Cardiopulmonary bypass and thyroid hormone metabolism. Discussion

Early investigations involving patient response to thyrotropin-releasing hormone during cardiac operations prompted researchers to consider that the cardiopulmonary bypass (CPB) procedure may affect this response. Results from several studies indicate that total T 3 (active thyroid hormone) concentrations are significantly reduced during and after CPB (ie, the euthyroid sick syndrome). Inhibition of the monodeiodinase pathway during CFB, and subsequent inhibition of peripheral thyroxine to T 3 conversion may partly explain these findings. These data prompted the investigation of intravenous T 3 administration to patients undergoing CFB. Clinical trials to date have shown that intravenous T 3 administered during or after CFB improves cardiac output and contractility