Combining reservoir mask oxygenation with high-flow nasal cannula in the treatment of hypoxemic respiratory failure among patients with COVID-19 pneumonia: a retrospective cohort study

Background: Concerns regarding positive-pressure-ventilation for the treatment of coronavirus disease 2019 (COVID-19) hypoxemia led the search for alternative oxygenation techniques. This study aimed to assess one such method, dual oxygenation, i.e., the addition of a reservoir mask (RM) on top of a high-flow nasal cannula (HFNC). Methods: In this retrospective cohort study, the records of all patients hospitalized with COVID-19 during 2020-2022 were reviewed. Patients over the age of 18 years with hypoxemia necessitating HFNC were included. Exclusion criteria were positive-pressure-ventilation for any indication other than hypoxemic respiratory failure, transfer to another facility while still on HFNC and "do-not-intubate/ resuscitate" orders. The primary outcome was mortality within 30 days from the first application of HFNC. Secondary outcomes were intubation and admission to the intensive care unit. Results: Of 659 patients included in the final analysis, 316 were treated with dual oxygenation and 343 with HFNC alone. Propensity for treatment was estimated based on background diagnoses, laboratories and vital signs upon admission, gender and glucocorticoid dose. Inverse probability of treatment weighted regression including age, body mass index, Sequential Organ Failure Assessment (SOFA) score and respiratory rate oxygenation index showed treatment with dual oxygenation to be associated with lower 30-day mortality (adjusted hazard ratio, 0.615; 95% confidence interval, 0.469-0.809). Differences in the secondary outcomes did not reach statistical significance. Conclusions: Our study suggests that the addition of RM on top of HFNC may be associated with decreased mortality in patients with severe COVID-19 hypoxemia.