Does the Bispectral Index Monitor have a Role in Intensive Care?

Abstract

Analysis of brain electrical activity is a method of assessing brain function. Interpreting the electroencephalogram is specialist and time-consuming. The bispectral index score (BIS) processes the EEG into manageable numbers. BIS was programmed on healthy individuals undergoing general anaesthesia and used to reduce the incidence of awareness. In the ICU, BIS has been investigated to assess sedation, to induce burst suppression, as a tool to provide early prognosis after brain injury and in scheduling timing for brain stem testing. From these investigations, the following conclusions may be drawn. BIS may be used to prevent both awareness and over-sedation in ICU in appropriate clinical settings. Inducing burst suppression in patients with refractory status epilepticus can be achieved by targeting BIS less than 30, although BIS appears to be an unreliable method for detecting breakthrough epilepsy. BIS less than 22 after anoxic brain injury may have a high likelihood to predict poor outcome, however false positives occur. Despite studies suggesting that BIS might be a useful monitor to prevent secondary brain injury and provide early prognostic information, the sensitivity and specificity are not high enough to be clinically reliable. Currently, clinical decisions made on the basis of BIS monitoring in the ICU should be limited to providing appropriate sedation, eg during neuromuscular blockade, and to providing feedback on induced burst suppression when continuous EEG is not available. Even in the latter situation, it is advisable to check correlation with a formal EEG.