We recently described the ROX index, defined as the ratio of SpO2/FIO2 to respiratory rate that outperformed the diagnostic accuracy of the two variables separately. Patients who had a ROX index ≥4.88 after 12 hours of HFNC therapy were less likely to be intubated, even after adjusting for potential covariates. Like any other scoring system, an independent validation of the score in a different population is necessary. We therefore undertook a multicenter, prospective study to validate the ROX index's diagnostic accuracy for determining which patients will fail on HFNC and will need to be intubated.

A growing interest in the non-invasive management of acute respiratory failure has been fuelled by the advent of high-flow nasal canula oxygen therapy (HFNC) and recent data showing that use of HFNC was associated with lower mortality, more ventilator-free days and lower risk for intubation in subsets of patients with PaO2/FIO2≤200mmHg or in those who were immunocompromised in comparison with non-invasive ventilation or standard oxygen. These positive results in favour of HFNC followed physiological studies indicating oxygenation and comfort improvements associated with HFNC use. This has led clinicians to try this technique in the most severe respiratory failure patients, those with ARDS.

Consubstantial to the increasing use of HFNC is the risk of delaying intubation. This is a major concern since a large body of evidence has shown that patients that fail non-invasive ventilatory management of de novo acute respiratory failure (ARF) have a worse outcome.

The variability in both the decision to intubate and its timing reported in several studies suggest that clinical parameters such as respiratory parameters alone are not sufficient and that the progression of the respiratory failure is not sufficiently taken into account. To address this need, we investigated a new score to identify patients at risk of intubation to help clinicians, with three goals simple to use, accurate, and immediately performable at the patients' bedside by any staff.

Inclusion Criteria:

- All consecutive patients admitted to the ICU with pneumonia and treated with HFNC were included

Exclusion Criteria:

• Patients younger than 18 years old
• Patients with indication for immediate intubation
• Patients with limitation of therapeutic effort
• Patients electively intubated for diagnostic or therapeutic procedures

Patients admitted to the ICU with pneumonia and treated with HFNC were included