Although it is now recognized that a variety of respiratory abnormalities, such as diaphragmatic dysfunction, can be present in primary hypothyroidism and reverse with adequate hormone treatment, the role of thyroid hormone replacement therapy on respiratory system in patients with the nonthyroidal illness syndrome (NTIS) remains to be clarified. The NTIS has been found to be an independent risk factor for prolonged (> 13 days) mechanical ventilation. It is unclear, however, whether the NTIS is only a biochemical prognostic marker or it actually contributes to the development and progression of respiratory failure.

The aim of this study will be to assess respiratory muscle function after thyroid hormone substitution therapy in mechanically ventilated patients with the NTIS.

Inclusion Criteria:

• Patients under mechanical ventilation for more than 48 hours who experience a spontaneous breathing trial and have a diagnosis of nonthyroidal illness syndrome

Exclusion Criteria:

• • age <18 yr;

  • pregnancy or estro-progestinic therapy;
  • tracheostomy;
  • neurological or neuromuscular pathology and/or known phrenic nerve dysfunction;
  • previously diagnosed intrinsic thyroid disease; known or suspected pituitary-hypothalamic disease;
  • severe obesity;
  • ischemic cardiopathy; complex ventricular arrhythmias;
  • serum cortisol level below 80 ng/ml; renal or hepatic failure (respectively, creatininemia ≥ 3.5 mg/dL and bilirubinemia ≥ 6.0 mg/dL);
  • transfusion of plasma within 48 h prior to thyroid hormone assessment; use of amiodarone in the previous 8 weeks;
  • use of iodine contrast agents in the previous 8 weeks;
  • hemodialysis;
  • expected poor outcomes

Patients admitted to the intensive care unit and mechanically ventilated for more than 48 hours who fail weaining from ventilator and with a diagnosis of nonthyroidal illness syndrome