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The respective effects of PEEP and pressure support delivered through the helmet interface in hypoxemic patients need to be better understood.To assess the respective effects of helmet pressure support (NIV) and continuous positive-airway pressure (CPAP) compared to high-flow nasal oxygen (HFNO) on effort to breathe, lung inflation and gas exchange in hypoxemic patients (PaO2/FiO2≤200).Fifteen patients underwent 1-hour phases (constant FiO2) of HFNO (60 L/min), helmet NIV (PEEP=14 cmH2O, pressure support=12 cmH2O) and CPAP (PEEP=14 cmH2O) in randomized sequence.Inspiratory esophageal (ΔPES) and transpulmonary pressure (ΔPL) 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.ΔPES was lower during NIV vs. CPAP and HFNO (5[3-9] cmH2O vs. 13[10-19] vs. 10[8-13], p=0.001 and p=0.01). ΔPL was not statistically different between treatments. PaO2/FiO2 ratio was significantly higher during NIV and CPAP vs. HFNO (166[136-215] and 175[158-281] vs. 120[107-149], p=0.002 and p=0.001). NIV and CPAP similarly increased VT vs. HFNO (mean change: 70%[95%CI: 17-122], p=0.02; 93% [95%CI: 30-155], p=0.002) and end-expiratory lung volume (mean change: 198%[95%CI: 67-330], p=0.001; 263%[95%CI: 121-407], p=0.001), mostly due to increased aeration/ventilation in dorsal lung regions. During HFNO, 14/15 patients had pendelluft involving10% of VT: pendelluft was mitigated by CPAP and further by NIV.Compared to HFNO, helmet NIV, but not CPAP, reduced ΔPES. CPAP and NIV similarly increased oxygenation, end-expiratory lung volume and VT, without affecting ΔPL. NIV, and to a lesser extent, CPAP, mitigated pendelluft. Clinical trial registration available at www.gov, ID: NCT04241861.

In non-COVID 19 acute hypoxemic respiratory failure, the entity of dyspnea has been associated with severity of hypoxemia, and represents a factor predicting noninvasive ventilation (NIV) failure, the need for endotracheal intubation and mortality [1].

BACKGROUND: The efficacy of noninvasive oxygenation strategies (NIOS) in treating COVID-19 disease is unknown. We conducted a prospective observational study to assess the rate of NIOS failure in subjects treated in the ICU for hypoxemic respiratory failure due to COVID-19. METHODS: Patients receiving first-line treatment NIOS for hypoxemic respiratory failure due to COVID-19 in the ICU of a university hospital were included in this study; laboratory data were collected upon arrival, and 28-d outcome was recorded. After propensity score matching based on Simplified Acute Physiology (SAPS) II score, age, P aO 2 /F IO 2 and P aCO 2 at arrival, the NIOS failure rate in subjects with COVID-19 was compared to a previously published cohort who received NIOS during hypoxemic respiratory failure due to other causes. RESULTS: A total of 85 subjects received first-line treatment with NIOS. The most frequently used methods were helmet noninvasive ventilation and high-flow nasal cannula; of these, 52 subjects (61%) required endotracheal intubation. Independent factors associated with NIOS failure were SAPS II score (P = .009) and serum lactate dehydrogenase at enrollment (P = .02); the combination of SAPS II score ≥ 33 with serum lactate dehydrogenase ≥ 405 units/L at ICU admission had 91% specificity in predicting the need for endotracheal intubation. In the propensity-matched cohorts (54 pairs), subjects with COVID-19 showed higher risk of NIOS failure than those with other causes of hypoxemic respiratory failure (59% vs 35%, P = .02), with an adjusted hazard ratio of 2 (95% CI 1.1–3.6, P = .01). CONCLUSIONS: As compared to hypoxemic respiratory failure due to other etiologies, subjects with COVID-19 who were treated with NIOS in the ICU were burdened by a 2-fold higher risk of failure. Subjects with a SAPS II score ≥ 33 and serum lactate dehydrogenase ≥ 405 units/L represent the population with the greatest risk.