Sudden and sustained elevation of bispectral index due to electromyographic interference during closed circuit inhalational anesthesia

Standard cardiorespiratory monitors including three lead electrocardiogram, pulse oximetry and noninvasive blood pressure were attached and a depth of anesthesia sensor, the BIS-XP ® four electrode sensor (Covidien Ilc, Mansfield, MA, USA) was placed on the patient's forehead. General anesthesia was induced with midazolam 2 mg intravenous (i.v.), propofol 150 mg i.v. and fentanyl 75 μg i.v. and endotracheal intubation was facilitated with rocuronium 40 mg i.v. Anesthesia was maintained with sevoflurane at 0.7-1.2 age - adjusted minimum alveolar concentration (MAC) in 30-40% oxygen in air mixture with the Drager Zeus ® auto control closed circuit system (Drager Medical, Lubeck, Germany) to maintain a BIS index between 40 and 60.