Study on the effect of thyroid function in assessing outcome of artificially ventilated critically ill patients

Background: Critically ill patients often develop non-thyroidal illness syndrome, reflecting disease severity rather than thyroid disease, and thyroid markers may improve prognostic assessment in intensive care. Aims and Objectives: This study aimed to evaluate thyroid function abnormalities in ventilated intensive care unit (ICU) patients, correlate thyroid function tests with acute physiology and chronic health evaluation II (APACHE II) scores, and assess their association with mortality. Materials and Methods: This prospective observational study was conducted in the Intensive Medical Care Unit of Government Thoothukudi Medical College. A total of 100 mechanically or non-invasively ventilated patients were enrolled. Thyroid function tests and APACHE II scores were recorded within 24 h of admission, and patients were followed until ICU outcome. Results: Overall mortality was high (64%). Patients aged over 60 years and males constituted the majority. Poisoning was the most common ICU admission diagnosis. Most patients required mechanical ventilation (62%). Low free triiodothyronine (FT3) levels were present in 21% of patients, whereas low thyroid-stimulating hormone (TSH) levels were observed in 17%. All patients with APACHE II scores ≥25 were non-survivors. Mortality occurred in all patients with low FT3 and low TSH levels. Low FT3 showed a statistically significant association with higher APACHE II scores (P=0.00002). Reduced or normal TSH levels were also associated with higher APACHE II scores (P=0.004). Higher APACHE II scores were significantly associated with invasive ventilation requirement and mortality. Conclusion: Thyroid dysfunction, particularly reduced FT3, reflects illness severity and mortality in critically ill ventilated patients. FT3 may be a useful adjunct prognostic marker alongside APACHE II scoring. Further multicentre studies with serial thyroid assessments are recommended.