Maternal blood pressure targets and neonatal outcomes at caesarean birth: a reply

We thank Lyons [1] for his interest in our study [2]. We agree that the conclusion, that maintaining a higher maternal systolic blood pressure target (>90% of baseline) during caesarean delivery under spinal anaesthesia protected against fetal acidaemia, should be interpreted with caution. Additionally, we acknowledge that the omission of a vasopressor infusion to prevent maternal hypotension was one of the significant limitations of our study. Current research on spinal anaesthesia for caesarean delivery is focusing increasingly on the influence of interventions on neonatal outcomes. Among these, factors such as maternal haemodynamics, fluid management, vasopressors and anaesthetic technique can all have an impact on neonatal outcomes. Our study focused primarily on the impact of different maternal blood pressure management targets on neonatal umbilical artery pH. In our study, the conclusion that maintaining a higher maternal systolic blood pressure target protected against fetal acidaemia was founded on the proportion of newborns with an umbilical artery pH < 7.2 in the two groups. The incidence of only 1% (16 cases) in the entire cohort rendered it unlikely that the analysis of this result had sufficient statistical power to substantiate this conclusion. Ngan Kee et al. compared the maintenance of maternal systolic blood pressure at >80%, 90% and 100% of baseline [3]. Although no cases of umbilical artery pH < 7.2 were observed in any of the groups, the 100% group showed a difference in umbilical artery pH compared with the 80% and 90% groups. This implies that maintaining a higher maternal systolic blood pressure might have a beneficial effect on the umbilical artery pH of newborns. A larger randomised controlled trial with higher targets (including >100% of baseline) for maternal blood pressure management may provide more robust evidence to support this conclusion and determine whether it can protect against fetal acidaemia. The preference rate for infusion only or infusion plus bolus regimens of noradrenaline and phenylephrine, as observed in Ngan Kee's pragmatic non-inferiority study, reached an impressive 99.7% [4]. We did not employ a prophylactic infusion of noradrenaline. Relying solely on a rescue bolus administration might not align with current clinical practice and fails to represent accurately the standard approach for managing maternal blood pressure. Moreover, in comparison with phenylephrine, the weaker β-receptor agonistic effect of noradrenaline can better preserve maternal cardiac output and mitigate the incidence of maternal bradycardia [5]. Consequently, future studies with enhanced research designs ought to incorporate a variable rate prophylactic infusion of noradrenaline to focus on the impact of maintaining different maternal blood pressure management targets on neonatal outcomes.