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What about High Flow?
A high-flow nasal cannula (HFNC) is a nasal cannula that has been designed to allow for much higher flow rates than a traditional nasal cannula (up to 70 L per minute) and precise adjustment of the FiO₂. Most models also offer heating of the air and supplemental humidity because of the high flow rates.

Some manufacturers are advertising HFNC as a “safe and effective [mode of] noninvasive ventilation” (NIV).¹ Is this true? Somewhat. HFNC is absolutely safe and effective for patients with a primary problem of oxygenation (acute hypoxemic respiratory failure). HFNC can provide up to 100 percent FiO₂ and a small amount of positive end-expiratory pressure (PEEP) because of the high flow rates. That PEEP, however, is dependent on a variety of factors, including whether the patient has their mouth open, and is therefore much less reliable than the PEEP delivered by a traditional facemask using NIV.² Because of this, HFNC can be less effective for patients who are dependent on PEEP, such as those with atelectasis, pulmonary edema, or acute respiratory distress syndrome (ARDS).

In contrast, HFNC falls short with patients with a primary disorder of ventilation (acute hypercapnic respiratory failure). HFNC offers no real control over respiratory rate and tidal volume, the two components of minute ventilation. As such, it cannot truly augment problems of ventilation and is generally inferior to traditional NIV.³

When I polled my EM Critical Care group to see whether anyone was using HFNC in place of traditional facemask ventilation, the response was “no,” except from Kyle Gunnerson, MD, FCCM, who wrote that he only used it “specifically for CO₂ washout for really tenuous patients who are pH sensitive with bad right heart failure and we want to avoid positive pressure for whatever reason.” So perhaps for very selected patients, yes, but for most patients, I’ll be reaching for a facemask and traditional NIV instead.