Comparing Two Different Doses of Intravenous Ondansetron With Placebo on Attenuation of Spinal-induced Hypotension and Shivering

BACKGROUND Side effects of spinal anesthesia are hypotension, bradycardia and shivering. Five-hydroxytriptamine (5-HT), a serotonergic receptor, may be an important factor associated with inducing the Bezold Jarish reflex (BJR) that may lead to the bradycardia and hypotension in the setting of decreased blood volume. OBJECTIVES This study aimed to investigate the effect of intravenous administration of ondansetron, a 5-HT3 receptor antagonist, which could attenuate spinal-induced hypotension, bradycardia and shivering. PATIENTS AND METHODS Two hundred and ten patients aged 20-50 years old were scheduled for spinal anesthesia and were divided randomly into three equal groups. The control group received normal saline and intervention groups received 6 mg or 12 mg of intravenous ondansetron 5 minutes before spinal anesthesia. Mean arterial pressure (MAP), heart rate (HR), and shivering were recorded before and after spinal anesthesia every 5 minutes during first 20 minutes of surgery. RESULTS Demographic data were not statistically different among groups. HR was statistically different between the experimental groups and the control group. Ten patients (14%) in the control group had HR < 50 bpm, that required intravenous atropine compared to experimental groups (P =0.02). In the control group 12 (17%) patients had MAP < 80 mm Hg and required vasopressors compared to experimental groups (P = 0.04). There were no significant differences in MAP and HR between the experimental groups (P =0.06). Incidence of shivering in the control group was 45% (32.70) that was statistically more than experimental groups (P = 0.02). CONCLUSIONS Administration of two different doses of intravenous ondansetron, 6 mg and 12 mg, significantly attenuates spinal induced hypotension, bradycardia and shivering compared to the control saline group. However, the hemodynamic profiles and shivering in experimental groups were not statistically different.