Cardiopulmonary bypass produces a state of functional hypothyroidism characterized by low levels of circulating tri-iodothyronine (T3). Theoretically, supplementing T3 should result in improved hemodynamics as well as patients' outcome. The aim of the present study was to determine whether pretreatment with single oral T3 could prevent serum T3 reduction, and improve hemodynamics and clinical outcome.

Forty-seven patients undergoing valvular heart surgery were included in the study. Patients were randomly assigned into two groups (T = T group; C = control group) the day before surgery and received single oral T3 40 µg or placebo before operation. Blood samples were collected for determination of serum levels of total T3, T4 and TSH before administration of oral T3 or placebo (baseline), 1, 6 and 18 hour after weaning of cardiopulmonary bypass. Hemodynamic parameters and medication were recorded during the intraoperative period and throughout the first 24 h after arrival at the intensive care unit.

T3 levels were significantly higher in the T group 1 hr after weaning of cardiopulmonary bypass. T3 levels in the T group were all maintained within the normal range throughout the study period, whereas it was decreased to below normal level in the C group at 18 hr after weaning of cardiopulmonary bypass. In the T group, vasoactive agent requirements were reduced during and after cardiopulmonary bypass.

Pretreatment with single oral T3 prevented the reduction in T3 level after valvular heart surgery, with subsequent reduction in vasoactive agent requirement.