ARX-Derived Auditory Evoked Potential Index and Bispectral Index During the Induction of Anesthesia with Propofol and Remifentanil

A new commercial auditory evoked potential (AEP) monitor (A-line AEP monitor) was developed to calculate an index (ARX AEP index; AAI) by automatically using the amplitudes and latencies of the AEP. We investigated 30 patients before spine surgery. AAI; bispectral index (BIS); relative (%) δ, θ, α, and β; spectral edge frequency; median frequency; mean arterial blood pressure; heart rate; and oxygen saturation were obtained simultaneously during stepwise (1.0 μg/mL) induction of target-controlled propofol concentration until 5.0 μg/mL, followed by an infusion of 0.3 μg · kg−1 · min−1 of remifentanil. Every minute, the patients were asked to squeeze the observer’s hand. Prediction probability (Pk), receiver operating characteristic, and logistic regression were used to calculate the probability to predict the conditions AWAKE, UNCONSCIOUSNESS (first loss of hand squeeze), and steady-state ANESTHESIA (5.0 μg/mL of propofol and 0.3 μg · kg−1 · min−1 of remifentanil). Although a statistically significant difference among the conditions was observed for AAI, BIS, mean arterial blood pressure, median frequency, and %α, only AAI and BIS were able to distinguish UNCONSCIOUSNESS versus AWAKE and ANESTHESIA versus AWAKE with better than Pk = 0.90. The modern electroencephalographic variables AAI and BIS were superior to the classic electroencephalographic and hemodynamic variables to distinguish the observed anesthetic conditions.