Three Irishmen walk onto a respiratory ward. One says, "I'm dying for a fag!"...

What is it?

Oxygen is a rather important part of air, used for respiration in cells. Normal air is 21% oxygen. Giving patients higher amounts of oxygen can help them if their lungs are screwed, they don't have enough blood, or other problems.

Oxygen is technically a drug, and should be prescribed when used in hospitals, although often it isn't.

Why is it dangerous?

Normal people have a breathing rate based on how much CO₂ there is in their body. However, some patients with long term COPD (Type II respiratory failure) get a respiratory rate based on the amount of O₂ in their body; this is called hypoxic drive.

Thus, with these patients, start them on a maximum of 24-28% oxygen and then work up slowly if needed. In emergencies, just chuck it in anyway.

The other danger with oxygen therapy is that oxygen is highly flammable. Every doctor knows at least one story of a chap on oxygen who decides to have a sly fag, and wakes up ten minutes later on the floor with no eyebrows.

Who to give it to?

• Emergencies - Almost anybody with a severe emergency will benefit from being put on oxygen. Common situations where it is needed include shock, acute coronary syndrome, pulmonary embolism and anaphylaxis.
• COPD - patients with COPD, as long as managed taking into account patients with hypoxic drive, are helped by being put on long term O₂ therapy, as it has been shown to prevent them from getting pulmonary hypertension and right sided heart failure.
• Burns - Patients who have inhaled a lot of smoke get carbon monoxide joining with haemoglobin to form carboxyhaemoglobin. This prevents the blood from carrying around oxygen. High flow oxygen gets rid of the carboxyhaemoglobin much faster.