Effects of ephedrine and phenylephrine on uterine and placental circulations and fetal outcome following fetal hypoxaemia and epidural-induced hypotension in a sheep model †

Abstract

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.

Randomised double‐blinded comparison of phenylephrine vs ephedrine for maintaining blood pressure during spinal anaesthesia for non‐elective Caesarean section*

“…Although this does not appear to be clinically relevant in healthy, low-risk elective cases [3][4][5], it has not been known whether the same would apply in the presence of [7,8] compared phenylephrine and ephedrine for correcting epidural-induced hypotension after a period of maternal hypoxaemia in a chronically-instrumented sheep model. In an earlier study, they found that, although ephedrine was associated with more favorable effects on uterine and placental circulations, there was no difference in fetal acid-base status or lactate concentration [7]. However, in a subsequent study, the sheep underwent placental embolisation 24 h prior to the main experiment [8].…”

“…Substantial differences in study design may be important. For example, Erkinaro et al [7,8] performed their studies in anaesthetised sheep that were ventilated in the supine position; this may not be a valid representation of spinal anaesthesia in pregnant humans. Species differences may also be important.…”

Ductus venosus velocimetry in acute fetal acidemia and impending fetal death in a sheep model of increased placental vascular resistance

“…The detailed surgical procedure has been described previously (9). Briefly, a laparotomy was performed under general anesthesia maintained with inhaled isoflurane-air-oxygen mixture.…”

“…A dry volume of 0.25-ml microspheres was suspended in 0.5 ml 20% albumin and diluted with 5 ml sterile saline solution. Bolus doses of 1 ml were injected via the femoral artery catheter into the descending aorta every 15 min until fetal arterial oxygen saturation decreased by ϳ30% from the preembolization value (9).…”

Anesthetic Techniques for Fetal Surgery

“…We designed the additional set of experiment using the tightly controlled maternal blood pressure protocol to mimic fetal and obstetric anesthesia clinical practice. We chose ephedrine as a first-line drug to treat maternal hypotension because ephedrine has been shown to increase, 23 or not change, 24 uterine blood flow; in contrast, phenylephrine is known to reduce uterine blood flow. 25 Phenylephrine is often used when high doses of ephedrine become ineffective and cause significant tachycardia.…”