Combining ropivacaine transversus abdominis plane block with intravenous lidocaine infusion in adults undergoing colorectal cancer surgery: an open-label, dose-escalation exploratory trial

Background The concurrent use of a ropivacaine transversus abdominis plane (TAP) block with intravenous lidocaine infusion, though effective for pain relief, raises safety concerns regarding local anesthetic systemic toxicity (LAST). This study aimed to assess the dose-risk relationship of LAST in this combination by escalating the ropivacaine dose while fixing the lidocaine dose. Methods In this dose-escalation study, adult patients undergoing colorectal cancer surgery received a 0.2% ropivacaine TAP block (1.5, 2.0 or 2.5 mg kg ^− 1 ) and intravenous lidocaine infusion (2 mg kg ^− 1 bolus, followed by 2 mg kg ^− 1 h ^− 1 ), both dosed according to ideal body weight (IBW). The primary outcome was the occurrence of LAST, identified by clinical symptoms, new-onset ECG irregularities, etc. Secondary outcomes included plasma concentrations of ropivacaine and lidocaine. Results Nine patients were included in the per-protocol analysis, and 26 were included in the intention-to-treat analysis. No signs of LAST were observed. Plasma ropivacaine concentrations remained consistently below 2.2 µg mL ^− 1 , however, eight patients in the intention-to-treat population and three patients in the per-protocol population had plasma lidocaine concentrations exceeding 5.0 µg mL ^− 1 at 10 minutes post-bolus. In the per-protocol population, peak plasma ropivacaine concentrations occurred 30 minutes (range, 20–60) post-TAP block, with median values of 1.14 (range, 0.85–1.18), 1.42 (range, 1.29–1.80), and 1.96 (range, 1.47–2.06) µg mL ^− 1 across dose groups. The peak plasma lidocaine concentrations in patients occurred at 10 minutes post-bolus infusion, with median values of 4.59 µg mL ^− 1 (range, 3.24–6.67) and gradually decreased after 2 hours. The intention-to-treat analysis found similar results. Conclusion Although no signs of LAST were observed with the combination of a 1.5 to 2.5 mg kg ^− 1 ropivacaine TAP block and intravenous lidocaine infusion under general anaesthesia, extreme caution is still warranted regarding the potential risk of LAST.