Noninvasive ventilation (NIV) is a commonly used mode of ventilation in critically ill patients in ICU that significantly reduces the work of breathing in patients with acute respiratory failure. Therefore, NIV might be effective in delaying and overall reducing the need for intubation in patients. Although NIV is commonly used it has a high failure rate of 25 – 59% and delay in detecting NIV failure and subsequent intubation can worsen the patient’s prognosis and increases mortality and duration of hospital stay. Therefore, it is necessary to predict NIV failure at an early stage.

Previous studies have demonstrated the prediction of NIV failure based on components like the patient’s vital signs, level of consciousness, and degree of acidosis. This led to the development of a scale that considers heart rate, acidosis, consciousness, oxygenation, and respiratory rate known as the HACOR scale to predict NIV failure which is defined as the need for intubation after NIV intervention. It is a rapid and convenient tool to effectively predict NIV failure in patients with hypoxemic respiratory failure. HACOR score > 5 is very high risk of NIV failure.

Currently there are no tools validated to objectively assess the effort of breathing during administration of NIV. Point of care ultrasound (POCUS) in the field of critical care medicine has received increased attention because of its rapid availability as a bed side tool, non-invasive, safe and lack of harmful radiation. Respiratory effort can be estimated using ultrasound assessment of the diaphragm. Diaphragmatic thickness, Diaphragmatic thickening fraction (DTF) and Diaphragmatic excursion (DE) are three commonly used tools to assess diaphragm function.

Diaphragm thickening fraction (DTF) is defined as the percentage change in diaphragm thickness during inspiration. Diaphragm thickness fraction (DTF) = (thickness at end-inspiration – Thickness at end-expiration)/Thickness at end expiration × 100. The thickening fraction (TF) represents diaphragm inspiratory activity effort.

The use of bedside ultrasound to study the diaphragmatic thickening fraction can help in early prediction of NIV failure and prevent delayed intubation and the poor outcomes associated with it. The diaphragmatic thickening fraction can further be compared along with HACOR score which is a validated tool for prediction of NIV failure to see if diaphragmatic thickening fraction along with HACOR score can predict NIV failure better than HACOR or thickening fraction alone. Most of the studies till date were conducted in either Emergency department or Respiratory ICU and majority studies were done either on COPD patients or COVID -19 patients which decreases generalizability to other patient population in ICU with acute respiratory failure (Pneumonia, Congestive heart failure, post operative etc). Most of the studies measured DTF only at initiation or for the first 1, 2 hours and not over time in a patient admitted in ICU. Most of the studies done were either pilot study, preliminary study or were small sample size of < 50 patients. None of the studies till date have assessed the efficacy of diaphragm thickening fraction in predicting NIV failure and compared it with HACOR score which is a validated tool for predicting NIV failure. It is not known whether diaphragmatic thickening fraction can be a sensitive test to predict NIV failure in ICU patients with acute respiratory failure and if it can be added on to the HACOR score for better prediction of NIV failure as compared to either HACOR alone or diaphragmatic thickness fraction alone. We postulate that serial measurements of DTF can predict early NIV failure and requirement of intubation in critically ill patients admitted to ICU with acute respiratory failure and can be a valuable tool to combine with HACOR for better prediction of NIV outcome.