Comparison of mepivacaine and lidocaine for intravenous regional anaesthesia: pharmacokinetic study and clinical correlation.

BACKGROUND Limitations to the use of lidocaine for intravenous regional anaesthesia (IVRA) include lack of optimal intraoperative analgesia and systemic toxic reactions. This randomized double-blind study was conducted to compare intraoperative and postoperative analgesia, adverse effects, and plasma concentrations of mepivacaine or lidocaine, on release of the tourniquet in patients undergoing IVRA for distal upper limb surgery. METHODS Forty-two adult patients were randomly allocated to receive either a 0.5% lidocaine solution 3 mg kg(-1) (n=20) or mepivacaine 5 mg kg(-1) (n=22). Plasma concentrations of both anaesthetic agents were measured at 5, 10, 20, 30, 45, and 60 min after deflation of the tourniquet by gas chromatography. RESULTS Although plasma concentrations of mepivacaine and lidocaine were comparable 5 min after deflation, concentrations of lidocaine decreased significantly thereafter, whereas plasma concentrations of mepivacaine were similar over the 60-min study period. Supplementary analgesia during the intraoperative period was required by 45% of patients in the lidocaine group as compared with 9% in the mepivacaine group (P=0.02). No adverse effects were observed in patients given mepivacaine. In the lidocaine group, adverse effects were observed in 10% of the patients. The total ischaemia time, volume of the local anaesthetic, and duration of the surgical procedure were not significantly different between the two groups. CONCLUSIONS Mepivacaine 5 mg kg(-1) ensured better intraoperative analgesia than lidocaine 3 mg kg(-1) when used for IVRA. Plasma concentrations of lidocaine decreased significantly between 5 and 60 min following tourniquet deflation, whereas blood concentrations of mepivacaine remained below the toxic concentration.