THE ROLE OF NEUROMONITORING IN CARDIOVASCULAR-SURGERY

This review describes the techniques currently used for quantitative n europhysiologic measurement during cardiac surgery and their potential impact on clinical outcome. Electroencephalography (EEG) characterize s cerebrocortical neuronal electrical activity and was part of some of the earliest cardiopulmonary bypass procedures, yet today it is not i n widespread use. Each of the common misunderstandings regarding a sup posed limitation of this technology is explained. Its major genuine sh ortcoming, a lack of selectivity, may now be overcome with the combine d use of additional monitoring modalities. The influence of intracrani al hemodynamics on observed EEG changes may be determined continuously and noninvasively with transcranial Doppler (TCD) ultrasound. TCD pro vides an indication of sudden change in either blood flow or vascular resistance as well as the detection of emboli. In addition, the metabo lic status of cortical neurons can be monitored by regional cerebral v enous oxygen saturation (rCVOS) using noninvasive transcranial near-in frared spectroscopy. The % rCVOS tends to remain remarkably stable ove r a wide range of temperatures, perfusion pressures, and anesthetic st ates. Marked change in either direction signifies a serious imbalance between oxygen delivery and consumption. Measurement of rCVOS does not require blood flow, pulsatile or otherwise, so that it offers the onl y means of monitoring during circulatory arrest. By characterizing the dynamic interplay among cerebral hemodynamics, metabolism, and electr ogenesis, these technologies permit the rapid detection and correction of potentially hazardous conditions. Copyright (C) 1996 by WB. Saunde rs Company.