Retrospective study of association between choice of vasopressor given during spinal anaesthesia for high-risk caesarean delivery and fetal pH.

BACKGROUND

Phenylephrine given during spinal anaesthesia for low-risk caesarean section is associated with higher fetal pH than ephedrine. However, there is little evidence on the effects of ephedrine and phenylephrine in complicated pregnancies. The aim of this study was to compare umbilical artery pH with phenylephrine and ephedrine given during spinal anaesthesia where caesarean section was performed because of an increased risk of fetal compromise.

METHODS

We reviewed the case notes of all women at our hospital from 2000-2003 who had undergone high-risk caesarean section under spinal anaesthesia, where umbilical artery and venous pH had been recorded at delivery. Umbilical artery pH was compared by choice of vasopressor and multiple regression analysis was used to investigate the effects of other possible confounding variables.

RESULTS

One hundred and fifteen patients received no vasopressor, 122 ephedrine (group E) and 148 phenylephrine (group P). The median umbilical artery pH was 7.26 (IQR 7.21-7.30) for the no-vasopressor group, 7.27 (7.22-7.30) for group E and 7.28 (7.22-7.32) for group P (P=0.21). Using multiple regression analysis, the only variable associated with altered umbilical artery pH was a non-reassuring fetal heart trace.

CONCLUSIONS

Umbilical artery pH was similar whether ephedrine or phenylephrine was used to maintain maternal arterial pressure, which contrasts with studies of low-risk caesarean section.