Use of High Flow Nasal Cannula Oxygen and Covid-19 Acute Hypoxemic Respiratory Failure

Nasal High Flow oxygen therapy (NHF) is commonly used as first line ventilatory support in patients with acute hypoxemic respiratory failure (AHRF). It's use has been initially limited in Covid-19 patients presenting with AHRF. The aim of the study is to describe the use of NHF in Covid-19-related AHRF and report the changes in the respiratory-oxygenation index (termed ROX index) over time in these patients.

Nasal High Flow oxygen therapy (NHF) is one of the newer methods of oxygenation commonly used in critical care during acute hypoxemic respiratory failure (AHRF). For various reasons (fear of a putative risk of viral dispersion; initial recommendations for rapid intubation due to the rapid deterioration of patients), NHF seems to have been seldomly used during the current Covid-19 epidemic in France. However, the World Health Organization, and other scientific societies list NHF among the possible options for ventilatory support. One of the risks however, identified with NHF is to delay an intubation that would have become necessary. This delay seems to be associated with a poorer prognosis for patients. The respiratory-oxygenation index (termed ROX index) (defined as the ratio of pulse oximetry (SpO2) over inspired fraction in oxygen (FiO2) over respiratory rate (RR); SpO2/FiO2/RR) is used - along with other criteria - to assist the clinician in deciding whether or not to intubate patients on NHF for AHRF. In investigators'ICU, NHF is used in patients admitted for AHRFrelated to Covid-19 and the ROX index is measured and monitoring in investigators' patients. Investigators' initial experience - consistent with feedback from other ICUs - suggests that the respiratory rate of patients with Covid-19-related AHRF is sometimes lower than would be expected given the depth of the hypoxemia. In this case, the ROX index thresholds previously identified for predicting the success or failure of NHF could be different in the case of Covid-19-associated AHRF. The purpose of this work is to describe the use of NHF in Covid-19 patients with AHRF and the evolution of the ROX score over time in patients initially treated with NHF.