Depth of anesthesia

The present review article provides a summary of the recent literature evaluating the technology for monitoring depth of anesthesia and patient outcomes associated with its use.

The tentative and controversial findings of a 2006 study suggesting a correlation of mortality with lower intraoperative bispectral index scores were reproduced in a more recent study, but the correlation could be accounted for by controlling for patient comorbidities, particularly malignancy. In a large trial involving patients at high risk for awareness, general anesthesia with volatile agents guided by bispectral index monitoring was associated with a low incidence of awareness, but no more so than the use of alarms for limits on volatile agent concentration. Studies comparing both emerging and more established brain function monitors suggest that, in spite of their different algorithms for processing and filtering electromyographic signal, many monitors are affected by the use of neuromuscular blocking agents. Recent evidence is consistent with previous studies that describe a nonlinear model for the dose-response of EEG parameters to increasing concentration of anesthetic agents with a dosing plateau response over a clinically relevant dose range.

The goal of precisely dosed general anesthesia guided by brain monitoring remains elusive.