Effect of Intravenous Ondansetron on Sensory and Motor Block after Spinal Anaesthesia with Hyperbaric Bupivacaine

Ondansetron is a potent antiemetic and a competitive antagonist at serotonin receptors, which are also involved in modulation of pain. This study was designed to assess the effect of systemic ondansetron on sensory and motor block after subarachnoid anaesthesia with hyperbaric bupivacaine. Sixty patients undergoing transurethral resection of bladder tumours were randomly assigned to one of two groups. Group 1 received 2 ml (4 mg) of ondansetron whereas patients in group 2 received 2 ml of normal saline 15 minutes prior to administration of subarachnoid block with 2.5 ml of hyperbaric bupivacaine 0.5%. Time to attain peak sensory block (P = 0.27), time to two segment regression (P = 0.19) and time to regression to the S, dermatome (P = 0.84) did not significantly differ between the two groups. No differences in regression of sensory block were noted at any time. The mean duration of motor block also did not differ (P = 0.44), with similar regression of block at all time intervals except at 90 minutes. We concluded that intravenous ondansetron does not affect the intensity or duration of sensory and motor block after spinal anaesthesia with hyperbaric bupivacaine.