Auditory evoked potential monitoring with the AAI™-index during spinal surgery:: decreased desflurane consumption

Background: The auditory evoked potential (AEP) is sensitive to the depth of anesthesia. The A-line monitor is a novel device that processes the amplitude and latency of the AEP during the mid-latency time window to provide a simple numerical index, the AAI(TM)-index. The hypothesis of the present study was that titration of anesthetic depth (desflurane) by means of the AAI(TM)-index could decrease the consumption of the main anesthetic and shorten emergence times. Methods: Thirty ASA I-II patients scheduled for elective open spine surgery under general anesthesia were randomly allocated to two groups. Group I (n=15), the main anesthetic, desflurane, was titrated with a target AAI(TM)-index of 20+/-5. Group II (n=15), desflurane was titrated according to routine clinical signs, including heart rate, blood pressure, sweating and tears. No fixed MAC-multiple was sought. The primary study variable was desflurane consumption; and secondary study variables were time to extubation and orientation. Results: All patients had an uncomplicated course and no patients showed signs of awareness or had any recall postoperatively. AAI(TM)-index guidance reduced desflurane consumption by 29% and improved emergence. Time until extubation and orientation and ability to state name and date of birth was significantly shortened among AAI(TM)-index titrated patients. Conclusion: Titrating depth of desflurane anesthesia using AAI(TM)-index guidance decreased main anesthetic consumption and improved emergence during spine surgery.