Fig. 1

Participant timeline. Patients in the medical intermediate COVID-19 cohort ward will be screened for eligibility according to the inclusion and exclusion criteria, given written and oral information and then asked for written informed consent. Secondary endpoints will be collected at 1 h, 24 h and 28 days from randomisation, when the primary endpoint of ventilator-free days will also be assessed. We plan to include 60 patients in each group and expect the HFNC group to have ~ 19.5 VFD and the Helmet CPAP group to have ~ 23.3 VFD at 28 days. The thickness of the lines corresponds to the expected patient density in intervention versus control group and treatment in ward versus intensive care and in patients who survive or die within 28 days from randomisation. Abbreviations: SpO2, peripheral oxygen saturation; FiO2 ratio, fractional inspired oxygen concentration; RR, respiratory rate; PEEP, positive expiratory end-pressure; NEWS, national early warning score; AE, adverse events; VFD, ventilator-free days (within 28 days); ICU, intensive care unit; CPAP, continuous positive airway pressure