Phenylephrine but not Ephedrine Reduces Frontal Lobe Oxygenation Following Anesthesia-Induced Hypotension

Background Vasopressor agents are used to correct anesthesia-induced hypotension. We describe the effect of phenylephrine and ephedrine on frontal lobe oxygenation (ScO2) following anesthesia-induced hypotension. Methods Following induction of anesthesia by fentanyl (0.15 mg kg(-1)) and propofol (2.0 mg kg(-1)), 13 patients received phenylephrine (0.1 mg iv) and 12 patients received ephedrine (10 mg iv) to restore mean arterial pressure (MAP). Heart rate (HR), MAP, stroke volume (SV), cardiac output (CO), and frontal lobe oxygenation (ScO2) were registered. Results Induction of anesthesia was followed by a decrease in MAP, HR, SV, and CO concomitant with an elevation in ScO2. After administration of phenylephrine, MAP increased (51 +/- 12 to 81 +/- 13 mmHg; P < 0.001; mean +/- SD). However, a 14% (from 70 +/- 8% to 60 +/- 7%) reduction in ScO2 (P < 0.05) followed with no change in ;CO (3.7 +/- 1.1 to 3.4 +/- 0.9 1 min(-1)). The administration of ephedrine led to a similar increase in MAP (53 +/- 9 to 79 +/- 8 mmHg; P < 0.001), restored CO (3.2 +/- 1.2 to 5.0 +/- 1.3 1 min(-1)), and preserved ScO2. Conclusions The utilization of phenylephrine to correct hypotension induced by anesthesia has a negative impact on ScO2 while ephedrine maintains frontal lobe oxygenation potentially related to an increase in CO.