Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients

† Phenylephrine, but not ephedrine, decreased cardiac output (CO) and brain oxygenation. † This study highlights the importance of CO in preserving brain oxygenation during management of intraoperative hypotension. Background. How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation (SctO2 )-guided management may improve postoperative outcome. The physiological variables responsible for SctO2 changes induced by phenylephrine and ephedrine bolus treatment in anaesthetized patients need to be defined. Methods. A randomized two-treatment cross-over trial was conducted: one bolus dose of phenylephrine (100‐200 mg) and one bolus dose of ephedrine (5‐20 mg) were given to 29 ASA I‐III patients anaesthetized with propofol and remifentanil. SctO2, mean arterial pressure (MAP), cardiac output (CO), and other physiological variables were recorded before and after treatments. The associations of changes were analysed using linear-mixed models. Results. The COdecreased significantlyafter phenylephrine treatment [△CO¼ 22.1 (1.4) litre min 21 , P,0.001], but was preserved after ephedrine treatment [△CO¼0.5 (1.4) litre min 21 , P.0.05]. The SctO2 was significantly decreased after phenylephrine treatment [△SctO2 ¼ 23.2 (3.0)%, P,0.01] but preserved after ephedrine treatment [△SctO2 ¼0.04 (1.9)%, P.0.05]. CO was identified to have the most significant association with SctO2 (P,0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with SctO2 (P.0.05). Conclusions. Associated with changes in CO, SctO2 decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and SctO2 implies a cause‐effect relationship between global and regional haemodynamics.