Table 2.

Risk of bias assessment of the included studies per outcome. D1: randomization process, D2: deviations from the intended interventions, D3: missing outcome data, D4: measurement of the outcome, D5: selection of the reported results, HFNC high-flow nasal cannula, NIV: non-invasive ventilation.

Study	Outcome	D1	D2	D3	D4	D5	Overall
APP
Ehrmann et al. [28]	Intubation or death at 28 days
Ehrmann et al.	Mortality rate at 28 days
Ehrmann et al.	Need for intubation within 28 days
Ehrmann et al.	Hospital length of stay (censored at 28 days)
Ehrmann et al.	Occurrence of skin lesions
Ehrmann et al.	Weaning of HFNC (time to event)
Rosén et al. [29]	Mortality rate at day 30
Rosén et al.	Need for intubation within 30 days
Rosén et al.	Occurrence of skin lesions
Rosén et al.	Hospital length of stay (censored at 30 days)
Rosén et al.	Days free of HFNC
HFNC vs. NIV
Grieco et al. [26]	Mortality rate at 28 days/60 days
Grieco et al.	In-hospital mortality
Grieco et al.	Intubation up to day 28
Grieco et al.	Respirator-free days at 30 days
Grieco et al.	Hospital length of stay
Grieco et al.	Adverse events
Perkins et al. [25]	Intubation or death at 30 days
Perkins et al.	In-hospital mortality
Perkins et al.	Mortality rate at 30 days
Perkins et al.	Hospital length of stay
Perkins et al.	Intubation up to day 30
Perkins et al.	Serious adverse events
Perkins et al.	Adverse events
Nair et al. [27]	In-hospital mortality
Nair et al.	Intubation rate at 7 days
Nair et al.	Intubation or death
Nair et al.	Hospital length of stay

low risk, some concerns, high risk.