Small-dose dopamine increases epidural lidocaine requirements during peripheral vascular surgery in elderly patients

We studied 20 patients over the age of 65 yr undergoing prolonged periphera l vascular surgery under continuous lidocaine epidural anesthesia, anticipa ting that the increased hepatic metabolism caused by small-dose IV dopamine would lower plasma lidocaine concentrations. Subjects were assigned (rando m, double-blinded) to receive either a placebo IV infusion or dopamine, 2 m u g . kg(-1) . min(-1) during and for 5 h after surgery. Five minutes after the IV infusion was started, 20 mL of 2% lidocaine was injected through th e epidural catheter. One-half hour later, a continuous epidural infusion of 2% lidocaine at 10 mL/h was begun. The epidural infusion was temporarily d ecreased to 5 mL/h or 5 mL boluses were added to maintain a T8 analgesic le vel. Arterial blood samples were analyzed for plasma lidocaine concentratio ns regularly during and for 5 h after surgery. Plasma lidocaine concentrati ons increased continuously during the epidural infusion and, despite wide i ndividual variation, were similar for the two groups throughout the observa tion period. During the observation period, the mean maximal plasma lidocai ne concentration was 5.8 +/- 2.3 mu g/mL in the control group and 5.7 +/- 1 .2 mu g/mL in the dopamine group. However, the mean hourly lidocaine requir ement during surgery was significantly different, 242 +/- 72 mg/h for contr ol and 312 +/- 60 mg/h for dopamine patients (P < 0.03). At the end of Hour 4, the last period when all 20 patients were still receiving the epidural lidocaine infusion, the total lidocaine requirement was significantly diffe rent, 1088 +/- 191 mg for the control group and 1228 +/- 168 mg for the dop amine group (P < 0.05). Despite very large total doses of epidural Lidocain e (1650 +/- 740 mg, control patients, and 3940 +/- 400, dopamine patients) mean maximal plasma concentrations remained below 6 mu g/mL, and no patient exhibited signs or symptoms of toxicity. We conclude that small-dose IV do pamine increased epidural lidocaine requirements, presumably as a consequen ce of increased metabolism. Implications: We tested dopamine, a drug that i ncreases liver metabolism of the local anesthetic lidocaine to determine if it would prevent excessively large amounts of lidocaine in the blood durin g prolonged epidural anesthesia in elderly patients. Dopamine did not alter the blood levels of lidocaine, but it did increase the lidocaine dose requ irement to maintain adequate epidural anesthesia.