Phenylephrine in treating maternal hypotension due to spinal anaesthesia for caesarean delivery: effects on neonatal catecholamine concentrations, acid base status and Apgar scores.

Maternal and neonatal catecholamine concentrations, following the use of either phenylephrine or ephedrine to treat a drop in maternal blood pressure after spinal anaesthesia for caesarean delivery, were compared. Patients were randomly assigned to one of two groups: Group 1 patients (n = 20) were treated with ephedrine given as 5 mg intravenous bolus injections; Group 2 patients (n = 20) were treated with phenylephrine given as 40 micrograms intravenous bolus injections, for decreases in maternal systolic blood pressure to maintain maternal systolic blood pressure above 100 mmHg. Maternal vein (MV), umbilical vein (UV), and umbilical artery (UA) blood samples were taken at the time of delivery. Samples were analyzed for catecholamine concentrations and blood gas values. Noradrenaline concentrations in UA, UV and MV (at delivery) samples were significantly higher in group 1 compared to group 2; they were 6858 +/- 3689 vs 1674 +/- 944 pg.ml-1 (P < 0.0001), 1265 +/- 758 vs 395 +/- 470 pg.ml-1 (P < 0.001) and 239 +/- 165 vs 103 +/- 93 pg.ml-1 (P < 0.01), respectively. Comparing blood gas values between groups 1 and 2, statistically significant differences were observed in UA pH (7.28 +/- 0.01 and 7.32 +/- 0.01 pH units, P = 0.01), UA pCO2 (7.32 +/- 0.24 and 6.68 +/- 0.21 kPa, P = 0.03), UA base excess (2.2 +/- 0.4 and 0.9 +/- 0.4 mmol.1-1, P = 0.04) and UV base excess (2.0 +/- 0.3 and 0.7 +/- 0.3 mmol.1-1, P = 0.004). No significant differences in maternal characteristics, acid base values, incidence of nausea and vomiting, and Apgar scores were observed between groups. Phenylephrine appears to be as safe and effective as ephedrine in treatment of drop in blood pressure in healthy non-labouring parturients undergoing caesarean delivery. The use of phenylephrine was also associated with significantly lower noradrenaline concentrations in both mother and neonate.