Background. Recent studies support the use of α-agonists during regional anaesthesia in uncomplicated term pregnancies. We hypothesized that ephedrine and phenylephrine, administered for maternal hypotension following fetal hypoxaemia, are equal in respect of fetal outcome. Methods. At 117-132 days gestation, chronically instrumented, anaesthetized and mechanically ventilated ewes were randomized to receive boluses of ephedrine (n=9) or phenylephrine (n=8) for maternal epidural-induced hypotension after a period of fetal hypoxaemia. Uterine (QUtA) and placental (QUA) volume blood flows were measured with perivascular transit-time ultrasonic flow probes, and uterine (RUtA) and placental (RUA) vascular resistances were computed from volume blood flows and maternal and fetal mean arterial pressures. Uterine (PlUtA) and umbilical artery (PlUA) pulsatility indices were obtained by Doppler ultrasonography. Results. Ephedrine increased QUtA and decreased RUtA and PlUtA from a hypotensive to baseline level and had no significant effect on umbilical circulation. With phenylephrine, QUtA remained lower (P=0.011) and RUtA higher (P=0.043) than at baseline, although PlUtA decreased to baseline level. PlUA increased from baseline with phenylephrine (P=0.007), whereas QUA decreased (P=0.050). Maternal volume expansion with hydroxyethyl starch decreased RUtA significantly irrespective of the vasopressor used. There were no significant differences in fetal blood gas values or lactate concentrations between the ephedrine and phenylephrine groups. Conclusions. Despite the more favourable effects on uterine and placental circulations of ephedrine over phenylephrine, no significant differences in fetal acid-base status or lactate concentrations were observed.
- Anaesthesia, obstetric
- Anaesthetic techniques, epidural
- Sympathetic nervous system, pharmacology, ephedrine
- Sympathetic nervous system, pharmacology, phenylephrine
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine