Thyroid hormone changes after cardiovascular surgery and clinical implications

Alterations in serum concentrations of total triiodothyronine (TT3), total thyroxine (TT4), and thyroid-stimulating hormone (TSH) frequently occur in patients with nonthyroidal illnesses. These changes correlate with the severity of the illness and the prognosis. In this study, 44 patients undergoing a cardiovascular operation had significant declines in serum TT3 and TT4 levels during cardiopulmonary bypass and thereafter. Serum TT3 and TT4 concentrations reached their nadir at 30 minutes after the start of cardiopulmonary bypass with values (mean +/- standard error of the mean) of 0.77 +/- 0.12 nmol/L (50.4 +/- 7.6 ng/dL) and 68.2 +/- 10.2 nmol/L (5.30 +/- 0.79 micrograms/dL), respectively. The mean serum concentrations of TSH and TT4 returned to preoperative levels by the sixth day after operation, whereas TT3 levels remained low throughout the study period. The patients whose recovery was uneventful had higher serum TT3, TT4, and TSH levels than those who had complications or died. The trend toward recovery was initiated by a sharp increase in the serum TSH level and increases in serum TT3 and TT4 concentrations on the fourth day after operation. Patients with complications either did not show these changes or had only a transient increase in TT3 and TT4 levels. All of the patients had a normal serum free T4 level before anesthesia. Those with an uneventful recovery had a higher serum free T4 level on the sixth day after operation than those with complications. Two patients in the latter group had serum free T4 levels less than normal at that time.(ABSTRACT TRUNCATED AT 250 WORDS)