Effects of prophylactic constant-rate infusion of norepinephrine or phenylephrine on neonatal outcomes during caesarean section

BACKGROUND: Prophylaxis of norepinephrine (NE) at a constant rate has been demonstrated to be as efficacious as prophylaxis of phenylephrine (PE) at equivalent doses for the prevention of maternal hypotension during cesarean section. Nevertheless, the impact of prophylactic infusion of NE or PE at a constant rate on pregnant women on fetal outcomes remains to be elucidated. METHODS: 90 women scheduled for caesarean section under spinal or combined spinal-epidural anesthesia were randomly assigned to either the NE or PE group. The "study drug" (NE or PE) was administered intravenously at a rate of 15 mL/h from the time of injection of subarachnoid solution until the time of delivery of the fetus. Fetal umbilical artery (UA) blood was collected for blood gas analysis. The primary outcome of the study was base excess, and the incidence of fetal acidosis (Defined as base excess < 6 mmol/l) and blood glucose levels were also assessed. RESULTS: The UA base excess mean (standard deviation) was not different from the NE group, - 1.6 (2.6) versus - 2.4 (2.9) in the PE group (P = 0.223). The incidence of fetal acidosis was 4.7% (NE) versus 14.3% (PE), with no statistically significant difference (P = 0.308). However, fetal blood glucose levels were significantly lower in the NE group, 3.16 (0.43) versus 3.43 (0.60) in the PE group (P = 0.019). CONCLUSIONS: Prophylactic infusion of equivalent doses of NE at a constant rate resulted in fetal base excess values and an incidence of acidosis comparable to that of PE. However, a lower fetal UA blood glucose value was observed in the NE group, a finding that warrants further investigation.