Optimal concentration of epinephrine for vasoconstriction in ear surgery

To determine the optimal concentration of epinephrine required for vasoconstriction in ear surgery by evaluating changes in laser doppler blood flow.

Prospective, randomized, double-blinded.

Forty subjects undergoing surgical procedures under general anesthesia were injected in a standard posterior external auditory canal block with 1 mL of 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 period using a laser doppler flow meter and compared with baseline blood flow.

The control solution of 1% lidocaine had a significantly higher blood flow than the epinephrine-containing solutions with an actual 200% increase in blood flow for the first 5 minutes before returning to baseline. All epinephrine-containing solutions had an approximately 50% decrease in blood flow from baseline over the 10-minute period as compared with the control 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).

One percent lidocaine control exhibited the expected initial vasodilatory effect for approximately 5 minutes. In this experimental model, using a lower concentration of 1:200,000 epinephrine would supply equivalent vasoconstriction in the ear compared with higher concentrations, thus reducing the possible systemic toxicity and related morbidity.