Table 2.

Studies on the use of HFNC in Covid-19-related pneumonia. Legenda: n. of pts: number of patients; HFNC: high flow nasal cannulae; NPPV: non invasive positive pressure ventilation; n.r.: not reported; PaO2/FiO2: the ratio between arterial oxygen partial pressure and fractional concentration of inspired oxygen; RR: respiratory rate; NRB: non rebreathing mask; SO2/FiO2: the ratio between oxygen saturation and fractional concentration of inspired oxygen.

Study	Design	n. of pts	Technique	Failure %	Starting criteria	Failure predictors
Wang et al.	Retrospective	17	HFNC	41% (7 needed NIV, 2 of which Escalated to ETI)	NR	PaO2/FiO2 < 200 And not improving in 1-2 h; high RR and not improving in 1-2 h
Vianello et al.	Retrospective	28	HFNC	32% (needed NPPV) 17,8% (intubation)	PaO2/FiO2 < 300 and Inability to maintain SpO2 > 92% with a NRB mask	PaO2/FiO2 < 100 Higher CRP
Patel et al.	Retrospective	104	HFNC	35.58% (intubation) 14.44% (deaths) 7.69% (needed NPPV)	Need for O2 > 15 L/min	SO2/FiO2 < 100 Renal failure Fibrinogen < 450 mg/dl