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Observation of bispectral index (BIS) score during sleep nasendoscopy for investigation of sleep related breathing disorders

Brearley J, McFadyen G

Department of Anaesthesia, Singleton Hospital, Swansea, UK

Introduction:

Sleep nasendoscopy using target controlled (TCI) propofol is a validated technique for the assessment of patients with a history suggestive of obstructive sleep apnoea (OSA) which has been used in our institution for a number of years. BIS has been shown to correlate well with clinical endpoints of hypnosis with TCI propofol but the BIS values at which snoring and airway obstruction occur in symptomatic patients have not been determined.

Methods:

Prospective observational study. The subjects were 27 consecutive patients with histories suggestive of OSA undergoing sleep nasendoscopy under general anaesthesia with TCI propofol over a 12 month period. Prior to commencement of the propofol infusion a BIS electrode strip was applied and a baseline, “awake”  BIS value was recorded. An incremental propofol TCI was then commenced and further BIS values noted at onset of unconsciousness (loss of response to verbal commands), onset of audible snoring and onset of airway obstruction (if it occurred) were recorded.

Results:

Awake BIS values were 97.1 ± 1.7 (mean ± SD). Loss of consciousness occurred at BIS values of 61.2 ± 13.2, snoring at 49.8 ± 13.7 and airway obstruction (21 of 27 subjects) at 44.5 ± 9.5. Four patients (14.8%) developed snoring, of which three  (11.1%) obstructed their airway, at BIS levels at which they still responded to verbal command.

Discussion:

BIS values at loss of consciousness in this group are similar to previously published values. The development of airway compromise prior to loss of consciousness in a proportion of patients highlights the need to be cautious if required to administer sedation to patients with a history suggestive of OSA.

Acknowledgements: Mr H Whittet, Dr H Slowey

References:

Berry S, Roblin G, Williams A, Watkins A, Whittet HB Validity of sleep nasendoscopy in the investigation of sleep related breathing disorders. Laryngoscope 2005 115(3):538-40

Gajraj RJ, Doi M, Mantzaridis H,Kenny GNC. Analysis of the EEG bispectrum, auditory evoked potentials and the EEG power spectrum during repeated transitions from consciousness to unconsciousness. BJA 1998 80:46-52