Alterations in Thyroid Hormone Levels after Open Heart Surgery

Kim, Kwang Hyu; Moon, Hyeong Sun; Oh, Jeong Woo; Cho, Sam Hyeon; Na, Kook Joo; Ahn, Byoung Hee; Kim, Sang Hyung; Song, Ho Cheon

Abstract

The hemodynamic effects of thyroid hormones which is well established, affect myocardial contractility, heart rate, and myocardial oxygen consumption. The alterations in thyroid function test are frequently seen in patients with nonthyroidal illness and often correlate with the severity of the illness and the prognosis. In this study, thyroid hormone changes were investigated in 20 patients who received cardiopulmonary bypass(CPB). All patients showed a state of biochemical euthyroidism preoperatively. The results were as follows : 1. Serum triiodothyronine(T3) reached to its nadir(30.05+/-17.5ng/dl, p<0.001) at 10 minutes after the start of CPB and remained low(p<0.05) throughout the study period. 2. Serum thyroxine(T4) concentration slightly decreased after CPB, but maintained within normal range. 3. Serum free thyroxine(fT4) concentration slightly increased after CPB, but maintained within normal range. 4. Serum thyroid stimulating hormone(TSH) concentration increased 10 minute after CPB, reached to its nadir(3.37+/-0.81uIU/ml, p<0.001) at 2 hours after CPB. After then, serum TSH concentration decreased and reached its normal levels at 24 hours after CPB. 5. The patients whose postoperative recovery was uneventful(Group 1) had higher serum T3 levels than those who had postoperative complications(Group 2)(p<0.05). Group 1 showed elevating patterns of serum T3 in the fourth day after operation, whereas group 2 did not show such an elevating pattern. These findings are similar to the euthyroid sick syndrome seen in severely ill patients and indicate that patients undergoing open heart surgery have suppression of the pituitary-thyroid axis.