Physiological Comparison of High-Flow Nasal Cannula and Helmet Noninvasive Ventilation in Acute Hypoxemic Respiratory Failure

RATIONALE: High-flow nasal cannula (HFNC) and helmet noninvasive ventilation (NIV) are used for the management of acute hypoxemic respiratory failure. OBJECTIVES: Physiological comparison of HFNC and helmet NIV in hypoxemic patients. MEASUREMENTS: Fifteen hypoxemic patients with PaO2/FiO2<200 mmHg received helmet NIV (PEEP≥10 cmH2O, pressure support=10-15 cmH2O) and HFNC (50 liters/minute) in randomized cross-over order. Arterial blood gases, dyspnea and comfort were recorded. Inspiratory effort was estimated by esophageal pressure (PES) swings. PES simplified pressure-time product and transpulmonary pressure swings were measured. MAIN RESULTS: As compared to HFNC, helmet NIV increased PaO2/FiO2 (median [interquartile range]: 255 mmHg [140-299] vs. 138 [101-172], p=0.001) and lowered inspiratory effort (7 cmH2O [4-11] vs. 15 [8-19], p=0.001) in all patients. Inspiratory effort-reduction by NIV was linearly related to inspiratory effort during HFNC (r=0.84, p<0.001). Helmet NIV reduced respiratory rate (24 breaths/minute [23-31] vs. 29 [26-32], p=0.027), PES simplified pressure-time product (93 cmH2O*sec*min-1 [43-138] vs. 200 [168-335], p=0.001) and dyspnea (visual analog scale 3 [2-5] vs. 8 [6-9], p=0.002), without affecting PaCO2 (p=0.80) and comfort (p=0.50). In the overall cohort, transpulmonary pressure swings were not different between treatments (NIV 18 cmH2O [14-21] vs. HFNC 15 [8-19], p=0.11), but patients exhibiting lower inspiratory effort on HFNC experienced increases in transpulmonary pressure swings with helmet NIV. Higher transpulmonary pressure swings during NIV were associated with subsequent need for intubation. CONCLUSION: As compared to HFNC in hypoxemic respiratory failure, helmet NIV improves oxygenation, reduces dyspnea, inspiratory effort and simplified pressure-time product, with similar transpulmonary pressure swings, PaCO2 and comfort.