Liposomal bupivacaine for prolonging analgesia with TAP blocks—two steps forward, one step back

Abstract

Strategies to selectively prolong the duration of sensory blockade have been a subject of both controversy and intense focus in regional anesthesia over the last two decades. Liposomal formulations of local anesthetics, once dubbed the holy grail of regional anesthesia, are one of the facets of such exploration. For decades, anesthesiologists have traditionally used continuous catheter techniques to prolong the duration of postoperative analgesia, but nerve block catheters are not without problems. Secondary failure is not uncommon for continuous catheters and, while such failures have decreased with the use of ultrasound guidance, they are still a pertinent problem. Additionally, continuous infusion of nerve blocks are relatively resource-intensive as they require added equipment, training, and monitoring. Hence, efforts to selectively prolong sensory blockade without the need for a continuous local anesthetic infusion have been gaining traction. Such attempts include the exploration of perineural adjuvants (dexmedetomidine, dexamethasone and clonidine), the development of novel drugs resulting in selective sodium channel blockade (saxitoxin and neosaxitoxin) and last, but not least, liposomal formulation of local anesthetics. Liposomal formulations of medications are widely adopted in clinical medicine as they offer several advantages such as increased efficacy, decreased toxicity, sustained therapeutic effects at the target site, and an increased therapeutic index. In theory, a liposomal formulation of a long-acting local anesthetic deposited close to the surgical field or its congruent terminal innervation should provide prolonged analgesic benefit with minimal motor or autonomic side effects. Liposomal bupivacaine (LB), first of the many candidate sustainedrelease local anesthetic formulations, has been popularized in the last decade ever since the U.S. Food and Drug Administration approved its use for postoperative pain in 2011. Its use was subsequently expanded to include transversus abdominis plane (TAP) blocks in 2015 and interscalene blocks for shoulder surgery in 2018. While LB seemed an attractive option to regional anesthesiologists by offering the prospect of prolonged analgesia similar to continuous catheter techniques with the convenience of single injection, the clinical evidence has not shown unequivocally superior analgesic benefits over unencapsulated local anesthetic solutions. In this issue of the Journal, Fidkowski et al. report on one such comparison of the analgesic properties of LB, unencapsulated bupivacaine hydrochloride (BH), or their combination when administered via TAP blocks for postoperative pain control after open abdominal hysterectomies. This three-arm, single centre, randomized trial included two primary outcomes and multiple secondary outcomes; they did not find a statistically or clinically significant difference in any of the outcomes between the three study groups. The findings of the study are in contrast to two previous randomized-controlled trials reporting decreased pain scores and opioid requirements for up to 72 hr after robotic-assisted hysterectomy and laparoscopic hand-assisted donor nephrectomy with the use of LB compared with BH. These two earlier studies have been critiqued for methodological and reporting Y. S. Ranganath, MBBS MD Department of Anesthesia, Roy J and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA