Active and inactive thyroid hormone levels in elective and acute surgery.

The changes in the plasma or serum concentration of thyrotrophin (TSH), thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5-triiodothyronine (reverse T3, rT3) and cortisol were examined in patients undergoing elective cholecystectomy (n = 10) or acute laparotomy due to peritonitis (n = 11). TSH and T4 showed no essential changes in either group. T3 was reduced already during initiation of anaesthesia and continued to fall during and after surgery in both groups. In the peritonitis group, T3 was reduced already before medical intervention. rT3 displayed changes opposite to those of T3. An increase in cortisol peceded the changes in T3 and rT3 in both groups. T3 and rT3 returned towards normal levels when the patients recovered and resumed oral nutrition. It seems likely that both elective and acute uncomplicated surgery is accompanied by a transient reduction in the extrathyroidal production of the most active hormone, T3, and by a reciprocal increase in the levels of the virtually inactive rT3. The underlying mechanism behind this metabolic adaptation is unclear but may be related to adrenocortical activation and/or to changes in the mode of nutrition.