<p>Oxygen is required for normal cell metabolism. Excessively high concentrations can cause oxygen toxicity such as lung damage or result in respiratory failure in those who are predisposed. Higher oxygen concentrations also increase the risk of fires, particularly while smoking, and without humidification can also dry out the nose. The target oxygen saturation recommended depends on the condition being treated. In most conditions a saturation of 94-98% is recommended, while in those at risk of carbon dioxide retention saturations of 88-92% are preferred, and in those with carbon monoxide toxicity or cardiac arrest they should be as high as possible. Air is typically 21% oxygen by volume while oxygen therapy increases this by some amount up to 100%.<br />
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The use of oxygen in medicine become common around 1917. It is on the&nbsp;World Health Organization&#39;s List of Essential Medicines, the most effective and safe medicines needed in a&nbsp;health system.</p>