ABSTRACT
Critical illness is dened as any life-threatening condition requiring the support of failing vital organ functions and is often associated with alterations in thyroid hormone concentrations in patients with no previous histories of thyroid diseases. For these reasons, the thyroidologist should be familiar with the thyroid axis changes in intensive care unit (ICU) patients. This chapter reviews the effects of critical illness on the function of the hypothalamus-pituitary-thyroid axis and on thyroid hormone metabolism, focusing on the so-called sick euthyroid syndrome (SES).
