Oxygen used in the medical setting is separated using several different methods including chemical reaction and fractional distillation. This oxygen is then either used immediately or stored for future use.
The main sources of oxygen therapy include:
- Liquid storage - Liquid oxygen is stored in tanks which are kept at a chilled temperature until the oxygen is needed. It is then boiled at a temperature of 90.188 K (−182.96 °C) and oxygen is emitted in the form of gas. This method is widely used in hospitals and other settings.
- Compressed gas - Oxygen gas can also be stored as compressed gas in a gas cylinder. This is a convenient storage method that eliminates the need for refrigeration. Large oxygen cylinders can provide a flow rate of 2 litres per minute over a period of two days. Smaller, portable cylinders that last around 4 to 6 hours when used with a conserving regulator, are also available. The regulator senses the patient’s respiration rate and adjusts the oxygen pulse accordingly.
- Instant usage - An electrically powered device called an oxygen concentrator can be used to generate enough oxygen for a patient to use immediately. These devices are widely used as home oxygen therapy tools or portable devices that can provide an instant oxygen supply, without the need for bulky cylinders.
Oxygen therapy may be given as an acute therapy or may be used in the home management of long-term illnesses. Before long-term oxygen therapy is prescribed, the patient undergoes a detailed examination to assess their suitability for the therapy. This involves measuring the amount of oxygen present in their blood, which can be achieved using a sample of arterial blood. An approximate blood oxygen concentration can also be obtained using oxygen sensors attached to the earlobe, wrist or finger. This is referred to as a pulse oximetry test. The breathing pattern is also assessed using a device called a spirometer.