The A-line ARX index may be a more sensitive detector of arousal than the bispectral index during propofol-fentanyl-nitrous oxide anesthesia: a preliminary investigation.

PURPOSE: To compare changes in the A-line ARX index (AAI) by the Alaris AEP monitor(TM) with those of the bispectral index (BIS) during propofol-fentanyl-nitrous oxide anesthesia.

METHODS: Eighty female patients undergoing partial mastectomy were randomly allocated to AAI or BIS (40 per group). Anesthesia was induced with propofol 2 mg x kg(-1) and fentanyl 3 micro g x kg(-1) during the inhalation of oxygen. A laryngeal mask airway (LMA) #3 was inserted. Anesthesia was maintained with propofol 4 mg x kg(-1) x hr(-1), fentanyl 1 micro g x kg(-1) given at the start of surgery, and nitrous oxide 4 L x min(-1) in oxygen 2 L x min(-1). Blood pressure, heart rate, and AAI or BIS were monitored, including recovery time of the index after disturbance by electrocautery.

RESULTS: The AAI but not the BIS increased significantly with LMA insertion and skin incision, while blood pressure and heart rate did not change. The BIS decreased from 87 +/- 7 to 30-60 while the AAI decreased from 75 +/- 8 to 10-25 during anesthesia. The increase of the AAI was larger than that of the BIS at recovery from anesthesia. The variation of the index was smaller in the AAI than in the BIS. Recovery time of the index after electrocautery was significantly longer in the BIS group (21 +/- 9 sec) than that in the AAI group (5 +/- 3 sec).

CONCLUSIONS: During propofol-fentanyl-nitrous oxide anesthesia, the AAI responded to LMA insertion or surgical incision, but not the BIS, and the AAI had smaller variations. The AAI recovered faster from the disturbance by electrocautery than the BIS. Thus, the AAI may be a more sensitive and useful detector of arousal than the BIS.