Conventional oxygen therapy versus CPAP as a ceiling of care in ward-based patients with COVID-19: a multi-centre cohort evaluation

Abstract

Background: Continuous positive airway pressure (CPAP) therapy is commonly used for respiratory failure due to severe COVID-19 pneumonitis, including in patients deemed not likely to benefit from invasive mechanical ventilation (nIMV). Little evidence exists demonstrating superiority over conventional oxygen therapy, whilst ward-level delivery of CPAP presents practical challenges. We sought to compare clinical outcomes of oxygen therapy versus CPAP therapy in patients with COVID-19 who were nIMV.

Methods: This retrospective multi-centre cohort evaluation included patients diagnosed with COVID-19 who were nIMV, had a treatment escalation plan of ward-level care and clinical frailty scale ≤ 6. Recruitment occurred during the first two waves of the UK COVID-19 pandemic in 2020; from 1^st March to May 31^st, and from 1^st September to 31^st December. Patients given CPAP were compared to patients receiving oxygen therapy that required FiO₂ ≥0_.4 for more than 12 hours at hospitals not providing ward-level CPAP. Logistic regression modelling was performed to compare 30-day mortality between treatment groups, accounting for important confounders and within-hospital clustering.

Findings: Seven hospitals provided data for 479 patients during the UK COVID-19 pandemic in 2020. Overall 30-day mortality was 75.6% in the oxygen group (186/246 patients) and 77.7% in the CPAP group (181/233 patients). A lack of evidence for a treatment effect persisted in the adjusted model (adjusted odds ratio 0.84 95% CI 0.57-1.23, p=0.37). 49.8% of patients receiving CPAP-therapy (118/237) chose to discontinue it.

Interpretation: No survival difference was found between using oxygen alone or CPAP to treat patients with severe COVID-19 who were nIMV. A high patient-initiated discontinuation rate for CPAP suggests a significant treatment burden. Further reflection is warranted on the current treatment guidance and widespread application of CPAP in this setting.

Funding: L Pearmain is supported by the MRC (MR/R00191X/1). TW Felton is supported by the NIHR Manchester Biomedical Research Centre.

Keywords: COVID-19; Ceiling of care; Invasive mechanical ventilation; Non-invasive ventilation; Oxygen; nIMV.

Figure 1

30 day mortality unadjusted odds ratios (OR, left) of variables and final Generalised Estimating Equations (GEE) model with estimated 30-day mortality adjusted odds ratios (aOR, right). Variables coloured grey were not included in the final GEE model. An OR>1 represents increased occurrence of 30 day mortality. Abbreviations used: FiO₂, fraction of inspired oxygen; RR, respiratory rate; SpO₂, pulse oximetry; CRP, C-reactive protein; BMI, body mass index; CFS, clinical frailty scale. Blue variables were subsequently used in the final adjusted OR model.

Figure 2

a) 30-day survival curve analysis stratified by treatment (unadjusted) with log-rank test p-value. There was no censored data at any time-point, b) Box and whisker plot showing time from inclusion to discharge of survivors (days). Boxes are bound by the upper and lower quartiles, whilst whiskers are bounded by these ± 1.5x the interquartile range.