Anterior Quadratus Lumborum block area comparison in the three different volumes of Ropivacaine: a double-blind, randomized controlled trial in healthy volunteers

BACKGROUND: In abdominal surgery, ultrasound-guided anterior quadratus lumborum blocks (QLB) are performed to induce analgesia. However, no study reported suitable volumes of the anterior QLB for the different postoperative analgesia regions. Therefore, this prospective randomized controlled study assessed the dermatomal spread and analgesic effects of the three different volumes of a local anesthetic for anterior QLB. METHODS: Ultrasound-guided anterior QLB was performed at the L2 level on 30 healthy volunteers. The volunteers were randomized to receive 20 ml (n = 10), 30 ml (n = 10), and 40 mL (n = 10) of 0.375% ropivacaine. The cutaneous sensory blocked area (CSBA), the number of block dermatomes, and the block duration time were measured by determining the extent of the cold sensation. RESULTS: The CSBA was significantly larger in the 40 ml group than in the 30 (P = 0.001; 1350.6 ± 234.4 vs. 1009.5 ± 151.6 cm(2)) and 20 ml groups (P < 0.001; 1350.6 ± 234.4 vs. 808.1 ± 120.5 cm(2)). Similarly, the number of blocked dermatomes was significantly higher in the 40 ml group than in the 30- and 20-ml groups. However, no significant difference was observed in block duration among the groups. CONCLUSIONS: No difference was observed in block duration with the various volumes of 0.375% ropivacaine. However, the larger volume for anterior QLB contributed to a larger area of cutaneous sensory blockade. Appropriate volumes in anterior QLB can create suitable postoperative analgesia levels for the different operative sites. TRIAL REGISTRATION: The study was registered in the Chinese Clinical Trial Registration Center on www.chictr.org.cn on 27th April 2018 (registration number: ChiCTR-IOR-17010853). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12871-022-01922-z.