Metabolic ability and enflurane defluorination in surgical patients

Antipyrine clearance and half-life, which are measures of the hepatic metabolic ability, were determined prior to anaesthesia in 14 surgical patients. The antipyrine results correlated neither with the highest serum fluoride concentrations nor with the fluoride excretion in urine following administration of enflurane. Enzyme induction may therefore have little influence on enflurane metabolism in man. Inorganic fluoride concentrations in serum and in excreted urine were determined following the exposure of a total of 21 surgical patients to measured doses of enflurane. In the group of 14 patients tested for metabolic ability, a mean dose of 0.4 end-tidal vol. % X h enflurane resulted in a mean peak serum fluoride concentration of 6.8 mumol/l (maximum 13.6 mumol/l) 2 h after enflurane exposure. In the material as a whole, the enflurane dose was positively correlated with both post-anaesthetic highest serum fluoride concentrations and the 24-h post-anaesthetic urine pH (P less than 0.01) as well as urinary volume and fluoride excretion in urine during that time. At a urinary pH below 5.0, the fluoride excretion was very low, while the highest excretions were associated with a urinary pH of about 7.0. Raising the patient's per- and post-anaesthetic urine pH and maintaining a good urinary output (which also tends to increase urine pH) may be enough to prevent accumulation of inorganic fluoride in the body following enflurane anaesthesia.