Intended for healthcare professionals

Student Education

Acute care: Treatment with oxygen

BMJ 2004; 328 doi: (Published 01 February 2004) Cite this as: BMJ 2004;328:040256
  1. Nicola Cooper, specialist registrar in general internal medicine and care of the elderly1
  1. 1St James's University Hospital, Leeds

In the second part of our series about acute care medicine, Nicola Cooper explains the principles behind treatment with oxygen

Oxygen is one of the most important drugs you will ever use, but it is poorly prescribed by medical staff. In 2000, a colleague and I did two surveys of treatment with oxygen. The first looked at prescriptions of oxygen in postoperative patients in a large district hospital. We found that there were many ways used to prescribe oxygen and that the prescriptions were rarely followed. The second study surveyed 50 medical and nursing staff working in acute care. We asked them to name different oxygen masks and to say how much oxygen each delivered. We then asked them to decide which mask was most appropriate for a given clinical situation (see quiz).

When you should use oxygen

Patients need oxygen when they have hypoxaemia, acute hypotension, or respiratory distress; when they have trauma or other acute illness, carbon monoxide poisoning, or severe anaemia; during the perioperative period; and when they have taken drugs that suppress ventilation, like opioids.

Oxygen masks

Oxygen masks are divided into two groups.

  • Low flow masks (nasal cannulase, simple face masks, and masks with a reservoir bag) deliver oxygen at less than the peak inspiratory flow rate. They therefore deliver a variable concentration of oxygen, depending on how the patients is breathing

  • High flow masks (sometimes called Venturi masks) deliver oxygen at a rate above the peak inspiratory flow rate, which is why they are noisier. They deliver fixed concentrations of oxygen.

Inspiratory flow rate

A person breathing normally inspires about 15 l/min of air--this is the inspiratory flow rate, which varies throughout respiration. Assuming a constant flow rate, if you give a person who is breathing normally a nasal cannula at 2 l/min, he or she would be breathing 2 l/min of 100% oxygen …

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