Auditory evoked potential index: a quantitative measure of changes in auditory evoked potentials during general anaesthesia

Abstract

SummaryWe describe a novel index derived from the auditory evoked potential, the auditory evoked potential index, and we compare it with latencies and amplitudes related to clinical signs of consciousness and unconsciousness. Eleven patients, scheduled for total knee replacement under spinal anaesthesia, completed the study. The initial mean (SD) value of the auditory evoked potential index was 72.5 (11.2). During the first period of unconsciousness it decreased to 39.6 (6.9) and returned to 66.8 (12.5) when patients regained consciousness. Thereafter, similar values were obtained whenever patients lost and regained consciousness. Latencies and amplitudes changed in a similar fashion. From all parameters studied, Na latencies had the greatest overlap between successive awake and asleep states. The auditory evoked potential index and Nb latencies had no overlap. The consistent changes demonstrated suggest that the auditory evoked potential index could be used as a reliable indicator of potential awareness during propofol anaesthesia instead of latencies and amplitudes.

Somatosensory-evoked potentials indicate increased unpleasantness of noxious stimuli in response to increasing stimulus intensities in the rat

“…The RDF, an expression of the overall shape of the SEP waveform in the latency range studied, is obtained by averaging the absolute differences between all pairs of subsequent sampled data points y k in a specified latency range from x to m (see Eq. (1)) [13,29,40]. Both decreases in amplitude and increases in latency of the SEP components, decrease the value of the RDF, whereas both increases in amplitude and decreases in latency of the SEP components increase the value of the RDF.…”

A review of the utility of EEG depth of anaesthesia monitors in the paediatric intensive care environment

“…The AEP Monitor uses active acoustic stimulation, delivered through headphones, to generate middle latency auditory evoked potentials (MLAEP) (Kurita et al 2001). Anaesthetics or sedation alters EEG latency and amplitude (Drummond 2000;Thornton and Sharpe 1998) and these changes are used to generate the A-line ARX Index TM (AAI) (Mantzaridis and Kenny 1997). BIS and AAI have a range from zero, where patient's EEG is isoelectric, to 100, when patients are awake (Nishiyama and Hanaoka 2004;Rampil 1998).…”

Effects of cardiopulmonary bypass and hypothermia on electroencephalographic variables

“…The AEPIndex is a mathematical derivative reflecting morphology of the AEP. The value was calculated as the sum of the square root of the absolute difference between every two successive 0.56-ms segments of the AEP waveform [19].…”

“…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.…”