Boiling point -182°C
Melting point -218°C
Critical temperature -119°C
Critical pressure 50 bar
Measurement of Oxygen
Various means are used to measure O2, depending on the sample type.
Mixture of gases
Dissolved in blood
Effects of oxygen
An improvement of all cardiovascular parameters will be seen if oxygen is used to correct hypoxaemia. However prolonged administration of 100% O2 will slightly reduce cardiac output and cause coronary vasoconstriction. It causes a fall in pulmonary vascular resistance and pulmonary artery pressure.
In healthy individuals high oxygen concentrations will cause mild respiratory depression. However a patient who is truly dependant on a hypoxic drive to maintain respiration, even a modest concentration of O2 could prove fatal.
O2 toxicity is caused by free radicals. These affect the nervous system resulting in anxiety, nausea and seizures when the partial pressure exceeds 200kPa. The alveolar capillary membrane undergoes lipid peroxidation and regions of lung may collapse.
Neonates may develop Retinopathy of Prematurity (retrolental fibroplasias).
Vascularisation of the fetal retina is not complete until term. Retinopathy of prematurity is a condition of premature babies in whom the peripheral retina is avascular. Those vessels present are very sensitive to oxygen and the terminal branches may constrict if levels are too high. In the early stages, the changes are reversible and normal development may ensue. Later, however, new vessels begin to proliferate from the constriction sites into the vitreous. They become covered in fibrous tissue so forming a fibrovascular membrane behind the lens. A tractional retinal detachment may occur. In severe cases, there may be impaired vision, large refractive errors particularly myopia, strabismus and even blindness. The condition is usually bilateral.