Correlation Between Pattern of Thyroid Dysfunction (ESS-Like Changes) and Outcome in Mechanically Ventilated Children in ICU Using PRISM III

Background: Non-thyroidal illness syndrome (NTIS), also known as euthyroid sick syndrome (ESS), is characterized by altered thyroid hormone profiles in critically ill patients without intrinsic thyroid disease. Mechanically ventilated children admitted to paediatric intensive care units (PICUs) frequently develop ESS-like hormonal alterations that may correlate with disease severity and clinical outcomes. The objective is to evaluate the correlation between thyroid hormone abnormalities (FT3, FT4, and TSH) and clinical outcomes in mechanically ventilated paediatric patients using PRISM III scoring, and to assess the prognostic significance of ESS-like changes. Material and Methods: A hospital-based prospective observational study was conducted in the PICU of MGM Medical College and M.Y. Hospital, Indore, India, over a period of 1 year. 100 mechanically ventilated children were enrolled. Serum FT3, FT4, and TSH levels were measured on Day 1 and Day 3 of mechanical ventilation. PRISM III scores were calculated within the first 24 hours of admission. Clinical outcomes including mortality, duration of mechanical ventilation, and PICU stay were analyzed. Correlations between thyroid hormone levels, PRISM III score, and clinical outcomes were assessed statistically. Results: NTIS was observed in 67% of mechanically ventilated children, with Type I NTIS (isolated low FT3) present in 34% and Type II NTIS (combined low FT3 and FT4) in 33% of patients. Overall mortality was 21%. Non-survivors had significantly lower FT4 levels on both Day 1 and Day 3 and lower FT3 levels on Day 3 compared with survivors (p<0.05). FT4 Day 1 showed significant negative correlations with PRISM III score (r= -0.230, p=0.021), duration of mechanical ventilation (r= -0.233, p=0.019), and PICU stay (r= -0.240, p=0.016). Type II NTIS was significantly associated with higher mortality (39.4%, p=0.007). ROC analysis demonstrated moderate predictive utility of FT4 Day 3 for mortality prediction (AUROC=0.747), while PRISM III showed excellent predictive performance (AUROC=0.914). Conclusion: ESS-like thyroid dysfunction is highly prevalent among mechanically ventilated paediatric patients and correlates significantly with illness severity and adverse clinical outcomes. Combined FT3 and FT4 suppression appears to have important prognostic significance and may complement PRISM III scoring for early risk stratification in critically ill children.

Keywords: Non-thyroidal illness syndrome, Mechanical ventilation, PICU, PRISM III, Free triiodothyronine, Thyroid dysfunction, Paediatrics.