Influence of injection rate of hyperbaric bupivacaine on spinal block in parturients: a randomized trial.

PURPOSE: A prospective, randomized, double-blind clinical trial was undertaken to determine whether a tenfold difference in the rate of intrathecal injection of bupivacaine would affect sensory block level in parturients. Secondary outcomes included onset of block and the incidence of hypotension and nausea.

METHODS: Following Research Ethics Board approval, 90 ASA I and II term parturients scheduled for Cesarean delivery were randomized to receive either fast injection (over four seconds, Group F) or slow injection (over 40 sec, Group S) of 0.75% hyperbaric bupivacaine 12 mg plus morphine 200 microg. Sensory block, motor block, and blood pressure were assessed every minute for the first 15 min, then every five minutes for the next 20 min. All occurrences of nausea, hypotension (decrease in systolic blood pressure > 30%) and ephedrine requirements were recorded.

RESULTS: Forty-three patients in Group F and 42 patients in Group S completed the study. No differences in maximum sensory block height (Group F = median T2, interquartile range [T2-T4], Group S = T3 [T2-T4], P = 0.077) or time to achieve block height (F = 9.3 +/- 4.3 min, S = 9.7 +/- 4.7, P = 0.64) were observed. The frequencies of hypotension (Group F = 35/43, Group S = 32/42, P = 0.56), ephedrine utilization (Group F = 32/43, Group S = 26/42, P = 0.21) and nausea (Group F = 15/43, Group S = 16/42, P = 0.76) were similar.

CONCLUSION: Rapid intrathecal injection of hyperbaric bupivacaine does not affect spread of spinal anesthesia or the incidence of hypotension and nausea in parturients.