Minimum Alveolar Concentrations of Sevoflurane for Maintaining Bispectral Index Below 50 in Morbidly Obese Patients

After ethical committee approval and written informed consent, 30 morbidly obese adult patients , BMI 40- 70Kg/m², ASA physical status 1 and 2 , aged 18-49 yr, , undergoing elective bariatric surgery under general anesthesia using sevoflurane, were included in this study.

Monitoring consisted of noninvasive blood pressure, Electrocardiogram (ECG) , pulse oximetry, and BIS. All subjects received a standard dose of 2 mcg/kg fentanyl approximately 20 min before induction of general anesthesia. a standard BIS® monitor strip was applied before fentanyl administration and induction of general anesthesia. Induction was performed in all patients with 2m/kg propofol, 0.2 mg/kg cisatracuruim, followed by direct laryngoscopy and tracheal intubation. Therefore, when BIS reached > 65 , sevoflurane was started immediately at the predetermined dose.

The endtidal sevoflurane concentration was adjusted with starting dose for the first cohort patients 1% and maintained for 10 min to ensure equilibration with the cerebral anesthetic partial pressure followed by a 1-min assessment of BIS taken at 10-s intervals. Briefly, a first dose is given to the first patient and the next doses are given according to the following rule: if the subject responds positively (BIS<50), the dose is decreased one step for the next subject, and conversely, if the subject does not respond (BIS>50), the dose is increased one step. The dose adjustment is 0.2% for sevoflurane. The CRM is used to calculate the dose adjustment for every cohort with the number of patients for every cohort .