Randomized trial of bolus phenylephrine or ephedrine for maintenance of arterial pressure during spinal anaesthesia for Caesarean section

Thirty-eight healthy women undergoing elective Caesarean section underspinal anaesthesia at term were allocated randomly to receive boluses ofeither phenylephrine 100 micrograms or ephedrine 5 mg for maintenance ofmaternal arterial pressure. The indication for administration ofvasopressor was a reduction in systolic pressure to < or = 90% ofbaseline values. Maternal arterial pressure (BP) and heart rate (HR) weremeasured every minute by automated oscillometry. Cardiac output (CO) wasmeasured by cross-sectional and Doppler echocardiography before and afterpreloading with 1500 ml Ringer lactate solution and then every 2 min afteradministration of bupivacaine. Umbilical artery pulsatility index (PI) wasmeasured using Doppler before and after spinal anaesthesia. The median(range) number of boluses of phenylephrine and ephedrine was similar; 6(1-10) vs 4 (1- 8) respectively. Maternal systolic BP and CO changes weresimilar in both groups, but the mean [95% CI] maximum percentage change inmaternal HR was larger in the phenylephrine group (-28.5 [-24.2, - 32.9]%)than in the ephedrine group (-14.4 [-10.6, -18.2]%). As a consequenceatropine was required in 11/19 women in the phenylephrine group comparedwith 2/19 in the ephedrine group (P < 0.01). Mean umbilical artery pH[95% CI] was higher in the phenylephrine group (7.29 [7.28-7.30]) than inthe ephedrine group (7.27 [7.25-7.28]). The results of the present studysupport the use of phenylephrine for maintenance of maternal arterialpressure during spinal anaesthesia for elective Caesarean section.