Thyroid hormone changes cardiovascular surgery and clinical implications

Abstract Alterations in serum concentrations of total triiodothyronine (TT 3 ), total thyroxine (TT 4 ), 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 TT 3 and TT 4 levels during cardiopulmonary bypass and thereafter. Serum TT 3 and TT 4 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 μg/dL), respectively. The mean serum concentrations of TSH and TT 4 returned to preoperative levels by the sixth day after operation, whereas TT 3 levels remained low throughout the study period. The patients whose recovery was uneventful had higher serum TT 3 , TT 4 , 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 TT 3 and TT 4 concentrations on the fourth day after operation. Patients with complications either did not show these changes or had only a transient increase in TT 3 and TT 4 levels. All of the patients had a normal serum free T 4 level before anesthesia. Those with an uneventful recovery had a higher serum free T 4 level on the sixth day after operation than those with complications. Two patients in the latter group had serum free T 4 levels less than normal at that time. The alterations in serum TT 4 , TT 3 , and TSH concentrations has no correlation with drugs (furosemide, dopamine hydrochloride, dobutamine hydrochloride, isoproterenol hydrochloride, norepinephrine, or epinephrine) administered during the study period. In summary, serum TT 3 , TT 4 and TSH levels declined in patients undergoing a cardiovascular operation, especially in those who had complications or died. The administration of catecholamines or furosemide was not an important factor in the development of abnormal thyroid function test results in our study.