Abstract
Oxygen was the rst treatment shown to increase survival in patients with chronic obstructive pulmonary disease (COPD). Current recommendations for the prescription of continuous domiciliary oxygen therapy (CDO) are based on the results of 2 clinical trials published over 30 years ago: the Nocturnal Oxygen Therapy Trial (NOTT) and the Medical Research Council (MRC) study. 1,2 CDO is indicated in patients with COPD and resting PaO2 �55 mmHg or resting PaO2 between 56 and 59 mmHg with evidence of chronic pulmonary hypertension or polycythemia. Based on the hypothesis that the benecial effect of oxygen is a result of the correction of hypoxemia, irrespective of the cause, this indication has been extended by analogy to chronic respiratory failure caused by other respiratory (idiopathic pulmonary brosis, cystic brosis, etc.) and non-respiratory diseases (heart failure). However, the effectiveness of continuous oxygen therapy on survival in these other disease entities has not been demonstrated, and studies justifying indication in these cases are required. 3 In contrast with the results of the MRC or NOTT clinical trials, supplementary oxygen has not been shown to improve survival in patients with COPD and moderate hypoxemia. 4 However, these studies have been criticized for reporting a small number of patients, an inappropriately short study period and inadequate average daily administration of oxygen–approximately 13.5 h, clearly insufcient for showing effects on mortality. It is known, for example, that patients with COPD and chronic respiratory failure receiving CDO have a rebound effect, with pulmonary vascular resistance increasing when oxygen is suspended for periods as short as 3 h a day. Moreover, it is clear that the mortality rate in COPD patients with comorbidities is higher. Nevertheless, none of the studies analyzing the effects of CDO evaluate the inuence of comorbidities in general or of cardiovascular disease in particular. It is currently unclear if continuous oxygen therapy reduces metabolic and/or cardiovascular death in hypoxemic COPD patients. Current guidelines do not provide any indications for “pure” patients (with no associated comorbidities), and the therapeutic effects of CDO are analyzed in groups that are poorly representative of COPD patients. 5
Published Version
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