What is Oxygen?
Oxygen is a colourless, odourless gas. It is present in the atmosphere at a concentration of approximately 21%. It is a vital part of the body's production of energy; the process of aerobic metabolism produces energy and carbon dioxide from glucose and oxygen. Oxygen is transported around the body in red cells in the cells haemoglobin)

Oxygen in its natural state (O2) is highly flammable and should be treated with great respect. However, in atmospheric concentration it will support combustion but not to a dangerous level.

Oxygen in pure form is a prescription only medicine (POM) and as such can only be given by qualified persons and its use MUST be recorded

Oxygen and Shock
Shock is defined as "inadequate tissue perfusion" since virtually all injuries will involve shock in some way, oxygen is required.
A typical trauma victim will be given oxygen at a high flow rate of 15 litres per minute via a non-rebreather mask (for spontaneously breathing casualties) or a bag and mask (BMV) with reservoir (for non-breathing casualties) which can deliver concentrations of oxygen close to 100%.

Contra-Indications
People who suffer from such diseases as chronic bronchitis or emphysema, known as Chronic Obstructive Airway Diseases (COADs) are the main contra-indicators of high-flow oxygen. The body normally triggers respiration automatically when the chemoreceptors detect higher levels of carbon dioxide. COAD sufferers get used to high concentrations of carbon dioxide and so their chemoreceptors become useless.

The body has a backup system; the baroreceptors which trigger breathing when a low level of oxygen is detected. When a casualty relies on their baroreceptors, their breathing is said to be controlled by "hypoxic drive". Giving a hypoxic drive casualty high levels of oxygen can remove the hypoxic drive and so the casualty simply will not breathe any more! COAD sufferers should therefore only be given oxygen at concentrations of 28% or less.
However, when they are not breathing anyway this is not important.

The other contra-indications are paraquat poisoning (because oxidised paraquat is more poisonous than the straight substance) and new-born babies -- too much oxygen can make them go blind, though again a respiratory arrest means that you would ignore this.
Oxygen should not be given to someone who is hyperventilating, although it is import to distinguish between hyperventilation and an increased respiratory rate due to Trauma. Hyperventilation should be treated by getting someone too re-breath their expired air from a paper bag.

Oxygen Equipment
Oxygen comes in three main cylinder sizes, each cylinder is pressurised to 2000psi or 137 bar.

The main parts of the equipment to identify are:

The cylinder with (Black with a white shoulder)
Flow controller (Usually allows flow rates from 1 to 15 litres per minute.)
Flow Gauge (Displays the flow rate achieved)
Pressure Gauge (Displays how much oxygen is left in the cylinder, though the cylinder needs to be open for this to work.)
Cylinder Key (Attaches to the top of the cylinder and twists to open or close the cylinder.)
Assembly (All the oxygen measuring and controlling kit which attaches to the cylinder.)

Leaks
If you suspect a leak is present in an oxygen system the affected area should be painted with soapy water and observed for bubbles.

When assembling equipment you should:

1/ Remove the plastic seal from the cylinder outlet if it is a new cylinder.
2/ Check that the cylinder and its outlet are undamaged.
3/ Ease open the cylinder valve while facing the outlet away from you to blow any dust out of the outlet. Close the cylinder again.
4/ Check that the fittings on the cylinder and assembly are compatible. Inspect the rubber seal (the "bodok" seal) on the assembly for signs of wear.
5/ Attach the assembly, and check that it is secure.
6/ Ensure that the flow controller is in the "off" position.
7/ Ease open the cylinder valve and check the contents gauge.
8/ Open the flow controller to check that oxygen is flowing freely, then turn off.

Note that the "bodok" seal is the main failure point of oxygen equipment.

Dangers
?You should never let oil or grease come into contact with outlet valves or associated equipment
?Don't let cylinders run empty
?Do not allow anyone to smoke or have naked flame near oxygen equipment, especially when in use.

Giving Oxygen
When giving oxygen to a spontaneously breathing casualty, you have the following options for giving oxygen:

Venturi - mask Delivers a variable rate of oxygen dependant on Mask Type

Non-rebreather mask
Has an extra bag on the front. This bag should be filled (by blocking the exit valve) before it is put on the casualty. Delivers 100% oxygen at 15 litres per minute

If the casualty is not breathing, your options are:
Pocket mask with oxygen inlet (Delivers approximately 40% oxygen at full flow)
Bag and mask with oxygen (Delivers approximately 60% oxygen at full flow)
Bag and mask with oxygen reservoir (Delivers practically 100% oxygen at full flow)
Hence the amount of oxygen delivered to a patient is a combination of the flow rate and Mask type.