Comparison of plasma bupivacaine concentrations during continuous extradural infusion for labour

Twenty patients who requested extradural analgesia for labour were allocated randomly to receive an infusion of either 0.25% or 0.08% solutions of bupivacaine. Following an initial bolus dose of 50 mg, the infusions were given at a rate of 20 mg h-1. Both solutions provided acceptable pain relief, but plasma concentrations were significantly lower with the weaker concentration.