Serum endogenous thyroxine levels in man during anaesthesia and surgery.

Determinations of serum thyroxine concentrations were made before induction of anaesthesia, after 20 minutes and 40 minutes of anaesthesia before operation, during operation, and after the end of operation in 36 patients. After 40 minutes of anaesthesia with diethyl ether and halothane there were significantly increased endogenous serum thyroxine concentrations, but thiopentone, nitrous oxide and oxygen anaesthesia definitely decreased the thyroxine level. Surgical operation further elevated the serum thyroxine level in both ether and halothane anaesthesia groups but no significant rise of thyroxine levels was observed in the thiopentone, nitrous oxide and oxygen groups.