Rapid Absorption of Tumescent Lidocaine above the Clavicles: A Prospective Clinical Study

Abstract

Tumescent local anesthesia has been adapted for surgery of the face and neck, but there are no data regarding drug absorption when tumescent injection is used in this region. The aim of this study was to characterize the changes in plasma lidocaine concentrations over time when a tumescent solution is injected into the subcutaneous tissue of the neck. The study was carried out in human volunteer subjects, and injection of lidocaine to the thighs provided control data. Eight healthy female volunteer subjects were studied twice using a prospective, crossover design. Tumescent lidocaine solution was injected into the subcutaneous tissue of the neck in one session and the thighs in another session. The order of injection was randomized. Blood samples were collected for 14 hours after injection, and the plasma concentration of lidocaine measured. The injected solution consisted of lidocaine 0.1%, NaHCO3 12.5 mEq/L, and epinephrine 1:1,000,000 in normal saline. A standardized dose of lidocaine (7 mg/kg) was used for each injection and no surgical procedure was performed. All subjects completed the study. Subject weight was 66.1 +/- 12.8 kg, body fat was 29.0 +/- 4.7 percent, and body mass index was 23.8 +/- 3.1 kg/m2. The average time to reach peak lidocaine concentration after neck injection was 5.8 hours, whereas peak lidocaine concentration after thigh injection did not occur until 12.0 hours. This difference of 6.2 hours was highly significant (p = 0.009). The average peak concentration after neck injection was 16 percent greater than that after thigh injection (0.94 microg/ml versus 0.81 microg/ml), with the difference approaching significance (p = 0.06). No adverse reactions were noted. Tumescent injection above the clavicles results in a rapid rise in plasma lidocaine concentration when compared with injection to the lower extremities. Toxic symptoms could occur much earlier than expected for lower extremity tumescent anesthesia. In addition, dangerous plasma levels could occur if tumescent anesthesia in the lower extremities is followed by tumescent injection above the clavicles, because the absorption curves would be superimposed.