Effect of prophylactic ondansetron on spinal anaesthesia - induced hypotension during caesarean section at Moi Teaching and Referral Hospital, Eldoret, Kenya.

Abstract

Background: Spinal anaesthesia (SA) technique is widely preferred for caesarean sections due to its safety and effectiveness. However, spinal anaesthesia-induced hypotension (SAIH) remains a common and serious complication, with global incidence rates between 50–80% and local rates around 64%. SAIH can lead to adverse maternal effects like cardiovascular collapse, and fetal risks such as hypoxia and acidosis. Existing prevention methods, such as fluid loading and prophylactic vasopressors, are inadequate when used individually. Ondansetron, a 5-HT3 receptor antagonist, may mitigate SAIH by inhibiting serotonin-mediated activation of the Bezold-Jarisch reflex via vagal cardiac receptors. While international data on its efficacy is controversial, its role at Moi Teaching and Referral Hospital (MTRH) also remains unexplored. This study investigates ondansetron’s potential to reduce SAIH and enhance maternal outcomes within the MTRH setting. Objectives: This study aimed to determine the effect of prophylactic ondansetron on the incidence of spinal anaesthesia-induced hypotension and bradycardia, and vasopressor requirements in pregnant women undergoing elective caesarean sections at MTRH. Methods: A randomized, double-blind, control trial was conducted at Moi Teaching and Referral Hospital (MTRH) involving 194 pregnant women undergoing elective caesarean sections under spinal anaesthesia. Block randomization and consecutive sampling were employed. Participants were assigned to two groups (97 each): one received 4 mg intravenous ondansetron (Group O), and the other received saline (Group S), both administered 15 minutes prior to anaesthesia. To minimize bias, blinding was applied to both the anaesthetists administering the intervention and the study participants. Data on demographics, clinical and surgical outcomes, vasopressor usage, and neonatal results were collected and analyzed using STATA version 16. Statistical tests included the two proportions z-test and Mann-Whitney U test, with significance set at P < 0.05. Results: SAIH incidence proportion was 85.6%. Group O had lower SAIH occurrence (77.3%, n=75) compared to group S (93.8%, n=91), P=0.001. Bradycardia was observed in 14.4% (n=14) of Group S and 8.2% (n=8) of Group O participants, with no significant difference (P=0.17). Ephedrine was administered more frequently in Group S (92.8%, n=90) than in Group O (75.3%, n=73), (P<0.001). However, the median total dose was comparable between the groups; 18.0 mg (IQR: 12.0–24.0) in Group S and 18.0 mg (IQR: 12.0–30.0; P ˃0.99). Phenylephrine was administered at almost similar frequencies in Group S (10.3%, n=10) and Group O (7.2%, n=7; P=0.446), though the total dose was significantly higher in Group S (200 mcg) than Group O (100 mcg; P=0.023). In addition, occurrence of nausea, vomiting, and shivering was significantly less in Group O (P<0.05). Conclusion: Prophylactic 4mg IV ondansetron is effective in reducing the occurrence of SAIH, the vasopressor requirement, and the total dose of vasopressors. Prophylactic ondansetron has no effect on the occurrence of bradycardia. Recommendations: Prophylactic administration of 4 mg IV ondansetron 15 minutes before spinal anaesthesia should be considered for elective caesarean sections at MTRH to reduce the incidence of SAIH and vasopressor requirement. The Anaesthesia Department should consider adding ondansetron in the prevention and management protocol of SAIH.