TRANSIENT SECONDARY HYPOTHYROIDISM IN CHILDREN AFTER CARDIAC-SURGERY

Thyroid hormone status was assessed in 132 children with congenital he art defects undergoing cardiac surgery (median age 3.1 y; range 2 d to 16.2 y). Plasma TSH, thyroxine (T-4), free thyroxine (fT(4)), triiodo thyronine (T-3), reverse triiodothyronine (rT(3)), thyroglobulin (Tg), and urinary iodine excretion were measured before and every other day after cardiac surgery (d 1-21). After surgery we observed strikingly low plasma concentrations of TSH (0.4 mU/L; 0.2-1.3), T-3 (0.6 nmol/L; 0.3-1.2), T-4 (48.9 nmol/L; 12.9-82.4), fT(4) (12.9 pmol/L; 5.1-19.3) , and Tg (9.4 mu g/L; 1.5-20.6), whereas rT(3) plasma concentrations i ncreased (0.13 pmol/L; 0.05-0.3; n = 40). The maximal postoperative ch anges of TSH and rT(3) preceded changes of T-3, T-4, fT(4), and Tg. Po stoperative urinary iodine excretion increased significantly (n = 109) . Thyroid hormone plasma concentrations were lowest after cardiopulmon ary bypass operations and in patients treated with dopamine. In patien ts with postoperative T-3 plasma concentrations less than 0.6 nmol/L ( n = 52) the period of mechanical ventilation and intensive care treatm ent was significantly prolonged. Furthermore, the cumulative doses of inotropic and vasoactive catecholamines and furosemide were significan tly higher in this patient group. Our results demonstrate transient se condary hypothyroidism in children after cardiac surgery that may cont ribute to postoperative cardiac and respiratory dysfunction and may de lay recovery. Possible benefits of thyroid hormone replacement therapy need to be thoroughly examined.