OBJECTIVES: Assessing gas exchange, diaphragm function, respiratory rate, and patient comfort during high-flow oxygen therapy and standard oxygen at the time of noninvasive ventilation discontinuation. DESIGN: Randomized crossover physiologic study.Two ICUs. PATIENTS: Thirty chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure receiving noninvasive ventilation greater than 24 hours. INTERVENTIONS: All patients underwent five 30-minute trials, the first, third, and fifth trial in noninvasive ventilation, whereas the second and fourth were randomly conducted with either standard oxygen and high-flow oxygen therapy. MEASUREMENTS AND MAIN RESULTS: Diaphragm displacement and thickening fraction were determined by sonographic evaluation at the end of each trial. Arterial blood gases, respiratory rate, and patient comfort were also assessed. PaCO2 (p = 0.153) and pH (p = 0.114) were not different among trials, while PaO2 was greater in noninvasive ventilation than with both standard oxygen (p ≤ 0.005) and high-flow oxygen therapy (p ≤ 0.001). The diaphragm displacement was no different among trials (p = 0.875), while its thickening fraction was greater with standard oxygen, compared with high-flow oxygen therapy and all noninvasive ventilation trials (p < 0.001 for all comparisons), without differences between high-flow oxygen therapy and noninvasive ventilation. Respiratory rate also increased with standard oxygen, compared with both high-flow oxygen therapy (p < 0.001) and noninvasive ventilation (p < 0.01). High-flow oxygen therapy improved comfort, compared with standard oxygen (p = 0.004) and noninvasive ventilation (p < 0.001). CONCLUSIONS: At the time of noninvasive ventilation interruption, PaCO2 and diaphragm displacement remained unchanged regardless of the modality of oxygen administration. However, although standard oxygen resulted in a remarkable increase in diaphragm thickening fraction, high-flow oxygen therapy allowed maintaining it unchanged, while improving patient comfort.
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