title: The ability of bispectral index to detect intra-operative wakefulness during isoflurane/air anaesthesia, compared with the isolated forearm technique.
abstract: Clinical signs are unreliable for guiding anaesthetic administration and it is suggested that using the bispectral index can improve anaesthetic delivery. In the current study, isoflurane administration was guided to a bispectral index range of 55-60. Intra-operative responsiveness, as assessed by the isolated forearm technique, was compared with whether the bispectral index predicted/identified a patient's appropriate hand movements in response to commands. Thirty-four women underwent major gynaecological surgery with isoflurane/air and atracurium. Eleven women responded on 32 occasions with appropriate hand movements to commands given during surgery, of which the bispectral index detected 17 (sensitivity 53%). The bispectral index suggested consciousness 660 times in the absence of any movement responses (specificity 69%). The positive predictive value of the bispectral index was 3%. The median (IQR [range]) bispectral index value associated with an intra-operative response was significantly lower than that associated with eye opening after surgery: 60 (50-68 [36-83]) vs 77 (75-84 [59-90]), respectively (p = 2.25 × 10(-8)). Conversely, end-tidal isoflurane concentration was significantly higher at intra-operative response than at eye opening: 0.3 (0.3-0.4 [0.2-0.9]) vs 0.2 (0.1-0.2 [0.1-0.3]), respectively (p = 7.36 × 10(-8)). For patients who responded more than once during surgery, the bispectral index value associated with a response was not constant. No patient had recall for surgery or the taped commands, and only one could remember dreaming (a good dream). Titrating isoflurane to target a bispectral index range of 55-60 may result in an unacceptable number of patients who are conscious during surgery (albeit without recall).
authors.affiliation: Department of Anaesthesia, Hull Royal Infirmary, Hull, UK.
authors.forename: I F
authors.initials: IF
authors.lastname: Russell
mesh_terms: D000293:Adolescent; D000328:Adult; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation; D056805:Consciousness Monitors; D003627:Data Interpretation, Statistical; D004576:Electromyography; D005260:Female; D005542:Forearm / Q000502:physiology*; D013509:Gynecologic Surgical Procedures; D006801:Humans; D058926:Intraoperative Awareness / Q000175:diagnosis*; D007432:Intraoperative Period; D007530:Isoflurane; D008875:Middle Aged; D009799:Ocular Physiological Phenomena; D014851:Wakefulness / Q000502:physiology*; D055815:Young Adult
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane