LIDOCAINE DOES NOT DEPRESS REFLEX DILATION OF THE PUPIL

Background and Objectives. Pupillary dilation in response to dermatoma l electrical stimulation is one method of determining sensory block le vel during combined epidural and general anesthesia. Use of this techn ique may, however, be confounded by systemic absorption of epidurally administered local anesthetics. Accordingly, the effects of intravenou s lidocaine on the magnitude and duration of reflex pupillary dilation were evaluated. Methods. Six volunteers were each anesthetized twice with desflurane 3.5-6.0%. During one anesthetic, intravenous lidocaine was administered to a plasma concentration of 5.3 +/- 1.5 mu g/mL. Wh en the plasma concentrations were stable, a 5-second tetanic electrica l stimulus was applied. Pupil size was then recorded for 8 minutes. Re sults. Lidocaine, at plasma concentrations near 5 mu g/mL, did not sig nificantly alter the pupillary response to electrical stimulation In c ontrast, stimulus-induced increase in heart rate was obliterated. Pain ful stimulation did not increase systolic blood pressure in either cas e. Conclusions. Typical plasma lidocaine concentrations observed durin g epidural anesthesia are unlikely to prevent the use of pupillary res ponses to evaluate sensory block level.