Physiologic Effects of High-Flow Nasal Cannula Oxygen in Critical Care Subjects

INTRODUCTION: High-flow nasal cannula (HFNC) can deliver heated and humidified gas (up to 100% oxygen) at a maximum flow of 60 L/min via nasal prongs or cannula. The aim of this study was to assess the short-term physiologic effects of HFNC. Inspiratory muscle effort, gas exchange, dyspnea score, and comfort were evaluated.

METHODS: Twelve subjects admitted to the ICU for acute hypoxemic respiratory failure were prospectively included. Four study sessions were performed. The first session consisted of oxygen therapy given through a high-F_IO2, non-rebreathing face mask. Recordings were then obtained during periods of HFNC and CPAP at 5 cm H₂O in random order, and final measurements were performed during oxygen therapy delivered via a face mask. Each of these 4 periods lasted ∼20 min.

RESULTS: Esophageal pressure signals, breathing pattern, gas exchange, comfort, and dyspnea were measured. Compared with the first session, HFNC reduced inspiratory effort (pressure-time product of 156.0 [119.2–194.4] cm H₂O × s/min vs 204.2 [149.6–324.7] cm H₂O × s/min, P < .01) and breathing frequency (P < .01). No significant differences were observed between HFNC and CPAP for inspiratory effort and breathing frequency. Compared with the first session, P_aO2/F_IO2 increased significantly with HFNC (167 [157–184] mm Hg vs 156 [110–171] mm Hg, P < .01). CPAP produced significantly greater P_aO2/F_IO2 improvement than did HFNC. Dyspnea improved with HFNC and CPAP, but this improvement was not significant. Subject comfort was not different across the 4 sessions.

CONCLUSIONS: Compared with conventional oxygen therapy, HFNC improved inspiratory effort and oxygenation. In subjects with acute hypoxemic respiratory failure, HFNC is an alternative to conventional oxygen therapy. (ClinicalTrials.gov registration NCT01056952.)