Institute for Clinical and Translational Science

Background

Multiple studies have shown that cerebral tissue oxygen saturation () is decreased after phenylephrine treatment. We hypothesized that the negative impact of phenylephrine administration on is affected by arterial blood carbon dioxide partial pressure () because CO₂ is a powerful modulator of cerebrovascular tone.

In 14 anaesthetized healthy patients, i.v. phenylephrine bolus was administered to increase the mean arterial pressure ∼20–30% during hypocapnia, normocapnia, and hypercapnia. and cerebral blood volume (CBV) were measured using frequency domain near-infrared spectroscopy, a quantitative technology. Data collection occurred before and after each treatment.

Phenylephrine caused a significant decrease in during hypocapnia [=−3.4 (1.5)%, P<0.001], normocapnia [=−2.4 (1.5)%, P<0.001], and hypercapnia [=−1.4 (1.5)%, P<0.01]. Decreases in 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.

The negative impact of phenylephrine treatment on and CBV is intensified during hypocapnia while blunted during hypercapnia.