Cerebral Oxygenation During Anesthesia

Abstract

Cerebral Oxygenation During Anesthesia: Correlation With Blood Pressure and Cardiac OutputWilliam W. Mantulin∗ and Lingzhong Meng∗∗University of California IrvineBeckman Laser Institute,∗ Laboratory for Fluorescence Dynamics∗ and Department of Anesthesiology∗∗Irvine, CADuring surgery, the anesthesiologist is tasked with monitoring, manipulating and maintaining the patient's key physiological parameters, especially of critical organs such as the brain. Generally, cerebral tissue oxygenation is not explicitly tracked, but a measure of Mean Arterial Pressure (MAP) is considered an adequate surrogate marker for sufficient cardiac output to satisfy cerebral oxygen demand. Avoidance of cerebral ischemia is an important consideration. Consequently, we have used a tissue oximeter (Oxipex TS; ISS, Inc.) to non-invasively and quantitatively monitor cerebral oxygenation (bilateral; frontal lobes) during surgery in more than two dozen patients (under IRB approved protocols). If blood pressure declines after inducing anesthesia, then the anesthesiologist pharmacologically intervenes with a pressor such as Ephedrine or Phenylephrine. Phenylephrine acts as a vasoconstrictor, whereas ephedrine stimulates cardiac output. We were intrigued by our preliminary observations that cerebral oxygenation (and oxygenated Hemoglobin concentrations) declined with administration of Phenylephrine, but remained unchanged with Ephedrine. Both pressors produced the anticipated increase in blood pressure. We sought a correlation of this observation through a direct monitor of cardiac output with a Doppler Esophageal device (Cardio Q, Deltex Inc.). The data clearly showed that administration of Phenylephrine induced a decrease in cardiac output and a correlation with (a decreasing) cerebral oxygenation. The cerebral blood volume and tissue oxygen saturation tracked with the blood pressure. Our observations are now engendering a reexamination amongst clinicians as to how best to understand the interplay between cardiac output, mean arterial pressure and the use of increased blood pressure as a means to better perfuse and oxygenate critical organs such as the brain.