SYMPATHETIC BLOCK DURING SPINAL-ANESTHESIA IN VOLUNTEERS USING LIDOCAINE, TETRACAINE, AND BUPIVACAINE

Background and Objectives. Spinal anesthesia to high thoracic dermatom es is alleged to result in almost complete block of all sympathetic ef ferent nerves. To examine the degree of sympathectomy during spinal an esthesia, the sympathetic response to a cold presser test (CPT) applie d to unblocked dermatomes before and during spinal anesthesia was meas ured with use of three different local anesthetics. Methods. Twelve he althy volunteers were studied in a randomized and double-blind fashion on three separate occasions. In random order, each volunteer received approximately equipotent spinal doses of tetracaine 15 mg, bupivacain e 15 mg, and lidocaine 100 mg in hyperbaric solutions. Prior to and 30 minutes after spinal injection of local anesthetic, a CPT was applied for 2 minutes, and changes from baseline resting conditions in five p hysiologic variables were measured. Results, The CPT 1 given before an esthetic administration resulted in an increase in heart rate, mean ar terial pressure, cardiac index, and plasma concentrations of norepinep hrine and epinephrine. Spinal anesthesia to a median level of T3 resul ted in a decease in mean arterial pressure by 10-12% but did not signi ficantly decrease the other variables. Spinal anesthesia did not chang e the increase in heart rate or cardiac index in response to the secon d CPT, but the increase in mean arterial pressure was attenuated compa red to the CPT before anesthesia. No increase in norepinephrine or epi nephrine concentration was observed during the CPT given during spinal anesthesia. There was no significant relationship between level of an algesia and sympathetic response to stress. Conclusions. Spinal anesth esia with hyperbaric solutions of tetracaine 15 mg, bupivacaine 15 mg, and lidocaine 100 mg attenuated sympathetic function but did not prod uce complete sympathectomy. The effects were independent of the local anesthetic used.