• Federico Longhini, Lara Pisani, Ramona Lungu, Vittoria Comellini, Andrea Bruni, Eugenio Garofalo, Maria Laura Vega, Gianmaria Cammarota, Stefano Nava, and Paolo Navalesi.
• Anesthesia and Intensive Care, Sant'Andrea Hospital, ASL VC, Vercelli, Italy.
• Crit. Care Med. 2019 Jun 1; 47 (6): e506-e511.

ObjectivesAssessing gas exchange, diaphragm function, respiratory rate, and patient comfort during high-flow oxygen therapy and standard oxygen at the time of noninvasive ventilation discontinuation.DesignRandomized crossover physiologic study.SettingTwo ICUs.PatientsThirty chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure receiving noninvasive ventilation greater than 24 hours.InterventionsAll 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 ResultsDiaphragm 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).ConclusionsAt 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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