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

Abstract

<b>Rationale:</b> High-flow nasal cannula (HFNC) and helmet noninvasive ventilation (NIV) are used for the management of acute hypoxemic respiratory failure.<b>Objectives:</b> Physiological comparison of HFNC and helmet NIV in patients with hypoxemia.<b>Methods:</b> Fifteen patients with hypoxemia with Pa_O₂/Fi_O₂ < 200 mm Hg received helmet NIV (positive end-expiratory pressure ≥ 10 cm H₂O, pressure support = 10-15 cm H₂O) and HFNC (50 L/min) in randomized crossover 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.<b>Measurements and Main Results:</b> As compared with HFNC, helmet NIV increased Pa_O₂/Fi_O₂ (median [interquartile range]: 255 mm Hg [140-299] vs. 138 [101-172]; <i>P</i> = 0.001) and lowered inspiratory effort (7 cm H₂O [4-11] vs. 15 [8-19]; <i>P</i> = 0.001) in all patients. Inspiratory effort reduction by NIV was linearly related to inspiratory effort during HFNC (<i>r</i> = 0.84; <i>P</i> < 0.001). Helmet NIV reduced respiratory rate (24 breaths/min [23-31] vs. 29 [26-32]; <i>P</i> = 0.027), Pes-simplified pressure-time product (93 cm H₂O ⋅ s ⋅ min^-1 [43-138] vs. 200 [168-335]; <i>P</i> = 0.001), and dyspnea (visual analog scale 3 [2-5] vs. 8 [6-9]; <i>P</i> = 0.002), without affecting Pa_CO₂ (<i>P</i> = 0.80) and comfort (<i>P</i> = 0.50). In the overall cohort, transpulmonary pressure swings were not different between treatments (NIV = 18 cm H₂O [14-21] vs. HFNC = 15 [8-19]; <i>P</i> = 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.<b>Conclusions:</b> As compared with HFNC in hypoxemic respiratory failure, helmet NIV improves oxygenation, reduces dyspnea, inspiratory effort, and simplified pressure-time product, with similar transpulmonary pressure swings, Pa_CO₂, and comfort.