Reducing by 50% the incidence of maternal hypotension during elective caesarean delivery under spinal anesthesia: Effect of prophylactic ondansetron and/or continuous infusion of phenylephrine - a double-blind, randomized, placebo controlled trial

BACKGROUND: Prophylactic administrations of ondansetron or phenylephrine have been reported to provide a protective effect against hypotension in women undergoing cesarean delivery under spinal anesthesia (SA). The main hypothesis is that ondansetron improves the hemodynamic response, especially combined with phenylephrine infusion. METHODS: This prospective, double-blind, randomized, placebo-controlled study included 265 healthy pregnant women scheduled for elective cesarean delivery under SA. Women were randomly allocated into four groups to receive either placebo (control), ondansetron (O) 8 mg intravenously before induction of SA, phenylephrine infusion (50 mcg/min) (P) or ondansetron plus phenylephrine (OP). Demographic, obstetric, intraoperative timing, and anesthetic variables were assessed at 16 time points. Anesthetic variables assessed included blood pressure, heart rate, oxygen saturation, nausea, vomiting, electrocardiographic changes, skin flushing, discomfort or pruritus, and vasopressor requirements. RESULTS: There were differences (P = 0.0001) in the number of patients with hypotension (50.8% control, 44.6% O, 20.9% P, 25.0% OP), the percentage of time points (P = 0.0001) with systolic hypotension per patient (17.4% control, 8.7% O, 2.1% P, 6.7% OP) and the number of patients requiring supplementary boluses of ephedrine (P = 0.003), phenylephrine (P = 0.017) or atropine (P = 0.0001). CONCLUSIONS: A 50 μg/min phenylephrine infusion reduces by 50%, the incidence of maternal hypotension compared with placebo, but infusions of phenylephrine are still not routine in our environment. Prophylactic ondansetron 8 mg might be considered in this situation, because it does not reduce the incidence of maternal hypotension but diminishes its severity, reducing the number of hypotensive events per patient by 50%.