Several variables derived from the MLAEP have been examined to assess the correlation with responsiveness or memory formation: latency of the Nb peak, 1,2,5amplitude of the Nb peak, 6latencies of the Na and Pa peaks, 3,4auditory evoked potential index, 19variables derived from the frequency spectrum 4,20,21or the joint time–frequency spectrogram, 21and wavelet analysis. 17,18In clinical practice, anesthesia results from the sum of effects of several agents, and therefore a neurophysiologic indicator of responsiveness for a variety of anesthetic regimens would be useful. Changes of 40-Hz power values of 20% (during desflurane) and 16% (during propofol) were associated with a change in probability of nonresponsiveness from 50% to 95%.Īnesthetic concentration is a highly predictive indicator of responsiveness the awake minimum alveolar concentration (MAC Awake) and its equivalent plasma concentration (Cp 50Awake) of an agent define the concentration at the 0.50 probability of wakeful response. The approximately 40-Hz power did not provide a significantly better prediction than anesthetic concentration the PK values for concentrations of desflurane and propofol were 0.91 and 0.94. The performance of the best combination of amplitude and latency variables was nearly equal to that of approximately 40-Hz power. The PK values for approximately 40-Hz power were 0.96 during both desflurane and propofol anesthesia, whereas the PK values for the best-performing latency and amplitude index, latency of the Nb wave, were 0.86 and 0.88 during desflurane and propofol (P = 0.10 for -40-Hz power compared with Nb latency), and for the next highest, latency of the Pb wave, were 0.82 and 0.84 (P < 0.05). The approximately 40-Hz power of the frequency spectrum predicted wakefulness better than all latency or amplitude indices, although not all differences were statistically significant. A PK value of 1.00 means perfect prediction and a PK of 0.50 means a correct prediction 50% of the time (e.g., by chance). They used prediction probability (PK) to rate midlatency auditory evoked potential indices and concentrations of end-tidal desflurane and arterial propofol for prediction of responsiveness. The authors measured latencies and amplitudes from raw waveforms and calculated indices from the frequency spectrum and the joint time-frequency spectrogram. Midlatency auditory evoked potentials were recorded, and wakeful response was tested by asking volunteers to squeeze the investigator's hand.
They applied stepwise increases of 0.5 vol% end-tidal desflurane or 0.5 microg/ml target plasma concentration of propofol to achieve sedation levels just bracketing wakeful response. The authors correlated midlatency auditory evoked potential indices with anesthetic concentrations permitting and suppressing response in 22 volunteers anesthetized twice (5 days apart), with desflurane or propofol.