UMEM Educational Pearls


High flow nasal cannula (HFNC) is a valid option in the management of acute hypoxic respiratory failure (AHRF) without hypercapnia, as evidenced by multiple studies including the FLORALI trial. Failure of HFNC, however, may result in delayed intubation and worsened clinical outcomes. 

Factors predicting HFNC failure and subsequent intubation include:

  • Lack of RR improvement at 30 and 45 minutes after initation of HFNC
  • Lack of SpO2% improvement at 15, 30, and 60 minutes
  • Persistence of paradoxic breathing (thoracoabdominal dyssynchrony) at 15, 30, 60, and 120 minutes
  • Presence of additional organ system failure, especially hemodynamic (shock) or neurologic (depressed mental status)

Consider whether or not HFNC is appropriate in your patient with AHRF, and if you use it, reevaluate your patient to ensure improvement, or escalate their respiratory support. 


For patients with acute hypoxic respiratory failure without hypercapnia, the FLORALI trial demonstrated that high flow nasal cannula (HFNC) therapy increases ventilator-free days, reduces 90-day mortality, and is associated with better comfort and lower dyspnea severity when compared to conventional oxygen therapy and non-invasive ventilation (NIV). Failure of HFNC, however, may result in delayed intubation and worse clinical outcomes in patients with acute hypoxic respiratory failure. So how do we predict in the ED which patients are going to fail?

Sztrymf et al. evaluated patients placed on HFNC for nonhypercapneic acute hypoxic respiratory failure, who later went on to require endotracheal intubation. The cohort who failed HFNC had significantly:

-     higher RR at 30 & 45 minutes after initiation of HFNC

-     lower SpO2% at 15, 30, and 60 minutes

-     higher incidence of paradoxical breathing (thoracoabdominal dyssynchrony) at 15, 30, 60, and 120 minutes

In an observational study of patients with ARDS,* Messika et al. found that factors predicting HFNC failure included:

-     a higher Simplified Acute Physiology Score II (SAPS II; 46 v. 29, p=.001)

-     additional organ system failure (mostly hemodynamic or neurological)

-   trends towards lower PaO2:FiO2 ratios and higher RR

So don’t set it and forget it! Consider a different method of respiratory support if your patient has multi-organ system failure, especially if they are in shock or have altered mental status. If you do use HFNC, reevaluate your patient at 15 minutes and again at 30 minutes to make sure their respiratory rate and SpO2 have improved and that there is no paradoxic breathing (or it is resolving). If not, move on to NIV or invasive mechanical ventilation. 

*acute respiratory failure occurring within 1 week of known clinical insult with PaO2:FiO2 <300mmHg and bilateral opacities on chest x-ray not attributable to cardiac failure/volume overload



1.   Frat JP, Thille AW, Mercat A, et al. High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. N Engl J Med. 2015;372:2185–96.

2.   Sztrymf B, Messika J, Bertrand F, et al. Beneficial effects of humidified high flow nasal oxygen in critical care patients: a prospective pilot study. Intensive Care Med. 2011;37:1780–6.

3.   Messika J, Ben Ahmed K, Gaudry S, et al. Use of high-flow nasal cannula oxygen therapy in subjects with ARDS: a 1-year observational study. Respir Care. 2015;60(2):162-9.

4.   Hernandez G, Roca O, Colinas L. High-flow nasal cannula support therapy: new insights and improving performance. Crit Care. 2017;21(1):62.