Background: Previous meta-analyses of the transversus abdominis plane (TAP) block have examined a maximum of 12 articles, including fewer than 650 participants, and have not examined the effect of ultrasound-guided techniques specifically. Recently, many trials that use ultrasound approaches to TAP block have been published, which report conflicting analgesic results. This meta-analysis aims to evaluate the analgesic efficacy of ultrasound-guided TAP blocks exclusively for all types of abdominal surgeries in adult patients.
Methods: This meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines. The primary outcome was cumulative IV morphine consumption at 6 hours postoperatively, analyzed according to the type of surgery, the type of surgical anesthesia, the timing of injection, the block approach adopted, and the presence of postoperative multimodal analgesia. Secondary outcomes included IV morphine consumption at 24 hours postoperatively; pain scores at rest and on movement at 6 and 24 hours postoperatively; and postoperative nausea and vomiting, pruritus, and rates of complications.
Results: Thirty-one controlled trials including 1611 adult participants were identified. Independent of the type of surgery (abdominal laparotomy, abdominal laparoscopy, and cesarean delivery) but not independent of the type of surgical anesthesia (general anesthesia, spinal anesthesia with or without intrathecal long-acting opioid), ultrasound-guided TAP block reduced IV morphine consumption at 6 hours postoperatively by a mean difference of 6 mg (95% confidence interval [CI], -7 to -4 mg; I2 = 94%; P < 0.00001). The magnitude of the reduction in morphine consumption at 6 hours postoperatively was not influenced by the timing of injection (I2 = 0%; P = 0.72), the block approach adopted (I2 = 0%; P = 0.72), or the presence of postoperative multimodal analgesia (I2 = 73%; P = 0.05). This difference persisted at 24 hours postoperatively (mean difference, -11 mg; 95% CI, -14 to -8 mg; I2 = 99%; P < 0.00001). Pain scores at rest and on movement were reduced at 6 hours postoperatively (mean difference at rest, -10; 95% CI, -15 to -5; I2 = 92%; P = 0.0002; mean difference on movement, -9; 95% CI, -14 to -5; I2 = 58%; P < 0.00001). There were neither differences in the incidence of postoperative nausea and vomiting (I2 = 1%; P = 0.59) nor in the pruritus (I2 = 12%; P = 0.58) Two minor complications (1 bruise and 1 anaphylactoid reaction) were reported in 1028 patients.
Conclusions: Ultrasound-guided TAP block provides marginal postoperative analgesic efficacy after abdominal laparotomy or laparoscopy and cesarean delivery. However, it does not provide additional analgesic effect in patients who also received spinal anesthesia containing a long-acting opioid. The minimal analgesic efficacy is independent of the timing of injection, the approach adopted, or the presence of postoperative multimodal analgesia. Because of heterogeneity of the results, these findings should be interpreted with caution.