Blood Levels of Mepivacaine during Continuous Epidural Anesthesia

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Venous blood concentrations of mepivacaine were measured in 30 patients during 5 hr of surgical anesthesia following either multiple epidural injections of mepivacaine with or without epinephrine or continuous epidural infusion of mepivacaine with epinephrine. Patients were divided into three groups: group 1 initially received 10 or 15 ml followed by 10 ml of 2% plain mepivacaine at 1-hr intervals; group 2 received 10 or 15 ml followed by 10 ml of epinephrine-containing 2% mepivacaine at 1-hr intervals; group 3 received 10 or 15 ml followed by a constant infusion of 10 ml/hr of epinephrine-containing 2% mepivacaine. There were no significant differences between groups 1 and 2, but the mean blood concentration was slightly lower for the first 3 hr in group 2 than group 1. The mean blood concentration of mepivacaine in group 3 remained significantly lower than the concentrations in groups 1 and 2 from 3.5 to 5 hr. These results demonstrate that the blood concentrations of mepivacaine are not reduced by the addition of epinephrine to mepivacaine solutions when intermittent epidural injections are repeated more than four times at 1-hr intervals, but that blood mepivacaine levels are reduced below levels seen with intermittent injections by the continuous epidural infusion of epinephrine-containing mepivacaine.