Correlation of bispectral index and Guedel's stages of ether anesthesia.

UNLABELLED: Bispectral index (BIS) analysis is a method of electroencephalograph (EEG) analysis based on the interfrequency phase relationships of the EEG, designed to quantify anesthetic hypnosis. The BIS was created after concurrent collection of EEG and clinical data from a large number of patients anesthetized with various drugs over a prolonged period and then performing a Fourier analysis followed by a bispectral calculation. The clinical stages of anesthetic depth are very well demonstrated in etherized patients. In this study, we studied the BIS changes during various stages of ether anesthesia and quantified the hypnotic depth during the surgical stage of ether anesthesia. The values for BIS under various stages and planes of ether anesthesia were recorded in 21 patients listed for short surgical procedures. During diethyl ether anesthesia, BIS initially increased and subsequently decreased. During surgical anesthesia, a BIS value of 30 was observed. IMPLICATIONS: For the first time, bispectral index (BIS) has been studied in patients being anesthetized solely with ether. Ether both causes an increase and decrease in BIS during induction and emergence. The index observed during the surgical stage of ether anesthesia is probably the correct value for the depth of hypnosis because no other volatile anesthetic can produce the true anesthetic state when used alone. This value could be taken as the value to be attained when balanced anesthesia is being practiced.