Ultrasound-Guided Posterior Quadratus Lumborum Block for Acute Postoperative Analgesia in Adult Patients: A Meta-Analysis of Randomized Controlled Trials

Objective: The quadratus lumborum block provides postoperative analgesia for patients undergoing abdominal surgery, although there are three common approaches to perform this block. The present meta-analysis investigated the effectiveness of posterior quadratus lumborum block (QLB2) after surgery. Methods: PubMed, Embase, and the Cochrane Central Register were searched from inception to 26 August 2021 for randomized controlled trials that evaluated the analgesic efficacy of QLB2 vs control (placebo or no block). The primary outcomes were pain scores at 6 h, 12 h, and 24 h after surgery. The secondary outcomes were morphine consumption at 24 h after surgery and the postoperative complications. Results: The present meta-analysis included 14 studies conducted with a total of 1001 patients. In comparison to control group, the QLB2 group presented significantly lower rest pain scores at 6 h (SMD -0.59; 95% CI: -1.05, -0.12; p = 0.01, I-2 = 84%; GRADE = moderate), 12 h (SMD: -0.83; 95% CI: -1.47, -0.19; p = 0.01; I-2 = 88%; GRADE = low), and 24 h (SMD: -0.37; 95% CI: -0.71, -0.03; p = 0.03; I-2 = 80%; GRADE = moderate) after surgery. The dynamic pain scores were significantly reduced, compared to control, in the QLB2 group at 12 h (SMD: -0.93; 95% CI: -1.52, -0.33; p = 0.002; I-2 = 83%; GRADE = low) and 24 h (SMD: -0.52; 95% CI: -0.93, -0.11; p = 0.01; I-2 = 83%; GRADE = moderate) after surgery. In addition, the QLB2 group presented reduced postoperative opioid consumption at 24 h (SMD: -0.45; 95% CI: -0.86, -0.03; p = 0.03; I-2 = 78%; GRADE = moderate). The subgroup analyses revealed that the analgesic benefit of QLB2 did not persist beyond 24 h when the patients were under spinal anesthesia. Conclusion: Ultrasound-guided QLB2 could provide effective analgesia for patients under general anesthesia by decreasing the intensity of pain and opioid requirement when used within 24 h after abdominal surgery.