Thinking outside the box. Off-label use of Bispectral Index within context and limitations for conditions other than depth of anesthesia.

Numerous articles appeared in literature using brain function monitors (BFM), such as Bispectral Index (BIS) to assess cerebral cognitive conditions not related to depth of anesthesia. BIS cannot be considered a "true" reflection of the electroencephalography (EEG) signal nor an independent measure of brain function. BIS algorithm was retrospectively derived from EEG changes with incremental doses of γ-amino butyric acid (GABA)ergic anesthetic agents while measuring 3 descriptors. In many instances we are confronted with BIS values that do not concur with clinically judged anesthetic state arising from an underlying alteration of the patients' own EEG. Because BIS is an EEG derived parameter; conditions that can "alter" the raw EEG signal would subsequently change BIS to reflect other unrelated EEG events of patient-dependent pathophysiologic perturbations. Could we use BIS monitor outside the scope of the operating room to "grade" other EEG conditions? Actually the answer to that seems to be a "very cautious" yes. Because BIS is a rather appealing scale from 100 to 0, it is tempting to find numerical cut-off values for conditions that are already clinically graded like West Haven hepatic encephalopathy. Having said that I strongly argue against going as far as using BIS in Critical Care Unit (CCU) setting, there are too much heterogeneity and many disease states in the CCU patients, other than sedatives /hypnotics, that would strongly influence BIS values, in effect rendering BIS not only useless most of the time but can also be misleading.