External carotid artery flow maintains near infrared spectroscopy-determined frontal lobe oxygenation during ephedrine administration

The effect of phenylephrine on ScO2 is governed by a decrease in external carotid blood flow since it increases cerebral blood flow as determined by flow in the internal carotid artery. In contrast, ScO2 is largely maintained with administration of ephedrine because blood flow to extracerebral tissue increases.