Bispectral index transiently decreased to "0" during per-embolization rupture of an intracranial aneurysm.

Interpreting a Bispectral Index (BIS) of "0", corresponding to an isolelectric electroencephalography, can be difficult. After ruling out technical issues, such as leads disconnection, several possible causes for a decrease in the BIS persists, including deep anesthesia, hypothermia, decrease in the cerebral perfusion pressure and cerebral ischemia. We report a sudden transient decrease of the BIS to "0" in a patient that underwent a coil embolization of a ruptured intracranial aneurysm and suggest that the change in BIS values could provide useful information about the cerebral hemodynamic during aneurysm treatment and might provide indications of a serious cerebral event.