[Comparison of effects in puerpera and fetus with ephedrine and phenylephrine during a cesarean delivery]

To compare the different effects in fetus and puerpera with an equivalent dose of ephedrine (E) and phenylephrine (Ph) for maintaining maternal blood pressure near baseline during spinal anesthesia for a cesarean delivery.

Ninety mature parturient women with single-embryo scheduled for an elective cesarean delivery under spinal anesthesia at our hospital during January-June 2010 were randomly divided into 3 groups (E, E + Ph and Ph, n = 30 each). Group E received an infusion of ephedrine (ephedrine 4 g/L), Group E + Ph ephedrine plus phenylephrine (ephedrine 2 g/L + phenylephrine 25 mg/L) and Group Ph phenylephrine (phenylephrine 50 mg/L). The blood pressure was maintained near baseline by adjusting the infusion rate during anesthesia. The maternal blood pressure, heart rate and fetal heart rate were measured at the time points of 1, 3, 5 and 10 min, skin incision and uterine incision after injecting anesthetic into subarachnoid space. Immediately after delivery, maternal arterial, umbilical arterial and umbilical venous blood samples were withdrawn for the measurements of blood gases and plasma concentrations of lactate and glucose.

The fetal heart rate of groups E and E + Ph significantly increased after infusion [5 min: (150 ± 10) times/min vs (142 ± 13) times/min, (146 ± 10) times/min vs (142 ± 9) times/min, both P < 0.05] while those of group Ph had no significant changes [5 min: (143 ± 9) times/min vs(143 ± 6) times/min, P > 0.05]. The incidence of fetal tachycardia in groups E and E + Ph was greater than that in group Ph. In group E, umbilical arterial and umbilical venous pH and base excess were lower than those in groups E + Ph and Ph [umbilical arterial: 7.20 ± 0.10 vs 7.27 ± 0.05, 7.28 ± 0.03, (-3.1 ± 3.1) mmol/L vs (-0.9 ± 1.7) mmol/L, (-0.3 ± 1.7) mmol/L, umbilical venous:7.29 ± 0.09 vs 7.34 ± 0.03, 7.34 ± 0.03, (-3.3 ± 2.9) mmol/L vs (-2.0 ± 1.7) mmol/L, (-0.9 ± 1.5) mmol/L, all P < 0.05]. Umbilical arterial PCO2 and plasma concentrations of lactate and glucose in group E were greater than those in group Ph (all P < 0.05). Umbilical arterial and umbilical venous plasma concentrations of lactate and glucose were greater in group E + Ph than those in group Ph (all P < 0.05). But base excess was lower (P < 0.05).

Phenylephrine may be more ideal for treating the hypotension of spinal anesthesia for a cesarean delivery. It corrects hypotension following spinal anesthesia, improves fetal oxygen supply and demand balance but induces no metabolic excitation in fetus as compared with ephedrine.