Hemodynamic Effects of Ephedrine, Phenylephrine, and the Coadministration of Phenylephrine with Oxytocin during Spinal Anesthesia for Elective Cesarean Delivery

Abstract

Bolus phenylephrine reduced maternal CO, and decreased CO when compared with ephedrine during elective spinal anesthesia for Cesarean delivery. CO changes correlated with heart rate changes after vasopressor administration, emphasizing the importance of heart rate as a surrogate indicator of CO. Coadministered phenylephrine obtunded hemodynamic responses to oxytocin.

Monitoramento não invasivo baseado na biorreatância revela instabilidade hemodinâmica significativa durante cesárea eletiva sob raquianestesia

“…In this study, this response was blunted by the administration of phenylephrine, and a much less-pronounced effect was observed. This effect has previously been noted by Dyer et al 15 .…”

“…Our results differ from those of Langesaeter et al 9 and Dyer et al 15 , who have documented a significant increase in cardiac output in the postspinal period followed by a significant decrease subsequent to vasoconstrictor administration. The difference between our results and their results may be explained by differences in the vasoconstrictor regimen used, and by the management of hypotension.…”

“…Particularly, the trigger for vasoconstrictor administration in their studies was a fall in mean arterial pressure to 80% of baseline value. Also, Langesaeter et al 9 used low-dose phenylephrine infusion (0.25 µg.kg -1 .min -1 ), and Dyer et al 15 used 80 µg intermittent bolus doses, which are much lower than the doses used in our study. It is also important to note that Langesaeter et al 9 and Dyer et al 15 have used different technologies for hemodynamic monitoring, which may also explain some differences in our findings.…”

“…The rapid changes in cardiac output in our patients were likely due to fluctuations in heart rate, as stroke volume did not vary significantly and total vascular resistance was maintained. A strong correlation between heart rate and cardiac output has been documented previously 15 . The rapid variation in heart rate was most likely due to the intermittent boluses of phenylephrine given to treat decreases in maternal systolic blood pressure.…”

“…However, hemodynamic changes during cesarean delivery have been assessed through a variety of different methods, including thoracic 15 and whole body impedance 8 , echocardiography and Doppler ultrasound 19 , all minimally invasive techniques 9 , as well as pulmonary artery catheterization and thermodilution. All of these methods have limitations, and are unlikely to become routine clinical practice especially as bedside monitoring techniques.…”