Predictors of CPAP outcome in hospitalised COVID-19 patients

Introduction: Throughout March - April 2020, many patients with COVID-19 presented to Southend University Hospital with Acute Hypoxaemic Respiratory Failure (AHRF). Patients were managed in a Specialist Respiratory High Dependency Unit. We present our experience on the usage of continuous positive airway pressure (CPAP) therapy and possible indicators of its success in this patient group. Methods: Data from patients (n=89) requiring mechanical ventilation during the months of March to April 2020, were retrospectively collected and analysed. 37 patients received IMV (Invasive Mechanical Ventilation) without a CPAP trial beforehand. 52 patients underwent a CPAP trial, of which 21 patients successfully avoided intubation and ITU admission. Results: The 52 patients, prior to receiving CPAP had significant respiratory failure as evidenced by a low PaO2: FiO2 (PFR) (mean +/- SD 123 +/- 60 mmHg) and mean SpO2:FiO2 (SFR) (mean +/- SD: 140+/- 50). The main indicators of CPAP success were: higher SFR before and after CPAP, lower respiratory rate (RR) , lower Neutrophil to Lymphocyte ratio (NLR) and higher PFR prior to CPAP. Discussion: CPAP proved successful in 40% of COVID-19 patients presenting with AHRF. SFR, PFR, RR and NLR are predictors of such success. SFR can be used for effective real time monitoring of patients before and after CPAP to identify likelihood of success. Based on our results, we have suggested a modified CPAP management protocol in COVID-19. These findings can guide future studies and will allow improved triage of patients to either CPAP or IMV, in the event of a future COVID peak.