Background and aims The optimal opioid-sparing analgesic regimen following laparoscopic colorectal surgery (LCS) remains uncertain. We sought to determine the efficacy of low-dose bupivacaine infusion via surgeon-inserted modified continuous transversus abdominis plane (mcTAP) catheters after LCS.

Methods With ethical committee approval, a parallel-group, placebo-controlled, randomized single-centre trial was conducted between April 2017 and February 2018. Block-of-four randomization and allocation concealment by sequentially-numbered, opaque sealed envelopes were used. Patients, surgeons and assessors were blinded. Fifty-two patients were randomized to receive either 0.2% bupivacaine or saline through mcTAP catheters. a 5 ml bolus followed by a 72h infusion at 2 ml/h was started, with patient-controlled fentanyl analgesia and oral paracetamol given on demand. Primary outcomes were fentanyl consumptions at 24, 48 and 72h. Secondary outcomes were pain numeric rating scores, recovery outcomes and complications.

Results Twenty-five patients in the bupivacaine group and twenty-six in the control group were analysed. Patients in the bupivacaine group required significantly less fentanyl at all time points (24h: 61.0 vs 324.3 mcg, p<0.001; 48h: 36.3 vs 119.0 mcg, p=0.033; 72h: 8.8 vs 41.2, p=0.030) when compared to placebo. Lower pain scores at rest (6h, 12h) and on coughing (6h, 12h, 24h) and reduced opioid-related complications were observed in the bupivacaine group. There were no major block-related complications, and recovery outcomes were otherwise similar in both groups.

Conclusions McTAP block reduces post-operative fentanyl consumption and pain scores after LCS, highlighting its role as a safe and useful opioid-sparing analgesia.