[Enzyme saturation of sevoflurane in piglets at clinically-used concentrations]

To investigate if sevoflurane saturates the metabolic capacity of the enzymes responsible for sevoflurane at clinically-used concentration ranges, we compared plasma fluoride levels and urinary excretion of inorganic fluoride in piglets after (1) low concentration sevoflurane anesthesia versus (2) high concentration sevoflurane anesthesia. Eleven male piglets, weighing 18-23.5 kg, were randomly divided into two groups: 1) L group: five animals were anesthetized for two hours with sevoflurane at 0.8% end-tidal concentration (0.4 MAC); 2) H group: six animals were anesthetized for two hours with sevoflurane at 3.0% end-tidal concentration (1.4 MAC). Plasma inorganic fluoride levels, blood sevoflurane concentration, urinary inorganic fluoride concentration and urine volume were measured. The blood sevoflurance concentration in both groups reached their plateau levels 30 min after the start of anesthesia. The plateau levels in the H and L groups were 275-306 microM and 105-115 microM, respectively. The plasma fluoride concentrations reached plateau levels 60 min after the start of anesthesia in both groups. The H group showed significantly higher plasma fluoride levels than the L group during sevoflurane anesthesia. The H group also showed significantly higher urinary excretion of inorganic fluoride than the L group. Therefore, metabolite production levels in the H group were significantly higher than the L group. These results suggest that low concentration sevoflurane anesthesia did not saturate the metabolic capacity of the enzymes responsible for defluorination of sevoflurane in piglets.