Placental Transfer and Fetal Metabolic Effects of Phenylephrine and Ephedrine during Spinal Anesthesia for Cesarean Delivery

Abstract

REGIONAL anesthesia is normally preferred for Cesarean delivery because it avoids the maternal risks of general anesthesia such as aspiration of gastric contents and difficulty with airway management.1 Although it is generally accepted that regional anesthesia confers greater safety for the mother compared with general anesthesia, its effects on neonatal outcome are controversial, particularly for spinal anesthesia. For example, several studies have shown that the risk of fetal acidosis is greater with spinal anesthesia compared with general anesthesia,2 and a recent large retrospective study has found that neonatal mortality of very preterm infants born by Cesarean delivery under spinal anesthesia was greater than that of comparable infants delivered under general anesthesia.3 The mechanism underlying these observations is uncertain, but recent data suggest that an important contributing factor may be the widespread use of ephedrine to treat and prevent hypotension during regional anesthesia.4,5 Historically, ephedrine was recommended as the vasopressor of choice in obstetrics but there is now increasing evidence that ephedrine has the propensity to decrease fetal pH and base excess, especially in comparison with other vasopressors such as phenylephrine4,6 and metaraminol.7