Vasopressor therapy for hypotension during epidural anesthesia for cesarean section: effects on maternal and fetal flow velocity ratios.

The purpose of this study was to identify the influence of hypotension as a result of epidural anesthesia and of its treatment with either ephedrine or methoxamine on uteroplacental and umbilical flow velocity ratios and fetal acid-base status. Fifty healthy women with an uncomplicated full-term pregnancy were studied during elective cesarean section under epidural anesthesia. A method of continuously recording flow velocity waveforms was used that allowed the identification of simultaneous values of maternal and fetal Doppler indices related to events during the induction of anesthesia. In 15 patients in whom arterial blood pressure did not decrease, the uteroplacental pulsatility index (UtPI) did not change, but the umbilical pulsatility index (UmPI) decreased from a mean (95% confidence interval) of 0.98 (0.88-1.09) to 0.91 (0.82-0.99) (P less than 0.05). In 32 patients who experienced hypotension of at least 15%, the UtPI increased from 0.82 (0.76-0.89) to 1.04 (0.92-1.17) (P less than 0.01). Treatment with ephedrine had no influence on either the UtPI or UmPI, but treatment with methoxamine resulted in brief increases in the UtPI of 0.47 (0.24-0.69) during the first 5 min after its administration; the increases were brief and resolved within 2 min. The choice of vasopressor drug had no influence on the UtPI recorded just before surgery commenced (final UtPI), but those patients who experienced hypotension had significantly larger final UtPIs (1.02 (0.91-1.10)) than those who never became hypotensive (0.86 (0.72-0.99)), and this was associated with significantly increased placental hydrogen ion gradients. The choice of vasopressor drug appears to be of minor importance compared with the avoidance of hypotension.