title: Comparison of conventional averaged and rapid averaged, autoregressive-based extracted auditory evoked potentials for monitoring the hypnotic level during propofol induction.
abstract: BACKGROUND
  The extraction of the middle latency auditory evoked potentials (MLAEP) is usually done by moving time averaging (MTA) over many sweeps (often 250-1,000), which could produce a delay of more than 1 min. This problem was addressed by applying an autoregressive model with exogenous input (ARX) that enables extraction of the auditory evoked potentials (AEP) within 15 sweeps. The objective of this study was to show that an AEP could be extracted faster by ARX than by MTA and with the same reliability.
  
  
  METHODS
  The MTA and ARX methods were compared with the Modified Observer's Assessment of Alertness and Sedation Scale (MOAAS) in 15 patients scheduled for cardiac surgery and anesthetized with propofol. The peak amplitudes and latencies were recorded continuously for the MTA- and ARX-extracted AEP. An index, AAI, was derived from the ARX-extracted AEP as well.
  
  
  RESULTS
  The best predictors of the awake and anesthetized states, in terms of the prediction probability, Pk, were the AAI (Pk [SE] = 0.93 [0.01]) and Na-Pa amplitude (MTA, Pk [SE] = 0.89 [0.02]; ARX, Pk [SE] = 0.87[0.02]). When comparing the AAI at the MOAAS levels 5-3 versus 2-0, significant differences were achieved. During the transitions from awake to asleep, the ARX-extracted AEP were obtained with significantly less delay than the MTA-extracted AEP (28.4 s vs. 6 s).
  
  
  CONCLUSIONS
  The authors conclude that the MLAEP peaks and the AAI correlate well to the MOAAS, whether extracted by MTA or ARX, but the ARX method produced a significantly shorter delay than the MTA.
authors.affiliation: Department of Cardiac Anesthesia, Hospital Santa Creu i Sant Pau, Universitat Autonoma de Barcelona, Barcelona, Spain. hlitvan@hsp.santpau.es
authors.forename: Héctor
authors.initials: H
authors.lastname: Litvan
authors.forename: Erik W
authors.initials: EW
authors.lastname: Jensen
authors.forename: Josefina
authors.initials: J
authors.lastname: Galan
authors.forename: Jeppe
authors.initials: J
authors.lastname: Lund
authors.forename: Bernardo E
authors.initials: BE
authors.lastname: Rodriguez
authors.forename: Steen W
authors.initials: SW
authors.lastname: Henneberg
authors.forename: Pere
authors.initials: P
authors.lastname: Caminal
authors.forename: Juan M
authors.initials: JM
authors.lastname: Villar Landeira
mesh_terms: D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D005072:Evoked Potentials, Auditory / Q000187:drug effects*; D006801:Humans; D011237:Predictive Value of Tests; D015742:Propofol / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol