Respective Effects of Helmet Pressure Support, Continuous Positive Airway Pressure, and Nasal High-Flow in Hypoxemic Respiratory Failure: A Randomized Crossover Clinical Trial.

The respective effects of positive end-expiratory pressure (PEEP) and pressure support delivered through the helmet interface in patients with hypoxemia need to be better understood. To assess the respective effects of helmet pressure support (noninvasive ventilation [NIV]) and continuous positive airway pressure (CPAP) compared with high-flow nasal oxygen (HFNO) on effort to breathe, lung inflation, and gas exchange in patients with hypoxemia (Pa/Fi ⩽ 200). Fifteen patients underwent 1-hour phases (constant Fi) of HFNO (60 L/min), helmet NIV (PEEP = 14 cm HO, pressure support = 12 cm HO), and CPAP (PEEP = 14 cm HO) in randomized sequence. Inspiratory esophageal (ΔP) and transpulmonary pressure (ΔP) swings were used as surrogates for inspiratory effort and lung distension, respectively. Tidal Volume (Vt) and end-expiratory lung volume were assessed with electrical impedance tomography. ΔP was lower during NIV versus CPAP and HFNO (median [interquartile range], 5 [3-9] cm HO vs. 13 [10-19] cm HO vs. 10 [8-13] cm HO;  = 0.001 and  = 0.01). ΔP was not statistically different between treatments. Pa/Fi ratio was significantly higher during NIV and CPAP versus HFNO (166 [136-215] and 175 [158-281] vs. 120 [107-149];  = 0.002 and  = 0.001). NIV and CPAP similarly increased Vt versus HFNO (mean change, 70% [95% confidence interval (CI), 17-122%],  = 0.02; 93% [95% CI, 30-155%],  = 0.002) and end-expiratory lung volume (mean change, 198% [95% CI, 67-330%],  = 0.001; 263% [95% CI, 121-407%],  = 0.001), mostly due to increased aeration/ventilation in dorsal lung regions. During HFNO, 14 of 15 patients had pendelluft involving >10% of Vt; pendelluft was mitigated by CPAP and further by NIV. Compared with HFNO, helmet NIV, but not CPAP, reduced ΔP. CPAP and NIV similarly increased oxygenation, end-expiratory lung volume, and Vt, without affecting ΔP. NIV, and to a lesser extent CPAP, mitigated pendelluft. Clinical trial registered with clinicaltrials.gov (NCT04241861).