Impact of phenylephrine administration on cerebral tissue oxygen saturation and blood volume is modulated by carbon dioxide in anaesthetized patients

Abstract

Background. Multiple studies have shown that cerebral tissue oxygen saturation (Scto2) is decreased after phenylephrine treatment. We hypothesized that the negative impact of phenylephrine administration on Scto2 is affected by arterial blood carbon dioxide partial pressure (Paco2) because CO2 is a powerful modulator of cerebrovascular tone. Methods. In 14 anaesthetized healthy patients, i.v. phenylephrine bolus was administered to increase the mean arterial pressure ∼20-30% during hypocapnia, normocapnia, and hypercapnia. Scto2 and cerebral blood volume (CBV) were measured using frequency domain near-infrared spectroscopy, a quantitative technology. Data collection occurred before and after each treatment. Results. Phenylephrine caused a significant decrease in Scto2 during hypocapnia [ΔScto2 -3.4 (1.5)%, P<0.001], normocapnia [ΔScto2=-2.4 (1.5)%, P<0.001], and hypercapnia [ΔScto2=-1.4 (1.5)%, P<0.01]. Decreases in Scto2 were significantly different between hypocapnia, normocapnia, and hypercapnia (P<0.001). Phenylephrine also caused a significant decrease in CBV during hypocapnia (P<0.01), but not during normocapnia or hypercapnia. Conclusion. The negative impact of phenylephrine treatment on Scto2 and CBV is intensified during hypocapnia while blunted during hypercapnia. © The Author [2012]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved.