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

Background. How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation (Sct(O2))-guided management may improve postoperative outcome. The physiological variables responsible for Sct(O2) 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 mu g) and one bolus dose of ephedrine (5-20 mu g) were given to 29 ASA I-III patients anaesthetized with propofol and remifentanil. Sct(O2), 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 CO decreased significantly after phenylephrine treatment [Delta CO = -2.1 (1.4) litre min(-1), P<0.001], but was preserved after ephedrine treatment [Delta CO = 0.5 (1.4) litre min(-1), P>0.05]. The Sct(O2) was significantly decreased after phenylephrine treatment [Delta Sct(O2) = -3.2 (3.0)%, P<0.01] but preserved after ephedrine treatment [Delta Sct(O2) = 0.04 (1.9)%, P>0.05]. CO was identified to have the most significant association with Sct(O2) (P<0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with Sct(O2) (P>0.05). Conclusions. Associated with changes in CO, Sct(O2) decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and Sct(O2) implies a cause-effect relationship between global and regional haemodynamics.