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Confusion and controversy continues over how much oxygen to give patients with chronic obstructive pulmonary disease (COPD) presenting with breathlessness. This article reviews the published literature dealing with this topic, identifies gaps in the debate that have not been addressed and makes recommendations for future research needed to resolve this issue. Based on this review guidelines for oxygen therapy, based on the best evidence currently available, are then constructed and presented in a subsequent issue.
Medline from 1966 to 2000 was searched for articles on oxygen therapy and carbon dioxide retention. In addition, colleagues in chest medicine, emergency medicine and intensive care medicine identified reports presented at recent scientific research meetings. As much of the literature on oxygen therapy in COPD was published before 1966, all references made in the literature obtained were examined. Any reports subsequently felt to be relevant, were then also obtained and analysed until it was felt that a complete search had been made.
It is useful to consider the published literature in the light of a series of clinically relevant questions:
What are the perceived dangers of hypoxia and at what Pao2 does it become dangerous?
Significant hypoxia for more than four to six minutes will cause sudden cardiorespiratory arrest and irreversible damage to the brain and other vital organs. However, it is not known how much hypoxia is required to cause this.
In 1908, Boycott and Haldane showed that a Pao2 below 45 mm Hg resulted in mental difficulties and memory loss.1 Later it was found that consciousness was lost at a Pao2 of about 30 mm Hg.2,3 Hutchison et al, in 1964, commented on this but also noted that acclimatisation to hypoxia is possible, most notably in patients with COPD.4 Subsequent studies supported this finding and recorded very low Pao2 levels when these patients have acute exacerbations …
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