Near infrared spectroscopy (NIRS) measures tissue oxygenation continuously at the bedside. Major disturbances of cerebral oxygenation can be detected by using NIRS, but the ability to observe smaller changes is poorly documented. Although anesthetics generally depress cerebral metabolism and enhance oxygen delivery, the administration of etomidate has been associated with cerebral desaturation. We used this difference to study the ability of NIRS to detect the small changes associated with the onset of anesthesia. Thirty-six healthy patients were randomly allocated to have anesthesia induced with either etomidate, propofol, or thiopental. We found that there was a temporal association between the onset of anesthesia and NIRS-derived indices of cerebral oxygenation. Etomidate was associated with a decrease in cerebral oxygenation, whereas propofol and thiopental were associated with an increase in cerebral oxygenation. We conclude that NIRS is capable of detecting the small changes in cerebral oxygenation associated with the induction of general anesthesia and shows promise as a bedside investigational tool for the noninvasive assessment of cerebral oxygenation.
Implications: We conclude that near infrared spectroscopy is capable of detecting the small changes in cerebral oxygenation associated with the induction of general anesthesia and shows promise as a bedside investigational tool for the noninvasive assessment of cerebral oxygenation.