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Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Background: Supplemental oxygen is a recommended therapy option in stable hypoxemic COPD patients. Often, supplemental oxygen is provided by continuous flow (CF). However, demand oxygen delivery systems (DODS) that provide an oxygen bolus only during inspiration have gained increasing use as they prolong oxygen cylinder life (beside battery life). However, there is a lack of evidence if different DODS and CF devices are equivalent., Methods: Seventy hypoxemic COPD patients (FEV 1 32 ± 9% predicted, PaO 2 56±7 mmHg) on long-term oxygen therapy were included in this prospective single-blinded, randomized cross-over trial. Following an initial incremental shuttle walk test, patients performed 3 endurance shuttle walk tests (ESWT) at 85% of their maximum walking speed in random order with: (A) CF (ESWT-CF), (B) a DODS based on liquid oxygen (ESWT-DL) and (C) an DODS oxygen concentrator (ESWT-DC). The primary outcome was oxygen saturation (SpO 2 ) at ESWT isotime. Secondary outcomes were total ESWT duration, heart rate (HR) and breathing frequency (BF) at isotime and dyspnea at end-exercise., Results: SpO 2 at ESWT isotime was not clinically different between devices: 90 ± 4% (CF), 89 ± 5% (DL) and 90 ± 5% (DC). However, 20% of the patients showed a ≥4% lower oxygen desaturation while using a DODS device. Secondary outcomes were similar under the three conditions., Conclusion: Oxygen supplementation via DODS (based on liquid oxygen or as a concentrator) yielded comparable physiological effects during standardized walking in stable hypoxemic COPD patients like CF. However, 20% of patients showed a clinically relevant lower oxygen saturation while using a DODS device. Therefore, we suggest individual testing of oxygen saturation of DODS suitability., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Background: Long-term oxygen therapy (LTOT) is an established treatment for patients with chronic hypoxemia. Its scientific basis is derived mainly from two trials from the early 1980s that showed a survival advantage for patients with chronic obstructive pulmonary disease (COPD) treated with LTOT. Robust data are not available for other diseases associated with hypoxemia., Methods: This review is based on pertinent publications retrieved by a selective search in PubMed., Results: The use of LTOT for 15 to 16 hours per day (or, better, 24 hours per day) is recommended in current guidelines for patients with chronic hypoxemia (PaO2 ≤ 55 mm Hg) because this treatment was found to be associated with a lower mortality rate compared to no LTOT (33% vs. 55%, p <0.05) based on data from the early 1980s. In the short term, oxygen administration to a hypoxemic patient can improve oxygen saturation by nine percentage points and improve physical performance to a clinically relevant extent (6-minute walking test: + 37 m, p <0.001). The available data do not support the use of LTOT for normoxemic patients. LTOT should only be administered for strict indications, in accordance with the guidelines, and only in a form suitable for the individual patient. Skin burns can occur as a side effect of LTOT because of contact explosions with any type of fire., Conclusion: The acquisition of further robust data would be desirable, particularly with respect to patient-relevant outcome parameters including quality of life, performance status, and mortality. Moreover, the German guidelines on oxygen therapy need to be updated.