Ondansetron versus Ephedrine for prophylaxis of Subarachnoid Block-Induced Hypotension in Pregnant Women

Abstract

BACKGROUND: Hypotension is the most frequent side effect of SAB in patients undergoing elective C/S. It is believed that the Bezold-Jarisch reflex, triggered by serotonin-mediated stimulation of 5-HT₃    receptors in cardiac chambers, could be a contributor to the mechanism of SAB-induced hypotension. Ondansetron, a 5-HT₃ receptor antagonist, could attenuate SAB-induced hypotension through blockage of 5-HT₃ receptors.

OBJECTIVE: The study aimed to compare the effects of prophylactic intravenous 4 mg ondansetron with intravenous 15 mg ephedrine on the incidence of SAB-induced hypotension in patients scheduled for elective caesarean section in the University of Ilorin Teaching Hospital.

METHODOLOGY: This was a randomised study that involved 80 ASA 2 patients aged 18-40 years who were scheduled for elective C/S under SAB. The patients were allocated to 2 groups of 40 each: Group OS received 4 mg intravenous ondansetron 10 minutes before SAB, and Group ES received 15 mg intravenous ephedrine immediately after SAB. The primary outcome measure was the incidence of hypotension while secondary outcome measures were phenylephrine and atropine consumption, incidence of post-spinal spinal shivering, and side effects of ondansetron: hiccups, skin flushing, and headaches.

 DATA ANALYSIS: Data were analysed using the Statistical Product and Service Solutions SPSS Statistic 20 (IBM Corp., Armonk, NY, USA). Variables were analysed using Chi-square test/ Fisher’s exact test) or independent student’s t-test as appropriate. P <0.05 was considered statistically significant.

RESULT: The demographic characteristics and baseline haemodynamic variables were comparable in the two groups. The incidence of hypotension was 60% in the ondansetron group and 47.5% in the ephedrine group, P = 0.37. The mean SBP values were significantly higher in the ephedrine group (P = 0.05) at 6 time-points of the study period. The mean DBP values were similar in both groups. Apart from the 4^th minute in which the mean MAP value was significantly higher in the ephedrine group (82.73 ± 14.37 in ES vs 74.65 ± 15.17 in OS, p = 0.02), the values were comparable at other times. The mean HR values were significantly higher (P <0.05) in the ephedrine group at all times except in the 2^nd minute in which no significant difference was observed. One patient in group OS experienced bradycardia (treated with 0.6 mg atropine) while none in group ES experienced it. The mean phenylephrine consumption (in µg) was 77.50 ± 96.71 in group ES and 102.50 ± 110.33 in group OS, P = 0.28. The incidence of shivering was 5% in group OS and 22.5% in group ES, P = 0.023. There was no difference in the incidence of side effects in both groups.

CONCLUSION: There was no significant difference between prophylactic 4 mg intravenous ondansetron and 15 mg intravenous ephedrine in attenuating the incidence of SAB-induced hypotension in pregnant women. Patients in the ondansetron group had a significantly lower incidence of post-spinal shivering.