Relationship between calculated blood concentration of propofol and electrophysiological variables during emergence from anaesthesia: comparison of bispectral index, spectral edge frequency, median frequency and auditory evoked potential index

Abstract

We studied four electrophysiological variables (bispectral index (BIS), 95% spectral edge frequency (SEF), median frequency (MF) and auditory evoked potential index (AEP index) in 10 patients during emergence from anaesthesia. We compared correlation of the signals with gradually decreasing calculated blood propofol concentrations, and evaluated the signal differences between preinduction and emergence from anaesthesia. Values of BIS, MF and SEF correlated with calculated blood concentrations of propofol during emergence from anaesthesia. The correlation was best with BIS, but was poor with MF and SEF at low calculated blood propofol concentrations. Although AEP index values did not correlate with calculated blood concentrations of propofol during emergence from anaesthesia, values after eye opening and before anaesthesia were well distinguished from those during emergence from anaesthesia. BIS correlated best with calculated blood concentrations of propofol. AEP index appeared to distinguish the awake from asleep state.

Non-instrumental clinical monitoring does not guarantee an adequate course of general anesthesia. A prospective clinical study

“…that AAI was one of the most sensitive variables of level of consciousness 21,[31][32][33][34][35][36] . The observations of others [37][38][39] showed the higher sensitivity of auditory evoked potentials in comparison to spontaneous electroencephalogram in evaluating the changes of consciousness.…”

“…Mean values of AAI after reversal of anesthesia was 60 in both groups, similarly to values observed before the induction of anesthesia. Because there was a good correlation between the level of conscience and AAI, use of neuromonitoring during anesthesia makes the prediction of the time of recovery over anesthesia more simple 39,41,46,47 and can reduce period between end of anesthesia and extubation 22,27,31,48,49 . The episodes of intraoperative awareness were surveyed using a questionnaire based on the work of Brice 29 , because of its efficacy and large number of studies 50 .…”

Effects of cardiopulmonary bypass and hypothermia on electroencephalographic variables

“…The AEP were obtained using a similar system to that described in our previous studies [15,20] from three electrodes (Zipprep) placed on the right mastoid (þ), middle forehead (¹) and Fp2 as the reference. The amplifier was custom-built with a 5-kV medical grade isolation.…”

“…However, the MLAEP are usually obtained intermittently and the waveforms are difficult to use in the clinical situation. More recently, the auditory evoked potential index (AEPIndex; formerly known as the level of arousal score) was derived from AEP and has been proposed as a single numerical value for anaesthetic depth monitoring [17][18][19][20]. The AEPIndex reflects the morphology of AEP waveforms and is calculated from the amplitude difference between successive segments of the curve [19,20].…”

“…More recently, the auditory evoked potential index (AEPIndex; formerly known as the level of arousal score) was derived from AEP and has been proposed as a single numerical value for anaesthetic depth monitoring [17][18][19][20]. The AEPIndex reflects the morphology of AEP waveforms and is calculated from the amplitude difference between successive segments of the curve [19,20]. Although Hett and colleagues [21] reported the effect of hypothermia and CPB on AEP, changes of AEPIndex during cardiac anaesthesia have not been reported.…”