Plasma levels of alfentanil and etomidate in patients and their relation to compressed power spectral analysis of the EEG.
In 22 patients alfentanil-etomidate anesthesia was used for orthopedic procedures using for the induction period 300 micrograms/kg of the hypnotic and 100 micrograms/kg of the opioid. Maintenance of anesthesia consisted of 20 micrograms/kg of alfentanil given every 15 min and 20 micrograms/kg/min of etomidate given over an infusion. The patients were intubated and mechanically ventilated with pure oxygen. In order to access the state of vigilance with respect to etomidate and alfentanil plasma levels, EEG power spectra were computed from electrical cortical activity of the occipital region (P3-O1); respectively venous blood samples were assayed by means of gas chromatography for alfentanil and etomidate plasma concentration. In the EEG power spectrum, anesthesia replaced the high dominant alpha-peaks of the control-awake period by a disharmonious pattern over the whole frequency range (0.5-16.0 Hz). At the end of anesthesia vigilance recording indicated a correlation with plasma etomidate level. Once concentration had dropped below 100 ng/ml power spectra were characterized by a stable harmonious peak in the alpha-range (8.0-10.0 Hz). Plasma levels above 100 ng/ml induced a fluctuating pattern with peaks in the theta to delta band (0.5-8.0 Hz); the latter was characterized by drowsiness and a reduced respiratory drive. Opioid plasma levels above 100 ng/ml with etomidate levels below 80 ng/ml did not influence to the same extent. EEG power spectra seem to be a useful tool in pinpointing to a reduced state of vigilance. Such a state when present with opioid ingestion is often accompanied by respiratory depression.
D000328:Adult; D015760:Alfentanil; D000768:Anesthesia, General; D004569:Electroencephalography; D005045:Etomidate / Q000097:blood* / Q000494:pharmacology; D005283:Fentanyl / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000097:blood*; D013997:Time Factors
D007093:Imidazoles; D015760:Alfentanil; D005283:Fentanyl; D005045:Etomidate