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The aim of this prospective study was to determine the effect site concentrations of remifentanil maintaining cardiovascular homeostasis in response to surgical stimuli during bispectral index (BIS) guided propofol anesthesia in seriously obese patients.Twenty-two patients, female/male 15/7, ASA physical status II - III, aged 29-69 years, body mass index (BMI) 54.5+/-12, undergoing major open bariatric surgery, were enrolled to receive a propofol-remifentanil total intravenous anesthesia. All patients were intubated by using a flexible fiberoptic bronchoscopic technique facilitated by a target controlled effect site concentration of remifentanil set at 2.5 ng/mL. After endotracheal intubation, anesthesia was started with a target controlled infusion of propofol initially set at 6 microg/mL, then adjusted to maintain a BIS value between 40 and 50. The mean effect site concentration of remifentanil was recorded at different intervals time during surgery: skin incision-opening of peritoneum (T1), bowel resection (T2), cholecystojejunal anastomosis (T3), ileojejunal anastomosis (T4), closing of peritoneum (T5).The mean plasma concentrations of propofol required to maintain a BIS value between 40 and 50 were 4+/-0.55, 3.8+/-0.64, 3.8+/- 0.63, 3.8+/-0.65 and 3.8+/-0.63 microg/mL at T1, T2, T3, T4 and T5 interval time, respectively. The mean values of remifentanil target effect site concentration were 5.2+/-1.3, 7.7+/-1.7, 9.1+/-1.8, 9.7+/- 2.2 and 9.9+/-2.5 ng/mL at T1, T2, T3, T4 and T5 interval time.This study suggests that tolerance to remifentanil infusion is profound and develops very rapidly in morbidly obese patients submitted to open bariatric surgery during BIS guided propofol anesthesia. The administration of opiates during anesthesia based on target-controlled infusion should include corrections for the development of tolerance. |
