FIGURE 1.

Recommended algorithm for high-flow nasal cannula use in acute hypoxaemic respiratory failure in immunocompetent or immunocompromised patients. ^#: arterial oxygen tension (P_aO2)/inspiratory oxygen fraction (F_iO2) <300 (patients with arterial carbon dioxide tension (P_aCO2) >45 mmHg and pH <7.35 are excluded); ^¶: systolic arterial blood pressure <90 mmHg despite adequate fluid administration; ⁺: the rationale for change in nasal high flow (NHF) settings are as follows. 1) Flow rate could be adjusted downwards by 5–10 L·min⁻¹ per 1–2 h if none of the negative prognostic factors are present. However, if targets of arterial oxygen saturation measured by pulse oximetry (S_pO2) and respiratory rate are not achieved, while the flow rate is <60 L·min⁻¹, increase of flow rate by 5–10 L·min⁻¹ is preferred to raising F_iO2; 2) increase in F_iO2 causes increases in P_aO2 and S_pO2; 3) temperature can be set at 37°C or lower (31–34°C), based on the patient's comfort; ^§: haemodynamic instability is defined by heart rate >140 beats·min⁻¹ or change >20% from baseline and/or systolic arterial blood pressure >180 mmHg, <90 mmHg or decrease >40 mmHg from baseline. MV: mechanical ventilation; SOT: standard oxygen treatment.