BACKGROUND: Differences in oxygen delivery between portable oxygen concentrators (POC) and liquid oxygen (LO) portable units, pose a question if POCs are equally effective as LOs in reducing exercise-induced hypoxaemia. DESIGN: Randomized, single-blind clinical trial. PATIENTS: Thirteen COPD patients (means: age 66 +/- 11 year, FEV1 35.2 +/- 13.7% predicted) and respiratory failure (means: PaO2 52 +/- 5 mmHg, PaCO2 51.3 +/- 7.5 mmHg). METHODS: All patients underwent a series of 6-min walk tests (6MWT) carried out in random order among one of the three devices: POC, LO cylinder and cylinder with compressed air (CA). Oxygen supplementation was 3 lpm for LO and an equivalent to 3 lpm in a pulse flow system for POC. RESULTS: The mean SpO2 was equally improved at rest: 92.9 +/- 2.8% with POC and 91.7 +/- 2.0% with LO compared to CA-87.8 +/- 2.7% (POC and LO versus CA p < 0.05). POC and LO significantly improved oxygenation during 6MWT (mean SpO2 was 84.3 +/- 5% and 83.8 +/- 4.2%, respectively) compared to breathing CA-77.6 +/- 7.4%, p < 0.05. Mean 6MWT distance increased with LO (350 +/- 83 m) and POC (342 +/- 96m) when compared to CA (317 +/- 84 m), however, these differences were not statistically significant. Dyspnoea score assessed at the end of the exercise (Borg scale) was significantly lower when breathing oxygen (4.2 +/- 1.2 with POC and 4.1 +/- 1.7 with LO versus 5.4 +/- 1.9 with CA, p < 0.05). CONCLUSIONS: Effectiveness of oxygen supplementation from a POC did not differ from the LO source during 6MWT in COPD patients with respiratory failure. Oxygen at 3 lpm flow was not sufficient to prevent hypoxaemia during strenuous exercise.

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