PLASMA INORGANIC FLUORIDE LEVELS WITH SEVOFLURANE ANESTHESIA IN MORBIDLY OBESE AND NONOBESE PATIENTS

Administration of several of the inhaled anesthetics result in plasma inorganic fluoride concentrations that are higher in obese compared to nonobese patients. Sevoflurane, a new inhaled anesthetic, is metaboli zed to inorganic fluoride; however, plasma inorganic fluoride levels w ith sevoflurane anesthesia in obese subjects have not been evaluated. We studied plasma inorganic fluoride concentrations during and after s evoflurane surgical anesthesia in morbidly obese (n = 13, body mass in dex > 35) and nonobese (n = 10) patients. Sevoflurane anesthesia in 60 % nitrous oxide/40% oxygen was administered with a semiclosed circle a bsorption system. Mean anesthetic duration was 1.4 minimum alveolar an esthetic concentration (MAC) hours (sevoflurane MAC = 2.05%) for both groups. Pre- and postoperative blood urea nitrogen, creatinine, and li ver function tests were evaluated. Venous blood samples were obtained during and after anesthesia for plasma inorganic fluoride analysis. In six morbidly obese and nonobese patients arterial blood samples were obtained during and after sevoflurane anesthesia for determining sevof lurane blood concentration. Plasma fluoride concentrations during and after anesthesia did not differ between morbidly obese and nonobese gr oups. Peak plasma inorganic fluoride ion concentrations were 30 +/- 2 mumol/L (mean +/- SEM) in obese and 28 +/- 2 mumol/L in nonobese patie nts 1 h after discontinuing anesthesia. The hourly rate of change of f luoride ion concentration in plasma during anesthesia was similar betw een the groups. The maximal recorded plasma fluoride concentrations we re 49 mumol/L in an obese patient and 42 mumol/L in a nonobese patient . Pre-and postoperative hepatic and renal tests did not differ signifi cantly in either group. Sevoflurane biotransformation and plasma fluor ide levels seem to be similar in morbidly obese and nonobese surgical patients. Therefore, obese patients seem to be at no greater risk for possible fluoride-induced renal injury than nonobese patients.