HEMODYNAMIC-RESPONSES TO INCISION AND STERNOTOMY IN RELATION TO THE AUDITORY-EVOKED POTENTIAL AND SPONTANEOUS EEG

We investigated the effect of incision and sternotomy on the auditory evoked potential (AEP) and EEG, to try to predict a haemodynamic respo nse to incision or sternotomy using the AEP and EEG in 41 patients und ergoing cardiac surgery during propofol and alfentanil anaesthesia. Th e AEP and EEG were recorded before incision, between incision and ster notomy, and after sternotomy. Peak latencies and amplitudes of AEP pea ks V, Na, Pa, Nb, Pb and Nc were determined. From the EEG the median, spectral edge and peak power frequencies, and percentages of delta, th eta, alpha and beta power were calculated. Each patient was classified as responsive, equivocally responsive or unresponsive to incision or sternotomy based on increase in arterial pressure and heart rate on in cision and sternotomy. Before incision, Nb and Pb latency and propofol concentration were higher for unresponsive patients but heart rate an d median frequency before incision were lower. sternotomy, Pa and Nb a mplitude, peak frequency and percentage alpha power were higher, and p ercentage theta power lower for responsive patients. Pa latency was hi gher after sternotomy for unresponsive patients. Using a combination o f heart rate, arterial pressures and features derived from the AEP (al l recorded before incision), the occurrence of a response to incision could be predicted in individual patients with a sensitivity of positi ve predictive accuracy of 63% and accuracy of 72%. We conclude that AE P are more sensitive to pain stimuli than spectral features of the spo ntaneous EEG. In addition, the AEP may help in predicting inadequate a naesthesia.