Cerebral state index: comparison between pairwise registrations from the left and the right sides of the brain

Lateralization of cerebral blood flow and EEG activity is known to vary during cognition, sleep and waking. In spite of this, electrode placement for the cerebral state index (CSI) monitor is not specified to a particular side of the brain. This study is designed to determine if pairwise registrations differ for CSI measured simultaneously from the left or right sides of the brain.

In total, 25 ASA I-II patients undergoing elective day surgery under general anaesthesia were recruited. Pairwise recordings were made every minute from two CSI monitors (Cerebral State Monitor, Danmeter A/S; Odense, Denmark) connected to the left and the right side of the head. Sedation was graded according to the observer's assessment of alertness/sedation rating scale and correlated with CSI.

A large overlap of indices, of similar magnitude, for each side of the brain was seen between different levels of sedation. The agreement between pairwise registrations was high, correlation between the 584 CSI pairs of recordings left/right was r(2)=0.92.

Despite known lateralization of the EEC, this study found a very high correlation in CSI derived simultaneously from the left and right sides of the brain by two independent monitors.