Sevoflurane versus isoflurane for maintenance of anesthesia: are serum inorganic fluoride ion concentrations of concern?

Sevoflurane administration can result in increased serum inorganic fluoride ion concentrations, which have been associated with inhibition of renal concentrating ability. We measured serum fluoride levels, renal function, and recovery variables as a function of time in ASA grade I-III patients administered general anesthesia with isoflurane or sevoflurane for at least 1 h. Fifty patients were exposed to sevoflurane (< or = 2.4% inspired concentration) or isoflurane (< or = 1.9% inspired concentration) for maintenance of anesthesia as part of a multicenter trial. Blood was collected for determination of serum fluoride ion concentration, electrolytes, blood urea nitrogen, and creatinine at various time points pre- and postoperatively. Mean serum fluoride levels were significantly increased in sevoflurane versus isoflurane groups at all time points; the mean peak serum levels were 28.2 +/- 14 mumol/L at 1 h for sevoflurane and 5.08 +/- 4.35 mumol/L at 12 h for isoflurane. Sevoflurane-mediated increases in serum fluoride levels peaked at 1 h and, in general, decreased rapidly after discontinuation of the anesthesia. Three of 24 patients exposed to sevoflurane had one or more fluoride levels > 50 mumol/L. One of these patients had a serum inorganic fluoride ion level > 50 mumol/L at 12 h after sevoflurane, and an additional patient had fluoride levels > 33 mumol/L for up to 24 h after sevoflurane discontinuation. Those two patients also demonstrated an increase in serum blood urea nitrogen and creatinine at 24 h after sevoflurane administration compared with baseline. The elimination half-life of serum fluoride ion was 21.6 h. The results of this study suggest the possibility of sevoflurane induced nephrotoxicity.