Depth of anesthesia monitoring needs a consistent and reliable measure in close to real time. The aim of this study was to compare auditory evoked potential (AEP) as determined using the autoregressive model with exogenous input (ARX-model) versus the bispectral index (BIS) by conventional averaging. The hypothesis of the present study was that since the ARX-model extracts AEP faster than BIS, the former should be able to detect changes during the brief, intense stimulus of endotracheal intubation.

Forty ASA physical status I or II patients scheduled for orthopaedic surgery were randomly assigned to 2 groups (group 1; BIS and group 2; AEP). Anesthesia was induced with target-controlled infusions of propofol. After the effect-site concentration of propofol was reached at 4 µlml, vecuronium 0.1 mg/kg was administered. The trachea was intubated 3 min after the administration of vecuronium. AAI and BIS were compared during endotracheal intubation.

During endotracheal intubation, the ARX-extracted AEP Index showed a significant increase (P < 0.05), the BIS did not change significantly. There is a significant difference between the ARX-extracted AEP and the BIS, in terms of response time.

The ARX-extracted AEP Index increases during the brief, intense stimulus of endotracheal intubation. For tracing short-term changes at the hypnotic level, ARX-extracted AEP is considered as the more useful monitoring device in terms of a real time measure.