Comparative Effectiveness of Two Ultrasound-Guided Regional Block Techniques for Surgical Anesthesia in Open Unilateral Inguinal Hernia Repair

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1 TECHNICAL INNOVATION Comparative Effectiveness of Two Ultrasound-Guided Regional Block Techniques for Surgical Anesthesia in Open Unilateral Inguinal Hernia Repair Lauren Steffel, MD, T. Edward Kim, MD, Steven K. Howard, MD, Daphne P. Ly, MD, Alex Kou, BS, Robert King, MS, Edward R. Mariano, MD, MAS Received February 23, 2015, from the Department of Anesthesiology, Perioperative and Pain Medicine (L.S., T.E.K., S.K.H., A.K., E.R.M.) and Division of General Surgery (D.P.L.), Stanford University School of Medicine, Stanford, California USA; and Anesthesiology and Perioperative Care Service (T.E.K., S.K.H., R.K., E.R.M.) and Surgical Service (D.P.L.), VA Palo Alto Health Care System, Palo Alto, California USA. Revision requested March 17, Revised manuscript accepted for publication April 16, Dr Mariano has received unrestricted educational program funding paid to his institution from I-Flow/Kimberly-Clark (Lake Forest, CA) and B. Braun (Bethlehem, PA) and research grant funding paid to his institution from the Foundation for Anesthesia Education and Research. These entities had absolutely no input into any aspect of the study conceptualization, design, and implementation; data collection, analysis, and interpretation; or manuscript preparation. Address correspondence to Edward R. Mariano, MD, MAS, Anesthesiology and Perioperative Care Service; VA Palo Alto Health Care System, 3801 Miranda Ave, 112A, Palo Alto, CA USA. Abbreviations GA, general anesthesia; II/IH, ilioinguinal/ iliohypogastric; MAC, monitored anesthesia care; TAP, transversus abdominis plane doi: /ultra Transversus abdominis plane (TAP) and ilioinguinal/iliohypogastric (II/IH) nerve blocks have been described as analgesic adjuncts for inguinal hernia repair, but the efficacy of these techniques in providing intraoperative anesthesia, either individually or together, is not known. We designed this retrospective cohort study to test the hypothesis that combining TAP and II/IH nerve blocks ( double TAP technique) results in greater accordance between the preoperative anesthetic plan and actual anesthetic technique provided when compared to TAP alone. Based on this study, double TAP may be preferred for patients undergoing open inguinal hernia repair who wish to avoid general anesthesia. Key Words ilioinguinal nerve block; inguinal hernia repair; monitored anesthesia care; outpatient surgery; point-of-care ultrasound; transversus abdominis plane block; ultrasound- guided regional anesthesia The transversus abdominis plane (TAP) block and ilioinguinal/ iliohypogastric (II/IH) nerve blocks, a variation of the TAP block targeting specific nerves, are well established as analgesic adjuncts for open inguinal hernia repair under general anesthesia (GA), 1,2 neuraxial anesthesia, 3,4 and monitored anesthesia care (MAC) with supplemental local anesthetic infiltration in the surgical field. 5 Although combining TAP and II/IH nerve blocks ( double TAP ) has been described in a case report as a feasible anesthetic technique, 6,7 its effectiveness when compared to other regional anesthetic techniques remains largely unstudied. Given the potential advantages of avoiding general and neuraxial anesthesia for outpatient open inguinal hernia repair, we designed this retrospective cohort study to further evaluate the double TAP technique. We hypothesized that, when compared to TAP alone, patients who receive double TAP blocks will have more successful intraoperative anesthesia, reflected by greater accordance between the preoperative anesthetic plan and actual intraoperative anesthetic delivered with fewer MAC-to-GA conversions by the American Institute of Ultrasound in Medicine J Ultrasound Med 2016; 34:

2 Materials and Methods The Institutional Review Board (Stanford University School of Medicine) and VA Palo Alto Research Committee (Research Administration, VA Palo Alto Health Care System) approved the study protocol with waiver of informed consent. We retrospectively reviewed the electronic medical records of sequential adult patients who underwent elective primary unilateral open inguinal hernia repair with mesh over the course of 2 years. We included only surgeries performed by a single surgeon to minimize confounding by the surgical technique. We excluded recurrent hernia repairs (revisions), repairs of multiple sites, and operations performed by surgeons other than the primary surgeon of interest. Patients who received a TAP block or double TAP were identified from their regional anesthesia procedure notes, which were also used to determine the local anesthetic type and dose. All blocks were performed preoperatively in a dedicated regional anesthesia induction area ( block room ) by an attending regional anesthesiologist or a regional anesthesiology and acute pain medicine fellow supervised one-onone by an attending physician. The regional anesthesiology and acute pain medicine service was staffed by a dedicated subgroup of physician-anesthesiologists who used standardized interventional techniques and equipment. During the procedures, patients were positioned supine, were monitored according to American Society of Anesthesiologists standards, and received supplemental oxygen (2 3 L/min) via nasal prongs. The skin in the vicinity of the anticipated needle insertion site was sterilely prepared with chlorhexidine gluconate and isopropyl alcohol (ChloraPrep One-Step; CareFusion, Leawood, KS). Blocks were then performed as follows: Double TAP Technique The double TAP technique is the combination of the TAP block with ultrasound-guided II/IH nerve blocks. After the TAP block as previously described, the high-frequency linear transducer was repositioned in the oblique plane on the ipsilateral lower abdomen along an imaginary line joining the anterior superior iliac spine with the umbilicus, and the sonoanatomy of the abdominal wall muscles was again identified. 9 The II/IH nerve blocks were then performed in a fashion similar to the TAP block, with the targets being the ilioinguinal and iliohypogastric nerves within the interfascial plane between the internal oblique and transversus abdominis muscles (Figure 2). Intraoperative anesthesia care was not standardized. All patients who were planned for MAC with blocks received up to 20 ml of either 1% or 2% lidocaine with epinephrine at 5 μg/ml as supplemental local anesthesia in the surgical field. Since the TAP block only anesthetizes the somatic innervation of the lower abdominal wall, 10 local anesthetic injection was routinely performed by the surgeon during the portions of the operation that elicited visceral pain (eg, exposure and dissection of the hernia sac). Outcomes The primary outcome was the actual anesthetic technique performed intraoperatively, as determined by review of the electronic anesthesia record; this technique was compared to the documented preoperative anesthetic plan detailed by the operating room anesthesiologist on the day of surgery. Figure 1. Sonoanatomy for the TAP block. Asterisks represent transducer position and orientation; arrow represents needle trajectory. EO indicates external oblique; IO, internal oblique; and TA, transversus abdominis. TAP Block With the use of a high-frequency linear array transducer (HFL50, Edge; Fujifilm SonoSite, Bothell, WA) placed in a transverse orientation on the abdominal wall at the anterior axillary line, between the subcostal margin and the iliac crest, the sonoanatomy of the external oblique, internal oblique, and transversus abdominis muscles was identified. 8 After infiltration of the skin and subcutaneous layer with 2% lidocaine, a 20-gauge, 100-mm Tuohy-tip needle (B. Braun, Bethlehem, PA) was advanced in plane to the target injection site between the fascial planes of the internal oblique and transversus abdominis muscles (Figure 1). The local anesthetic solution was injected incrementally. 178 J Ultrasound Med 2016; 35:

3 General anesthesia was defined as continuous propofol infusion of 100 μg/kg/min or higher intravenously or administration of any volatile anesthetic gas. Other outcome measurements included patients baseline characteristics, surgical duration (minutes), and dose of the local anesthetic administered used for the block. Since the local anesthetic injectate consisted of mepivacaine (most commonly used), ropivacaine, bupivacaine, or separate injections of mepivacaine and ropivacaine (double TAP only), all local anesthetic doses were converted to milligram mepivacaine equivalents using a 3:1 ratio for mepivacaine: bupivacaine 11 or a 2:1 ratio for mepivacaine:ropivacaine. 12,13 Statistical Analysis A convenience sample was selected 1 year before and after introduction of the double TAP technique. Statistical analysis was performed with NCSS statistical software (NCSS, LLC, Kaysville, UT) and R (R Foundation for Statistical Computing, Vienna, Austria). Normality of distribution was determined for all scale variables. For normally distributed data, single comparisons were performed with the Student t test; for continuous data in distributions other than normal, the Mann-Whitney U test was used. The χ 2 test or Fisher exact test (n < 5 in any field) was used for comparisons of categorical data. For the primary outcome, the McNemar test of paired proportions was used to compare the actual anesthetic delivered intraoperatively to the preoperative anesthetic plan for each group. To control for variation between different types and doses of local Figure 2. Sonoanatomy for II/IH nerve blocks. Notations are as in Figure 1. anesthetics, as a secondary subgroup analysis of patients who were planned preoperatively to receive MAC with blocks, log-linear analysis was used to identify factors associated with conversion to GA. For all comparisons, P <.05 was considered statistically significant. Results From 2012 to 2014, 187 open inguinal hernia repairs were performed. After exclusion criteria were applied, 51 patients with similar baseline characteristics (Table 1) were included in analyses (32 TAP and 19 double TAP). There was no difference in the overall use of GA: 21 of 32 (66%) for the TAP group compared to 8 of 19 (42%) for the double TAP group (P =.101). Primary Outcome There was a statistically significant difference in the actual anesthetic received intraoperatively when compared to the preoperative anesthetic plan (P =.045) in the TAP group. For the double TAP group, there was no difference between the actual intraoperative anesthetic and the preoperative plan (P =.564). Secondary Outcomes The volume of the local anesthetic used for the block [median (10th 90th percentiles)] was 30 (25 30) ml in the TAP group compared to 40 (35 40) ml in the double TAP group (P <.001). In the subgroup analysis of patients who were preoperatively planned for MAC anesthesia with blocks, the dose influenced the frequency of conversion from MAC to GA in the TAP group, whereas dose had no an influence on conversion from MAC to GA in the double TAP group (P =.003). In the TAP group, 3 of 4 MAC-to- GA conversions were associated with a lower dose of 100 to 200 mg mepivacaine equivalents (Figure 3). By comparison, 3 patients in the double TAP group who received this dose successfully received MAC without conversion to GA (Figure 3). Table 1. Baseline Characteristics of the Study Sample TAP Double Characteristic (n = 32) (n = 19) P Age, y 65 (45 77) 67 (55 78).718 Female/male, n 0/32 1/ ASA physical status 3 (2 3) 3 (2 4).273 Surgical duration, min 89 (61 119) 79 (57 109).164 Values are reported as median (10th 90th percentiles) where applicable. ASA indicates American Society of Anesthesiologists. J Ultrasound Med 2016; 35:

4 Discussion The use of double TAP block for patients undergoing open unilateral inguinal hernia repair may provide more reliable intraoperative anesthesia and ensure greater accordance between the preoperative anesthetic plan and the actual intraoperative anesthetic technique when compared to TAP alone. Although previous studies have established the postoperative analgesic indications for TAP and II/IH nerve blocks, the results of our study support double TAP as a potential option for surgical anesthesia. The preoperative discussion between the patient and anesthesiologist regarding the anesthetic plan is a key component of perioperative care, and the ability to provide the agreed-on anesthetic technique may directly influence patient perceptions of success and satisfaction. To date, there has been one case report published describing bilateral double TAP blocks as the primary anesthetic technique for cesarean delivery, 7 but to our knowledge, this study is the first that compared the anesthetic effectiveness of double TAP with a single abdominal wall block. A wide range of anesthetic techniques for inguinal hernia repair exist, 14 including local anesthesia administered by the surgeon alone. 15 When patients receive this technique, intraoperative pain can be expected. 15 Therefore, the double TAP technique described offers advantages, given the broader anesthetic distribution of the block along the lower abdominal wall 16,17 as well as specific targeting of the ilioinguinal and iliohypogastric nerves. 18 In addition, avoidance of general or spinal anesthesia may speed postoperative recovery 14,19,20 and produce greater cost savings and patient satisfaction in inguinal hernia repair. 20 Although our data Figure 3. Data for the subgroup of patients who were preoperatively planned for MAC with blocks. 180 J Ultrasound Med 2016; 35:

5 suggest that the local anesthetic dosage may be more likely to influence MAC-to-GA conversion with a TAP block versus a double TAP, this study was not designed to determine dose response. These findings require confirmation by further prospective studies. To date, dose ranging for TAP blocks has only been studied for postoperative analgesic and quality-of-recovery outcomes to date. 21,22 This study had several limitations. First, since the study involved a retrospective cohort, it was not blinded or randomized. We attempted to minimize confounders by only including sequential patients under the care of a single surgeon; the resulting small sample size should also be considered a limitation. In addition, the only techniques studied were the TAP block alone and the combination of the TAP block with II/IH nerve blocks, although other peripheral nerve block techniques, such as the paravertebral block, have also been described for inguinal hernia repair. 23,24 We cannot speculate as to how the techniques described will compare to these other block techniques or local anesthetic infiltration alone. 15 Furthermore, the success rates of the procedures performed may be influenced by the equipment and techniques used. Although the anesthesiologist performing the block was not the same for all patients, we believe that the use of uniform techniques and equipment, including ultrasound guidance, among a specialized subgroup of physicians limits the potential for variability in block success. We also acknowledge that block success may be influenced by the volume of the local anesthetic used and that there was a difference in volume used between the two groups involved in this comparison. Unfortunately, volume alone does not take into account the local anesthetic concentration or type of local anesthetic used factors that have been shown to influence block characteristics in other regional anesthesia applications. Therefore for the purposes of this study, we chose to compare doses in mepivacaine equivalents to account for local anesthetic drug selection, concentration, and volume. Finally, the results of this study involve the patient population of an academically affiliated Veterans Administration hospital, which may affect the generalizability of our outcomes. In conclusion, the double TAP technique may be useful for providing intraoperative anesthesia when combined with MAC during open unilateral inguinal hernia surgery and is more likely to ensure accordance between the actual anesthetic technique and the preoperative anesthetic plan. Future prospective studies to further evaluate this regional anesthetic technique are warranted. References 1. Bærentzen F, Maschmann C, Jensen K, Belhage B, Hensler M, Børglum J. Ultrasound-guided nerve block for inguinal hernia repair: a randomized, controlled, double-blind study. Reg Anesth Pain Med 2012; 37: Aveline C, Le Hetet H, Le Roux A, et al. Comparison between ultrasoundguided transversus abdominis plane and conventional ilioinguinal/iliohypogastric nerve blocks for day-case open inguinal hernia repair. Br J Anaesth 2011; 106: Toivonen J, Permi J, Rosenberg PH. 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