• ARX index;
  • auditory evoked potential;
  • depth of anesthesia;
  • general anesthesia;
  • isolated forearm technique;
  • propofol

Background: The rapidly extracted auditory evoked potentials index (A-lineTM ARX Index or AAI) has been proposed as a method to measure the depth of anesthesia. A prospective study was designed to assess the performance of AAI to detect the recovery and loss of wakefulness in anesthetized and paralyzed patients.

Methods: Fourteen adult patients undergoing elective surgery were anesthetized with propofol 1.5 mg kg−1, vecuronium 0.1 mg kg−1 and further propofol 1.0 mg kg−1. Wakefulness was measured by the ability of the patient to respond to command using the isolated forearm technique (IFT). After the patient responded, propofol was infused at 10 mg kg−1 · h−1 until wakefulness (responsiveness) was lost. The AAI was recorded continuously throughout the study and analyzed off-line.

Results: The AAI showed a significant difference between the values registered during, 30 s before and 30 s after the recovery, and also between 30 s before and 30 s after the loss of wakefulness. The prediction probability (Pk) values for AAI were 0.786 and 0.864 during the transitions from unresponsiveness to responsiveness and from responsiveness to unresponsiveness. The area under the receiver operating characteristic curve for the responsive and unresponsive values was 0.926 (SE 0.002, 95% CI 0.922–0.931), and the AAI values of approximately 5%, 50% and 95% predicted probability of wakefulness were 19, 29 and 39, respectively.

Conclusion: The AAI may be a good predictor of recovery and loss of wakefulness for anesthetized and paralyzed patients.