Outpatient vs Inpatient Anterior Cervical Discectomy and Fusion: A Population-Level Analysis of Outcomes and Cost

Outpatient vs Inpatient Anterior Cervical Discectomy and Fusion: A Population-Level Analysis of... Abstract BACKGROUND Outpatient anterior cervical discectomy and fusion (ACDF) is a promising candidate for US healthcare cost reduction as several studies have demonstrated that overall complications are relatively low and early discharge can preserve high patient satisfaction, low morbidity, and minimal readmission. OBJECTIVE To compare clinical outcomes and associated costs between inpatient and ambulatory setting ACDF. METHODS Demographics, comorbidities, emergency department (ED) visits, readmissions, reoperation rates, and 90-d charges were retrospectively analyzed for patients undergoing elective ACDF in California, Florida, and New York from 2009 to 2011 in State Inpatient and Ambulatory Databases. RESULTS A total of 3135 ambulatory and 46 996 inpatient ACDFs were performed. Mean Charlson comorbidity index, length of stay, and mortality were 0.2, 0.4 d, and 0% in the ambulatory cohort and 0.4, 1.8 d, and 0.04% for inpatients (P < .0001). Ambulatory patients were younger (48.0 vs 53.1) and more likely to be Caucasian. One hundred sixty-eight ambulatory patients (5.4%) presented to the ED within 30 d (mean 11.3 d), 51 (1.6%) were readmitted, and 5 (0.2%) underwent reoperation. Among inpatient surgeries, 2607 patients (5.5%) presented to the ED within 30 d (mean 9.7 d), 1778 (3.8%) were readmitted (mean 6.3 d), and 200 (0.4%) underwent reoperation. Higher Charlson comorbidity index increased rate of ED visits (ambulatory operating room [OR] 1.285, P < .05; inpatient OR 1.289, P < .0001) and readmission (ambulatory OR 1.746, P < .0001; inpatient OR 1.685, P < .0001). Overall charges were significantly lower for ambulatory ACDFs ($33 362.51 vs $74 667.04; P < .0001). CONCLUSION ACDF can be performed in an ambulatory setting with comparable morbidity and readmission rates, and lower costs, to those performed in an inpatient setting. ACDF, Ambulatory surgery, Cost, Outcomes, Outpatient ABBREVIATIONS ABBREVIATIONS ACDF anterior cervical discectomy and fusion ASCA Ambulatory Surgery Center Association CCI Charlson Comorbidity Index CCR cost-to-charge ratio CNS central nervous system ED emergency department HCUP Healthcare Cost and Utilization Project HOPDs hospital outpatient departments OR odds ratio OR operating room SASD State Ambulatory Surgery and Services Databases SEDD State Emergency Department Databases SID State Inpatient Databases Spine surgery represents an ideal target for cost reduction within the United States healthcare system due to increasing utilization1 and high payer costs in the face of an aging population.2 One dramatic strategy involves shifting traditionally inpatient procedures to the ambulatory setting. Surgeries performed in an inpatient or hospital-based encounter are estimated to cost 2 to 3 times more than those conducted in an ambulatory surgery center.3 Anterior cervical discectomy and fusion (ACDF) has been identified as a promising candidate to be transitioned into the outpatient setting, given that it is a common procedure that has been shown in the literature to have a low complication rate and early patient discharge in many cases.4-14 Before this cost-reduction strategy can be widely adopted, outpatient ACDF must demonstrate “noninferiority” and produce equivalent or superior outcomes while maintaining patient satisfaction and reducing cost.15,16 The Healthcare Cost and Utilization Project (HCUP) provides state-level encounter and clinical data for all ambulatory, inpatient, and emergency department visits. We retrospectively studied demographics, 30-d outcomes, cost, and predictors of readmission and reoperation after 1- and 2-level ACDF performed in an inpatient and ambulatory setting in 3 highly populated states over a 3-yr period. METHODS Patient Selection An ambulatory or inpatient index procedure was defined as the first discharge record appearing in the HCUP of the US Department of Health and Human Services’ Agency for Healthcare Research and Quality State Inpatient Databases (SID),17 the State Ambulatory Surgery and Services Databases (SASD),18 and the State Emergency Department Databases (SEDD)19 in the 3-yr study period that contained ICD-9 or CPT procedure codes for initial, nonrevision ACDF. These databases contain records of every patient discharge from an inpatient facility, an ambulatory surgery center, or an emergency department, respectively, in a given state in a given year. Additionally, patients with diagnoses on record indicating central nervous system (CNS) neoplasm, CNS infection/inflammatory process, or trauma to the spine or spinal cord, or patients with a flag indicating the presence of any ICD-9 E-codes (representing external injury), were excluded. For each included discharge record, the Charlson Comorbidity Index (CCI), a weighted comorbid illness severity score,20 was calculated. The number of vertebral segments on which ACDF was performed was recorded for ambulatory index procedures only, as only codes in the CPT system are granular enough to distinguish 1-, 2-, and 3-level ACDF procedures (vs ICD-9, where 1- and 2-level procedures are indistinguishable). IRB/Ethics committee approval was not applicable; however, all researchers completed the HCUP Data Use Agreement Training Course and signed the user agreement. Patient consent was not applicable as the source data referenced de-identified patients in a national database. Outcomes Analyzed Using visit linkage and event timing variables, reappearances in SASD, SID, or SEDD after index procedure in SASD or SID were identified and classified as ED visit, inpatient readmission, inpatient reoperation (as indicated by ICD-9 procedure codes representing revision ACDF, hematoma incision and drainage, debridement, other wound complication repair, or esophageal repair), ambulatory readmission, or ambulatory reoperation. For each subsequent patient appearance in the 3 databases, primary diagnosis was categorized into a complication category (infection/hematoma/disruption/dehiscence of wound or complications from implant and routine postoperative care; neck pain/injury, radiculopathy, and cervical spinal degenerative disease; laryngeal and airway complications; dysphagia and esophageal complications; and other). Total charges associated with ambulatory or inpatient index procedure and any reappearance in SASD, SID, or SEDD over a 90-d period was calculated. Actual costs of index ACDF procedure were calculated in the inpatient setting by dividing total charges associated with the hospitalization by the cost-to-charge ratio (CCR) as provided by HCUP. No CCR information is provided for outpatient procedures; for procedures performed in an ambulatory surgery center affiliated with an inpatient hospital (also known as hospital outpatient departments; HOPDs), the inpatient facility's CCR was used. For unaffiliated, freestanding outpatient surgical centers, CCR was estimated by multiplying the average CCR for HOPDs in a given state and a given year by that year's estimated cost differential between inpatient units and HOPDs, as provided by the Ambulatory Surgery Center Association. Data Analysis Descriptive statistics were calculated for age, mortality, CCI, number of diagnoses on record, number of chronic conditions, time to emergency department (ED) presentation, time to inpatient readmission and/or reoperation, time to ambulatory surgery center readmission and/or reoperation, and 90-d total charges. For selected analyses, patient cohorts were stratified into groups with CCI = 0 and CCI > 0. Chi-square tests were used to compare categorical variables such as patient demographics, ED admission rates, and inpatient readmission/reoperation rates. Kolmogorov-Smirnov tests were performed to determine that the distributions of age, CCI, number of diagnoses on record, number of chronic conditions, length of stay (LOS), 90-d total charges, and actual costs were nonnormal; therefore, Wilcoxon–Mann–Whitney tests were used to compare these variables. Logistic regression was used to model the odds of ED visits, readmissions, and reoperations based on number of levels fused and, independently, based on zero vs nonzero CCI. Stepwise model selection was used to define a multiple linear regression model that was then used to assess the relationship between 90-d total charge and patient demographics and comorbidity indicators. The Farrington–Manning score test with noninferiority margin M = 0.1 was used to determine noninferiority of ambulatory vs inpatient ACDF in terms of postoperative outcomes. The noninferiority of ambulatory vs inpatient ACDF was concluded when the lower confidence bound of the risk difference (inpatient – ambulatory) is greater than –0.1. RESULTS Patient Population A total of 46 996 index procedures were identified in the SID compared to 3135 procedures in the SASD. The populations were significantly different as outlined in Table 1. SID patients had an average age of 53 yr compared to 48 yr in the SASD group (P < .0001). SID patients were 53% female compared to 50.8% in SASD (P = .0163) and were 78.7% Caucasian compared to 85.7% in the SASD cohort (P < .0001). With respect to primary payer, With respect to primary payer, 56.25% of SID patients utilized private insurance compared to 67.9% in the SASD group (P < .0001). The 2 groups also differed in medical comorbidities. Average CCI for SID patients was 0.37 compared to 0.17 in SASD (P < .0001). This difference was also conserved in the total number of diagnoses on record and number of chronic conditions on record in SID vs SASD (4.8 vs 3.1, P < .0001; 3.2 vs 2.1; P < .0001), respectively. The most common preoperative primary diagnoses for SID were intervertebral disc disorder with myelopathy, cervical region (15.8%), followed by cervical spondylosis without myelopathy (14.7%) and with myelopathy (12%). The most common SASD primary preoperative diagnosis was displacement of cervical intervertebral disc without myelopathy (56%) followed by cervical spondylosis without myelopathy (12.6%; Table 2). In the SASD cohort, CPT codes enabled stratification by number of ACDF levels as follows: 1-level 57.96%; 2-level 36.52%; and 3-level: 5.52%. TABLE 1. Patient Demographics and Preoperative Characteristics.   Ambulatory  Inpatient    Variable  (n = 3135)  (n = 46 996)  P value  Age (yr)      < .0001   Mean ± SD  48.0 ± 9.5  53.1 ± 11.5     Median [range]  48 [20-85]  52 [18-94]    Sex      .0163   Female  1593 (50.8%)  24 928 (53.0%)     Male  1542 (49.2%)  22 068 (47.0%)    Race      < .0001   Caucasian  2622 (85.7%)  36 272 (78.7%)     Black  175 (5.7%)  3432 (7.4%)     Hispanic  186 (6.1%)  4108 (8.9%)     Asian/Pacific Islander  28 (0.9%)  1008 (2.2%)     Native American  2 (0.1%)  55 (0.1%)     Other  48 (1.6%)  1202 (2.6%)    Primary payer      < .0001   Private insurance  2129 (67.9%)  26 437 (56.25%)     Medicare  154 (4.9%)  10 196 (21.7%)     Medicaid  271 (8.6%)  2404 (5.1%)     Self-pay  60 (1.9%)  624 (1.3%)     No charge  12 (0.4%)  131 (0.3%)     Other  509 (16.2%)  7203 (15.33%)    Median household income quartile for ZIP code      < .0001   1st  549 (19.7%)  5973 (21.3%)     2nd  984 (35.3%)  8385 (29.9%)     3rd  787 (28.2%)  7860 (28.1%)     4th  468 (16.8%)  5790 (20.67%)    Rural–urban continuum location      < .0001   Metro area, population >1m  1295 (41.3%)  28 537 (60.7%)     Metro area, population 250k-1m  1324 (42.2%)  11 573 (24.6%)     Metro area, population <250k  100 (3.2%)  3083 (6.6%)     Urban adjacent to metro, population >20k  207 (6.6%)  2093 (4.4%)     Urban nonadjacent to metro, population >20k  45 (1.4%)  185 (0.4%)     Urban adjacent to metro, population 2500-20k  146 (4.7%)  1201 (2.6%)     Urban nonadjacent to metro, population 2500-20k  11 (0.4%)  180 (0.4%)     Rural or urban adjacent to metro, population <2500  6 (0.2%)  136 (0.3%)     Rural or urban nonadjacent to metro, population <2500  0 (0%)  0 (0%)    Charlson Comorbidity Index (CCI)      < .0001   Mean ± SD  0.17 ± 0.46  0.37 ± 0.73     Median [range]  0 [0-7]  0 [0-16]    Number of diagnoses on record      < .0001   Mean ± SD  3.1 ± 2.2  4.8 ± 3.2     Median [range]  2 [1-23]  4 [1-31]    Number of chronic conditions on record      < .0001   Mean ± SD  2.1 ± 1.5  3.2 ± 2.1     Median [range]  1 [0-9]  3 [0-19]      Ambulatory  Inpatient    Variable  (n = 3135)  (n = 46 996)  P value  Age (yr)      < .0001   Mean ± SD  48.0 ± 9.5  53.1 ± 11.5     Median [range]  48 [20-85]  52 [18-94]    Sex      .0163   Female  1593 (50.8%)  24 928 (53.0%)     Male  1542 (49.2%)  22 068 (47.0%)    Race      < .0001   Caucasian  2622 (85.7%)  36 272 (78.7%)     Black  175 (5.7%)  3432 (7.4%)     Hispanic  186 (6.1%)  4108 (8.9%)     Asian/Pacific Islander  28 (0.9%)  1008 (2.2%)     Native American  2 (0.1%)  55 (0.1%)     Other  48 (1.6%)  1202 (2.6%)    Primary payer      < .0001   Private insurance  2129 (67.9%)  26 437 (56.25%)     Medicare  154 (4.9%)  10 196 (21.7%)     Medicaid  271 (8.6%)  2404 (5.1%)     Self-pay  60 (1.9%)  624 (1.3%)     No charge  12 (0.4%)  131 (0.3%)     Other  509 (16.2%)  7203 (15.33%)    Median household income quartile for ZIP code      < .0001   1st  549 (19.7%)  5973 (21.3%)     2nd  984 (35.3%)  8385 (29.9%)     3rd  787 (28.2%)  7860 (28.1%)     4th  468 (16.8%)  5790 (20.67%)    Rural–urban continuum location      < .0001   Metro area, population >1m  1295 (41.3%)  28 537 (60.7%)     Metro area, population 250k-1m  1324 (42.2%)  11 573 (24.6%)     Metro area, population <250k  100 (3.2%)  3083 (6.6%)     Urban adjacent to metro, population >20k  207 (6.6%)  2093 (4.4%)     Urban nonadjacent to metro, population >20k  45 (1.4%)  185 (0.4%)     Urban adjacent to metro, population 2500-20k  146 (4.7%)  1201 (2.6%)     Urban nonadjacent to metro, population 2500-20k  11 (0.4%)  180 (0.4%)     Rural or urban adjacent to metro, population <2500  6 (0.2%)  136 (0.3%)     Rural or urban nonadjacent to metro, population <2500  0 (0%)  0 (0%)    Charlson Comorbidity Index (CCI)      < .0001   Mean ± SD  0.17 ± 0.46  0.37 ± 0.73     Median [range]  0 [0-7]  0 [0-16]    Number of diagnoses on record      < .0001   Mean ± SD  3.1 ± 2.2  4.8 ± 3.2     Median [range]  2 [1-23]  4 [1-31]    Number of chronic conditions on record      < .0001   Mean ± SD  2.1 ± 1.5  3.2 ± 2.1     Median [range]  1 [0-9]  3 [0-19]    Demographic information including age, sex, race, primary payer, median household income quartile for ZIP code, and location on the rural–urban continuum, as well as preoperative patient characteristics, including CCI, number of diagnoses on record, and number of chronic conditions on record, are presented for 3135 patients who underwent ambulatory ACDF and 46 996 patients who underwent inpatient ACDF. Cohorts are significantly different in all variables analyzed. View Large TABLE 2. Most Common Preoperative Primary Diagnoses (ICD-9-CM) on Record. Ambulatory  Frequency  Inpatient  Frequency  722.0: Displacement of cervical intervetebral disc without myelopathy  1755 (56.0%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  7422 (15.8%)  721.0: Cervical spondylosis without myelopathy  395 (12.6%)  721.0: Cervical spondylosis without myelopathy  6903 (14.7%)  722.4: Degeneration of cervical intervertebral disc  219 (7.0%)  721.1: Cervical spondylosis with myelopathy  5643 (12.0%)  723.0: Spinal stenosis in cervical region  161 (5.1%)  722.4: Degeneration of cervical intervertebral disc  4942 (10.5%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  158 (5.0%)  723.0: Spinal stenosis in cervical region  2767 (5.9%)  721.1: Cervical spondylosis with myelopathy  137 (4.4%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  438 (0.9%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  122 (3.9%)  722.91: Other and unspecified disc disorder, cervical region  397 (0.8%)  723.1: Cervicalgia  45 (1.4%)  738.4: Acquired spondylolisthesis  231 (0.5%)  Ambulatory  Frequency  Inpatient  Frequency  722.0: Displacement of cervical intervetebral disc without myelopathy  1755 (56.0%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  7422 (15.8%)  721.0: Cervical spondylosis without myelopathy  395 (12.6%)  721.0: Cervical spondylosis without myelopathy  6903 (14.7%)  722.4: Degeneration of cervical intervertebral disc  219 (7.0%)  721.1: Cervical spondylosis with myelopathy  5643 (12.0%)  723.0: Spinal stenosis in cervical region  161 (5.1%)  722.4: Degeneration of cervical intervertebral disc  4942 (10.5%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  158 (5.0%)  723.0: Spinal stenosis in cervical region  2767 (5.9%)  721.1: Cervical spondylosis with myelopathy  137 (4.4%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  438 (0.9%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  122 (3.9%)  722.91: Other and unspecified disc disorder, cervical region  397 (0.8%)  723.1: Cervicalgia  45 (1.4%)  738.4: Acquired spondylolisthesis  231 (0.5%)  The 8 most common diagnoses listed as primary diagnosis on record for patients undergoing index ACDF are presented by ambulatory and inpatient cohort. View Large Perioperative Outcomes LOS, disposition, and mortality were analyzed in SASD and SID cohorts (Table 3). LOS was lower in the SASD group compared to SID (0.36 d vs 1.78 d, respectively; P < .0001). To adjust for differences in patient comorbidities, patients were stratified into groups of CCI of zero and greater than zero. The significance of difference in LOS was conserved when populations were stratified into CCI zero vs nonzero groups. Overall, 98.6% of SASD patients were discharged while 10 (0.3%) were transferred to a short-term hospital. No patients died in the SASD cohort while 20 deaths (0.04%) were reported in the SID cohort. TABLE 3. Perioperative Outcomes. Outcomes, Including LOS, Mortality, and Disposition, are Presented for Patients Undergoing Ambulatory or Inpatient ACDF.   Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 3135)  (n = 2664)  (n = 471)  (n = 46 996)  (n = 33 834)  (n = 13 161)  Overall  CCI = 0  CCI > 0  Length of stay (d)              < .0001  < .0001  < .0001   Mean ± SD  0.36 ± 0.52  0.35 ± 0.52  0.42 ± 0.57  1.78 ± 2.18  1.61 ± 1.42  2.20 ± 3.40         Median [range]  0 [0-3]  0 [0-3]  0 [0-3]  1 [0-198]  1 [0-41]  1 [0-198]        Mortality  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)  .633  1.000  1.000  Disposition              < .0001  < .0001  < .0001   Routine discharge to home or law enforcement, with or without plan for acute care inpatient hospital readmission  3090 (98.6%)  2621 (98.39%)  469 (99.58%)  42 318 (90.0%)  31 185 (92.17%)  11 133 (84.59%)         Discharge to home healthcare or hospice  28 (0.9%)  26 (0.98%)  2 (0.42%)  3423 (7.3%)  2126 (6.28%)  1297 (9.85%)         Transfer to short-term hospital  10 (0.3%)  10 (0.38%)  0 (0%)  32 (0.1%)  11 (0.03%)  21 (0.16%)         Transfer to skilled nursing facility, intermediate care facility, or other facility  7 (0.22%)  7 (0.26%)  0 (0%)  1159 (2.5%)  484 (1.43%)  675 (5.13%)         Patient left against medical advice  0 (0%)  0 (0%)  0 (0%)  40 (0.1%)  22 (0.07%)  18 (0.14%)         Patient died  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)         Discharge alive, destination unknown  0 (0%)  0 (0%)  0 (0%)  3 (0.01%)  1 (0.00003%)  2 (0.02%)          Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 3135)  (n = 2664)  (n = 471)  (n = 46 996)  (n = 33 834)  (n = 13 161)  Overall  CCI = 0  CCI > 0  Length of stay (d)              < .0001  < .0001  < .0001   Mean ± SD  0.36 ± 0.52  0.35 ± 0.52  0.42 ± 0.57  1.78 ± 2.18  1.61 ± 1.42  2.20 ± 3.40         Median [range]  0 [0-3]  0 [0-3]  0 [0-3]  1 [0-198]  1 [0-41]  1 [0-198]        Mortality  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)  .633  1.000  1.000  Disposition              < .0001  < .0001  < .0001   Routine discharge to home or law enforcement, with or without plan for acute care inpatient hospital readmission  3090 (98.6%)  2621 (98.39%)  469 (99.58%)  42 318 (90.0%)  31 185 (92.17%)  11 133 (84.59%)         Discharge to home healthcare or hospice  28 (0.9%)  26 (0.98%)  2 (0.42%)  3423 (7.3%)  2126 (6.28%)  1297 (9.85%)         Transfer to short-term hospital  10 (0.3%)  10 (0.38%)  0 (0%)  32 (0.1%)  11 (0.03%)  21 (0.16%)         Transfer to skilled nursing facility, intermediate care facility, or other facility  7 (0.22%)  7 (0.26%)  0 (0%)  1159 (2.5%)  484 (1.43%)  675 (5.13%)         Patient left against medical advice  0 (0%)  0 (0%)  0 (0%)  40 (0.1%)  22 (0.07%)  18 (0.14%)         Patient died  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)         Discharge alive, destination unknown  0 (0%)  0 (0%)  0 (0%)  3 (0.01%)  1 (0.00003%)  2 (0.02%)        Patient cohorts are also stratified by CCI of zero or greater than zero. Cohorts differ significantly in LOS and distribution of postoperative disposition; mortality rates are not significantly different. View Large ED Visits Within 30 d Of the ambulatory (SASD) cohort, 168 patients presented to the emergency department on 197 occasions (5.359%; Table 4, Figure). Average time to presentation was 11.3 d. When comparing a CCI of zero vs nonzero, the percentage of ED visits within 30 d was 5.2% vs 6.4% (not significant; Figure). Cervicalgia was the most frequent diagnosis cited as reason for visit (24.87%) followed by chest pain (4.57%), postoperative pain (3.55%), and dysphagia (2.54%). FIGURE. View largeDownload slide Postoperative outcomes 30 d after index procedure. Rates of unique emergency department visits, inpatient readmission, and inpatient reoperation within 30 d of index ambulatory or inpatient ACDF are presented, stratified by CCI of zero or greater than zero. Patients undergoing ambulatory ACDF were readmitted to inpatient units within 30 d significantly less frequently than patients undergoing inpatient ACDF. There was no difference in rates of 30-d ED visits or 30-d reoperations. ****P < .0001. n.s. indicates P > .05. FIGURE. View largeDownload slide Postoperative outcomes 30 d after index procedure. Rates of unique emergency department visits, inpatient readmission, and inpatient reoperation within 30 d of index ambulatory or inpatient ACDF are presented, stratified by CCI of zero or greater than zero. Patients undergoing ambulatory ACDF were readmitted to inpatient units within 30 d significantly less frequently than patients undergoing inpatient ACDF. There was no difference in rates of 30-d ED visits or 30-d reoperations. ****P < .0001. n.s. indicates P > .05. TABLE 4. Reasons for Inpatient Readmission or Emergency Department Visit within 30 D of Index Procedure. Reason for visit  Frequency (ambulatory to ED) (n = 168)  Frequency (ambulatory to inpatient) (n = 51)  Frequency (inpatient to ED) (n = 2607)  Frequency (inpatient to inpatient) (n = 1778)  Infection, hematoma, or disruption of surgical site or complications from implant  4 (2.0%)  16 (29.6%)  121 (4.1%)  276 (14.0%)  Neck pain or injury, radiculopathy, and degenerative disease of the cervical spine  50 (25.4%)  2 (3.7%)  456 (15.3%)  174 (8.8%)  Laryngeal and airway complications  0 (0%)  0 (0%)  1 (0.03%)  6 (0.3%)  Dysphagia and esophageal complications  5 (2.5%)  2 (3.7%)  66 (2.2%)  52 (2.6%)  Other  138 (70.1%)  34 (63.0%)  2,332 (78.4%)  1,460 (74.2%)  Reason for visit  Frequency (ambulatory to ED) (n = 168)  Frequency (ambulatory to inpatient) (n = 51)  Frequency (inpatient to ED) (n = 2607)  Frequency (inpatient to inpatient) (n = 1778)  Infection, hematoma, or disruption of surgical site or complications from implant  4 (2.0%)  16 (29.6%)  121 (4.1%)  276 (14.0%)  Neck pain or injury, radiculopathy, and degenerative disease of the cervical spine  50 (25.4%)  2 (3.7%)  456 (15.3%)  174 (8.8%)  Laryngeal and airway complications  0 (0%)  0 (0%)  1 (0.03%)  6 (0.3%)  Dysphagia and esophageal complications  5 (2.5%)  2 (3.7%)  66 (2.2%)  52 (2.6%)  Other  138 (70.1%)  34 (63.0%)  2,332 (78.4%)  1,460 (74.2%)  Primary diagnoses on record for 30-d readmissions or 30-d emergency department visits, grouped by complication type, are presented for patients who underwent ambulatory or inpatient ACDF. View Large For the inpatient (SID) cohort, 2607 unique patients presented in 2976 ED encounters (5.547%) within 30 d. Mean time to presentation was 9.7 d. When stratified into CCI zero vs nonzero groups, 5.3% and 6.1% of patients experienced an ED readmission, respectively (Figure). Cervicalgia was again the most common visit diagnosis (13.65%), followed by postoperative pain (3.19%). Fifty-nine patients presented with dysphagia (1.98%). Readmissions Within 30 d Readmission rates were also identified for SASD and SID groups (Table 4). Fifty-one (1.6%) unique patients who underwent ambulatory ACDF were readmitted to an inpatient hospital after the date of the index procedure; 1.58% of patients with CCI of 0% and 1.9% of patients with CCI greater than zero were readmitted within 30 d (Figure). Time to readmission averaged 11.2 d and most common visit diagnoses were postoperative infection (11.11%), seroma complicating a procedure (7.41%), and hematoma complicating a procedure (5.56%). Two patients presented for dysphagia (3.7%). A total of 1778 (3.78%) unique patients whose index procedure was inpatient were readmitted to an inpatient setting 1968 times following the index procedure, representing 2.94% of CCI zero patients and 5.96% of CCI nonzero patients. Mean time to presentation was 6.3 d. The most common visit diagnosis was care involving other specified rehabilitation (28.11%) followed by postoperative infection (3.8%), hematoma complicating a procedure (3.65%), and cervical spondylosis with myelopathy (3.34%). Patients undergoing inpatient ACDF were significantly more likely to have an inpatient readmission at 30 d compared to the ambulatory group (P < .001). This effect was maintained when stratified into CCI zero and nonzero groups (Figure). Reoperations Within 30 d Five patients (0.16%) underwent a reoperation after the outpatient index procedure. Mean time to reoperation was 10.8 d. Three out of the 5 reoperations occurred within 1 wk. Three patients carried the diagnosis of postoperative infection, 1 had seroma complicating a procedure and 1 had “other mechanical complication.” Two-hundred unique patients (0.43%) underwent 201 operations after inpatient index ACDF (0.40% with CCI zero and 0.5% with CCI nonzero; Figure). Average time to reoperation was 12.5 d. Seventy-two patients underwent reoperation within 1 wk, including 7 patients who underwent reoperation the same day. Most common visit diagnosis was cervical spondylosis with myelopathy (20.5%), followed by mechanical complication (13%), postoperative infection (11%), and hematoma complicating a procedure (10%). Patients undergoing inpatient ACDF were significantly more likely to undergo a reoperation (P < .05). However, this effect was not preserved in CCI stratified subgroups. Noninferiority Analysis Ambulatory ACDF was noninferior (margin = 0.1) to inpatient ACDF in terms of mortality, 30-d ED visits, 30-d inpatient readmissions, and 30-d reoperations for all patients as well as patients stratified by CCI (all comparisons P < .0001) as the lower confidence bounds of all differences (inpatient – ambulatory) were greater than –0.1 (Table 5). TABLE 5. Anterior Cervical Discectomy and Fusion Performed in the Ambulatory setting is Noninferior to Inpatient Surgery.   Risk      Comparison  difference  90% CI  P  Mortality     All CCI  0.0004  −0.0084 to 0.0093  <.0001   CCI = 0  0.0001  −0.0094 to 0.0097  <.0001   CCI > 0  0.0011  −0.0217 to 0.0240  <.0001  30-d ED visits     All CCI  0.0019  −0.0088 to 0.0126  <.0001   CCI = 0  0.0015  −0.0100 to 0.0131  <.0001   CCI > 0  −0.0027  −0.0306 to 0.0253  <.0001  30-d readmissions     All CCI  0.0216  0.0114 to 0.0317  <.0001   CCI = 0  0.0136  0.0029 to 0.0243  <.0001   CCI > 0  0.1523  0.1160 to 0.1886  <.0001  30-d reoperations     All CCI  0.0027  −0.0063 to 0.0116  <.0001   CCI = 0  0.0021  −0.0076 to 0.0118  <.0001   CCI > 0  0.005  −0.0182 to 0.0283  <.0001    Risk      Comparison  difference  90% CI  P  Mortality     All CCI  0.0004  −0.0084 to 0.0093  <.0001   CCI = 0  0.0001  −0.0094 to 0.0097  <.0001   CCI > 0  0.0011  −0.0217 to 0.0240  <.0001  30-d ED visits     All CCI  0.0019  −0.0088 to 0.0126  <.0001   CCI = 0  0.0015  −0.0100 to 0.0131  <.0001   CCI > 0  −0.0027  −0.0306 to 0.0253  <.0001  30-d readmissions     All CCI  0.0216  0.0114 to 0.0317  <.0001   CCI = 0  0.0136  0.0029 to 0.0243  <.0001   CCI > 0  0.1523  0.1160 to 0.1886  <.0001  30-d reoperations     All CCI  0.0027  −0.0063 to 0.0116  <.0001   CCI = 0  0.0021  −0.0076 to 0.0118  <.0001   CCI > 0  0.005  −0.0182 to 0.0283  <.0001  The farrington–manning score test (with noninferiority margin of 0.1) was used to determine that ACDF performed in the ambulatory setting is noninferior to inpatient ACDF in terms of patient mortality and rates of 30-d emergency department visits, 30-d readmissions, and 30-d reoperations, including when patients are stratified by CCI. 90% CI = 90% confidence interval of the risk difference of inpatient – ambulatory. View Large Predictors of Readmission and Reoperation Using CPT procedure codes in SASD, we stratified patients by how many levels were fused. Number of fused levels was a predictor of readmission into an inpatient setting at 30 (P < .05; odds ratio [OR] 1.699) and 90 d (P < .001; OR 1.692). Number of ACDF levels was also a significant predictor of reoperation at 30 (P < .5; OR 4.909) and 90 d (P < .001; OR 3.266). When stratified by CCI, CCI greater than zero was a significant predictor of ER readmission in the ambulatory cohort (P < .05; OR 1.285) and inpatient group (P < .0001; OR 1.289; Table 6). CCI greater than zero was also a significant predictor of readmission in ambulatory (P < .001; OR 1.746) and inpatient cohorts (P < .001; OR 1.685). CCI was not a significant predictor of reoperation for ambulatory patients but patients with CCI greater than zero in the inpatient setting were slightly more likely to undergo a reoperation (P < .01; OR 1.160). TABLE 6. CCI as a Predictor of Postoperative Outcomes. Variable  OR  95% CI  P  Ambulatory     All ED visits  1.285  1.041 to 1.586  .0197   All inpatient readmissions  1.746  1.370 to 2.223  <.0001   All reoperations  1.087  0.609 to 1.943  .7774   30-d ED visits  1.245  0.828 to 1.872  .2914   30-d inpatient readmissions  1.216  0.588 to 2.515  .5975   30-d reoperations  –  –  –  Inpatient     All ED visits  1.289  1.234 to 1.346  <.0001   All inpatient readmissions  1.685  1.609 to 1.764  <.0001   All reoperations  1.160  1.054 to 1.276  .0023   30-d ED visits  1.154  1.059 to 1.257  .0011   30-d inpatient readmissions  2.098  1.906 to 2.309  <.0001   30-d reoperations  1.268  0.943 to 1.703  .1157  Variable  OR  95% CI  P  Ambulatory     All ED visits  1.285  1.041 to 1.586  .0197   All inpatient readmissions  1.746  1.370 to 2.223  <.0001   All reoperations  1.087  0.609 to 1.943  .7774   30-d ED visits  1.245  0.828 to 1.872  .2914   30-d inpatient readmissions  1.216  0.588 to 2.515  .5975   30-d reoperations  –  –  –  Inpatient     All ED visits  1.289  1.234 to 1.346  <.0001   All inpatient readmissions  1.685  1.609 to 1.764  <.0001   All reoperations  1.160  1.054 to 1.276  .0023   30-d ED visits  1.154  1.059 to 1.257  .0011   30-d inpatient readmissions  2.098  1.906 to 2.309  <.0001   30-d reoperations  1.268  0.943 to 1.703  .1157  Higher CCI was associated with increased rates of ED visits and inpatient readmissions for patients undergoing ambulatory ACDF and with ED visits (total and within 30 d), inpatient readmissions (total and within 30 d), and reoperations in patients undergoing inpatient ACDF. Logistic regression could not be performed with 30-d reoperation rates after ambulatory ACDF as a dependent variable due to the low rate of that outcome. OR = odds ratio. 95% CI = 95% confidence interval. ED, emergency department. View Large Charges, Costs, and Predictors of Charges In examining 90-d cumulative charges (USD), overall charges were significantly lower when ACDF was performed in the ambulatory setting ($33 362.51 vs $74 667.04; P < .0001). The difference remained significant when CCI zero and CCI greater than zero populations were compared separately (Table 7). Outpatient ACDF was also associated with a lower average actual cost vs inpatient ACDF ($9305.57 vs $15 624.63; P < .0001). For institutions with both inpatient hospitals and attached outpatient departments, we also compared the mean cost of ACDF performed at either location. Costs were more than 2-fold higher for inpatient ACDF ($19 465.55 ± $7974.73) vs outpatient ACDF performed at the same institution ($9479.25 ± $3675.04; P < .0001, n = 247 pairs). TABLE 7. 90-D Bundled Charges and Actual Costs.   Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 2794)  (n = 2365)  (n = 429)  (n = 45 366)  (n = 32 803)  (n = 12 563)  Overall  CCI = 0  CCI > 0  90-d bundled charges (USD)              < .0001  < .0001  < .0001   Mean ± SD  33 362.51 ± 24 395.95  33 524.19 ± 22 372.09  32 471.22 ± 33 442.64  74 667.04 ± 69 492.34  71 294.29 ± 60 413.94  83 473.57 ± 88 327.84         Median [range]  28 308 [3427-598 102]  28 361 [3464-298 538]  28 192 [3 427-598 102]  58 744 [218-2 376 586]  57 465 [311-1 623 411]  62 633 [218-2 376 586]        Actual costs (USD)              < .0001  –  –   Mean ± SD  9305.57 ± 3894.78  –  –  15 624.63 ± 9341.03  –  –         Median [range]  9129.39 [651.54-27 032.23]  –  –  13 457.70 [55.17-316 652.52]  –  –          Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 2794)  (n = 2365)  (n = 429)  (n = 45 366)  (n = 32 803)  (n = 12 563)  Overall  CCI = 0  CCI > 0  90-d bundled charges (USD)              < .0001  < .0001  < .0001   Mean ± SD  33 362.51 ± 24 395.95  33 524.19 ± 22 372.09  32 471.22 ± 33 442.64  74 667.04 ± 69 492.34  71 294.29 ± 60 413.94  83 473.57 ± 88 327.84         Median [range]  28 308 [3427-598 102]  28 361 [3464-298 538]  28 192 [3 427-598 102]  58 744 [218-2 376 586]  57 465 [311-1 623 411]  62 633 [218-2 376 586]        Actual costs (USD)              < .0001  –  –   Mean ± SD  9305.57 ± 3894.78  –  –  15 624.63 ± 9341.03  –  –         Median [range]  9129.39 [651.54-27 032.23]  –  –  13 457.70 [55.17-316 652.52]  –  –        Charges associated with the index ACDF procedure plus all inpatient readmissions, reoperations, and emergency department visits within 90 d after index procedure, as well as actual costs associated with the index procedure, were significantly less for patients undergoing ambulatory vs inpatient ACDF, including when stratified by CCI. View Large In the ambulatory cohort, race, median household income national quartile for patient ZIP code, rural–urban continuum location, number of diagnoses on record, number of chronic conditions, and number of levels fused were significant predictors of 90-d cumulative charges in a multiple regression model (Table 8). In the inpatient cohort, age, sex, median household income national quartile for patient ZIP code, number of diagnoses and chronic conditions on record, and CCI were all significant predictors in a multiple regression model (Table 9). TABLE 8. Predictors of 90-d Bundled Charges in a Multiple Regression Model (Ambulatory Index Procedure). Variable  Coefficient  Standard error  95% CI  P  Intercept  21 170  2194.4  –  –  Race  3044.5  556.4  1953.4 to 4135.6  <.0001  Median household income quartile for ZIP code  966.6  479.5  26.3 to 1906.8  .0439  Rural–urban continuum location  –2850.2  354.2  –3544.8 to –2155.7  <.0001  Number of diagnoses on record  2215.3  373.4  1483.1 to 2947.4  <.0001  Number of chronic conditions on record  –2655.0  561.4  –3755.9 to –1554.1  <.0001  Number of levels fused  7062.4  746.5  5598.6 to 8526.1  <.0001  Variable  Coefficient  Standard error  95% CI  P  Intercept  21 170  2194.4  –  –  Race  3044.5  556.4  1953.4 to 4135.6  <.0001  Median household income quartile for ZIP code  966.6  479.5  26.3 to 1906.8  .0439  Rural–urban continuum location  –2850.2  354.2  –3544.8 to –2155.7  <.0001  Number of diagnoses on record  2215.3  373.4  1483.1 to 2947.4  <.0001  Number of chronic conditions on record  –2655.0  561.4  –3755.9 to –1554.1  <.0001  Number of levels fused  7062.4  746.5  5598.6 to 8526.1  <.0001  Significant predictors in a multiple regression model of 90-d total charges after ambulatory ACDF were patient race, median household income quartile for patient's ZIP code, location on the rural–urban continuum, number of diagnoses on record, number of chronic conditions on record, and number of levels fused. View Large TABLE 9. Predictors of 90-d Bundled Charges in a Multiple Regression Model (Inpatient Index Procedure). Variable  Coefficient  Standard error  95% CI  P  Intercept  33 077  1297.6  –  –  Age (yr)  323.5  21.6  281.1 to 365.9  <.0001  Sex  –3099.3  472.4  –4025.3 to –2173.3  <.0001  Median household income quartile for ZIP code  –1377.2  226.3  –1820.8 to –933.6  <.0001  Number of diagnoses on record  5301.4  158.5  4990.8 to 5612.1  <.0001  Number of chronic conditions on record  –4413.0  247.7  –4898.6 to –3927.5  <.0001  CCI  2394.6  416.6  1578.0 to 3211.2  <.0001  Variable  Coefficient  Standard error  95% CI  P  Intercept  33 077  1297.6  –  –  Age (yr)  323.5  21.6  281.1 to 365.9  <.0001  Sex  –3099.3  472.4  –4025.3 to –2173.3  <.0001  Median household income quartile for ZIP code  –1377.2  226.3  –1820.8 to –933.6  <.0001  Number of diagnoses on record  5301.4  158.5  4990.8 to 5612.1  <.0001  Number of chronic conditions on record  –4413.0  247.7  –4898.6 to –3927.5  <.0001  CCI  2394.6  416.6  1578.0 to 3211.2  <.0001  Significant predictors in a multiple regression model of 90-d total charges after inpatient ACDF were patient age, sex, median household income quartile for patient's ZIP code, number of diagnoses on record, number of chronic conditions on record, and CCI. 95% CI = 95% confidence interval. View Large DISCUSSION We reviewed all patients undergoing ACDF in either an inpatient or ambulatory setting in 3 states over 3 yr. Our study found ambulatory ACDF to be statistically noninferior to inpatient ACDF in all clinical outcomes, including when patients were stratified by CCI. Additionally, our study found that actual costs associated with initial operation as well as 90-d cumulative charges (including charges associated with the initial operation as well as all emergency department visits, hospital readmissions, and revisits to ambulatory surgery centers), were significantly lower for outpatient ACDF vs inpatient ACDF. Recently, significant attention has been paid to potential methods of reducing cost per episode, with spine surgery a particular area of focus for healthcare policy makers and payers.21 One method may involve performing elective, high volume surgeries in the outpatient setting. Several studies have shown good outcomes for procedures in other surgical subspecialties when performed in an outpatient setting.22,23 According to the Ambulatory Surgery Center Association (ASCA), the Centers for Medicare and Medicaid Services uses the same fee schedule, known as the hospital market basket, to calculate payments for hospital-affiliated ambulatory surgery centers, also known as HOPDs, as for their affiliated inpatient facility.24 At the same time, procedures performed at freestanding ambulatory surgery centers are reimbursed according to a different schedule (the Consumer Price Index-Urban) at rates that are lower than payments to HOPDs (with average payments 59% of the HOPD rate in 2009, 58% in 2010, and 56% in 2011).24 In this light, a hospital's incentive to transfer its ACDF procedures from its inpatient facility to its own outpatient facility would be the ability to bill on a similar schedule, but with presumably lower overhead costs of keeping a patient in the outpatient department for an average of 0.36 d vs in the inpatient unit for an average of 1.78 d (see length of stay data in Table 3). Surgeons may be reluctant to perform more procedures in the ambulatory setting if they perceive additional risk involved in same-day discharge vs longer inpatient monitoring or if they believe they will be reimbursed at lower rates for these procedures. Although our financial data do not contain information on surgeon compensation, we do not believe there to be a difference in surgeon reimbursement rates between procedures performed at a hospital's inpatient unit vs that hospital's outpatient department, and, therefore, no incentive for a surgeon to limit his or her practice to the inpatient unit. Given the novelty of independent, freestanding ambulatory surgery centers not affiliated with inpatient hospitals, it is difficult to understand how surgeon reimbursement rates at such centers compare with those at hospital-affiliated centers. It is true that patient selection based on surgeon preference for higher reimbursement (especially in the case of surgeon-owned ambulatory surgery centers, that have, since the years accounted for by our data, been allowed to continue operations under existing ownership schemes by the Patient Protection and Affordable Care Act in 2012) and risk avoidance likely accounts for some of the differences in outcomes we show in our manuscript, but nonetheless, the differences in clinical outcomes especially when stratified by CCI reflect the advantages of performing ACDF in an outpatient setting regardless of financial motives. We believe our study to be the first to demonstrate such an effect on a large, nationwide scale, suggesting that ACDF is safe and cost-effective when performed in an outpatient environment. When comparing the cost of ACDF at an institution's inpatient hospital vs the same institution's attached outpatient department, we found that costs were significantly higher for inpatient ACDF ($19 465.55 ± $7974.73) outpatient ACDF performed at the same institution ($9479.25 ± $3675.04). Interestingly, while the average cost of inpatient hospital-affiliated outpatient ACDF was similar to all outpatient ACDF regardless of the center's inpatient hospital affiliation, the cost of inpatient ACDF was higher when performed at a hospital with an affiliated outpatient center ($19 465.55 ± $7974.73) than the average cost of ACDF performed at any inpatient hospital regardless of presence of affiliated outpatient unit ($15 624.63 ± $9341.03). This finding suggests that the presence of an attached ambulatory surgery center is associated with an increased cost of inpatient surgery. The reasons for this discrepancy are likely multifactorial but may include more staff contact and more technology utilized at centers large enough to have an affiliated ambulatory surgery center. This study demonstrates ambulatory ACDF to be noninferior to inpatient ACDF in terms of mortality, 30-d ED visit rates, 30-d readmission rates, and 30-d reoperation rates, and less costly than inpatient ACDF in terms of actual costs and 90-d bundled charges. In the ambulatory cohort, there were no occurrences of early returns to the OR for these complications, no postoperative deaths, and no increase in 30-d ER visits after surgery. We further demonstrate noninferiority of outpatient 1 or 2 level ACDF when compared to inpatient surgery, even when CCI was adjusted for. However, there were significant differences in the baseline characteristics of both groups (Table 1). The outpatient cohort was more likely to be younger, male, and white; more likely to reside in wealthier ZIP codes and to live in urban areas; and less likely to suffer from comorbid conditions, suggesting we cannot rule out confounding based on this observational study. Our findings expand upon several previously reported clinical series. Silvers et al4 first reported a comparison of 50 outpatient and 53 inpatient single- and 2-level noninstrumented anterior cervical decompressions, revealing an average savings of approximately $1800 per patient for outpatient procedures. Stieber et al5 further demonstrated that when outpatient ACDF is performed at C4 to C5 or below as the primary surgery in the absence of myelopathy, the major complication rate was 0% with no readmissions, and transient dysphagia was the most common complaint in 10% of the population.5 Several groups have described outpatient single- and multiple-level ACDF in single-center clinical series, demonstrating feasibility of safely discharging patients postoperatively. More recently, McGirt et al25 analyzed 7288 ACDF cases from the NSQIP database to demonstrate that morbidity and reoperation rates were significantly lower in outpatient vs inpatient ACDF. The statistical significance of the findings remained after propensity score matching of the inpatient and outpatient cohorts. Our study, however, remains the largest such series to date, and is the first to study this issue on a population level with 30-d outcomes and ED visits. This has particular significance given the move towards value based healthcare and potential implementation of 90-d bundled payments.26 Early complications after ACDF can be life-threatening, including wound hematoma causing airway compromise and acute esophageal injury causing mediastinitis.27 The concern for these, and of inadequate pain control upon discharge, are often cited as reasons for performing ACDF as an inpatient, to ensure a prolonged period of monitoring for these complications.28 The data from this analysis suggest that the risk may not be reduced by performing the procedure as an inpatient, and may be safely minimized in an outpatient setting. An alternative explanation is that surgeons are already self-selecting for inpatient surgery patient cohorts more likely to suffer a perioperative complication or readmission. The inpatient and ambulatory cohorts were significantly different in age, CCI, number of diagnoses, and number of chronic conditions on record, and suggest a preoperative self-selection; this stands as a caveat to our data on readmission rates. An alternative explanation may be related to density of ambulatory surgical centers in higher income areas.3 Optimal patient selection for outpatient ACDF requires further investigation. Optimal postoperative monitoring in the outpatient setting may include several hours of observation, swallowing evaluation, wound and neurological monitoring, and pain assessments. Furthermore, the ability to transfer the patient for further observation and treatment expeditiously if necessary to an inpatient setting is likely important. Adamson et al29 recently reported 1000 consecutive patients undergoing ACDF in an outpatient setting with a surgical complication rate of 1%.29 Moreover, all 8 patients needing transfer to inpatient setting were appropriately identified during the 4-h postoperative monitoring window. Lied et al9 stratified postoperative ACDF patients into 3 windows (less than 6 h, 6-72 h, and greater than 72 h) and studied complication rates. Of the 9% of patients experiencing complications, all but one fell into the less than 6 or greater than 72 h window suggesting further observation may not be needed.9 Several predictors of cumulative 90-d charges for patients undergoing ACDF, including number of levels fused, age, sex, number of comorbidities, and several socioeconomic variables including race, median income quartile of ZIP code, and rural vs urban geographic location are identified in this study (Tables 7 to 9). Further research is warranted to clarify the role of socioeconomic factors in determining hospital and ambulatory surgery center charges for surgical procedures such as ACDF. Limitations One limitation was that the location and number of surgical levels were not classified in the inpatient ACDF cohort. However, the proportion of 1-level cases to 2-level cases in the ambulatory group was consistent with the overall literature of all inpatient ACDFs performed,29 and it is likely that the inpatient cohort (all inpatient ACDFs in 3 large US states) are representative of the literature in terms of levels fused. Similarly, our study omits comparison of 3-level ACDF. Our study was also limited to 3 states within the country, and it is possible the results are not generalizable. These states, however, account for 3 geographically distinct regions of the United States and a significant proportion of the US population, and each of these states includes counties with a diverse range of socioeconomic characteristics. In addition, these particular state databases represent an advantage over national databases such as NIS, as they include all discharges from hospitals, ambulatory surgery centers, or emergency departments in a given year, irrespective of insurance status, and provide linkage between healthcare encounters to provide follow-up beyond the initial hospitalization. Our study utilized data grouped by year of admission, and thus may have underestimated re-encounter rates for patients closer to the end of the 3-yr study period, as we did not analyze re-encounters for our patient cohort after 2011. However, the re-encounter rates we report are concordant with existing data,29,30 suggesting that our methodology accurately estimates complication and re-encounter rates. Another limitation is that long-term outcomes could not be analyzed given the constraints of our data source. However, our focus in this work was on short-term clinical outcomes, with an emphasis on safety, of outpatient ACDF. Performing this procedure in an ambulatory setting should not affect patients’ baseline factors; whether performing ACDF in an outpatient setting affects surgical technique in another way, or generates a hitherto unrecognized surgical factor that affects long-term outcomes, remains a topic for further investigation. However, no study to date, to our knowledge, poses a reason to believe that long-term outcomes are significantly different after outpatient surgery. As with all studies utilizing large sample sizes, statistically significant odds ratios, as for nonzero CCI as a predictor for reoperations after inpatient ACDF (Table 6), may not necessarily represent a clinically significant risk. An additional limitation to these results, inherent in analyses of administrative datasets, is the potential for incorrectly coded encounters. Importantly, difference in key patient characteristics between the two cohorts and the observational nature of this study cannot allow us to rule out the possibility of the presence of confounding. Finally, the analyses include only hospital, ER, and surgical center-based encounters and potentially exclude postoperative complications addressed in a primary care physician's office or a specialist's outpatient clinic. These, however, likely represent only a relatively small contribution to cumulative costs and overall postoperative morbidity. CONCLUSION ACDF may be performed in an ambulatory setting with comparable morbidity and readmission rates, and lower costs, to those performed in an inpatient setting. Further studies are warranted to optimize patient selection for outpatient surgery. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. Notes This work was presented as a poster at the Annual Scientific Meeting, American Association of Neurological Surgeons, April 30-May 4, 2016, in Chicago, Illinois and the Annual Meeting, Congress of Neurological Surgeons, September 24 to 28, 2016, in San Diego, California. REFERENCES 1. Davis MA, Onega T, Weeks WB, Lurie JD. Where the United States spends its spine dollars: expenditures on different ambulatory services for the management of back and neck conditions. Spine . 2012; 37( 19): 1693- 1701. Google Scholar CrossRef Search ADS PubMed  2. Weiss AJ, Elixhauser A, Andrews RM. Characteristics of Operating Room Procedures in U.S. Hospitals, 2011. HCUP Statistical Brief #170. February 2014. Agency for Healthcare Research and Quality, Rockville, MD. Available at: http://www.hcup-us.ahrq.qov/reports/statbriefs/sb170-Operatinq-Room-Procedures-United-States-2011.pdf. Accessed May 9, 2017. 3. Cullen KA, Hall MJ, Golosinskiy A. Ambulatory Surgery in the United States, 2006. Natl Health Stat Report . 2009; 11( 11): 1- 25. 4. Silvers HR, Lewis PJ, Suddaby LS, Asch HL, Clabeaux DE, Blumenson LE. Day surgery for cervical microdiscectomy. J Spinal Disord . 1996; 9( 4): 287- 293. Google Scholar CrossRef Search ADS PubMed  5. Stieber JR, Brown K, Donald GD, Cohen JD. Anterior cervical decompression and fusion with plate fixation as an outpatient procedure. Spine J . 2005; 5( 5): 503- 507. Google Scholar CrossRef Search ADS PubMed  6. Villavicencio AT, Pushchak E, Burneikiene S, Thramann JJ. The safety of instrumented outpatient anterior cervical discectomy and fusion. Spine J . 2007; 7( 2): 148- 153. Google Scholar CrossRef Search ADS PubMed  7. Erickson M, Fites BS, Thieken MT, McGee AW. Outpatient anterior cervical discectomy and fusion. Am J Orthop . 2007; 36( 8): 429- 432. Google Scholar PubMed  8. Liu JT, Briner RP, Friedman JA. Comparison of inpatient vs. outpatient anterior cervical discectomy and fusion: a retrosp ective case series. BMC Surg . 2009; 9: 3. doi:10.1186/1471-2482-9-3. Google Scholar CrossRef Search ADS PubMed  9. Lied B, Sundseth J, Helseth E. Immediate (0-6 h), early (6-72 h) and late (>72 h) complications after anterior cervical discectomy with fusion for cervical disc degeneration; discharge six hours after operation is feasible. Acta Neurochir . 2008; 150( 2): 111- 118, discussion 118. Google Scholar CrossRef Search ADS PubMed  10. Lied B, Rønning PA, Halvorsen CM, Ekseth K, Helseth E. Outpatient anterior cervical discectomy and fusion for cervical disk disease: a prospective consecutive series of 96 patients. Acta Neurol Scand . 2012; 127( 1): 31- 37. Google Scholar CrossRef Search ADS PubMed  11. Sheperd CS, Young WF. Instrumented outpatient anterior cervical discectomy and fusion: is it safe? Int Surg . 2012; 97( 1): 86- 89. Google Scholar CrossRef Search ADS PubMed  12. Garringer SM, Sasso RC. Safety of anterior cervical discectomy and fusion performed as outpatient surgery. J Spinal Disord Tech . 2010; 23( 7): 439- 443. Google Scholar CrossRef Search ADS PubMed  13. Trahan J, Abramova MV, Richter EO, Steck JC. Feasibility of anterior cervical discectomy and fusion as an outpatient procedure. World Neurosurg . 2011; 75( 1): 145- 148, discussion 43–4. Google Scholar CrossRef Search ADS PubMed  14. Tally WC, Tarabadkar S, Kovalenko BV. Safety and feasibility of outpatient ACDF in an ambulatory setting: a retrospective chart review. Int J Spine Surg . 2013; 7( 1): e84- e87. Google Scholar CrossRef Search ADS PubMed  15. Meyer B. Anterior cervical discectomy and fusion is feasible as an outpatient procedure. World Neurosurg . 2011; 75( 1): 43. Google Scholar CrossRef Search ADS   16. Wang MY. Outpatient Anterior Cervical Discectomy and Fusion. World Neurosurg . 2011; 75( 1): 44. doi:10.1016/j.wneu.2010.10.055. Google Scholar CrossRef Search ADS   17. HCUP State Inpatient Databases (SID). Healthcare Cost and Utilization Project (HCUP). 2009-2011. Available at: www.hcup-us.ahrq.gov/sidoverview.jsp. Accessed May 9, 2017. 18. HCUP State Ambulatory Surgery and Services Databases (SASD). Healthcare Cost and Utilization Project (HCUP) . 200–2011. Available at: www.hcup-us.ahrq.gov/sasdoverview.jsp. Accessed May 9, 2017. 19. HCUP State Emergency Department Databases (SEDD). Healthcare Cost and Utilization Project (HCUP) . 2009-2011. Available at: www.hcup-us.ahrq.gov/seddoverview.jsp. Accessed May 9, 2017. 20. Whitmore RG, Stephen JH, Vernick C et al.   ASA grade and Charlson Comorbidity Index of spinal surgery patients: correlation with complications and societal costs. Spine J . 2014; 14( 1): 31- 38. Google Scholar CrossRef Search ADS PubMed  21. Resnick DK, Tosteson ANA, Groman RF, Ghogawala Z. Setting the equation: establishing value in spine care. Spine . 2014; 39( 22 Suppl 1): S43- S50. Google Scholar CrossRef Search ADS PubMed  22. Al-Qurayshi Z, Srivastav S, Kandil E. Comparison of inpatient and outpatient thyroidectomy: demographic and economic disparities. Eur J Surg Oncol . 2016; 42(7): 1- 7. 23. Garofalo F, Denis R, Abouzahr O, Garneau P, Pescarus R, Atlas H. Fully ambulatory laparoscopic sleeve gastrectomy: 328 consecutive patients in a single tertiary bariatric center. Obes Surg . 2015; 26(7): 1- 7. 24. Association A. ASCs: a positive trend in health care. Available at: http://www.ascassociation.org/advancingsurgicalcare/aboutascs/industryoverview/apositivetrendinhealthcare. Accessed May 9, 2017. 25. McGirt MJ, Godil SS, Asher AL, Parker SL, Devin CJ. Quality analysis of anterior cervical discectomy and fusion in the outpatient versus inpatient setting: analysis of 7288 patients from the NSQIP database. Neurosurg Focus . 2015; 39( 6): E9. doi:10.3171/2015.9.FOCUS15335. Google Scholar CrossRef Search ADS PubMed  26. Ugiliweneza B, Kong M, Nosova K et al.   Spinal surgery. Spine . 2014; 39( 15): 1235- 1242. Google Scholar CrossRef Search ADS PubMed  27. MD AV, BS TC, MD BJ, FACS JKRM. Revision rates and complication incidence in single- and multilevel anterior cervical discectomy and fusion procedures: an administrative database study. Spine J . 2014; 14( 7): 1125- 1131. Google Scholar CrossRef Search ADS PubMed  28. Fountas KN, Kapsalaki EZ, Nikolakakos LG et al.   Anterior cervical discectomy and fusion associated complications. Spine . 2007; 32( 21): 2310- 2317. Google Scholar CrossRef Search ADS PubMed  29. Adamson T, Godil SS, Mehrlich M, Mendenhall S, Asher AL, McGirt MJ. Anterior cervical discectomy and fusion in the outpatient ambulatory surgery setting compared with the inpatient hospital setting: analysis of 1000 consecutive cases. J Neurosurg Spine . 2016; 24( 6): 878- 884. Google Scholar CrossRef Search ADS PubMed  30. Lovecchio F, Hsu WK, Smith TR, Cybulski G, Kim B, Kim JYS. Predictors of thirty-day readmission after anterior cervical fusion. Spine . 2014; 39( 2): 127- 133. Google Scholar CrossRef Search ADS PubMed  COMMENT The use of outpatient surgical centers for select spinal procedures such as anterior cervical discectomy and fusion (ACDF) has steadily gained acceptance. This growth will likely continue in tandem with a growing body of literature concluding that ambulatory centers are a more cost-effective option for ACDF, relative to the inpatient setting, for select patients. This report builds upon that experience, describing the results in a large cohort of 46 996 inpatients vs 3135 outpatients treated. The results were culled from administrative databases in 3 large US states. Not surprisingly, the rates of readmission and reoperation for the outpatient operations were acceptable and not higher than with inpatients. However, the comparison of inpatient and outpatient ACDF is mired by heterogeneity in study cohorts, financial driving forces such as reimbursement that affects patient selection, differences in patient demographics, and study design. This is reflected by the selection of patients through “cherry picking” for ambulatory surgery: the mean age was 5.1 years younger, the private insurance rate was 11.65% higher, and patients were more likely to be Caucasian. The zip code data informs us of important statistically significant socioeconomic differences in these cohorts as well. Perhaps the most interesting finding in this study was that inpatient direct costs for ACDFs were highest in an inpatient institution with an attached outpatient surgical center, relative to a hospital without an attached surgical center. Left with more questions than answers, perhaps future studies will address the numerous obstacles impeding the comparison of healthcare costs for cervical surgery in different settings. One proposal is to overhaul the oversimplified method of valuation that utilizes fixed costs and/or charges as a primary endpoint. One fundamentally different method of healthcare valuation, time-driven activity-based costing (TDABC), accounts for the entire cycle of care with costs being the aggregate of fractional resource utilization along the care process. Regardless, in the design of future studies of financial healthcare environments in spinal surgery, the sophistication of the data being collected should be reflected by an equally sophisticated methodology. George M. Ghobrial Michael Y. Wang Miami, Florida Copyright © 2017 by the Congress of Neurological Surgeons http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Neurosurgery Oxford University Press

Outpatient vs Inpatient Anterior Cervical Discectomy and Fusion: A Population-Level Analysis of Outcomes and Cost

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Congress of Neurological Surgeons
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Copyright © 2017 by the Congress of Neurological Surgeons
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0148-396X
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1524-4040
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10.1093/neuros/nyx215
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Abstract

Abstract BACKGROUND Outpatient anterior cervical discectomy and fusion (ACDF) is a promising candidate for US healthcare cost reduction as several studies have demonstrated that overall complications are relatively low and early discharge can preserve high patient satisfaction, low morbidity, and minimal readmission. OBJECTIVE To compare clinical outcomes and associated costs between inpatient and ambulatory setting ACDF. METHODS Demographics, comorbidities, emergency department (ED) visits, readmissions, reoperation rates, and 90-d charges were retrospectively analyzed for patients undergoing elective ACDF in California, Florida, and New York from 2009 to 2011 in State Inpatient and Ambulatory Databases. RESULTS A total of 3135 ambulatory and 46 996 inpatient ACDFs were performed. Mean Charlson comorbidity index, length of stay, and mortality were 0.2, 0.4 d, and 0% in the ambulatory cohort and 0.4, 1.8 d, and 0.04% for inpatients (P < .0001). Ambulatory patients were younger (48.0 vs 53.1) and more likely to be Caucasian. One hundred sixty-eight ambulatory patients (5.4%) presented to the ED within 30 d (mean 11.3 d), 51 (1.6%) were readmitted, and 5 (0.2%) underwent reoperation. Among inpatient surgeries, 2607 patients (5.5%) presented to the ED within 30 d (mean 9.7 d), 1778 (3.8%) were readmitted (mean 6.3 d), and 200 (0.4%) underwent reoperation. Higher Charlson comorbidity index increased rate of ED visits (ambulatory operating room [OR] 1.285, P < .05; inpatient OR 1.289, P < .0001) and readmission (ambulatory OR 1.746, P < .0001; inpatient OR 1.685, P < .0001). Overall charges were significantly lower for ambulatory ACDFs ($33 362.51 vs $74 667.04; P < .0001). CONCLUSION ACDF can be performed in an ambulatory setting with comparable morbidity and readmission rates, and lower costs, to those performed in an inpatient setting. ACDF, Ambulatory surgery, Cost, Outcomes, Outpatient ABBREVIATIONS ABBREVIATIONS ACDF anterior cervical discectomy and fusion ASCA Ambulatory Surgery Center Association CCI Charlson Comorbidity Index CCR cost-to-charge ratio CNS central nervous system ED emergency department HCUP Healthcare Cost and Utilization Project HOPDs hospital outpatient departments OR odds ratio OR operating room SASD State Ambulatory Surgery and Services Databases SEDD State Emergency Department Databases SID State Inpatient Databases Spine surgery represents an ideal target for cost reduction within the United States healthcare system due to increasing utilization1 and high payer costs in the face of an aging population.2 One dramatic strategy involves shifting traditionally inpatient procedures to the ambulatory setting. Surgeries performed in an inpatient or hospital-based encounter are estimated to cost 2 to 3 times more than those conducted in an ambulatory surgery center.3 Anterior cervical discectomy and fusion (ACDF) has been identified as a promising candidate to be transitioned into the outpatient setting, given that it is a common procedure that has been shown in the literature to have a low complication rate and early patient discharge in many cases.4-14 Before this cost-reduction strategy can be widely adopted, outpatient ACDF must demonstrate “noninferiority” and produce equivalent or superior outcomes while maintaining patient satisfaction and reducing cost.15,16 The Healthcare Cost and Utilization Project (HCUP) provides state-level encounter and clinical data for all ambulatory, inpatient, and emergency department visits. We retrospectively studied demographics, 30-d outcomes, cost, and predictors of readmission and reoperation after 1- and 2-level ACDF performed in an inpatient and ambulatory setting in 3 highly populated states over a 3-yr period. METHODS Patient Selection An ambulatory or inpatient index procedure was defined as the first discharge record appearing in the HCUP of the US Department of Health and Human Services’ Agency for Healthcare Research and Quality State Inpatient Databases (SID),17 the State Ambulatory Surgery and Services Databases (SASD),18 and the State Emergency Department Databases (SEDD)19 in the 3-yr study period that contained ICD-9 or CPT procedure codes for initial, nonrevision ACDF. These databases contain records of every patient discharge from an inpatient facility, an ambulatory surgery center, or an emergency department, respectively, in a given state in a given year. Additionally, patients with diagnoses on record indicating central nervous system (CNS) neoplasm, CNS infection/inflammatory process, or trauma to the spine or spinal cord, or patients with a flag indicating the presence of any ICD-9 E-codes (representing external injury), were excluded. For each included discharge record, the Charlson Comorbidity Index (CCI), a weighted comorbid illness severity score,20 was calculated. The number of vertebral segments on which ACDF was performed was recorded for ambulatory index procedures only, as only codes in the CPT system are granular enough to distinguish 1-, 2-, and 3-level ACDF procedures (vs ICD-9, where 1- and 2-level procedures are indistinguishable). IRB/Ethics committee approval was not applicable; however, all researchers completed the HCUP Data Use Agreement Training Course and signed the user agreement. Patient consent was not applicable as the source data referenced de-identified patients in a national database. Outcomes Analyzed Using visit linkage and event timing variables, reappearances in SASD, SID, or SEDD after index procedure in SASD or SID were identified and classified as ED visit, inpatient readmission, inpatient reoperation (as indicated by ICD-9 procedure codes representing revision ACDF, hematoma incision and drainage, debridement, other wound complication repair, or esophageal repair), ambulatory readmission, or ambulatory reoperation. For each subsequent patient appearance in the 3 databases, primary diagnosis was categorized into a complication category (infection/hematoma/disruption/dehiscence of wound or complications from implant and routine postoperative care; neck pain/injury, radiculopathy, and cervical spinal degenerative disease; laryngeal and airway complications; dysphagia and esophageal complications; and other). Total charges associated with ambulatory or inpatient index procedure and any reappearance in SASD, SID, or SEDD over a 90-d period was calculated. Actual costs of index ACDF procedure were calculated in the inpatient setting by dividing total charges associated with the hospitalization by the cost-to-charge ratio (CCR) as provided by HCUP. No CCR information is provided for outpatient procedures; for procedures performed in an ambulatory surgery center affiliated with an inpatient hospital (also known as hospital outpatient departments; HOPDs), the inpatient facility's CCR was used. For unaffiliated, freestanding outpatient surgical centers, CCR was estimated by multiplying the average CCR for HOPDs in a given state and a given year by that year's estimated cost differential between inpatient units and HOPDs, as provided by the Ambulatory Surgery Center Association. Data Analysis Descriptive statistics were calculated for age, mortality, CCI, number of diagnoses on record, number of chronic conditions, time to emergency department (ED) presentation, time to inpatient readmission and/or reoperation, time to ambulatory surgery center readmission and/or reoperation, and 90-d total charges. For selected analyses, patient cohorts were stratified into groups with CCI = 0 and CCI > 0. Chi-square tests were used to compare categorical variables such as patient demographics, ED admission rates, and inpatient readmission/reoperation rates. Kolmogorov-Smirnov tests were performed to determine that the distributions of age, CCI, number of diagnoses on record, number of chronic conditions, length of stay (LOS), 90-d total charges, and actual costs were nonnormal; therefore, Wilcoxon–Mann–Whitney tests were used to compare these variables. Logistic regression was used to model the odds of ED visits, readmissions, and reoperations based on number of levels fused and, independently, based on zero vs nonzero CCI. Stepwise model selection was used to define a multiple linear regression model that was then used to assess the relationship between 90-d total charge and patient demographics and comorbidity indicators. The Farrington–Manning score test with noninferiority margin M = 0.1 was used to determine noninferiority of ambulatory vs inpatient ACDF in terms of postoperative outcomes. The noninferiority of ambulatory vs inpatient ACDF was concluded when the lower confidence bound of the risk difference (inpatient – ambulatory) is greater than –0.1. RESULTS Patient Population A total of 46 996 index procedures were identified in the SID compared to 3135 procedures in the SASD. The populations were significantly different as outlined in Table 1. SID patients had an average age of 53 yr compared to 48 yr in the SASD group (P < .0001). SID patients were 53% female compared to 50.8% in SASD (P = .0163) and were 78.7% Caucasian compared to 85.7% in the SASD cohort (P < .0001). With respect to primary payer, With respect to primary payer, 56.25% of SID patients utilized private insurance compared to 67.9% in the SASD group (P < .0001). The 2 groups also differed in medical comorbidities. Average CCI for SID patients was 0.37 compared to 0.17 in SASD (P < .0001). This difference was also conserved in the total number of diagnoses on record and number of chronic conditions on record in SID vs SASD (4.8 vs 3.1, P < .0001; 3.2 vs 2.1; P < .0001), respectively. The most common preoperative primary diagnoses for SID were intervertebral disc disorder with myelopathy, cervical region (15.8%), followed by cervical spondylosis without myelopathy (14.7%) and with myelopathy (12%). The most common SASD primary preoperative diagnosis was displacement of cervical intervertebral disc without myelopathy (56%) followed by cervical spondylosis without myelopathy (12.6%; Table 2). In the SASD cohort, CPT codes enabled stratification by number of ACDF levels as follows: 1-level 57.96%; 2-level 36.52%; and 3-level: 5.52%. TABLE 1. Patient Demographics and Preoperative Characteristics.   Ambulatory  Inpatient    Variable  (n = 3135)  (n = 46 996)  P value  Age (yr)      < .0001   Mean ± SD  48.0 ± 9.5  53.1 ± 11.5     Median [range]  48 [20-85]  52 [18-94]    Sex      .0163   Female  1593 (50.8%)  24 928 (53.0%)     Male  1542 (49.2%)  22 068 (47.0%)    Race      < .0001   Caucasian  2622 (85.7%)  36 272 (78.7%)     Black  175 (5.7%)  3432 (7.4%)     Hispanic  186 (6.1%)  4108 (8.9%)     Asian/Pacific Islander  28 (0.9%)  1008 (2.2%)     Native American  2 (0.1%)  55 (0.1%)     Other  48 (1.6%)  1202 (2.6%)    Primary payer      < .0001   Private insurance  2129 (67.9%)  26 437 (56.25%)     Medicare  154 (4.9%)  10 196 (21.7%)     Medicaid  271 (8.6%)  2404 (5.1%)     Self-pay  60 (1.9%)  624 (1.3%)     No charge  12 (0.4%)  131 (0.3%)     Other  509 (16.2%)  7203 (15.33%)    Median household income quartile for ZIP code      < .0001   1st  549 (19.7%)  5973 (21.3%)     2nd  984 (35.3%)  8385 (29.9%)     3rd  787 (28.2%)  7860 (28.1%)     4th  468 (16.8%)  5790 (20.67%)    Rural–urban continuum location      < .0001   Metro area, population >1m  1295 (41.3%)  28 537 (60.7%)     Metro area, population 250k-1m  1324 (42.2%)  11 573 (24.6%)     Metro area, population <250k  100 (3.2%)  3083 (6.6%)     Urban adjacent to metro, population >20k  207 (6.6%)  2093 (4.4%)     Urban nonadjacent to metro, population >20k  45 (1.4%)  185 (0.4%)     Urban adjacent to metro, population 2500-20k  146 (4.7%)  1201 (2.6%)     Urban nonadjacent to metro, population 2500-20k  11 (0.4%)  180 (0.4%)     Rural or urban adjacent to metro, population <2500  6 (0.2%)  136 (0.3%)     Rural or urban nonadjacent to metro, population <2500  0 (0%)  0 (0%)    Charlson Comorbidity Index (CCI)      < .0001   Mean ± SD  0.17 ± 0.46  0.37 ± 0.73     Median [range]  0 [0-7]  0 [0-16]    Number of diagnoses on record      < .0001   Mean ± SD  3.1 ± 2.2  4.8 ± 3.2     Median [range]  2 [1-23]  4 [1-31]    Number of chronic conditions on record      < .0001   Mean ± SD  2.1 ± 1.5  3.2 ± 2.1     Median [range]  1 [0-9]  3 [0-19]      Ambulatory  Inpatient    Variable  (n = 3135)  (n = 46 996)  P value  Age (yr)      < .0001   Mean ± SD  48.0 ± 9.5  53.1 ± 11.5     Median [range]  48 [20-85]  52 [18-94]    Sex      .0163   Female  1593 (50.8%)  24 928 (53.0%)     Male  1542 (49.2%)  22 068 (47.0%)    Race      < .0001   Caucasian  2622 (85.7%)  36 272 (78.7%)     Black  175 (5.7%)  3432 (7.4%)     Hispanic  186 (6.1%)  4108 (8.9%)     Asian/Pacific Islander  28 (0.9%)  1008 (2.2%)     Native American  2 (0.1%)  55 (0.1%)     Other  48 (1.6%)  1202 (2.6%)    Primary payer      < .0001   Private insurance  2129 (67.9%)  26 437 (56.25%)     Medicare  154 (4.9%)  10 196 (21.7%)     Medicaid  271 (8.6%)  2404 (5.1%)     Self-pay  60 (1.9%)  624 (1.3%)     No charge  12 (0.4%)  131 (0.3%)     Other  509 (16.2%)  7203 (15.33%)    Median household income quartile for ZIP code      < .0001   1st  549 (19.7%)  5973 (21.3%)     2nd  984 (35.3%)  8385 (29.9%)     3rd  787 (28.2%)  7860 (28.1%)     4th  468 (16.8%)  5790 (20.67%)    Rural–urban continuum location      < .0001   Metro area, population >1m  1295 (41.3%)  28 537 (60.7%)     Metro area, population 250k-1m  1324 (42.2%)  11 573 (24.6%)     Metro area, population <250k  100 (3.2%)  3083 (6.6%)     Urban adjacent to metro, population >20k  207 (6.6%)  2093 (4.4%)     Urban nonadjacent to metro, population >20k  45 (1.4%)  185 (0.4%)     Urban adjacent to metro, population 2500-20k  146 (4.7%)  1201 (2.6%)     Urban nonadjacent to metro, population 2500-20k  11 (0.4%)  180 (0.4%)     Rural or urban adjacent to metro, population <2500  6 (0.2%)  136 (0.3%)     Rural or urban nonadjacent to metro, population <2500  0 (0%)  0 (0%)    Charlson Comorbidity Index (CCI)      < .0001   Mean ± SD  0.17 ± 0.46  0.37 ± 0.73     Median [range]  0 [0-7]  0 [0-16]    Number of diagnoses on record      < .0001   Mean ± SD  3.1 ± 2.2  4.8 ± 3.2     Median [range]  2 [1-23]  4 [1-31]    Number of chronic conditions on record      < .0001   Mean ± SD  2.1 ± 1.5  3.2 ± 2.1     Median [range]  1 [0-9]  3 [0-19]    Demographic information including age, sex, race, primary payer, median household income quartile for ZIP code, and location on the rural–urban continuum, as well as preoperative patient characteristics, including CCI, number of diagnoses on record, and number of chronic conditions on record, are presented for 3135 patients who underwent ambulatory ACDF and 46 996 patients who underwent inpatient ACDF. Cohorts are significantly different in all variables analyzed. View Large TABLE 2. Most Common Preoperative Primary Diagnoses (ICD-9-CM) on Record. Ambulatory  Frequency  Inpatient  Frequency  722.0: Displacement of cervical intervetebral disc without myelopathy  1755 (56.0%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  7422 (15.8%)  721.0: Cervical spondylosis without myelopathy  395 (12.6%)  721.0: Cervical spondylosis without myelopathy  6903 (14.7%)  722.4: Degeneration of cervical intervertebral disc  219 (7.0%)  721.1: Cervical spondylosis with myelopathy  5643 (12.0%)  723.0: Spinal stenosis in cervical region  161 (5.1%)  722.4: Degeneration of cervical intervertebral disc  4942 (10.5%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  158 (5.0%)  723.0: Spinal stenosis in cervical region  2767 (5.9%)  721.1: Cervical spondylosis with myelopathy  137 (4.4%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  438 (0.9%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  122 (3.9%)  722.91: Other and unspecified disc disorder, cervical region  397 (0.8%)  723.1: Cervicalgia  45 (1.4%)  738.4: Acquired spondylolisthesis  231 (0.5%)  Ambulatory  Frequency  Inpatient  Frequency  722.0: Displacement of cervical intervetebral disc without myelopathy  1755 (56.0%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  7422 (15.8%)  721.0: Cervical spondylosis without myelopathy  395 (12.6%)  721.0: Cervical spondylosis without myelopathy  6903 (14.7%)  722.4: Degeneration of cervical intervertebral disc  219 (7.0%)  721.1: Cervical spondylosis with myelopathy  5643 (12.0%)  723.0: Spinal stenosis in cervical region  161 (5.1%)  722.4: Degeneration of cervical intervertebral disc  4942 (10.5%)  722.71: Intervertebral disc disorder with myelopathy, cervical region  158 (5.0%)  723.0: Spinal stenosis in cervical region  2767 (5.9%)  721.1: Cervical spondylosis with myelopathy  137 (4.4%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  438 (0.9%)  723.4: Brachial neuritis or radiculitis, not otherwise specified  122 (3.9%)  722.91: Other and unspecified disc disorder, cervical region  397 (0.8%)  723.1: Cervicalgia  45 (1.4%)  738.4: Acquired spondylolisthesis  231 (0.5%)  The 8 most common diagnoses listed as primary diagnosis on record for patients undergoing index ACDF are presented by ambulatory and inpatient cohort. View Large Perioperative Outcomes LOS, disposition, and mortality were analyzed in SASD and SID cohorts (Table 3). LOS was lower in the SASD group compared to SID (0.36 d vs 1.78 d, respectively; P < .0001). To adjust for differences in patient comorbidities, patients were stratified into groups of CCI of zero and greater than zero. The significance of difference in LOS was conserved when populations were stratified into CCI zero vs nonzero groups. Overall, 98.6% of SASD patients were discharged while 10 (0.3%) were transferred to a short-term hospital. No patients died in the SASD cohort while 20 deaths (0.04%) were reported in the SID cohort. TABLE 3. Perioperative Outcomes. Outcomes, Including LOS, Mortality, and Disposition, are Presented for Patients Undergoing Ambulatory or Inpatient ACDF.   Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 3135)  (n = 2664)  (n = 471)  (n = 46 996)  (n = 33 834)  (n = 13 161)  Overall  CCI = 0  CCI > 0  Length of stay (d)              < .0001  < .0001  < .0001   Mean ± SD  0.36 ± 0.52  0.35 ± 0.52  0.42 ± 0.57  1.78 ± 2.18  1.61 ± 1.42  2.20 ± 3.40         Median [range]  0 [0-3]  0 [0-3]  0 [0-3]  1 [0-198]  1 [0-41]  1 [0-198]        Mortality  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)  .633  1.000  1.000  Disposition              < .0001  < .0001  < .0001   Routine discharge to home or law enforcement, with or without plan for acute care inpatient hospital readmission  3090 (98.6%)  2621 (98.39%)  469 (99.58%)  42 318 (90.0%)  31 185 (92.17%)  11 133 (84.59%)         Discharge to home healthcare or hospice  28 (0.9%)  26 (0.98%)  2 (0.42%)  3423 (7.3%)  2126 (6.28%)  1297 (9.85%)         Transfer to short-term hospital  10 (0.3%)  10 (0.38%)  0 (0%)  32 (0.1%)  11 (0.03%)  21 (0.16%)         Transfer to skilled nursing facility, intermediate care facility, or other facility  7 (0.22%)  7 (0.26%)  0 (0%)  1159 (2.5%)  484 (1.43%)  675 (5.13%)         Patient left against medical advice  0 (0%)  0 (0%)  0 (0%)  40 (0.1%)  22 (0.07%)  18 (0.14%)         Patient died  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)         Discharge alive, destination unknown  0 (0%)  0 (0%)  0 (0%)  3 (0.01%)  1 (0.00003%)  2 (0.02%)          Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 3135)  (n = 2664)  (n = 471)  (n = 46 996)  (n = 33 834)  (n = 13 161)  Overall  CCI = 0  CCI > 0  Length of stay (d)              < .0001  < .0001  < .0001   Mean ± SD  0.36 ± 0.52  0.35 ± 0.52  0.42 ± 0.57  1.78 ± 2.18  1.61 ± 1.42  2.20 ± 3.40         Median [range]  0 [0-3]  0 [0-3]  0 [0-3]  1 [0-198]  1 [0-41]  1 [0-198]        Mortality  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)  .633  1.000  1.000  Disposition              < .0001  < .0001  < .0001   Routine discharge to home or law enforcement, with or without plan for acute care inpatient hospital readmission  3090 (98.6%)  2621 (98.39%)  469 (99.58%)  42 318 (90.0%)  31 185 (92.17%)  11 133 (84.59%)         Discharge to home healthcare or hospice  28 (0.9%)  26 (0.98%)  2 (0.42%)  3423 (7.3%)  2126 (6.28%)  1297 (9.85%)         Transfer to short-term hospital  10 (0.3%)  10 (0.38%)  0 (0%)  32 (0.1%)  11 (0.03%)  21 (0.16%)         Transfer to skilled nursing facility, intermediate care facility, or other facility  7 (0.22%)  7 (0.26%)  0 (0%)  1159 (2.5%)  484 (1.43%)  675 (5.13%)         Patient left against medical advice  0 (0%)  0 (0%)  0 (0%)  40 (0.1%)  22 (0.07%)  18 (0.14%)         Patient died  0 (0%)  0 (0%)  0 (0%)  20 (0.04%)  5 (0.01%)  15 (0.11%)         Discharge alive, destination unknown  0 (0%)  0 (0%)  0 (0%)  3 (0.01%)  1 (0.00003%)  2 (0.02%)        Patient cohorts are also stratified by CCI of zero or greater than zero. Cohorts differ significantly in LOS and distribution of postoperative disposition; mortality rates are not significantly different. View Large ED Visits Within 30 d Of the ambulatory (SASD) cohort, 168 patients presented to the emergency department on 197 occasions (5.359%; Table 4, Figure). Average time to presentation was 11.3 d. When comparing a CCI of zero vs nonzero, the percentage of ED visits within 30 d was 5.2% vs 6.4% (not significant; Figure). Cervicalgia was the most frequent diagnosis cited as reason for visit (24.87%) followed by chest pain (4.57%), postoperative pain (3.55%), and dysphagia (2.54%). FIGURE. View largeDownload slide Postoperative outcomes 30 d after index procedure. Rates of unique emergency department visits, inpatient readmission, and inpatient reoperation within 30 d of index ambulatory or inpatient ACDF are presented, stratified by CCI of zero or greater than zero. Patients undergoing ambulatory ACDF were readmitted to inpatient units within 30 d significantly less frequently than patients undergoing inpatient ACDF. There was no difference in rates of 30-d ED visits or 30-d reoperations. ****P < .0001. n.s. indicates P > .05. FIGURE. View largeDownload slide Postoperative outcomes 30 d after index procedure. Rates of unique emergency department visits, inpatient readmission, and inpatient reoperation within 30 d of index ambulatory or inpatient ACDF are presented, stratified by CCI of zero or greater than zero. Patients undergoing ambulatory ACDF were readmitted to inpatient units within 30 d significantly less frequently than patients undergoing inpatient ACDF. There was no difference in rates of 30-d ED visits or 30-d reoperations. ****P < .0001. n.s. indicates P > .05. TABLE 4. Reasons for Inpatient Readmission or Emergency Department Visit within 30 D of Index Procedure. Reason for visit  Frequency (ambulatory to ED) (n = 168)  Frequency (ambulatory to inpatient) (n = 51)  Frequency (inpatient to ED) (n = 2607)  Frequency (inpatient to inpatient) (n = 1778)  Infection, hematoma, or disruption of surgical site or complications from implant  4 (2.0%)  16 (29.6%)  121 (4.1%)  276 (14.0%)  Neck pain or injury, radiculopathy, and degenerative disease of the cervical spine  50 (25.4%)  2 (3.7%)  456 (15.3%)  174 (8.8%)  Laryngeal and airway complications  0 (0%)  0 (0%)  1 (0.03%)  6 (0.3%)  Dysphagia and esophageal complications  5 (2.5%)  2 (3.7%)  66 (2.2%)  52 (2.6%)  Other  138 (70.1%)  34 (63.0%)  2,332 (78.4%)  1,460 (74.2%)  Reason for visit  Frequency (ambulatory to ED) (n = 168)  Frequency (ambulatory to inpatient) (n = 51)  Frequency (inpatient to ED) (n = 2607)  Frequency (inpatient to inpatient) (n = 1778)  Infection, hematoma, or disruption of surgical site or complications from implant  4 (2.0%)  16 (29.6%)  121 (4.1%)  276 (14.0%)  Neck pain or injury, radiculopathy, and degenerative disease of the cervical spine  50 (25.4%)  2 (3.7%)  456 (15.3%)  174 (8.8%)  Laryngeal and airway complications  0 (0%)  0 (0%)  1 (0.03%)  6 (0.3%)  Dysphagia and esophageal complications  5 (2.5%)  2 (3.7%)  66 (2.2%)  52 (2.6%)  Other  138 (70.1%)  34 (63.0%)  2,332 (78.4%)  1,460 (74.2%)  Primary diagnoses on record for 30-d readmissions or 30-d emergency department visits, grouped by complication type, are presented for patients who underwent ambulatory or inpatient ACDF. View Large For the inpatient (SID) cohort, 2607 unique patients presented in 2976 ED encounters (5.547%) within 30 d. Mean time to presentation was 9.7 d. When stratified into CCI zero vs nonzero groups, 5.3% and 6.1% of patients experienced an ED readmission, respectively (Figure). Cervicalgia was again the most common visit diagnosis (13.65%), followed by postoperative pain (3.19%). Fifty-nine patients presented with dysphagia (1.98%). Readmissions Within 30 d Readmission rates were also identified for SASD and SID groups (Table 4). Fifty-one (1.6%) unique patients who underwent ambulatory ACDF were readmitted to an inpatient hospital after the date of the index procedure; 1.58% of patients with CCI of 0% and 1.9% of patients with CCI greater than zero were readmitted within 30 d (Figure). Time to readmission averaged 11.2 d and most common visit diagnoses were postoperative infection (11.11%), seroma complicating a procedure (7.41%), and hematoma complicating a procedure (5.56%). Two patients presented for dysphagia (3.7%). A total of 1778 (3.78%) unique patients whose index procedure was inpatient were readmitted to an inpatient setting 1968 times following the index procedure, representing 2.94% of CCI zero patients and 5.96% of CCI nonzero patients. Mean time to presentation was 6.3 d. The most common visit diagnosis was care involving other specified rehabilitation (28.11%) followed by postoperative infection (3.8%), hematoma complicating a procedure (3.65%), and cervical spondylosis with myelopathy (3.34%). Patients undergoing inpatient ACDF were significantly more likely to have an inpatient readmission at 30 d compared to the ambulatory group (P < .001). This effect was maintained when stratified into CCI zero and nonzero groups (Figure). Reoperations Within 30 d Five patients (0.16%) underwent a reoperation after the outpatient index procedure. Mean time to reoperation was 10.8 d. Three out of the 5 reoperations occurred within 1 wk. Three patients carried the diagnosis of postoperative infection, 1 had seroma complicating a procedure and 1 had “other mechanical complication.” Two-hundred unique patients (0.43%) underwent 201 operations after inpatient index ACDF (0.40% with CCI zero and 0.5% with CCI nonzero; Figure). Average time to reoperation was 12.5 d. Seventy-two patients underwent reoperation within 1 wk, including 7 patients who underwent reoperation the same day. Most common visit diagnosis was cervical spondylosis with myelopathy (20.5%), followed by mechanical complication (13%), postoperative infection (11%), and hematoma complicating a procedure (10%). Patients undergoing inpatient ACDF were significantly more likely to undergo a reoperation (P < .05). However, this effect was not preserved in CCI stratified subgroups. Noninferiority Analysis Ambulatory ACDF was noninferior (margin = 0.1) to inpatient ACDF in terms of mortality, 30-d ED visits, 30-d inpatient readmissions, and 30-d reoperations for all patients as well as patients stratified by CCI (all comparisons P < .0001) as the lower confidence bounds of all differences (inpatient – ambulatory) were greater than –0.1 (Table 5). TABLE 5. Anterior Cervical Discectomy and Fusion Performed in the Ambulatory setting is Noninferior to Inpatient Surgery.   Risk      Comparison  difference  90% CI  P  Mortality     All CCI  0.0004  −0.0084 to 0.0093  <.0001   CCI = 0  0.0001  −0.0094 to 0.0097  <.0001   CCI > 0  0.0011  −0.0217 to 0.0240  <.0001  30-d ED visits     All CCI  0.0019  −0.0088 to 0.0126  <.0001   CCI = 0  0.0015  −0.0100 to 0.0131  <.0001   CCI > 0  −0.0027  −0.0306 to 0.0253  <.0001  30-d readmissions     All CCI  0.0216  0.0114 to 0.0317  <.0001   CCI = 0  0.0136  0.0029 to 0.0243  <.0001   CCI > 0  0.1523  0.1160 to 0.1886  <.0001  30-d reoperations     All CCI  0.0027  −0.0063 to 0.0116  <.0001   CCI = 0  0.0021  −0.0076 to 0.0118  <.0001   CCI > 0  0.005  −0.0182 to 0.0283  <.0001    Risk      Comparison  difference  90% CI  P  Mortality     All CCI  0.0004  −0.0084 to 0.0093  <.0001   CCI = 0  0.0001  −0.0094 to 0.0097  <.0001   CCI > 0  0.0011  −0.0217 to 0.0240  <.0001  30-d ED visits     All CCI  0.0019  −0.0088 to 0.0126  <.0001   CCI = 0  0.0015  −0.0100 to 0.0131  <.0001   CCI > 0  −0.0027  −0.0306 to 0.0253  <.0001  30-d readmissions     All CCI  0.0216  0.0114 to 0.0317  <.0001   CCI = 0  0.0136  0.0029 to 0.0243  <.0001   CCI > 0  0.1523  0.1160 to 0.1886  <.0001  30-d reoperations     All CCI  0.0027  −0.0063 to 0.0116  <.0001   CCI = 0  0.0021  −0.0076 to 0.0118  <.0001   CCI > 0  0.005  −0.0182 to 0.0283  <.0001  The farrington–manning score test (with noninferiority margin of 0.1) was used to determine that ACDF performed in the ambulatory setting is noninferior to inpatient ACDF in terms of patient mortality and rates of 30-d emergency department visits, 30-d readmissions, and 30-d reoperations, including when patients are stratified by CCI. 90% CI = 90% confidence interval of the risk difference of inpatient – ambulatory. View Large Predictors of Readmission and Reoperation Using CPT procedure codes in SASD, we stratified patients by how many levels were fused. Number of fused levels was a predictor of readmission into an inpatient setting at 30 (P < .05; odds ratio [OR] 1.699) and 90 d (P < .001; OR 1.692). Number of ACDF levels was also a significant predictor of reoperation at 30 (P < .5; OR 4.909) and 90 d (P < .001; OR 3.266). When stratified by CCI, CCI greater than zero was a significant predictor of ER readmission in the ambulatory cohort (P < .05; OR 1.285) and inpatient group (P < .0001; OR 1.289; Table 6). CCI greater than zero was also a significant predictor of readmission in ambulatory (P < .001; OR 1.746) and inpatient cohorts (P < .001; OR 1.685). CCI was not a significant predictor of reoperation for ambulatory patients but patients with CCI greater than zero in the inpatient setting were slightly more likely to undergo a reoperation (P < .01; OR 1.160). TABLE 6. CCI as a Predictor of Postoperative Outcomes. Variable  OR  95% CI  P  Ambulatory     All ED visits  1.285  1.041 to 1.586  .0197   All inpatient readmissions  1.746  1.370 to 2.223  <.0001   All reoperations  1.087  0.609 to 1.943  .7774   30-d ED visits  1.245  0.828 to 1.872  .2914   30-d inpatient readmissions  1.216  0.588 to 2.515  .5975   30-d reoperations  –  –  –  Inpatient     All ED visits  1.289  1.234 to 1.346  <.0001   All inpatient readmissions  1.685  1.609 to 1.764  <.0001   All reoperations  1.160  1.054 to 1.276  .0023   30-d ED visits  1.154  1.059 to 1.257  .0011   30-d inpatient readmissions  2.098  1.906 to 2.309  <.0001   30-d reoperations  1.268  0.943 to 1.703  .1157  Variable  OR  95% CI  P  Ambulatory     All ED visits  1.285  1.041 to 1.586  .0197   All inpatient readmissions  1.746  1.370 to 2.223  <.0001   All reoperations  1.087  0.609 to 1.943  .7774   30-d ED visits  1.245  0.828 to 1.872  .2914   30-d inpatient readmissions  1.216  0.588 to 2.515  .5975   30-d reoperations  –  –  –  Inpatient     All ED visits  1.289  1.234 to 1.346  <.0001   All inpatient readmissions  1.685  1.609 to 1.764  <.0001   All reoperations  1.160  1.054 to 1.276  .0023   30-d ED visits  1.154  1.059 to 1.257  .0011   30-d inpatient readmissions  2.098  1.906 to 2.309  <.0001   30-d reoperations  1.268  0.943 to 1.703  .1157  Higher CCI was associated with increased rates of ED visits and inpatient readmissions for patients undergoing ambulatory ACDF and with ED visits (total and within 30 d), inpatient readmissions (total and within 30 d), and reoperations in patients undergoing inpatient ACDF. Logistic regression could not be performed with 30-d reoperation rates after ambulatory ACDF as a dependent variable due to the low rate of that outcome. OR = odds ratio. 95% CI = 95% confidence interval. ED, emergency department. View Large Charges, Costs, and Predictors of Charges In examining 90-d cumulative charges (USD), overall charges were significantly lower when ACDF was performed in the ambulatory setting ($33 362.51 vs $74 667.04; P < .0001). The difference remained significant when CCI zero and CCI greater than zero populations were compared separately (Table 7). Outpatient ACDF was also associated with a lower average actual cost vs inpatient ACDF ($9305.57 vs $15 624.63; P < .0001). For institutions with both inpatient hospitals and attached outpatient departments, we also compared the mean cost of ACDF performed at either location. Costs were more than 2-fold higher for inpatient ACDF ($19 465.55 ± $7974.73) vs outpatient ACDF performed at the same institution ($9479.25 ± $3675.04; P < .0001, n = 247 pairs). TABLE 7. 90-D Bundled Charges and Actual Costs.   Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 2794)  (n = 2365)  (n = 429)  (n = 45 366)  (n = 32 803)  (n = 12 563)  Overall  CCI = 0  CCI > 0  90-d bundled charges (USD)              < .0001  < .0001  < .0001   Mean ± SD  33 362.51 ± 24 395.95  33 524.19 ± 22 372.09  32 471.22 ± 33 442.64  74 667.04 ± 69 492.34  71 294.29 ± 60 413.94  83 473.57 ± 88 327.84         Median [range]  28 308 [3427-598 102]  28 361 [3464-298 538]  28 192 [3 427-598 102]  58 744 [218-2 376 586]  57 465 [311-1 623 411]  62 633 [218-2 376 586]        Actual costs (USD)              < .0001  –  –   Mean ± SD  9305.57 ± 3894.78  –  –  15 624.63 ± 9341.03  –  –         Median [range]  9129.39 [651.54-27 032.23]  –  –  13 457.70 [55.17-316 652.52]  –  –          Ambulatory  Inpatient  P value    Overall  CCI = 0  CCI > 0  Overall  CCI = 0  CCI > 0        Variable  (n = 2794)  (n = 2365)  (n = 429)  (n = 45 366)  (n = 32 803)  (n = 12 563)  Overall  CCI = 0  CCI > 0  90-d bundled charges (USD)              < .0001  < .0001  < .0001   Mean ± SD  33 362.51 ± 24 395.95  33 524.19 ± 22 372.09  32 471.22 ± 33 442.64  74 667.04 ± 69 492.34  71 294.29 ± 60 413.94  83 473.57 ± 88 327.84         Median [range]  28 308 [3427-598 102]  28 361 [3464-298 538]  28 192 [3 427-598 102]  58 744 [218-2 376 586]  57 465 [311-1 623 411]  62 633 [218-2 376 586]        Actual costs (USD)              < .0001  –  –   Mean ± SD  9305.57 ± 3894.78  –  –  15 624.63 ± 9341.03  –  –         Median [range]  9129.39 [651.54-27 032.23]  –  –  13 457.70 [55.17-316 652.52]  –  –        Charges associated with the index ACDF procedure plus all inpatient readmissions, reoperations, and emergency department visits within 90 d after index procedure, as well as actual costs associated with the index procedure, were significantly less for patients undergoing ambulatory vs inpatient ACDF, including when stratified by CCI. View Large In the ambulatory cohort, race, median household income national quartile for patient ZIP code, rural–urban continuum location, number of diagnoses on record, number of chronic conditions, and number of levels fused were significant predictors of 90-d cumulative charges in a multiple regression model (Table 8). In the inpatient cohort, age, sex, median household income national quartile for patient ZIP code, number of diagnoses and chronic conditions on record, and CCI were all significant predictors in a multiple regression model (Table 9). TABLE 8. Predictors of 90-d Bundled Charges in a Multiple Regression Model (Ambulatory Index Procedure). Variable  Coefficient  Standard error  95% CI  P  Intercept  21 170  2194.4  –  –  Race  3044.5  556.4  1953.4 to 4135.6  <.0001  Median household income quartile for ZIP code  966.6  479.5  26.3 to 1906.8  .0439  Rural–urban continuum location  –2850.2  354.2  –3544.8 to –2155.7  <.0001  Number of diagnoses on record  2215.3  373.4  1483.1 to 2947.4  <.0001  Number of chronic conditions on record  –2655.0  561.4  –3755.9 to –1554.1  <.0001  Number of levels fused  7062.4  746.5  5598.6 to 8526.1  <.0001  Variable  Coefficient  Standard error  95% CI  P  Intercept  21 170  2194.4  –  –  Race  3044.5  556.4  1953.4 to 4135.6  <.0001  Median household income quartile for ZIP code  966.6  479.5  26.3 to 1906.8  .0439  Rural–urban continuum location  –2850.2  354.2  –3544.8 to –2155.7  <.0001  Number of diagnoses on record  2215.3  373.4  1483.1 to 2947.4  <.0001  Number of chronic conditions on record  –2655.0  561.4  –3755.9 to –1554.1  <.0001  Number of levels fused  7062.4  746.5  5598.6 to 8526.1  <.0001  Significant predictors in a multiple regression model of 90-d total charges after ambulatory ACDF were patient race, median household income quartile for patient's ZIP code, location on the rural–urban continuum, number of diagnoses on record, number of chronic conditions on record, and number of levels fused. View Large TABLE 9. Predictors of 90-d Bundled Charges in a Multiple Regression Model (Inpatient Index Procedure). Variable  Coefficient  Standard error  95% CI  P  Intercept  33 077  1297.6  –  –  Age (yr)  323.5  21.6  281.1 to 365.9  <.0001  Sex  –3099.3  472.4  –4025.3 to –2173.3  <.0001  Median household income quartile for ZIP code  –1377.2  226.3  –1820.8 to –933.6  <.0001  Number of diagnoses on record  5301.4  158.5  4990.8 to 5612.1  <.0001  Number of chronic conditions on record  –4413.0  247.7  –4898.6 to –3927.5  <.0001  CCI  2394.6  416.6  1578.0 to 3211.2  <.0001  Variable  Coefficient  Standard error  95% CI  P  Intercept  33 077  1297.6  –  –  Age (yr)  323.5  21.6  281.1 to 365.9  <.0001  Sex  –3099.3  472.4  –4025.3 to –2173.3  <.0001  Median household income quartile for ZIP code  –1377.2  226.3  –1820.8 to –933.6  <.0001  Number of diagnoses on record  5301.4  158.5  4990.8 to 5612.1  <.0001  Number of chronic conditions on record  –4413.0  247.7  –4898.6 to –3927.5  <.0001  CCI  2394.6  416.6  1578.0 to 3211.2  <.0001  Significant predictors in a multiple regression model of 90-d total charges after inpatient ACDF were patient age, sex, median household income quartile for patient's ZIP code, number of diagnoses on record, number of chronic conditions on record, and CCI. 95% CI = 95% confidence interval. View Large DISCUSSION We reviewed all patients undergoing ACDF in either an inpatient or ambulatory setting in 3 states over 3 yr. Our study found ambulatory ACDF to be statistically noninferior to inpatient ACDF in all clinical outcomes, including when patients were stratified by CCI. Additionally, our study found that actual costs associated with initial operation as well as 90-d cumulative charges (including charges associated with the initial operation as well as all emergency department visits, hospital readmissions, and revisits to ambulatory surgery centers), were significantly lower for outpatient ACDF vs inpatient ACDF. Recently, significant attention has been paid to potential methods of reducing cost per episode, with spine surgery a particular area of focus for healthcare policy makers and payers.21 One method may involve performing elective, high volume surgeries in the outpatient setting. Several studies have shown good outcomes for procedures in other surgical subspecialties when performed in an outpatient setting.22,23 According to the Ambulatory Surgery Center Association (ASCA), the Centers for Medicare and Medicaid Services uses the same fee schedule, known as the hospital market basket, to calculate payments for hospital-affiliated ambulatory surgery centers, also known as HOPDs, as for their affiliated inpatient facility.24 At the same time, procedures performed at freestanding ambulatory surgery centers are reimbursed according to a different schedule (the Consumer Price Index-Urban) at rates that are lower than payments to HOPDs (with average payments 59% of the HOPD rate in 2009, 58% in 2010, and 56% in 2011).24 In this light, a hospital's incentive to transfer its ACDF procedures from its inpatient facility to its own outpatient facility would be the ability to bill on a similar schedule, but with presumably lower overhead costs of keeping a patient in the outpatient department for an average of 0.36 d vs in the inpatient unit for an average of 1.78 d (see length of stay data in Table 3). Surgeons may be reluctant to perform more procedures in the ambulatory setting if they perceive additional risk involved in same-day discharge vs longer inpatient monitoring or if they believe they will be reimbursed at lower rates for these procedures. Although our financial data do not contain information on surgeon compensation, we do not believe there to be a difference in surgeon reimbursement rates between procedures performed at a hospital's inpatient unit vs that hospital's outpatient department, and, therefore, no incentive for a surgeon to limit his or her practice to the inpatient unit. Given the novelty of independent, freestanding ambulatory surgery centers not affiliated with inpatient hospitals, it is difficult to understand how surgeon reimbursement rates at such centers compare with those at hospital-affiliated centers. It is true that patient selection based on surgeon preference for higher reimbursement (especially in the case of surgeon-owned ambulatory surgery centers, that have, since the years accounted for by our data, been allowed to continue operations under existing ownership schemes by the Patient Protection and Affordable Care Act in 2012) and risk avoidance likely accounts for some of the differences in outcomes we show in our manuscript, but nonetheless, the differences in clinical outcomes especially when stratified by CCI reflect the advantages of performing ACDF in an outpatient setting regardless of financial motives. We believe our study to be the first to demonstrate such an effect on a large, nationwide scale, suggesting that ACDF is safe and cost-effective when performed in an outpatient environment. When comparing the cost of ACDF at an institution's inpatient hospital vs the same institution's attached outpatient department, we found that costs were significantly higher for inpatient ACDF ($19 465.55 ± $7974.73) outpatient ACDF performed at the same institution ($9479.25 ± $3675.04). Interestingly, while the average cost of inpatient hospital-affiliated outpatient ACDF was similar to all outpatient ACDF regardless of the center's inpatient hospital affiliation, the cost of inpatient ACDF was higher when performed at a hospital with an affiliated outpatient center ($19 465.55 ± $7974.73) than the average cost of ACDF performed at any inpatient hospital regardless of presence of affiliated outpatient unit ($15 624.63 ± $9341.03). This finding suggests that the presence of an attached ambulatory surgery center is associated with an increased cost of inpatient surgery. The reasons for this discrepancy are likely multifactorial but may include more staff contact and more technology utilized at centers large enough to have an affiliated ambulatory surgery center. This study demonstrates ambulatory ACDF to be noninferior to inpatient ACDF in terms of mortality, 30-d ED visit rates, 30-d readmission rates, and 30-d reoperation rates, and less costly than inpatient ACDF in terms of actual costs and 90-d bundled charges. In the ambulatory cohort, there were no occurrences of early returns to the OR for these complications, no postoperative deaths, and no increase in 30-d ER visits after surgery. We further demonstrate noninferiority of outpatient 1 or 2 level ACDF when compared to inpatient surgery, even when CCI was adjusted for. However, there were significant differences in the baseline characteristics of both groups (Table 1). The outpatient cohort was more likely to be younger, male, and white; more likely to reside in wealthier ZIP codes and to live in urban areas; and less likely to suffer from comorbid conditions, suggesting we cannot rule out confounding based on this observational study. Our findings expand upon several previously reported clinical series. Silvers et al4 first reported a comparison of 50 outpatient and 53 inpatient single- and 2-level noninstrumented anterior cervical decompressions, revealing an average savings of approximately $1800 per patient for outpatient procedures. Stieber et al5 further demonstrated that when outpatient ACDF is performed at C4 to C5 or below as the primary surgery in the absence of myelopathy, the major complication rate was 0% with no readmissions, and transient dysphagia was the most common complaint in 10% of the population.5 Several groups have described outpatient single- and multiple-level ACDF in single-center clinical series, demonstrating feasibility of safely discharging patients postoperatively. More recently, McGirt et al25 analyzed 7288 ACDF cases from the NSQIP database to demonstrate that morbidity and reoperation rates were significantly lower in outpatient vs inpatient ACDF. The statistical significance of the findings remained after propensity score matching of the inpatient and outpatient cohorts. Our study, however, remains the largest such series to date, and is the first to study this issue on a population level with 30-d outcomes and ED visits. This has particular significance given the move towards value based healthcare and potential implementation of 90-d bundled payments.26 Early complications after ACDF can be life-threatening, including wound hematoma causing airway compromise and acute esophageal injury causing mediastinitis.27 The concern for these, and of inadequate pain control upon discharge, are often cited as reasons for performing ACDF as an inpatient, to ensure a prolonged period of monitoring for these complications.28 The data from this analysis suggest that the risk may not be reduced by performing the procedure as an inpatient, and may be safely minimized in an outpatient setting. An alternative explanation is that surgeons are already self-selecting for inpatient surgery patient cohorts more likely to suffer a perioperative complication or readmission. The inpatient and ambulatory cohorts were significantly different in age, CCI, number of diagnoses, and number of chronic conditions on record, and suggest a preoperative self-selection; this stands as a caveat to our data on readmission rates. An alternative explanation may be related to density of ambulatory surgical centers in higher income areas.3 Optimal patient selection for outpatient ACDF requires further investigation. Optimal postoperative monitoring in the outpatient setting may include several hours of observation, swallowing evaluation, wound and neurological monitoring, and pain assessments. Furthermore, the ability to transfer the patient for further observation and treatment expeditiously if necessary to an inpatient setting is likely important. Adamson et al29 recently reported 1000 consecutive patients undergoing ACDF in an outpatient setting with a surgical complication rate of 1%.29 Moreover, all 8 patients needing transfer to inpatient setting were appropriately identified during the 4-h postoperative monitoring window. Lied et al9 stratified postoperative ACDF patients into 3 windows (less than 6 h, 6-72 h, and greater than 72 h) and studied complication rates. Of the 9% of patients experiencing complications, all but one fell into the less than 6 or greater than 72 h window suggesting further observation may not be needed.9 Several predictors of cumulative 90-d charges for patients undergoing ACDF, including number of levels fused, age, sex, number of comorbidities, and several socioeconomic variables including race, median income quartile of ZIP code, and rural vs urban geographic location are identified in this study (Tables 7 to 9). Further research is warranted to clarify the role of socioeconomic factors in determining hospital and ambulatory surgery center charges for surgical procedures such as ACDF. Limitations One limitation was that the location and number of surgical levels were not classified in the inpatient ACDF cohort. However, the proportion of 1-level cases to 2-level cases in the ambulatory group was consistent with the overall literature of all inpatient ACDFs performed,29 and it is likely that the inpatient cohort (all inpatient ACDFs in 3 large US states) are representative of the literature in terms of levels fused. Similarly, our study omits comparison of 3-level ACDF. Our study was also limited to 3 states within the country, and it is possible the results are not generalizable. These states, however, account for 3 geographically distinct regions of the United States and a significant proportion of the US population, and each of these states includes counties with a diverse range of socioeconomic characteristics. In addition, these particular state databases represent an advantage over national databases such as NIS, as they include all discharges from hospitals, ambulatory surgery centers, or emergency departments in a given year, irrespective of insurance status, and provide linkage between healthcare encounters to provide follow-up beyond the initial hospitalization. Our study utilized data grouped by year of admission, and thus may have underestimated re-encounter rates for patients closer to the end of the 3-yr study period, as we did not analyze re-encounters for our patient cohort after 2011. However, the re-encounter rates we report are concordant with existing data,29,30 suggesting that our methodology accurately estimates complication and re-encounter rates. Another limitation is that long-term outcomes could not be analyzed given the constraints of our data source. However, our focus in this work was on short-term clinical outcomes, with an emphasis on safety, of outpatient ACDF. Performing this procedure in an ambulatory setting should not affect patients’ baseline factors; whether performing ACDF in an outpatient setting affects surgical technique in another way, or generates a hitherto unrecognized surgical factor that affects long-term outcomes, remains a topic for further investigation. However, no study to date, to our knowledge, poses a reason to believe that long-term outcomes are significantly different after outpatient surgery. As with all studies utilizing large sample sizes, statistically significant odds ratios, as for nonzero CCI as a predictor for reoperations after inpatient ACDF (Table 6), may not necessarily represent a clinically significant risk. An additional limitation to these results, inherent in analyses of administrative datasets, is the potential for incorrectly coded encounters. Importantly, difference in key patient characteristics between the two cohorts and the observational nature of this study cannot allow us to rule out the possibility of the presence of confounding. Finally, the analyses include only hospital, ER, and surgical center-based encounters and potentially exclude postoperative complications addressed in a primary care physician's office or a specialist's outpatient clinic. These, however, likely represent only a relatively small contribution to cumulative costs and overall postoperative morbidity. CONCLUSION ACDF may be performed in an ambulatory setting with comparable morbidity and readmission rates, and lower costs, to those performed in an inpatient setting. Further studies are warranted to optimize patient selection for outpatient surgery. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. Notes This work was presented as a poster at the Annual Scientific Meeting, American Association of Neurological Surgeons, April 30-May 4, 2016, in Chicago, Illinois and the Annual Meeting, Congress of Neurological Surgeons, September 24 to 28, 2016, in San Diego, California. REFERENCES 1. Davis MA, Onega T, Weeks WB, Lurie JD. Where the United States spends its spine dollars: expenditures on different ambulatory services for the management of back and neck conditions. Spine . 2012; 37( 19): 1693- 1701. Google Scholar CrossRef Search ADS PubMed  2. Weiss AJ, Elixhauser A, Andrews RM. Characteristics of Operating Room Procedures in U.S. Hospitals, 2011. HCUP Statistical Brief #170. February 2014. Agency for Healthcare Research and Quality, Rockville, MD. Available at: http://www.hcup-us.ahrq.qov/reports/statbriefs/sb170-Operatinq-Room-Procedures-United-States-2011.pdf. Accessed May 9, 2017. 3. Cullen KA, Hall MJ, Golosinskiy A. Ambulatory Surgery in the United States, 2006. Natl Health Stat Report . 2009; 11( 11): 1- 25. 4. Silvers HR, Lewis PJ, Suddaby LS, Asch HL, Clabeaux DE, Blumenson LE. Day surgery for cervical microdiscectomy. J Spinal Disord . 1996; 9( 4): 287- 293. Google Scholar CrossRef Search ADS PubMed  5. Stieber JR, Brown K, Donald GD, Cohen JD. Anterior cervical decompression and fusion with plate fixation as an outpatient procedure. Spine J . 2005; 5( 5): 503- 507. Google Scholar CrossRef Search ADS PubMed  6. Villavicencio AT, Pushchak E, Burneikiene S, Thramann JJ. The safety of instrumented outpatient anterior cervical discectomy and fusion. Spine J . 2007; 7( 2): 148- 153. Google Scholar CrossRef Search ADS PubMed  7. Erickson M, Fites BS, Thieken MT, McGee AW. Outpatient anterior cervical discectomy and fusion. Am J Orthop . 2007; 36( 8): 429- 432. Google Scholar PubMed  8. Liu JT, Briner RP, Friedman JA. Comparison of inpatient vs. outpatient anterior cervical discectomy and fusion: a retrosp ective case series. BMC Surg . 2009; 9: 3. doi:10.1186/1471-2482-9-3. Google Scholar CrossRef Search ADS PubMed  9. Lied B, Sundseth J, Helseth E. Immediate (0-6 h), early (6-72 h) and late (>72 h) complications after anterior cervical discectomy with fusion for cervical disc degeneration; discharge six hours after operation is feasible. Acta Neurochir . 2008; 150( 2): 111- 118, discussion 118. Google Scholar CrossRef Search ADS PubMed  10. Lied B, Rønning PA, Halvorsen CM, Ekseth K, Helseth E. Outpatient anterior cervical discectomy and fusion for cervical disk disease: a prospective consecutive series of 96 patients. Acta Neurol Scand . 2012; 127( 1): 31- 37. Google Scholar CrossRef Search ADS PubMed  11. Sheperd CS, Young WF. Instrumented outpatient anterior cervical discectomy and fusion: is it safe? Int Surg . 2012; 97( 1): 86- 89. Google Scholar CrossRef Search ADS PubMed  12. Garringer SM, Sasso RC. Safety of anterior cervical discectomy and fusion performed as outpatient surgery. J Spinal Disord Tech . 2010; 23( 7): 439- 443. Google Scholar CrossRef Search ADS PubMed  13. Trahan J, Abramova MV, Richter EO, Steck JC. Feasibility of anterior cervical discectomy and fusion as an outpatient procedure. World Neurosurg . 2011; 75( 1): 145- 148, discussion 43–4. Google Scholar CrossRef Search ADS PubMed  14. Tally WC, Tarabadkar S, Kovalenko BV. Safety and feasibility of outpatient ACDF in an ambulatory setting: a retrospective chart review. Int J Spine Surg . 2013; 7( 1): e84- e87. Google Scholar CrossRef Search ADS PubMed  15. Meyer B. Anterior cervical discectomy and fusion is feasible as an outpatient procedure. World Neurosurg . 2011; 75( 1): 43. Google Scholar CrossRef Search ADS   16. Wang MY. Outpatient Anterior Cervical Discectomy and Fusion. World Neurosurg . 2011; 75( 1): 44. doi:10.1016/j.wneu.2010.10.055. Google Scholar CrossRef Search ADS   17. HCUP State Inpatient Databases (SID). Healthcare Cost and Utilization Project (HCUP). 2009-2011. Available at: www.hcup-us.ahrq.gov/sidoverview.jsp. Accessed May 9, 2017. 18. HCUP State Ambulatory Surgery and Services Databases (SASD). Healthcare Cost and Utilization Project (HCUP) . 200–2011. Available at: www.hcup-us.ahrq.gov/sasdoverview.jsp. Accessed May 9, 2017. 19. HCUP State Emergency Department Databases (SEDD). Healthcare Cost and Utilization Project (HCUP) . 2009-2011. Available at: www.hcup-us.ahrq.gov/seddoverview.jsp. Accessed May 9, 2017. 20. Whitmore RG, Stephen JH, Vernick C et al.   ASA grade and Charlson Comorbidity Index of spinal surgery patients: correlation with complications and societal costs. Spine J . 2014; 14( 1): 31- 38. Google Scholar CrossRef Search ADS PubMed  21. Resnick DK, Tosteson ANA, Groman RF, Ghogawala Z. Setting the equation: establishing value in spine care. Spine . 2014; 39( 22 Suppl 1): S43- S50. Google Scholar CrossRef Search ADS PubMed  22. Al-Qurayshi Z, Srivastav S, Kandil E. Comparison of inpatient and outpatient thyroidectomy: demographic and economic disparities. Eur J Surg Oncol . 2016; 42(7): 1- 7. 23. Garofalo F, Denis R, Abouzahr O, Garneau P, Pescarus R, Atlas H. Fully ambulatory laparoscopic sleeve gastrectomy: 328 consecutive patients in a single tertiary bariatric center. Obes Surg . 2015; 26(7): 1- 7. 24. Association A. ASCs: a positive trend in health care. Available at: http://www.ascassociation.org/advancingsurgicalcare/aboutascs/industryoverview/apositivetrendinhealthcare. Accessed May 9, 2017. 25. McGirt MJ, Godil SS, Asher AL, Parker SL, Devin CJ. Quality analysis of anterior cervical discectomy and fusion in the outpatient versus inpatient setting: analysis of 7288 patients from the NSQIP database. Neurosurg Focus . 2015; 39( 6): E9. doi:10.3171/2015.9.FOCUS15335. Google Scholar CrossRef Search ADS PubMed  26. Ugiliweneza B, Kong M, Nosova K et al.   Spinal surgery. Spine . 2014; 39( 15): 1235- 1242. Google Scholar CrossRef Search ADS PubMed  27. MD AV, BS TC, MD BJ, FACS JKRM. Revision rates and complication incidence in single- and multilevel anterior cervical discectomy and fusion procedures: an administrative database study. Spine J . 2014; 14( 7): 1125- 1131. Google Scholar CrossRef Search ADS PubMed  28. Fountas KN, Kapsalaki EZ, Nikolakakos LG et al.   Anterior cervical discectomy and fusion associated complications. Spine . 2007; 32( 21): 2310- 2317. Google Scholar CrossRef Search ADS PubMed  29. Adamson T, Godil SS, Mehrlich M, Mendenhall S, Asher AL, McGirt MJ. Anterior cervical discectomy and fusion in the outpatient ambulatory surgery setting compared with the inpatient hospital setting: analysis of 1000 consecutive cases. J Neurosurg Spine . 2016; 24( 6): 878- 884. Google Scholar CrossRef Search ADS PubMed  30. Lovecchio F, Hsu WK, Smith TR, Cybulski G, Kim B, Kim JYS. Predictors of thirty-day readmission after anterior cervical fusion. Spine . 2014; 39( 2): 127- 133. Google Scholar CrossRef Search ADS PubMed  COMMENT The use of outpatient surgical centers for select spinal procedures such as anterior cervical discectomy and fusion (ACDF) has steadily gained acceptance. This growth will likely continue in tandem with a growing body of literature concluding that ambulatory centers are a more cost-effective option for ACDF, relative to the inpatient setting, for select patients. This report builds upon that experience, describing the results in a large cohort of 46 996 inpatients vs 3135 outpatients treated. The results were culled from administrative databases in 3 large US states. Not surprisingly, the rates of readmission and reoperation for the outpatient operations were acceptable and not higher than with inpatients. However, the comparison of inpatient and outpatient ACDF is mired by heterogeneity in study cohorts, financial driving forces such as reimbursement that affects patient selection, differences in patient demographics, and study design. This is reflected by the selection of patients through “cherry picking” for ambulatory surgery: the mean age was 5.1 years younger, the private insurance rate was 11.65% higher, and patients were more likely to be Caucasian. The zip code data informs us of important statistically significant socioeconomic differences in these cohorts as well. Perhaps the most interesting finding in this study was that inpatient direct costs for ACDFs were highest in an inpatient institution with an attached outpatient surgical center, relative to a hospital without an attached surgical center. Left with more questions than answers, perhaps future studies will address the numerous obstacles impeding the comparison of healthcare costs for cervical surgery in different settings. One proposal is to overhaul the oversimplified method of valuation that utilizes fixed costs and/or charges as a primary endpoint. One fundamentally different method of healthcare valuation, time-driven activity-based costing (TDABC), accounts for the entire cycle of care with costs being the aggregate of fractional resource utilization along the care process. Regardless, in the design of future studies of financial healthcare environments in spinal surgery, the sophistication of the data being collected should be reflected by an equally sophisticated methodology. George M. Ghobrial Michael Y. Wang Miami, Florida Copyright © 2017 by the Congress of Neurological Surgeons

Journal

NeurosurgeryOxford University Press

Published: Apr 1, 2018

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