A randomised controlled trial of phenylephrine and noradrenaline boluses for treatment of postspinal hypotension during elective caesarean section

Abstract

Phenylephrine is currently the vasopressor of choice during elective caesarean section, but it can cause reflex bradycardia. Noradrenaline, a potent α-agonist and weak β-agonist, may be associated with a lower incidence of bradycardia. However, comparative information is limited. This double-blind randomised controlled trial compared the effects of 100 μg phenylephrine and 5 μg noradrenaline administered as boluses for the treatment of postspinal hypotension during elective caesarean section in women with an uncomplicated singleton pregnancy. Hypotension was defined as a decrease of ≥ 20% from baseline systolic arterial pressure, or an absolute value < 100 mmHg. Ninety women were included in the study. The primary outcome was the incidence of maternal bradycardia < 60 beats.min^-1 . There was no difference in the incidence of bradycardia (37.8% with phenylephrine vs. 22.2% with noradrenaline; p = 0.167), number of hypotensive episodes, number of boluses required to treat the first hypotensive episode or reactive hypertension. The total number of boluses used was higher in the phenylephrine group (p = 0.01). Maternal heart rate at 1 min after vasopressor administration was non-significantly lower using phenylephrine vs. noradrenaline (p = 0.034, considering p < 0.01 as statistically significant). The umbilical artery pH was higher using phenylephrine than with noradrenaline (p = 0.034). In conclusion, both vasopressors reversed postspinal hypotension without a statistically significant difference in maternal bradycardia. However, in view of the lower umbilical artery pH when using noradrenaline, further research is warranted to study its placental transfer and fetal metabolic effects.

Keywords: alpha-agonist; anaesthesia; spinal; blood pressure; caesarean section; hypotension, treatment; noradrenaline; phenylephrine.