In confirmed resting hypoxemia (oxygen partial pressure [pO2] ≤ 55 mm Hg) over a period of 4 weeks, long-term oxygen therapy (LTOT) can improve patients’ prognosis. Twenty-four percent of our blood gas analyses with LTOT indication had a pO2 of exactly 55 mm Hg.
In patients with moderate exercise-induced hypoxemia (pulse oximetry saturation [SpO2] 80–88%) and resting pO2 >55 mmHg, oxygen therapy, however, should be viewed critically. In our opinion, prescription of oxygen (O2) therapy is too liberal in Germany in this setting, and is frequently not reviewed properly. Exercise-induced hypoxemia (median minimal exercise SpO2 of 84%) with resting pO2 >55 mm Hg was found in 29% of the 575 patients with chronic obstructive pulmonary disease (COPD) referred to our center in the period from 2015 to 2018 for lung transplantation (median forced expiratory volume in 1 second of 22%). Sixty-three percent of this subgroup had a current O2 prescription (compare LOTT study: 33%).
The effects of oxygen administration in patients with isolated exercise-induced hypoxemia are below the minimal clinically important difference. Air flow alone can alleviate shortness of breath. In a meta-analysis, oxygen administration on exertion improved the 6-minute walking distance (6MWD) in COPD patients only by 18.8 m compared to placebo (compressed air) (1). In a meta-analysis of 16 studies on COPD patients with exercise-induced hypoxemia, dyspnea was reduced by oxygen administration only by 0.7 points on a scale from 0 to 10, compared to placebo (2). Moreover, in 84 patients with pulmonary fibrosis and isolated exercise-induced hypoxemia, quality of life improved with oxygen therapy by just 4% in a 4-week crossover study (oxygen administration versus no oxygen administration) and 6MWD only by 18.5 m, compared to compressed air (3). Oxygen therapy has no effect on survival in patients with isolated exercise-induced hypoxemia.
Oxygen therapy is costly and associated with side effects. In patients with isolated exercise-induced hypoxemia, home oxygen therapy should only be prescribed if a mobile patient describes severe exercise-induced dyspnea, oxygen compared to compressed air has a clinically important effect and the patient is willing to use oxygen therapy.
References
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