow-up      37 (18)  Potentially related to block‡   Improbable      29 (14)   Possible      112 (55)   Probable      64 (31)  Subset: duration > 6 mo and “probably related to anesthesia” (N = 12)   Age, y  42.5 (21–75)  NSTIM  11 (92)   Female sex  5 (42)  USG  8 (67)   ASA  2.1  Volume, mL  33 (25–50)   BMI  26.6 (21–35)  Adjunct¶     Diabetes  0   None  3 (25)   Preop numbness  1 (8)   Dexamethasone, 8 mg  3 (25)   Tourniquet time, min  0–82   C+D‖  6 (50)   Blocks    CPNB  2 (17)    Upper extremity  4 (33)  Gen anesthesia  7 (58)    Lower extremity§  8 (67)  Dysesthesia  7 (58)   0.5% ropivacaine  12 (100)  Weakness  4 (33)  PONS = postoperative neurological symptoms. * Patients who were available for follow-up regarding possible residual block. † % of PONS population (N = 208). ‡ Based on authors’ review of each case including targeted history and physical as well as neurological consultations and studies, if available. § Including six popliteal blocks. ¶ Epinephrine was used as a vascular marker in five (42%) cases. ‖ Clonidine dose: mean 100 ug + dexamethasone dose: mean 2.8 mg. Postoperative Neurologic Sequelae Postoperative neurologic symptoms (PONS), defined as neurological symptoms lasting more than 72 hours after the nerve block, were diagnosed in 208 patients (2.3%) in our study population, of whom 14 (7% of those with PONS diagnosis) complained of motor function involvement. Table 6 summarizes PONS information including symptoms, onset, duration, and possible relation to block, as well as a subset analysis of prolonged PONS cases that were “probably related to anesthesia.” Tourniquet ischemia was not a major contributor as only one patient had a tourniquet time beyond 120 minutes and most tourniquets were simply ankle Esmarch wraps. While 190 (93%) patients complained of persistent sensory deficits within seven days following surgery, 10 patients (5% of PONS patients) did not complain of symptoms until at least two weeks following surgery despite reported return of full motor and sensory function during the primary postoperative follow-up phone calls. Duration of symptoms varied substantially, with 85% resolution within six months and 93% resolution within 18 months. Table 5 Catheter information Catheter types (N = 1261)*, No. (%)   Popliteal sciatic  699 (55.4)   Interscalene  430 (34.1)   Supra/infraclavicular  64 (5.0)   Infragluteal sciatic  20 (1.6)   Other†  48 (3.9)  Catheter analgesia (N = 1215)   Excellent  733 (60.3)   Very good  298 (24.5)   Good  103 (8.5)   Fair  36 (3.0)   Poor  45 (3.7)  Issues, complications   None  911 (74.1)   Leaking, overall‡  212 (17.3)   Dislodgement‡  45 (3.7)   Catheter needing  manipulation/replacement  28 (2.3)   Mechanical pump/catheter  issue (usually not infusing)  11 (0.9)   Skin reaction, allergic  10 (0.8)   Pulled prematurely  7 (0.6)   Infection  4 (2 superficial, 2 deep) (0.3)  Catheter types (N = 1261)*, No. (%)   Popliteal sciatic  699 (55.4)   Interscalene  430 (34.1)   Supra/infraclavicular  64 (5.0)   Infragluteal sciatic  20 (1.6)   Other†  48 (3.9)  Catheter analgesia (N = 1215)   Excellent  733 (60.3)   Very good  298 (24.5)   Good  103 (8.5)   Fair  36 (3.0)   Poor  45 (3.7)  Issues, complications   None  911 (74.1)   Leaking, overall‡  212 (17.3)   Dislodgement‡  45 (3.7)   Catheter needing  manipulation/replacement  28 (2.3)   Mechanical pump/catheter  issue (usually not infusing)  11 (0.9)   Skin reaction, allergic  10 (0.8)   Pulled prematurely  7 (0.6)   Infection  4 (2 superficial, 2 deep) (0.3)  * Total catheters in 1,228 patients (some with multiple continuous peripheral nerve blocks). † Other locations include saphenous/adductor canal, cervical plexus, femoral, dual catheter combinations, other. ‡ Cyano-acrylate adhesive applied at the catheter insertion site decreased leaking during second half of study period (P = 0.48 when adjusted for age, gender, body mass index, American Society of Anesthesiologists classification, and ultrasound guidance/nerve stimulation). Of the patients who had PONS more than six months (26 patients), 12 patients had neurologic sequelae that were determined to be “probably related to anesthesia.” Although a statistical analysis of 12 patients was not possible, we performed a detailed chart review to elucidate any possible patterns within this subset of patients (Table 6). Eight (66.7%) received lower extremity blocks including six popliteal blocks. Both nerve stimulation (with no stimulation below 0.3 mA prior to injection) and ultrasound were utilized in most cases. All blocks incorporated ropivacaine 0.5% with median volume of 33.7 mL, and six (50%) blocks included both clonidine (mean 100 ug) and dexamethasone (mean 2.8 mg). General anesthesia was used in conjunction with regional anesthesia in seven (58%) patients. Of the four patients with motor involvement, all were male, half received upper extremity blocks, and half received general anesthesia. Two of these four patients had dexamethasone only (8 mg), while one patient had dexamethasone 4 mg and clonidine 100 ug. Regarding risk factors for PONS, there was no consistent pattern related to age, sex, ASA status, BMI, specific anesthesia providers, diabetes, or tourniquet within the subset analysis. When risk factors were analyzed within the entire PONS group (N = 208), there was no evidence of an association between PONS and obesity, ASA classification, use of ultrasound vs nerve stimulation, presence of paresthesia during the block, or pain catheters. Significant risk factors for PONS were the combination of clonidine and dexamethasone (OR= 5.6, 95% CI = 3.84–8.20, P < 0.001), lower extremity blocks (primarily femoral and popliteal blocks; OR=3.9, 95% CI = 2.78–5.42, P < 0.001), clonidine (OR=2.2, 95% CI = 1.40–3.43, P < 0.001), and female sex (OR=1.9, 95% CI = 1.38–2.56, P < 0.001). Risk factors associated with reduced PONS were older age (OR=0.6, 95% CI = 0.47–0.76, P < 0.001, nonlinear effect) and dexamethasone alone (OR=0.1, 95% CI = 0.01–0.70, P = 0.02) (Figure 5). Figure 5 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative neurologic symptoms. Calculations were based on logistical regression analysis with robust sandwich standard error estimates. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: Quartiles of age had a nonlinear association (P < 0.001). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE Blocks compared upper extremity blocks vs lower extremity blocks. Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. Pairwise comparisons were conducted between block types (Table 2). Other block type comparisons and paresthesia during block were eliminated from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS= postoperative neurological symptoms; UE = upper extremity; USG = ultrasound guidance. Figure 5 View largeDownload slide Odds ratios (95% confidence intervals) of postoperative neurologic symptoms. Calculations were based on logistical regression analysis with robust sandwich standard error estimates. ORs (x-axis) were plotted on a logarithmic scale. Explanations of comparisons as follows: Older age: Quartiles of age had a nonlinear association (P < 0.001). Obesity: body mass index > 30 vs < 30. Higher ASA status: III/IV vs I/II. NSTIM vs USG (±NSTIM). LE vs UE Blocks compared upper extremity blocks vs lower extremity blocks. Adjunct dexamethasone (D) vs no D or clonidine (C). Adjunct clonidine vs no D or C. Adjunct Dex + Clon vs no D or C. Pairwise comparisons were conducted between block types (Table 2). Other block type comparisons and paresthesia during block were eliminated from the figure for nonsignificance, clarity, and/or minimal relevance. ASA = American Society of Anesthesiologists classification; LE = lower extremity; NSTIM = nerve stimulation; OR = odds ratio; PONS= postoperative neurological symptoms; UE = upper extremity; USG = ultrasound guidance. Discussion This large comprehensive database study using prospectively collected and audited data corroborates previous evidence that a regional anesthesia-based practice provides excellent postoperative analgesia, with a high rate of both success (97.4%) and patient satisfaction (98.9%) [17,18]. Significant complications were rare; in fact, no patient experienced major symptoms of LAST or pneumothorax. However, even with USG, the concern for PONS remains, particularly when using combined dexamethasone and clonidine or administering lower extremity blocks. Success We demonstrated that a high degree of success and safety could be achieved even in a busy, primarily orthopedic, ambulatory surgery center that involves teaching residents and fellows. Our overall block success rate of 97.4% compares favorably to other studies involving regional anesthetics in academic medical centers, while our observed tendency for decreased success rates with nerve stimulation alone compared with USG as well as with obesity reinforces the findings of previous publications [19,20]. Female sex as an independent risk factor for increased success (OR = 1.6, P < 0.001) is a new finding, which could be further examined in future research. Duration Based on the analysis using “blocks for elbow-hand procedures,” adding clonidine, dexamethasone, or both significantly increased block duration by 1.2 hours (P < 0.001), 5.2 hours (P < 0.001), and 8.4 hours (P < 0.001), respectively. Combinations of low-dose adjuncts (“multimodal peripheral nerve blocks”) together with local anesthetics have been reported to substantially increase duration compared with single adjuncts with local anesthetics in orthopedic patients [21]. PNBs with dexamethasone demonstrated large variance with an interquartile range of 15 to 24 hours. Unlike previous investigations [22,23], the prolonged duration effect with dexamethasone was dose dependent in our study, with 4 mg increasing duration by 2.5 hours and 8 mg increasing duration seven hours. Increased durations from clonidine and dexamethasone are postulated to be the results of hyperpolarization of cyclic nucleotide–gated channels and inhibition of nociceptive C-fiber transmission, respectively [16]. Postoperative Pain On the day of surgery, 94% of our patients noted “none” or “mild” postoperative pain. Excellent pain control persisted in 67% and 76% of patients through POD1 and POD2, respectively, and only 0.2% of patients required unexpected hospital admissions due to severe pain. These findings are quite favorable compared with prior studies, including a review of 5,703 ambulatory surgical patients done by McGrath et al. [24] in 2004 in which they found that 47% of ambulatory orthopedic patients with both regional and general anesthesia had “moderate” to “severe” pain, with a 1.4% rate of unplanned visits to a physician for poor pain control. Other studies have shown that 25% to 40% of ambulatory patients report moderate to severe pain, with orthopedic patients reporting the greatest pain [25,26]. Previous authors reported that unexpected admissions after ambulatory surgery, frequently due to severe pain, range from 0.28% to 1.42% [27,28]. Increased postoperative pain has been associated with obesity, opioid tolerance, prolonged surgical duration, general anesthesia, and high PACU pain scores [24,25,26]. While direct comparisons are difficult between studies due to varying methodology and types of surgery, we attribute our lower pain scores primarily to the use of long-acting local anesthetic blocks, aggressive CPNB use when appropriate, and minimizing the use of general anesthesia and/or opioid administration. Our results demonstrated that lower pain scores and fewer unexpected admissions may be possible with a robust regional anesthesia program. Patient Satisfaction Patient satisfaction scores in our study were high, with 98.9% reporting good, very good, or excellent satisfaction, similar to other studies [29]. Our study reveals new independent risk factors for poor patient satisfaction, namely poor analgesia from CPNB (OR < 0.1, P < 0.001) and any complications from regional anesthesia including PONS (OR = 0.3, P < 0.001), while confirming that severe postoperative pain (OR = 0.2, P < 0.001) and PONV (OR = 0.7, P < 0.001) lead to diminished patient satisfaction [30]. Our patient satisfaction scores did not differ significantly from previous studies with patients under general anesthesia [30], which is probably a result of overall patient satisfaction being multifactorial, involving administrative, psychological, logistical, and socioeconomic stressors, as well as clinical performance. Postoperative Nausea and Vomiting For an ambulatory surgery orthopedic population, we observed a low PONV rate (12% nausea, 3.2% vomiting) compared with historical norms. In our population, as in other studies, PONV was most associated with the level of postoperative pain, as well as female sex and presence of general anesthesia [31]. Odom-Forren et al. [32] and Gan et al. [33] recently reported postoperative nausea and vomiting as high as 57% and 19%, respectively, for outpatient surgery performed with general anesthesia. Similar to our results, Lin et al. [34] previously published a PONV rate of 5% to 12% when regional anesthesia was used alone for various orthopedic procedures compared with 32% to 62% with general anesthesia alone. Block Complications Compared with previous studies regarding regional anesthesia involving primarily nerve stimulation [8], our rate of LAST was significantly reduced, with no patient presenting major signs or symptoms consistent with LAST. Our LAST outcome is consistent with more recent publications that reported that the incidence of LAST in a predominately USG-based practice was much less than previously described. Orebaugh et al. [6] in their 2012 study reported no cases of LAST in a consecutive series of 9,238 USG blocks compared with six LAST events in 5,436 NSTIM-only blocks (1.1/1,000). Likewise, Barrington et al. [35] demonstrated the benefit of USG blocks, reporting a LAST rate of 0.59 per 1,000 blocks utilizing ultrasound guidance vs a rate of 2.1 per 1,000 blocks using nerve stimulation. With ultrasound guidance, the ability to visualize the needle in relation to vessels, to use lower local anesthetic dosages, and to use a mobile needle technique may have significantly reduced this complication. Similarly, we report no clinically evident cases of pneumothorax in 856 supraclavicular and 49 patients with multiple paravertebral blocks, which is less than the previously established rates of pleural injury [36]. Again, with the advent of USG regional anesthesia, other authors have also reported a precipitous decline in pneumothorax with the use of ultrasound [7,37]. However, we did find an incidence of a 0.2% rate of other symptomatic pulmonary complications, primarily involving symptomatic hemidiaphragmatic paresis with interscalene blocks. Regarding the two postoperative deaths, perioperative opioids combined with other sedatives, obesity, and OSA significantly elevated their risk of postoperative respiratory depression secondary to greater opioid requirements, opioid-induced central sleep apnea, and decreased pharyngeal patency and muscle tone [38,39]. Anesthesiologists should be active participants in deciding whether surgery is most appropriately performed in an ambulatory surgery center vs a hospital with possible admission for observation in high-risk patients [40]. Our overall PONS rate of 2.3% is consistent with previously published studies, some of which publish much higher rates. We agree with the “theory of Hebl” that PONS is most likely multifactorial and may be difficult to ascertain exact etiologies in most clinical situations [7,41]. Most of the PONS in this study was transient in nature, resolving within weeks to months; however, 12 (7% of all PONS) cases that were “probably related to anesthesia” lasted beyond six months. The detailed chart review of these 12 patients did not reveal a consistent pattern relating to demographics, diabetes, or nerve localization technique. While popliteal blocks constituted 11.5% of all blocks in this study, six (50%) of these more severe PONS cases had popliteal blocks. As in other studies, USG did not reduce PONS compared with nerve stimulation alone [7,8]. Previous investigators demonstrated little difference between the regional anesthesia technique and the incidence of PONS, with rates between 0.3 per 1,000 and 2.1 per 1,000 depending on how and when the patient was asked about persistent neurological symptoms [7,8,42]. In fact, our rate of PONS lasting beyond 18 months was 13.3 per 10,000, which is higher than most previously published studies, with rates of 2.7 to 9 per 10,000 [6,7,8]. The off-label use of clonidine and/or dexamethasone as adjuncts in regional anesthesia has not previously been associated with PONS [23], yet in our study, the combination of clonidine and dexamethasone and, to a lesser extent, clonidine alone in blocks with 0.5% ropivacaine were independent risk factors for PONS, consistent with a study by Williams et al. analyzing the effect of ropivacaine with or without combination adjuncts on rat sensory neurons [43]. Our results suggest that dexamethasone may be paradoxical, providing some PONS protection at lower doses while increasing concern for PONS at higher doses (based on our subset review). Although previous clinical studies are reassuring regarding dexamethasone or clonidine in PNBs [16,23], the studies were not powered to analyze PONS, and only one study reported clinical results with the combination of dexamethasone and clonidine [21]. The data suggest a potential benefit to using lower concentrations of local anesthetics when a block is combined with general anesthesia and minimizing the dose of adjuncts (e.g., dexamethasone, clonidine) in order to reduce the risk of PONS. In addition, the combination of dexamethasone and clonidine adjuncts, especially in lower extremity blocks, should be used cautiously until further delineation by future clinical trials. Falls occurred in 25 patients (0.28%). Most patients had femoral or popliteal blocks, although three patients had CNBs and 56% of patients were obese (mean BMI = 33). Falls occurred as late as the postoperative day 3. Of the 25 patients with falls, 18 patients (72%) did not seek medical attention, four patients were evaluated and released without sequelae, and three patients (12%) were treated for complications (one facial laceration and two wrist fractures). Fall prevention remains a critical element of any robust ambulatory regional anesthesia program. Catheter Outcome Finally, our CPNB outcomes demonstrated the ability for continuous ambulatory regional analgesia to provide very good analgesia in most patients for an extended period of time with minimal complications. The quality of catheter analgesia was rated as either very good or excellent in 85% of the patients, with an additional 9% rating their analgesia as “good.” Seventeen percent of patients noted leaking symptoms around their catheter site, which is consistent with other studies [44]. While skin reactions have been previously reported with benzoin [45], 10 (0.8%) patients had allergic reactions to one or a combination of our adhesives. There were four (0.3%) cases of infection, two deep and two superficial. One deep infection occurred in a patient on chronic steroids for systemic lupus erythematosus in addition to a concurrent enoxaparin bridge for history of thrombosis. The catheter was removed on postoperative day 5, at which time a local infection was noted. Subsequent work-up with imaging noted a local soft tissue abscess on POD7, yet the patient refused care until POD10. At this time, surgical irrigation and debridement were performed in addition to administration of intravenous antibiotics. The infection ultimately resolved with no subsequent sequelae. Even though most catheters remained in place longer than most studies, our 0.3% rate of significant infection is consistent with previous studies on catheter-related infections [9,44]. Limitations Several important limitations must be considered when interpreting the results of this study. As in all observational studies, specific risk factors for observed associations may not be causal if there was an unmeasured variable accounting for the difference (e.g., preoperative opioid tolerance). However, we feel that this comprehensive analysis reflects an accurate representation of an actual ambulatory surgical anesthesia practice. Reporting of block duration, patient pain scores, satisfaction, and neurologic symptoms was often done only by phone, not by direct examination, and may be affected by reporting bias, the method with which questions were asked, and variations in expectation management. Assessment tools for postoperative pain and patient satisfaction may differ from other studies’ assessment tools, thereby making direct comparisons difficult. No controls were undertaken regarding the perioperative oral and intravenous pain management strategy, which was left to the discretion of the supervising anesthesia and surgical teams. Postoperative opioid or multimodal oral medications were not tracked. Conclusions This study provides further evidence that utilization of regional-based anesthesia for mainly orthopedic, ambulatory procedures is a safe and effective means of providing excellent postoperative analgesia and is associated with a low rate of PONV and unexpected admissions. In our data set involving ropivacaine 0.5%, the combination of dexamethasone (doses most commonly exceeding 2 mg) and clonidine (median dose 100 ug), as well as clonidine alone, may be associated with a higher risk of PONS, especially in lower extremity blocks. However, these adjuncts incur associated benefits including a lower PONV risk and a longer analgesic duration. Further research is needed to delineate patient-specific comorbidities and/or adjuvant-associated postoperative neurologic symptoms. Future adjunct research specifically involving combined ropivacaine, clonidine, and dexamethasone should entail doses/concentrations that are less than those reported herein. Acknowledgments The authors would like to acknowledge the assistance of the following individuals: Jonathan P. Wanderer, MD, MPhil, Assistant Professor, Departments of Anesthesiology and Biomedical Informatics, Vanderbilt University School of Medicine, Nashville, Tennessee (assisted with data collection); Damon R. 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Pain MedicineOxford University Press

Published: Feb 1, 2018

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