Internal jugular venous sampling to monitor cerebral oxygenation is not a new technique, 47 but recent advances in technology, as well as understanding of cerebrovascular physiology, have revived interest in this monitoring modality. This technique allows estimation of the global balance between cerebral oxygen demand and supply. With appropriate modification using inert gas washin and the simultaneous measurement of arterial O 2 content, the actual hemispheric cerebral blood flow (CBF) and cerebral metabolic rate (CMRO 2 ) can be determined. 38 Jugular venous oximetry, although not yet definitive care for patients at risk of cerebral ischemia, has found useful application in a variety of clinical settings. Appropriate interpretation of this monitoring, however, is dependent on a thorough understanding of the underlying physiologic principles and the realization that no single physiologic monitor should be interpreted in isolation. Moreover, this is a global measurement, and neither regional desaturation nor cross-contamination from the contralateral cerebral hemisphere can be detected.