Comparison of EEG monitoring techniques: an evaluation during cardiac surgery.

A single channel EEG recording was made in 25 patients undergoing cardiac surgery and analysed using 5 different techniques--amplitude, cerebral function monitor, Fourier, Hjorth, and zero-crossing analyses. The results of the analyses were plotted as trend information on paper. These trends were studied for changes in the EEG during surgery. In the majority of cases changes were noted simultaneously by all 5 techniques. There were, however, some cases in which an amplitude-only technique showed no changes while frequency contributions were changing, and a frequency-only technique showed no changes while amplitudes were changing. The conclusion drawn is that major EEG changes are observed with any of the techniques studied, but that for improved sensitivity a technique analysing both frequency and amplitude information should be used.