Comparision of granisetron and ondansetron for attenuation of subarachnoid block induced hypotension in parturients undergoing elective caesarean section: a randomized double-blind placebo-controlled study

Background: Maternal hypotension after subarachnoid block (SAB) for cesarean section can jeopardize the fetus and the mother. Bezold Jarisch Reflex (BJR), mediated through serotonin or 5-hydroxytryptamine (5-HT), has been implicated as a cause. Antagonism of serotonin, therefore, alleviates BJR, inhibits peripheral vasodilatation, increases venous return to the heart, thereby alleviating hypotension
Aims: Aims of our study were to compare the effects of two selective 5-HT3 receptor antagonists Ondansetron and Granisetron on SAB induced hypotension, regression of sensory and motor blockade and the incidence of nausea and vomiting in parturients undergoing elective LSCS.
Methods: We had randomized 120 pregnant women, aged 20-40 years with uncomplicated pregnancies, ASA grade 1 and 2, scheduled for elective LSCS to one of the three groups with 40 patients each. Study drugs were administered intravenously 5min prior to SAB; Group A: Inj Ondansetron 4 mg (in 10 ml NS); Group B: Inj Granisetron 1 mg (in 10 ml); Group C: NS 10 ml. Patient’s systolic, diastolic and mean arterial pressure and heart rate were recorded at pre-assigned regular intervals till the end of surgery. Time to maximum sensory and motor block as well as regression of blocks and any nausea/vomiting or shivering were also recorded. The statistical analysis was done using Statistical Package for Social Sciences Version 15.0. ANOVA was used to compare the intergroup differences and change within groups was compared using paired‘t’ test. Proportional differences were analysed using Chi-square test. p value < 0.05 was considered to be significant.
Results: We observed significant differences in MAP between all three groups (p <0.001) at most time intervals. In Group A, there was no steep decline in MAP as compared to other two groups. Consequently, requirement of vasopressor was significantly lesser in Group A (p<0.001). No significant changes in HR was noted between the groups. The sensory regression (p<0.001), maximum motor block (p=0.02) and time to motor recovery by one level (p=0.018) were significantly earlier in Group B. Nausea/vomiting was experienced in a significantly lesser (p <0.001) number of cases in Group B (7.5%) as compared to Group A (22.5%) and Group C (47.5%)
Conclusions: Both ondansetron and granisetron significantly decreased the degree of hypotension and hence the requirement of vasopressor, however ondansetron was more effective and prevented maternal hypotension for a longer time period, thus providing better haemodynamic stability. Granisetron induced faster motor blockade as well as sensory recovery compared to both ondansetron and placebo. Both the drugs significantly reduced the incidence of nausea and vomiting, granisetron being more effective.