Changes of BIS and AEPex at the return of consciousness during emergence from general anaesthesia during complete neuromuscular block

Changes of BIS and AEPex at the return of consciousness during emergence from general anaesthesia during complete neuromuscular block

H. Kang¹, N.B. Scott², N. Sutcliffe³ and G.N.C. Kenny⁴

¹Department of Anesthesiology and Pain Medicine, School of Medicine,
Chungbuk National University, Cheongju, Korea
^2,3Golden Jubilee National Hospital, Beardmore Street, Clyde bank, Glasgow G81 4HX,UK

⁴Glasgow University Department of Anaesthesia, Royal Infirmary, 8-16 Alexandra Parade, Glasgow G31 2ER, UK

Background: The Bispectral Index (BIS) and Auditory Evoked Potential Index (AEPex) have been suggested to reflect depth of anaesthesia. Previously, the BIS was shown to have the ability to predict the return of consciousness from totally paralysed general anaesthesia. But the capability of AEPex indicating the recovery of consciousness from general anaesthesia while paralysed has not been studied. This study was performed to determine whether BIS and AEPex could detect awareness in totally paralysed patients.

Methods: This study was performed in 15 patients undergoing body surface surgery. Vecuronium was provided using isolated forearm technique after losing consciousness with propofol (TCI) (3-4 µg ml^-l) and fentanyl (75 µg) and a laryngeal mask airway (LMA) insertion. BIS and AEPex were recorded at the following time points: before anaesthetic induction (baseline), at loss of consciousness and 1 min after LMA insertion before neuromuscular relaxation, at complete neuromuscular block before starting surgery, at the end of surgery, 2 min after propofol off and at the return of consciousness during complete neuromuscular block.

Results: Mean awake BIS and AEPex values decreased significantly with loss of consciousness. There was no significant difference in mean BIS and AEPex values before and after complete neuromuscular block. Mean unconscious values of BIS and AEPex significantly increased at the recovery of consciousness while completely paralysed. However, there was some overlapping in individual values of BIS between consciousness and unconsciousness during total neuromuscular block.

Conclusions: Both BIS and AEPex could detect wakefulness in recovery period during complete neuromuscular block. However, BIS was more variable than AEPex in detecting the return of consciousness.