Endocrine and cytokine changes during elective surgery

Elective surgery was used as a model of severe non-thyroidal illness (SNTI) to study the inter-relation between changes in serum thyroid hormones, thyroid stimulating hormone (TSH), cortisol, and interleukin 6 concentrations. The study was designed to determine whether the expected interleukin 6 increases after surgery are the cause of decreased serum tri-iodothyronine (T3) concentration normally observed following severe trauma. Blood was sampled for 24 hours before, during, and for 48 hours after abdominal surgery under general anaesthesia in 11 patients. Total T3 decreased 30 minutes after induction and continued to decrease at 24 hours. After a transient increase at 30 minutes, free T3 also decreased, and free thyroxine (T4) concentrations, other than a similar transient increase, did not change. TSH concentrations were increased at four hours and the nocturnal surge was suppressed. The increase in the serum interleukin 6 concentration was not observed until four hours. Cortisol concentrations were increased at 30 minutes and peaked at four hours. Therefore, the early changes in thyroid hormones and TSH accompanying surgery do not seem to be caused by changes in interleukin 6 concentrations.