The COVID-19 pandemic caused a surge of admissions to intensive care unit (ICU) of patients with severe hypoxemic acute respiratory failure (ARF). Due to the specificities of COVID-19 ARF and a risk of viral aerosolization, the different oxygenation strategies were widely debated, including high-flow nasal oxygen therapy (HFNO). Few studies have compared ICU populations between the different waves of the pandemic and the impact of the oxygenation strategy on patient outcomes.

We conducted a retrospective study to compare the clinical characteristics, ventilatory management and the outcomes of patients with COVID-19 ARF during the first three waves of the pandemic in France. We also assessed patient outcomes according to the time to intubation, i.e., the duration of HFNO before intubation (HFNO late failure: > 48 h, FiO ₂ ≥ 80% and flow rate ≥ 60 L./min).

Between March 2020 and April 2021, 198 patients were included in the study 56, 85 and 57 patients, respectively in the three waves. Despite similar clinical characteristics at admission, the use of HFNO increased significantly between the three waves (62.5%, 96.5%, 98.2% respectively; p < 0.001) with a trend for HFNO success (46.4%, 65.9%, 63.2%; p = 0.057). When HFNO failed, the time from ICU admission to intubation was longer (p < 0.001), the duration of HFNO before intubation was longer (1.8, 3.0, 5.2 days, respectively; p = 0.015, and with more severe underlying hypoxemia (PaO ₂ /FiO ₂ ratio; p = 0.012). ICU length of stay and mortality were similar between the three waves. Finally, all waves combined, the time to intubation (early n = 20 intermediate n = 24, late n = 31) had no effect on patient outcomes.

Our study confirms that HFNO was an effective oxygenation strategy for the management of patients with severe COVID-19 ARF, and was used increasingly over the first three waves. HFNO is a non-invasive treatment that should be preferred to intubation as a first-line respiratory support of patients with acute respiratory failure.