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Comparison of the effects of phenylephrine versus ephedrine on maternal ECG changes and cardiac output during cesarean delivery under spinal anesthesia
Abstract Number: O-05
Abstract Type: Original Research
Introduction: ECG changes during cesarean delivery (CD) under spinal anesthesia are common. Ischemic changes may occur due to an imbalance of myocardial oxygen demand and supply, phenylephrine may have a favorable oxygen supply: demand ratio compared to ephedrine. Previous studies used intermittent boluses to maintain blood pressure (BP) rather than the currently accepted prophylactic infusion regimen. We studied the effect of titrated infusions of phenylephrine and ephedrine to maintain systolic BP (SBP) in women undergoing elective CD. Primary outcome was incidence of ischemic ECG changes when maternal BP is maintained with infusions of phenylephrine or ephedrine. Secondary outcomes included evidence of myocardial ischemia related to ECG changes and troponin levels; SBP, maternal heart rate (HR), cardiac output (CO) and neonatal outcome.
Methods: Single center, randomized, double-blind study of 29 women for elective CD under spinal anesthesia. A Holter monitor was used to analyze the ECG during and 4-hours post-CD. Spinal anesthesia was administered (11mg of 0.5% hyperbaric bupivacaine plus 15μg fentanyl). Infusions of phenylephrine at 50μg/min or ephedrine 4mg/min were commenced and titrated as per protocol to maintain baseline SBP. Crystalloid co-load (1L) was administered. A suprasternal Doppler measured CO, stroke volume (SV), flow time corrected (FTc) and peak velocity every 5 min post-spinal to 5 min post-delivery. Troponin-T was measured at 24 hours. Apgar scores and umbilical cord gases were recorded. Data were analyzed using mixed linear models, analysis of covariance (ANCOVA); Tukey-Kramer post-tests, Student t, Mann-Whitney U- and Fisher exact tests. Significance was defined as P <0.05.
Results: Arrhythmia occurred more frequently with ephedrine (50% v 31%, P=0.43) but this was not significant. There were higher troponin levels with ephedrine (≤0.003ng/mL, P=0.093). Ephedrine was more effective at maintaining maternal SBP, significantly higher at 5, 20, 25 and 30 min post-spinal (13%, P=0.0036), but HR was similar (P=0.11). Although CO was similar (P=0.20), there were significant effects over time for FTc and SV. Neonatal outcomes such as Apgar scores, umbilical pH, HCO3, base excess and PCO2 were not significantly different.
Discussion: We found non-significant, higher rates of arrhythmia and troponin levels with ephedrine. Ephedrine also resulted in significantly higher SBP post-spinal. However, in the choice between phenylephrine and ephedrine for maintenance of BP during CD under spinal anesthesia, phenylephrine appears favorable in reducing maternal myocardial work, and could be associated with fewer arrhythmias. Further research with larger trials is required.
1. Zakowski MI. Electrocardiographic Changes during Cesarean Section: A Cause for Concern? Anesthesia Analgesia 1993;76: 162-7
2. Warwick NKD. Vasopressors in obstetrics: what should we be using? Current Opinion in Anaesthesiology 2006;19: 238-243