TY - JOUR
AU1 - Soberón , José R
AU2 - Awoniyi, Caleb A
AU3 - Perez, Melissa Alvarez
AU4 - Vasilopoulos, Terrie
AU5 - Canales, Benjamin K
AB - Abstract Background The obturator nerve runs along the posterolateral walls of the bladder and electrosurgical stimulation in this region can result in adductor spasm which can occur suddenly and unexpectedly with potentially catastrophic results. Methods Sixty patients were prospectively randomized to receive either a single-injection ultrasound-guided obturator nerve block (ONB) or intravenous rocuronium after induction of general anesthesia (i.e., neuromuscular block [NMB]). The primary objective was to compare the incidence of adductor spasm during posterolateral bladder tumor resection when ONB or NMB was used. Secondary objectives included assessment of fall risk and incidence of adverse events. Results Five patients in the ONB group and six in the NMB group had nonlateral wall lesions. One patient in the ONB group suffered a cardiac arrest after induction of general anesthesia. Of the remaining 48 patients, six (10.2%) experienced adductor spasm. Most of these patients were in the NMB group (5/24, 20.8%), with only one patient (1/24, 4.2%) experiencing obturator reflex in the ONB group; this difference was not statistically significant (P=0.19). Patients in the ONB group had a greater decrease in mean hip adductor strength. Our study population was found to be at high risk of falls before surgery. There were no statistically significant group differences in the Timed Up and Go test, with time to perform the test increasing in both groups. Conclusions Both techniques are safe and efficacious for preventing adductor spasm. Our data and experience suggest that the ONB is relatively easy to perform and should be considered in patients with posterolateral bladder tumors. Nerve Block, Randomized Controlled Trial, Ultrasound, Surgery, Anesthesiology Introduction Patients with bladder cancer tend to be elderly and medically complex and should be evaluated with flexible cystoscopy, renal function testing, and upper urinary tract imaging [1]. Transurethral resection of the bladder tumor (TURBT) allows the urologist to diagnose, stage, and treat this disease. In addition to the medically complex nature of this patient population, tumors located along the posterolateral region of the bladder can pose an additional challenge. The obturator nerve (L2–4) travels alongside the posterolateral bladder wall before exiting the pelvis, where it separates into the anterior and posterior branches [2]. The anterior branch innervates the adductor longus and brevis muscles, whereas the adductor magnus receives dual innervation from the posterior branch of the obturator nerve and from the sciatic nerve [2–4]. An accessory obturator nerve branch is present in 10–30% of individuals [5, 6]. These muscles play important roles in gait and balance and are responsible for adduction, external and internal rotation, and extension of the hip joint, in addition to providing leg stability in the standing position [3]. Stimulation of the obturator nerve during TURBT can result in sudden and unexpected adductor spasm which can result in bladder perforation, infection, hemorrhage, cancer dissemination, and incomplete surgical resection with worse oncologic outcomes [2, 7]. Nondepolarizing neuromuscular blocking agents (NMBs) and obturator nerve blocks (ONBs) have been used to prevent or minimize adductor spasm. The existing literature suggests that ONBs are safe and efficacious in preventing adductor spasm [2, 7–16]. In two studies comparing patients who received spinal anesthesia for TURBT of the lateral wall, the incidence of bladder perforation with and without ONB was 0% and 5.7%, respectively [7, 14]. Limited data suggest that adductor spasm may still occur despite the use of NMBs [15, 16], and a search of the published literature found no citations comparing NMBs and ONBs. The primary objective of our investigation was to compare the incidence of adductor spasm during posterolateral bladder tumor resection under general anesthesia and ONB or NMB. Secondary objectives included assessing leg weakness and fall risks, as measured with a dynamometer and the Timed Up and Go (TUG) test, respectively. Adverse events were also recorded. Methods This study was approved by the University of Florida Institutional Review Board and registered before patient enrollment at clinicaltrials.gov (NCT03063255). A Consolidated Standards of Reporting Trials (CONSORT) flow diagram is shown in Figure 1. Before surgery, all patients underwent flexible diagnostic cystoscopy (Figure 2) and were scheduled for TURBT. Written informed consent was obtained from all participants. Upon enrollment, patients were randomized (n=60) to the ONB or NMB groups in randomized permutated blocks of six (GraphPad Software, San Diego, CA, USA). The allocation sequence was generated by a research coordinator. The principal investigator (JS) enrolled participants before surgery, and the assigned intervention was determined on the basis of a randomly generated list that was accessed after patient enrollment. After induction of general anesthesia, those randomized to the ONB group would receive an ultrasound-guided ONB, whereas those randomized to the NMB group would receive intravenous rocuronium, incrementally titrated to 0–1 twitches. Neither the patients nor the surgeons were told of their assigned group, and members of the surgical team were not present during induction of general anesthesia and subsequent study interventions. All pre- and postoperative assessments, as well as the ONBs, were performed by the principal investigator (JS). Figure 1. Open in new tabDownload slide CONSORT flow diagram. MH = Malignant Hyperthermia. Figure 2. Open in new tabDownload slide An illustration depicting a flexible endoscope viewing a posterolateral bladder tumor. The obturator nerve is depicted in yellow. Inclusion criteria for participation were age ≥18 years, planned TURBT for unilateral posterolateral bladder tumors, and the ability to understand and provide informed consent. Exclusion criteria were patient refusal or inability to provide informed consent; true allergy (not sensitivity) to local anesthetics, propofol, or general anesthetic agents; pregnancy; severe hepatic impairment; evidence of infection at or near the proposed needle insertion site; any sensorimotor deficit of the lower extremity, as determined by the principal investigator; inability to walk without assistance; and lower-extremity joint replacement surgery in the preceding 6 months. Preoperative Assessments Fall risk assessments were performed with adductor strength testing and the TUG test before surgery. Maximum voluntary isometric contraction of hip adduction was recorded with a dynamometer (Lafayette Instrument Manual Muscle Test System, Lafayette, Indiana, USA), which is a reliable means of assessing hip strength [17]. With the patient in the supine position and the hip slightly abducted, the dynamometer was placed on the medial aspect of the knee on the ipsilateral side of the bladder tumor. Baseline measurements were obtained three times in the preoperative holding area and again in the post-anesthesia care unit (PACU). The TUG test requires the participant to stand from a seated position, walk 10 feet, turn around, and return to a seated position. The test is freely available and is a sensitive and specific tool for evaluating fall risk, with excellent intra- and interrater reliability [18]. It is easy to perform, does not require specialized equipment or training, and correlates well with other balance and gait measures [19]. Times ≥13.5 seconds are associated with an increased risk of falls [18, 19]. Anesthesia Induction No preoperative medications were administered. All patients were transported into the operating room, where general anesthesia was induced with 1–2 mg/kg of propofol and tracheal intubation was facilitated with 1 mg/kg of succinylcholine. If a difficult intubation was anticipated, an awake fiber-optic intubation was performed before induction of general anesthesia. A STIMPOD NMS 450 (Xavant Technology, Silverton, South Africa) accelerometer was used to measure twitches and train-of-four (TOF) ratios of the ulnar nerve throughout the surgical procedure. Continuous electromyography and clinical observation were used to potentially anticipate and observe adductor spasm. Adhesive skin electrodes were placed on the ipsilateral thigh and connected to a Nerve Integrity Monitor Response 3.0 (Medtronic Xomed, Inc., Jacksonville, Florida, USA) to detect and document adductor spasm. All patients were maintained with 0.8–1.2 minimum alveolar concentration of sevoflurane in 40% oxygen concentration. ONB Group Resolution of succinylcholine was confirmed with an ulnar nerve TOF ratio ≥0.9, and a time-out procedure was performed to confirm the laterality of the bladder wall lesion. An ultrasound-guided ONB was performed via an in-plane approach in which the technique previously described by Sinha et al. (2009) [20] was used. A GE LOGIQ E ultrasound machine (Fairfield, CT, USA) was used, and the L4–12t transducer was placed on the medial aspect of the inguinal crease. Once the adductor and pectineus muscles were identified (Figure 3), a 21-gauge SonoPlex needle (PAJUNK Medical Systems L.P., Norcross, Georgia, USA) was inserted in-plane in a lateral-to-medial direction. Once the needle tip was placed at the junction of the pectineus, adductor longus, and adductor brevis muscles, 15 mL of 2% mepivacaine were incrementally injected. The needle was then inserted between the adductor brevis and magnus muscles, and an additional 15 mL of 2% mepivacaine were similarly injected. If intramuscular injection was detected, local anesthetic injection was halted, and the needle was repositioned until interfascial separation occurred. Figure 3. Open in new tabDownload slide An ultrasound image obtained during obturator block placement illustrating the pertinent anatomy. No additional succinylcholine or rocuronium was administered for the remainder of the procedure. NMB Group Once resolution of succinylcholine was confirmed with an ulnar nerve TOF ratio ≥0.9, intravenous rocuronium was administered incrementally to a goal of one to zero twitches. The STIMPOD NMS 450 was programmed in the Neuromuscular Blocking Agent Monitoring mode with TOF measurements every 2 minutes. If fewer than four twitches were present, the accelerometer reported the number of twitches detected (0–3). Surgical Procedure and Anesthetic Care Clinical staff were asked to refrain from administering opioids or benzodiazepines before completion of repeat TUG testing and dynamometer measurements. All patients were placed in the dorsal lithotomy position, and the bladder was entered transurethrally with a rigid cystoscope. After pancystoscopy was performed, suspected lesions were resected by using a bipolar loop, and resection bases were fulgurated to ensure hemostasis. Specimens were evacuated through the cystoscope sheath out of the bladder, and the resectoscope was removed. The patient was then placed in the supine position, and a Foley catheter was placed at the discretion of the surgical team. Intravenous acetaminophen and ondansetron were administered before emergence from general anesthesia. Patients randomized to the NMB group received intravenous neostigmine and glycopyrrolate or sugammadex at the conclusion of surgery. All patients in both groups had a TOF ratio ≥0.9 at the time of extubation. All patients were extubated and transferred to the PACU. One hour after arrival there, repeat dynamometer measurements and TUG tests were performed. A gait belt was placed around the patient’s waist and held by the principal investigator during TUG testing to prevent or lessen the impact of a potential fall. All patients were subsequently discharged home or to the surgical ward without restrictions on ambulation. All patients were contacted 24–48 hours after discharge to inquire about falls or evidence of nerve injury as well as patient satisfaction. Statistical Analysis Categorical measures were summarized as percentages (%). Continuous measures were summarized as means and standard deviations (SDs). Differences in the primary outcome of block success were examined with χ2 tests or Fisher’s exact tests. Similar tests were performed for other categorical outcomes. Changes in hip adduction strength and the TUG test were assessed with linear regression analyses, with postoperative measurement as the dependent variable and block group and preoperative measurement as independent variables. Including the preoperative measurement as an independent variable created a “residual change score” and controls for potential baseline group differences. In this model, a statistically significant effect of group status can be interpreted as a group difference in the change between pre- and postoperative measurements. Preoperative differences in hip adduction strength and the TUG test were tested with t tests. P <0.05 was considered statistically significant. Before the initiation of the study, the incidence of adductor spasm during TURBT in patients with posterolateral tumors was reported to be as high as 40–55% by some investigators [9, 12, 14, 21]. A more conservative estimate of incidence of 35% was used for a priori sample size determination. With n=60, our sample could detect a minimum 29% difference (i.e., 35% – 6%) in adductor spasm incidence between the NMB group and ONB group, assuming 80% power and alpha=0.05. This difference is similar to that found in another randomized controlled trial comparing adductor spasm rates between patients undergoing TURBT under spinal anesthesia with and without ONB [14]. This sample size would also be able to detect a minimum group mean difference of 7.4 on the TUG (SD=10.0). This article adheres to the applicable CONSORT guidelines. Results Sixty-four male patients met the inclusion criteria for participation in the study. Of these, one declined to participate, and the principal investigator deemed three potential subjects to be at a prohibitively high risk under general anesthesia (comorbidities included severe chronic obstructive pulmonary disease, supplemental oxygen dependence, severe pulmonary hypertension, and a personal history of malignant hyperthermia); these three patients received a spinal anesthetic and an ONB without sedation. The study was concluded after 60 subjects were enrolled. Eleven patients (five in the ONB group and six in the NMB group) were found to have nonlateral wall lesions during TURBT, which was due to misidentification of tumor location on preoperative cystoscopy. These patients were excluded from primary outcome analysis, but the remaining data were used for secondary outcome analysis. One patient in the ONB group suffered a cardiac arrest shortly after induction of general anesthesia and was excluded from further analysis. The analytical sample for primary analysis was n=48. Because of the potential risk of benzodiazepines and opioids to increase falls, particularly in the elderly [22, 23], providers were asked to avoid administration of these medications to this study population. Despite these requests, one patient in the ONB group inadvertently received intravenous midazolam, and another in the NMB group received intravenous morphine. Postoperative dynamometer and TUG testing results for these two patients were excluded from data analysis. Table 1 reports patient characteristics for the ONB and the NMB groups. The groups were similar in age, American Society of Anesthesiologists physical status, and body mass index. Patients in the ONB group had a slightly shorter PACU time. Table 1. Patient characteristics in the two block groups Measure . NMB (n=30) . ONB (n=29) . Age, y, mean±SD 72.2±6.3 70.2±7.3 ASA status, % (n) 2 0% (0) 3.4% (1) 3 86.7% (26) 82.8% (24) 4 13.3% (4) 13.8% (4) Body mass index, kg/m2, mean±SD 28.3±5.5 28.6±4.9 Time in PACU, min, mean±SD 109.0 ± 64.2 92.0±37.4 Measure . NMB (n=30) . ONB (n=29) . Age, y, mean±SD 72.2±6.3 70.2±7.3 ASA status, % (n) 2 0% (0) 3.4% (1) 3 86.7% (26) 82.8% (24) 4 13.3% (4) 13.8% (4) Body mass index, kg/m2, mean±SD 28.3±5.5 28.6±4.9 Time in PACU, min, mean±SD 109.0 ± 64.2 92.0±37.4 ASA=American Society of Anesthesiologists. Open in new tab Table 1. Patient characteristics in the two block groups Measure . NMB (n=30) . ONB (n=29) . Age, y, mean±SD 72.2±6.3 70.2±7.3 ASA status, % (n) 2 0% (0) 3.4% (1) 3 86.7% (26) 82.8% (24) 4 13.3% (4) 13.8% (4) Body mass index, kg/m2, mean±SD 28.3±5.5 28.6±4.9 Time in PACU, min, mean±SD 109.0 ± 64.2 92.0±37.4 Measure . NMB (n=30) . ONB (n=29) . Age, y, mean±SD 72.2±6.3 70.2±7.3 ASA status, % (n) 2 0% (0) 3.4% (1) 3 86.7% (26) 82.8% (24) 4 13.3% (4) 13.8% (4) Body mass index, kg/m2, mean±SD 28.3±5.5 28.6±4.9 Time in PACU, min, mean±SD 109.0 ± 64.2 92.0±37.4 ASA=American Society of Anesthesiologists. Open in new tab Six patients (12.5%) experienced obturator reflex. A majority of these patients were in the NMB group (5/24, 20.8%), with only one patient (1/24, 4.2%) with reflex in the ONB group; however, this difference was not statistically significant (P=0.19, Fisher’s exact test). Of the five patients in the NMB group who had adductor spasm, TOF monitoring revealed 0/4 twitches in one patient, 1/4 twitches in three patients, and 2/4 twitches in one patient immediately before the event. In the ONB group, only one patient had intraoperative adductor spasm. Notably, this patient was found to have a profound decrease in thigh adduction strength postoperatively, which suggests a successful ONB. The mean ONB performance time, defined as the duration elapsed from initial needle insertion to conclusion of the nerve block, was 2.97 minutes. A majority of patients (62.7%) had a postoperative Foley catheter. The proportion of patients with a Foley catheter in both groups was similar (P=0.79). Preoperative hip adduction strength was not statistically different between the ONB (13.6±3.4 kg) and NMB (14.7±5.6 kg) groups (P=0.35). Similarly, preoperative performance on TUG testing was not statistically different between the ONB (13.8±2.9 s) and NMB (17.0±11.3 s) groups (P=0.15). There were statistically significant differences in pre–post change in hip adductor strength between groups (beta=2.39, standard error=0.38, P<0.001). Patients in the ONB group had a greater decrease in mean hip adductor strength (−5.9 kg±4.1) than that of the patients in the NMB group (−4.7 kg±2.8; Figure 4). There were no statistically significant group differences in pre–post change in TUG testing (beta=−1.76, standard error=1.04, P=0.10), with time to perform the TUG test increasing in both groups (Figure 5). Figure 4. Open in new tabDownload slide Differences in hip adduction strength between groups. Error bars represent 95% confidence intervals. There was a greater decrease in hip adductor strength in the ONB group (−5.7±4.0 kg) than in the NMB group (−1.7±2.8 kg) (P<0.001). Figure 5. Open in new tabDownload slide Differences in the TUG test between groups. Error bars represent 95% confidence intervals. The difference in the change in the TUG test between the ONB group (10.3±8.1 s) and the NMB group (8.1±9.0 s) was not statistically significant (P=0.11). There were no postoperative adverse events or falls in either study group. No patient required escalation of care or hospital admission for anesthetic- or study-related reasons. Discussion We found overall low rates of obturator reflex. However, although not statistically significant, the majority of patients (5/6) who experienced obturator reflex received NMB. No instances of bladder perforation or serious adverse events occurred, which we believe reflects the efficacy of the ONB, as well as the efficacy of deep neuromuscular blockade. Although temporarily disruptive to the surgical procedure, obturator reflex was usually ameliorated with reduced electrocautery current and short incremental (staccato) resection. Furthermore, although the incidence of adductor spasm was not statistically significant between the two groups, our study illustrated that adductor spasm can still occur despite the use of deep neuromuscular blockade, as four of the five patients who experienced this in the NMB group had 0–1 twitch(es) at the time. Although electromyography has been used previously during TURBT [24], we do not recommend its routine use because we found that it was prone to artifact and did not predict adductor spasm. Because adductor spasm usually occurred unexpectedly, detecting adductor spasm on electromyography in real time is akin to activating the turn signal in the middle of a turn while driving. Close discussion with the surgical team is warranted before TURBT to confirm the tumor location and the need for prevention of adductor spasm. Despite these discussions and a review of preoperative records, there were instances in which the bladder lesion location was mistakenly reported to be on the lateral wall on preoperative cystoscopy but was later found in a location at low risk for adductor spasm. ONB placement may be deferred until after pancystoscopy in the operating room to confirm tumor location. Because the mean block performance time in our study was approximately 3 minutes, an ONB may be performed without substantial delay (assuming block-related materials and an ultrasound machine are immediately available). The block may also be performed in a block room or preoperative holding area before the surgical procedure. An advantage of the ONB is that it can also be performed for awake patients undergoing spinal anesthesia without the need for controlled ventilation. In our population, 59/60 patients were assigned an American Society of Anesthesiologists physical status of III or IV. Depending on underlying pathology and comorbidities, avoiding general anesthesia and its concomitant risks may be desired. A major limitation of our investigation is a small sample size that is underpowered to detect uncommon or rare events. Although we recruited 60 subjects, only 48 were able to be in the final analysis, which resulted in the final analysis for the primary outcome being underpowered. Additionally, we found a 12.5% incidence of adductor spasm in our patient population of patients with posterolateral tumors, which is substantially lower than the previously reported incidence of 40–55% [9, 12, 14, 21]. Because of the observed rates of adductor spasm in the NMB group (20.8%) and ONB group (4.2%), a sample of n=120 would be needed to better detect differences in a future investigation. Bipolar electrocautery was used exclusively in our study, and the incidence of adductor spasm with its use is not known. Bolat et al. (2016) found a lower incidence of adductor spasm in patients undergoing TURBT randomized to bipolar vs. monopolar electrocautery (4.5% vs. 21.5%, respectively) [25]. In another trial comparing bipolar vs. monopolar electrocautery use in TURBT, Venkatramani et al. (2014) found no statistically significant difference in the incidence of adductor spasm (49.2% vs. 60%, respectively) [21]. Additional research is required to determine the incidence of adductor spasm in patients undergoing TURBT with bipolar electrocautery. A second drawback of our study is that the blocks were not performed in a preoperative holding area to assess block onset. Because we wanted to minimize exposure to anesthetic agents (such as opioids and benzodiazepines) that could potentially increase fall risk [22, 23], coupled with the potential discomfort associated with performing the ONB on awake patients, we decided to perform the block after induction of general anesthesia. Our data on postoperative adductor muscle weakness suggest that the blocks were successful. We found the patients receiving ONBs had greater decreases in hip adduction strength postoperatively than did those receiving NMBs (41.1% mean decrease vs. 10.9%). Previous reports have varied in the adductor strength reduction obtained from successful ONBs [5, 20, 26, 27]. Given the contribution of the sciatic nerve to the adductor magnus, adductor muscle strength and stability appear to be at least somewhat preserved [2–4]. This, coupled with the use of an intermediate-acting local anesthetic (mepivacaine), may account for the lack of falls in our patients. It is unclear why those in the NMB group also experienced a reduction of hip adduction strength (10.9%) despite the reversal of neuromuscular agents and resolution of the effects of general anesthesia. Although no patients experienced a fall at home or in the PACU, it is unknown what support (if any) was provided by the gait belt. Because of the paucity of data on the incidence of falls in patients undergoing TURBT with ONBs, we could not ethically allow someone to attempt ambulation without the ability to halt or soften a fall. Muscle strength, however, is only one factor to consider in the assessment of fall risk. Causes of falls are often multifactorial in nature; strength, vision and lighting, impaired sensorium, and walking surfaces also play key roles. Our patient population was identified by the TUG test to be at high risk of falls before surgery. The importance of avoiding falls and a thorough explanation of risk factors should be discussed with all patients deemed to be at elevated risk of falls, as well as their caregivers, before discharge. In summary, although our study was underpowered with regard to our primary outcome, the ONB was quick and relatively easy to perform without increasing fall risk in a patient population susceptible to falls. 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TI - Obturator Nerve Blockade vs. Neuromuscular Blockade for the Prevention of Adductor Spasm in Patients Undergoing Transurethral Resection of Bladder Tumors: A Randomized Controlled Trial
JF - Pain Medicine
DO - 10.1093/pm/pnaa448
DA - 2021-06-04
UR - https://www.deepdyve.com/lp/oxford-university-press/obturator-nerve-blockade-vs-neuromuscular-blockade-for-the-prevention-1XPgDFhbnM
SP - 1253
EP - 1260
VL - 22
IS - 6
DP - DeepDyve
ER -