Analgesic efficacy of two different volumes of local anaesthetics in ultrasound-guided modified approach to the thoracolumbar interfascial plane block in patients undergoing lumbar spine surgeries: a randomized controlled trial

Background: There is a lack of clarity regarding the ideal local anaesthetic volume for modified thoracolumbar interfascial plane (mTLIP) block. This study was designed to investigate the analgesic efficacy of two different volumes of bupivacaine 0.25% (20 mL, and 10 mL) for ultrasound-guided mTLIP block in patients undergoing lumbar spine surgeries. Methods: A total of 80 patients received single shot of bilateral mTLIP block at the midlevel of the operative intervention and were randomly allocated into one of the two groups to receive either 10 or 20 mL 0.25% bupivacaine on each side. Total morphine consumption in the first 24 hours postoperative was set as the primary outcome. Time to first rescue analgesia and Numeric Rating Scale (NRS) were set as secondary outcomes. Results: There was no significant difference in the primary outcome: 6.20 +/- 2.18 mg (10 mL Group) vs. 5 +/- 0.00 mg (20 mL Group), P = 0.056. The time of first request of rescue morphine was significantly shorter in 10 mL Group (7.80 +/- 3.98 hours) as compared to the 20 mL Group (13.23 +/- 3.00 hours), P < 0.001. NRS at rest and movement in all time measurements was significantly higher in 10 mL Group. Conclusions: Bilateral mTLIP block using 40 mL of 0.25% bupivacaine (20 mL on each side) increased the postoperative total analgesic duration for lumbar spine surgeries, and was associated with a lower postoperative pain scores compared to 20 mL of 0.25% bupivacaine (10 mL on each side).