Unchanged Characteristics and Survival among Critically Ill COVID-19 Patients during First, Second, and Third Waves: A Prospective Observational Cohort.

Background: This study was carried out to compare characteristics and outcomes in patients with acute respiratory failure related to COVID-19 during first, second, and third waves.

Methods: We included consecutive adults admitted to the intensive care unit between March 2020 and July 2021. We compared three groups defined by the epidemic intake phase: waves 1 (W1), 2 (W2), and 3 (W3).

Results: We included 289 patients. Two hundred and eight (72%) patients were men with a median age of 63 years (IQR: 54-72), of whom 68 (23.6%) died in hospital. High-flow nasal oxygen (HFNO) was inversely associated with the need for invasive mechanical ventilation (MV) in multivariate analysis (p = 0.003) but not dexamethasone (p = 0.25). The day-90 mortality rate did not vary from W1 (27.4%) to W2 (23.9%) and W3 (22%), p = 0.67. By multivariate analysis, older age (odds ratio [OR]: 0.94/year, p < 0.001), immunodeficiency (OR: 0.33, p = 0.04), acute kidney injury (OR: 0.26, p < 0.001), and invasive MV (OR: 0.13, p < 0.001) were inversely associated with higher day-90 survival as opposed to the use of intermediate heparin thromboprophylaxis dose (OR: 3.21, p = 0.006). HFNO use and dexamethasone were not associated with higher day-90 survival (p = 0.24 and p = 0.56, respectively).

Conclusions: In patients with acute respiratory failure due to COVID-19, survival did not change between first, second, and third waves while the use of invasive MV decreased. HFNO or intravenous steroids were not associated with better outcomes, whereas the use of intermediate dose of heparin for thromboprophylaxis was associated with higher day-90 survival. Larger multicentric studies are needed to confirm our findings.