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Uterine and umbilical artery pulsatilty index following phenylephrine infusion versus bolus in cesarean section
Abstract Number: S-66
Abstract Type: Original Research
Introduction: Phenylephrine (PE) is commonly used for spinal-induced hypotension in women undergoing cesarean delivery (CD). PE has been shown to decrease maternal heart rate (HR) and cardiac output (CO). Previous studies suggest that maternal CO correlates with the uterine artery pulsatility index (PI), and poor fetal outcomes have been associated with increased PI. Phenylephrine infusions induce a more profound decrease in maternal HR and CO compared with intermittent phenylephrine boluses. The aim of this pilot study was to compare maternal hemodynamics and PI in patients receiving PE as boluses for the treatment of hypotension versus prophylactic infusions.
Methods: In this prospective, observational study, ASA 1-2 women undergoing CD under spinal anesthesia were alternately assigned to either a PE bolus (n=6) or infusion (n=5). Baseline CO, non-invasive blood pressure (NIBP), uterine and umbilical artery PIs were recorded in the preoperative holding area. CO was measured continuously using bioimpedance cardiography. Following a standardized spinal anesthetic with 12 mg bupivacaine, 15 mcg fentanyl, and 150 mcg morphine, patients were positioned in left uterine displacement. NIBP was measured every minute for 10 minutes and then every 2.5 minutes. Uterine and umbilical artery PIs were measured 5 and 10 min after spinal. In the infusion group, PE was initiated at 50 mcg/min and adjusted according to a predefined algorithm to maintain SBP within 20% of baseline. In the bolus group, hypotension defined as a drop of SBP of at least 20 % from baseline was treated with 100 mcg PE boluses. Maternal hemodynamics were compared using within- and between-group analyses. We also compared changes in umbilical and uterine artery PI between groups.
Results: Results are summarized in the table. There were no significant differences between groups in baseline measures. More PE was used in the infusion group (p =0.0004). There were no differences between groups in PI changes or maternal hemodynamic parameters after spinal, save for lower HR in the infusion group.
Discussion: Our pilot study finds no significant differences in maternal hemodynamics or uteroplacental perfusion in women receiving PE as bolus or infusion other than a decrease in HR. A sample size of 32 per group and 62 per group would have 80% power to detect a difference of the size we observed in umbilical artery and uterine artery PI respectively.