Plasma inorganic fluoride concentrations during and after prolonged (greater than 24 h) isoflurane sedation: effect on renal function.

We studied the effect of prolonged sedation (greater than 24 h) with isoflurane on plasma inorganic fluoride concentrations and renal function in 60 critically ill patients allocated randomly to receive either isoflurane or midazolam for sedation. In the isoflurane group, plasma fluoride increased from a mean concentration of 3.1 mumol/L to 20.0 mumol/L at the end of sedation, continued to increase to a peak of 25.3 mumol/L 16 h later, and then decreased exponentially (t1/2 = 111 h) to reach normal levels by the fifth day. In the midazolam group, the plasma fluoride increased from a mean concentration of 4.2 mumol/L to a peak of 6.8 mumol/L 12 h after starting the sedation and then decreased toward normal. Serum and urinary electrolytes, urine osmolality, and creatinine clearance during and after sedation were similar in the two groups. Isoflurane sedation was associated with an increase in plasma fluoride concentration without any clinical deterioration of renal function.