Long-term oxygen therapy:
Long-term oxygen therapy (LTOT) reverses hypoxaemia. A trial that compared LTOT with no oxygen therapy in patients with COPD and severe hypoxaemia (arterial oxygen tension (PaO2) ⩽55 mmHg) found that LTOT improved survival [191], whereas another trial that compared oxygen administered 19 h per day with oxygen administered 12 h per day found that the longer duration improved survival [192]. In contrast, a trial that compared LTOT with no oxygen therapy in patients with COPD and moderate hypoxaemia (PaO2 ⩽69 mmHg) found no effect on survival, regardless of the duration used per day [193]. The evidence has important limitations: the trials included relatively few patients and events (only 370 patients and 164 deaths, collectively), there was a paucity of women enrolled in the trials, and two of the three trials were conducted more than 30 years ago. A trial that compared nocturnal oxygen therapy (as opposed to continuous oxygen therapy) with no nocturnal oxygen therapy in patients with COPD and hypoxaemia found no effect on survival [194].