BISPECTRAL ANALYSIS OF THE ELECTROENCEPHALOGRAM DURING INDUCTION OF ANESTHESIA MAY PREDICT HEMODYNAMIC-RESPONSES TO LARYNGOSCOPY AND INTUBATION

The use of electroencephalography as a measure of adequacy of anesthes ia has achieved limited success. Our purpose was to determine whether the non-linear properties of the electroencephalogram (EEG) as defined by the bispectral index was a better predictor of autonomic responses to endotracheal intubation during opioid-based anesthesia than the li near statistical properties of the EEG formulated by power spectral an alysis. Thirty-nine adults scheduled for elective non-cranial surgery had a continuous EEG recorded during induction of anesthesia and endot racheal intubation. Anesthesia consisted of thiopental and nitrous oxi de in oxygen, followed by 1 of 5 randomized opioid dose regimens. The EEG was continuously recorded and blood pressure was measured every mi nute. All electroencephalographic parameters were derived for the 3 mi n before and after intubation and were compared to the blood pressure and heart rate responses. Responders were defined by 2 analyses: patie nts who had a 20% or greater increase (1) in blood pressure or (2) in heart rate to laryngoscopy. Responders and non-responders were compare d using Student's unpaired t test, and differences due to dose regimen s were examined with logistic regression. Based on the criterion for b lood pressure change, there were 27 responders and 12 non-responders. Heart rate changes did not differentiate between the two groups. There was a significant difference between response groups as measured by t he bispectral index which distinguished responders from non-responders independently of the amount of drug given. None of the variables of p ower spectral analysis accurately distinguished responder from non-res ponder. We conclude that the bispectral index of the EEG may accuratel y predict blood pressure responses in patients undergoing endotracheal intubation after induction of general anesthesia.