Background and Objectives The quadratus lumborum block (QLB) is an abdominal truncal block, similar to transversus abdominis plane block (TAPB). However, the characteristics of QLB with regard to its duration and safety are not well known. The primary aim of this study was to determine the block duration and the cutaneous sensory block area. Our secondary analysis included assessment of the chronological change in arterial local anesthetic concentrations after QLB.

Methods This study included 11 patients scheduled for laparoscopic ovarian surgery under general anesthesia. The patients received bilateral single-injection QLBs (20 mL of 0.375% ropivacaine per side). Arterial blood was sampled at 10, 20, 30, 45, 60, 90, and 120 minutes after ropivacaine administration. The results were retrospectively compared with the results of our previous study on lateral TAPB.

Results The median duration of analgesia after QLB exceeded 24 hours and was significantly longer than the duration of lateral TAPB (P = 0.003). Quadratus lumborum block affected the T7-T12 dermatomes, whereas TAPB affected T10-T12. Arterial ropivacaine levels after block peaked at comparable time in the QLB and lateral TAPB groups (T _max: 35 [SD, 13] vs 35 [SD, 11] minutes; P = 0.93). Peak ropivacaine concentrations were significantly lower in QLB than in lateral TAPB (C _max: 1.0 [SD, 0.5] vs 1.8 [SD, 0.4] μg/mL; P = 0.0003).

Conclusions Quadratus lumborum block resulted in a widespread and long-lasting analgesic effect after laparoscopic ovarian surgery and resulted in lower peak arterial ropivacaine concentrations as compared with those of lateral TAPB after 150 mg ropivacaine injection.