Cerebral oxygenation and hemodynamic changes during ephedrine and phenylephrine administration for transient intraoperative hypotension in patients undergoing major abdominal surgery: a randomized controlled trial.

Background: Phenylephrine and ephedrine are frequently used vasopressors for treating intraoperative hypotension. However, their impact on cerebral oxygenation and blood flow remains a subject of debate. This study aims to understand their effects on cerebral oxygen saturation and hemodynamics when used for treatment of intraoperative hypotension.

Methods: The adult patients undergoing major abdominal surgery under general anesthesia were randomly assigned into ephedrine (ED) group or phenylephrine (PE) group. They received an intravenous bolus of either ephedrine or phenylephrine for treating intraoperative transient hypotension. The primary outcome was their effects on regional cerebral oxygen saturation (rScO₂). The secondary outcomes included cerebral hemodynamics middle cerebral artery velocity (MCAvm), pulsatility index (PI), and resistance index (RI), as well as systemic hemodynamics arterial blood pressure (ABP), heart rate (HR), cardiac output (CO), cardiac index (CI), stroke volume (SV) and stroke volume index (SVI). Additionally, two indices of cerebral autoregulation, mean flow index (Mx_a) and cerebral oximetry index (CO_X), were calculated in real-time via ICM + software.

Results: Forty patients were included in this study. The initial results showed ephedrine increased rScO₂ (p < 0.001), while phenylephrine increased Mx_a (p < 0.02) and CO_X (p < 0.007), respectively. However, upon further linear-mix model analysis, the effects of both drugs on rScO₂ (p = 0.944), Mx_a (p = 0.093) and CO_X (p = 0.084) were found to be non-significant. Compared with the hemodynamic parameters during hypotension, the systolic blood pressure (SBP) (p < 0.001), diastolic blood pressure (DBP) (p < 0.001), mean arterial pressure (MAP) (p < 0.001), and MCAvm (p < 0.001) significantly increased after both ephedrine and phenylephrine administration. However, no significant differences were found between the two groups in terms of the changes in MAP (p = 0.549) and MCAvm (p = 0.173). And there were significant increases in CO (p < 0.001), HR (p < 0.001), and CI (p < 0.001) following ephedrine administration, while decreases in HR (p < 0.001), CO (p < 0.001), and CI (p < 0.001) after phenylephrine administration.

Conclusion: In the management of intraoperative hypotension, both phenylephrine and ephedrine effectively increase MAP and MCAvm, albeit with their differential effects on CO and HR. It seems that neither vasopressor has a significant impact on cerebral oxygenation and cerebral autoregulation.