A Skeptical Perspective on High-Flow Nasal Cannula in the Treatment of Acute Hypoxemic Respiratory Failure.

The delivery of oxygen, whether as treatment for hypoxemia or supportive adjunct in shock or surgery, is a mainstay of modern medical therapy, yet conventional oxygen therapy, delivered either by nasal cannula or face mask, remains limited by the high oxygen delivery demand of the acute and critically ill patient. By employing a tight fitting mask or mask-like interface, noninvasive ventilation (NIV) overcomes these limitations and has been shown to improve outcomes in acute-on-chronic respiratory failure1 or cardiogenic pulmonary edema (congestive heart failure),2 albeit at the expense of comfort and patient compliance. Enter the high-flow nasal cannula (HFNC), a device not only capable of delivering high flow (up to 60 L/min) of heated and humidified gas through wide-bore nasal prongs, but also proficient at counteracting the limitations of conventional oxygen delivery devices.3 A touted advantage is comfort, probably a result of the combination of the physical characteristics of the device, and a reduction in desiccation commonly associated with the cold, dry air flow of conventional oxygen therapy. Nonetheless, the evidence for the use of HFNC to date has been conflicting and has been derived from highly screened and specific patient populations, limiting the ability to provide generalized treatment recommendations for its use by the acute care respiratory therapist or practitioner in the patient with hypoxemic failure (Table 1). Although it remains the growing perception that HFNC represents a reasonable therapeutic alternative for situations where conventional oxygen delivery and NIV fail to provide adequate symptom relief of acute-on-chronic respiratory failure,4,5 high quality clinical investigations of the efficacy of HFNC in the critical care arena remain lacking. A recent multi-center, randomized, controlled trial by Frat et al6 explored a more prominent role for HFNC as first-line therapy in acute, non-hypercapnic hypoxemia. Although no difference in the primary end point of intubation rate was found, subjects receiving HFNC experienced more ventilator-free days and a lower mortality when compared with subjects that received conventional oxygen therapy or NIV. However, the limited patient population, comparatively disparate mortality in the shock subgroups, and the non-protective ventilation strategy (average tidal volume [VT] in excess of 9 mL/kg) in the NIV group preclude a definitive conclusion from these results.