Lidocaine levels during the first two hours of infiltration of dilute anesthetic solution for tumescent liposuction: Rapid versus slow delivery

BACKGROUND. Tumescent anesthesia for liposuction with dilute lidocaine has been well documented to result in peak serum levels 4-14 hours after infiltration. Pharmacokinetic studies have shown that the rate of lidocaine absorption is related not only to dilution, but also to the speed of subcutaneous infiltration. Early studies with a more concentrated solution of lidocaine (1.0%) have shown that with rapid infusion, peak plasma levels may occur within 30 minutes. OBJECTIVE. To determine whether rapid absorption of lidocaine may occur during infusion of tumescent solution by varying the rate of infusion of dilute lidocaine solution (0.05 % or 0.1%) and observing serum levels of lidocaine within the first 2 hours of the procedure. METHODS. Eighteen patients participated in this study and were infused with a standard liposuction tumescent formula consisting of lidocaine either 0.05% or 0.1%. The rates of infusion of tumescent anesthesia ranged from 27.1 mg/min up to 200 mg/min infused over a period of 5 minutes to 2 hours. Total lidocaine infused ranged from 7.4 to 57.7 mg/kg. Serum levels of lidocaine were taken every 15 minutes during the first hour of the procedure and repeated at 2 hours. RESULTS. In all 18 patients, lidocaine levels remained significantly below the toxic range and were always less than 2.0 mu g/ml. In 11 patients, lidocaine levels at all time intervals were less than 0.5 mu g/ml. In seven patients, the lidocaine levels ranged from 0.6 to 1.9 mu g/ml at varying intentals. There was no correlation between the maximum dose of lidocaine (mg/kg) or rate of lidocaine delivered (mg/ml) with plasma levels of lidocaine. CONCLUSION. Despite variability, the serum levels of lidocaine remained well within safety limits during infusion of tumescent solution and the first hours of the procedure when infused in rates up to 200 mg/min with spinal needles and/or small diameter multiholed infusion cannulas.