Effect of adrenaline on plasma concentrations of bupivacaine following lower limb nerve block

Abstract

Twenty-two patients undergoing total knee arthroplasty received combined sciatic plus femoral "3 in 1" blocks as adjuncts to general anaesthesia. Eleven patients received 0.375% bupivacaine 45 ml (168.75 mg) with adrenaline 1 in 200000 and the remaining 11 received plain solution according to a previously prepared, randomized list. The mean maximum plasma bupivacaine concentration was significantly greater with plain solution than when adrenaline was added (1.66 μg ml-1 compared with 0.98 μg ml-1) (P < 0.05). Bupivacaine concentrations were greater at all times in the plain group compared with the group receiving adrenaline. These differences were statistically significant at 10, 15 and 20 min (P < 0.05). The greatest peak concentration recorded was 3.13 μg ml-1 in one patient receiving plain bupivacaine. No patient developed signs of systemic toxic effects. Peak plasma concentrations were related inversely to body weight in patients receiving solution containing adrenaline (P < 0.005), but no relationship existed in patients who received plain solution. © 1991 Copyright: 1991 British Journal of Anaesthesia.