Low triiodothyronine (T3) state: a predictor of outcome in respiratory failure? Results of a clinical pilot study

BACKGROUND AND AIM: Various low triiodothyronine (T3) states have been described in severe nonthyroidal diseases and associated with a poor prognosis in cardiovascular disease patients. We assessed thyroid function in patients with severe respiratory failure from pulmonary disorders, and needing invasive or noninvasive mechanical ventilation, in order to evaluate the prognostic value of nonthyroidal illness syndrome. METHODS: We studied 32 consecutive patients with acute or acute-on-chronic respiratory failure. Measured variables upon admission included APACHE II score, the ratio of the partial pressure of oxygen in arterial blood to the fraction of oxygen in inspired gas (PaO(2)/FiO(2)), and plasma levels of free T3 (fT3) and free thyroxine (fT4), and TSH levels. Thyroid function was further evaluated at discharge. RESULTS: Plasma levels of fT3 were below normal in 17 patients (53%). Plasma fT3 was correlated with PaO(2)/FiO(2) (P<0.001), and with APACHE II score (P=0.003). In four patients (12.5%) who died, fT3 levels were significantly lower (P=0.002) than in patients who survived. In univariate logistic regression analysis, fT3 was the only factor significantly associated with an increased risk of death (odds ratio, 64.23; 95% confidence interval, 1.78-2316.86, P=0.023). Normalization of thyroid function was observed at discharge with a significant correlation between the percent increase in both fT3 and PaO(2)/FiO(2) (P=0.015). P values were calculated using Spearman's Correlation Coefficient. CONCLUSION: Our preliminary data suggest that the low T3 state is a predictor of outcome in pulmonary patients with respiratory failure.