Effect of Intravenous Ondansetron on Spinal Anesthesia-Induced Hypotension and Bradycardia: A Randomized Controlled Double-Blinded Study

BACKGROUND: Spinal anesthesia is a safe anesthetic technique commonly practiced. However, it is associated with hypotension (33%), bradycardia (13%), and shivering which are induced by hypovolemia, sympathetic blockade, and Bezold–Jarisch reflex through intracardiac serotonin (5HT3) receptors and vagus nerve. AIM: To study the effect of intravenous (i.v.) ondansetron on hypotension and bradycardia induced by spinal anesthesia. SETTING AND DESIGN: This was a randomized controlled double-blinded study done in a tertiary care teaching hospital. METHODS: Of 140 patients, 70 in Group A received 2 mL of i.v. ondansetron 4 mg and 70 in the Group B received 2 mL of i.v. normal saline. 3 mL of 0.5% hyperbaric bupivacaine was injected intrathecally. Measurements of blood pressure and heart rate (HR) were taken every 3 min for 30 min after spinal anesthesia was performed. Mean arterial pressure (MAP) drop more than 20% was considered as incidence of hypotension and ephedrine 6 mg i.v. was given. HR drop >20% was regarded as bradycardia and atropine 0.5 mg i.v. was given. STATISTICAL TESTS: Quantitative data were analyzed using ANOVA test and qualitative data were analyzed using Chi-square test. RESULTS: Both groups are comparable in demographic data. Four (5.7%) patients in Group B and no patients in Group A had incidence of bradycardia and atropine requirement (P = 0.120). There was no statistically significant difference in systolic blood pressure, diastolic blood pressure, and MAP. 19 (27%) patients in Group A and 33 (47.1%) in Group B required ephedrine with P = 0.029. 12 (17.1%) in Group B and no patients in Group A had shivering with P = 0.0001. CONCLUSION: Our study indicates that prophylactic use of ondansetron before spinal anesthesia significantly reduces the requirement of ephedrine and shivering.