Low Free T₃ Is Associated With Worse Outcomes in Patients in the ICU Requiring Invasive Mechanical Ventilation

<jats:sec><jats:title>Objective:</jats:title><jats:p> Critical illness causes a decrease in serum free triiodothyronine (T<jats:sub>3</jats:sub>) levels. This condition, known as nonthyroidal illness syndrome (NTIS), is associated with poor outcomes. The association of NTIS and outcomes in patients in the intensive care unit (ICU) requiring mechanical ventilation has not been well studied. This study aimed to determine the impact of NTIS on the outcomes of these patients. </jats:p></jats:sec><jats:sec><jats:title>Methods:</jats:title><jats:p> This prospective study included 162 patients in the ICU who underwent mechanical ventilation. Serum free T<jats:sub>3</jats:sub> levels were tested on the day of initiation of mechanical ventilation. The rates of in-hospital mortality and ventilator-free days (VFDs) at day 28 after the initiation of mechanical ventilation were compared between patients with low (<2.3 pg/mL) and normal (≥2.3 pg/mL) free T<jats:sub>3</jats:sub> levels. Patients who died while on mechanical ventilation were assigned a VFD of 0. </jats:p></jats:sec><jats:sec><jats:title>Results:</jats:title><jats:p> Low T<jats:sub>3</jats:sub> was present in 60% of study patients. The in-hospital mortality rate of the entire cohort was 39%, and the mean and median VFDs at day 28 were 13.5 and 21 days, respectively. Compared to patients with normal free T<jats:sub>3</jats:sub>, patients with low free T<jats:sub>3</jats:sub> had higher in-hospital mortality (52% vs 19%, P < .001) and less mean and median VFDs at day 28 (10.7 vs 18 and 0 vs 23, respectively. P < .001 for both mean and median VFDs). </jats:p></jats:sec><jats:sec><jats:title>Conclusions:</jats:title><jats:p> The presence of low T<jats:sub>3</jats:sub> due to NTIS in patients in the ICU requiring mechanical ventilation is associated with poor outcomes. </jats:p></jats:sec>