Optimal concentration of epinephrine for vasoconstriction in ear surgery

Objective: To determine the optimal concentration of epinephrine required f or vasoconstriction in ear surgery by evaluating changes in laser doppler b lood flow. Study Design: Prospective, randomized, double-blinded. Methods. Forty subjects undergoing surgical procedures under general anesthesia were injected in a standard posterior external auditory canal block with I mL o f 1% lidocaine containing varying concentrations of epinephrine (nil, 1:50, 000, 1:100,000, or 1:200,000) determined by randomization. Ear canal blood flow measurements were then made at 1-minute intervals for a 10-minute peri od using a laser doppler flow meter and compared with baseline blood flow. Results. The control solution of 1% lidocaine had a significantly higher bl ood flow than the epinephrine-containing solutions with an actual 200% incr ease in blood flow for the first 5 minutes before returning to baseline. Al l epinephrine-containing solutions had an approximately 50% decrease in blo od flow from baseline over the 10-minute period as compared with the contro l which was statistically significant (P < .0001). There was no significant difference between the blood flow reduction of 1:50,000, 1:100,000, and 1: 200,000 epinephrine-containing solutions (P = .8875). Conclusions. One perc ent lidocaine control exhibited the expected initial vasodilatory effect fo r approximately 5 minutes. In this experimental model, using a lower concen tration of 1:200,000 epinephrine would supply equivalent vasoconstriction i n the ear compared with higher concentrations, thus reducing the possible s ystemic toxicity and related morbidity.