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Appropriate use of oxygen in acute medicine

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Oxygen use in acute medicine requires regular monitoring to maintain saturation levels within the prescribed range

It may seem intuitive that oxygen is “good”, so, for the ill or even just distressed, more must be better! However, the evidence for this common clinical approach is at best anecdotal and mainly cultural.1 In fact, both (very) low and high oxygen levels are bad and, indeed, inappropriate use of oxygen in acute medical treatment may be harmful.24 Hyperoxia leads to vasoconstriction, and oxygen uptake actually falls.5 Overly vigorous prehospital use of oxygen may well be a significant contributor to death in common acute medical conditions.6

When is a human truly hypoxaemic?

Technically, hypoxaemia occurs when tissues begin to produce lactic acid because of anaerobic metabolism. In the 1960s, a study showed that heart muscle in healthy people did not produce lactic acid until the circulating blood oxygen saturation level was in the region of 50% (equivalent to a partial pressure of less than 30 mmHg), but in people with ischaemic heart disease, oxygen saturation levels were usually in the range of 70%–79%, occasionally as high as 85%, (around 55 mmHg) when cardiac lactate was produced.5