Monitoring of cerebral perfusion during anesthesia by time-compressed Fourier analysis of the electroencephalogram

Time-compressed Fourier analysis of the electroencephalogram has proven to be a useful analytical procedure during anesthesia and surgery which simplifies data interpretation by presenting the EEG in a time-compressed frequency domain rather than the conventional time domain. This method of data analysis graphically accentuates the electroencephalographic correlates of ischemia-induced cerebral dysfunction and other cerebral oxygen consumption abnormalities. The ability to accentuate trends in frequency and power is derived from sequential plotting of spectra to produce a graph with three dimensional axes of frequency, time, and power. In carotid endarterectomies the system has proven more useful than the conventional EEG in assessing the need for a vascular shunt to maintain internal carotid flow during endarterectomy. In open-heart surgery time-compressed EEG spectral analysis has allowed early recognition of cerebral ischemia resulting from arterial hypotension and venous hypertension. Five cases are presented which demonstrate the ability of our system to reflect developing cerebral ischemia.