[Comparative development of sympathetic and sensitive blocks during spinal anesthesia].

The extent and duration of sympathetic and sensory blockade were compared in 13 patients after spinal anaesthesia with 0.5% tetracaine (20 mg) in either isobaric (n = 6) or hyperbaric solution (n = 7). Sensory blockade was assessed by pin-prick and sympathetic blockade by the sympathogalvanometric method respectively at L5/S1, L2, T8 and C8/T1 levels. The time to onset and the duration of sensory or sympathetic blockade was identical. The mean extent of sympathetic blockade was 6 segments greater than that of sensory blockade. Hypotension was related to the extent of sensory but not sympathetic blockade. This study confirms that sympathetic blockade is more extended than sensory blockade during spinal anesthesia but does not allow to predict the occurrence of hypotension.