A Dose-Response Study in Man of the Metabolism of Enflurane Used as a Supplement

Abstract

The metabolism of enflurane, used as a supplement to muscle relaxant and nitrous oxide anaesthesia, was studied in 19 healthy adult male surgical patients; seven control patients received halothane.

Patients receiving enflurane were randomly allocated to three groups:

Group I—1/2 MAC for 1/2 hour (dosage=1/4 MAC hour)

Group II—1/2 MAC for 2 hours (dosage=1 MAC hour)

Group III—1/2 MAC for 4 hours (dosage=2 MAC hours)

Metabolism of enflurane to inorganic fluoride (F^-) was indicated by elevated serum F^-concentration and elevated urinary excretion of F^-. Peak serum F^- concentration was measured in samples collected immediately at the end of enflurane anaesthesia and fell thereafter, approaching pre-operative levels at 48 hours; mean peak serum F^- was 23·6±4·2 μmol/l after 2 MAC hours of enflurane, 17·7±2·8 μmol/l after 1 MAC hour and 10·5±0·9 μmol/l after 1/4 MAC hour. Nephrotoxic levels of serum F^- (50 μmol/l) were not reached in any patient. Post anaesthetic renal function, including response to vasopressin, was normal in all groups. A dose-response relationship between enflurane dose and F^- in serum and urine was established.