1. <chemistry> A colourless, tasteless, odorless, gaseous element occurring in the free state in the atmosphere, of which it forms about 23 per cent by weight and about 21 per cent by volume, being slightly heavier than nitrogen. Symbol O. Atomic weight 15.96.

It occurs combined in immense quantities, forming eight ninths by weight of water, and probably one half by weight of the entire solid crust of the globe, being an ingredient of silica, the silicates, sulphates, carbonates, nitrates, etc.

Oxygen combines with all elements (except fluorine), forming oxides, bases, oxyacid anhydrides, etc, the process in general being called oxidation, of which combustion is only an intense modification.

at ordinary temperatures with most substances it is moderately active, but at higher temperatures it is one of the most violent and powerful chemical agents known. It is indispensable in respiration, and in general is the most universally active and efficient element.

It may be prepared in the pure state by heating potassium chlorate. This element (called dephlogisticated air by Priestley) was named oxygen by Lavoisier because he supposed it to be a constituent of all acids. This is not so in the case of a very few acids (as hydrochloric, hydrobromic, hydric sulphide, etc), but these do contain elements analogous to oxygen in property and action. Moreover, the fact that most elements approach the nearer to acid qualities in proportion as they are combined with more oxygen, shows the great accuracy and breadth of Lavoisier's conception of its nature.

Pharmacologic action: Increases the supply of oxygen to ischaemic tissues. It is the most effective agent in emergency cardiac care.

Uses: Always administer oxygen during emergency cardiac care.

Dose: Nasal cannula with oxygen flow of 4 litres per minute provides FiO2 of about 30%. Nasal cannula with oxygen flow of 6-8 litres per minute provides FiO2 of 35-40%. Venturi mask can provide higher and more precise oxygen concentrations.

Potential complications: Ensure that oxygen is being delivered. Carefully check all connections. Oxygen toxicity develops only after several days of exposure to high FiO2. Increased FiO2 may cause hypoventilation in COPD patients dependent on hypoxic ventilatory drive. This is very rare and simply requires starting at lower FiO2, careful observation, and assisted ventilation if necessary.

Origin: F. Oxygene, from Gr. Sharp, acid + root of to be born. So called because originally supposed to be an essential part of every acid.

(17 Mar 2000)

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