Myths about oxygen

Oxygen was discovered by Joseph Priestley in 1777 and has become one of the most commonly used drugs in medical practice. Yet it is poorly prescribed by most medical staff. In 2000 we carried out two surveys of oxygen therapy. The first looked at oxygen prescriptions in postoperative patients in a large district general hospital. It found that there were several dozen ways used to prescribe oxygen and that the prescriptions were rarely followed. The second surveyed 50 medical and nursing staff working on a medical admissions, coronary care, and respiratory unit of another district hospital. They were asked questions about oxygen masks and the concentration of oxygen delivered by each mask. They were also asked which mask was most appropriate for a range of clinical situations and how much oxygen may be given to patients with chronic obstructive pulmonary disease (COPD). The answers were very revealing:

• Many people could not name the different types of oxygen mask.

• The relationship between litres per minute and oxygen concentration (%) was poorly understood - for example, most people thought that a patient receives 28% oxygen from nasal cannulae at 2 litres per minute and 100% oxygen from a mask with a reservoir bag at 15 litres per minute.

• One-third chose a 28% Venturi mask for an unwell patient with asthma.

• Just over one-third thought that a diagnosis of COPD meant that one could never give more than 28% oxygen.

• Not one person understood the different reasons why PaCO2 rises - the difference between "CO2 retention" from uncontrolled oxygen therapy and hypercapnic respiratory failure owing to other causes. Reducing the oxygen concentration in order to "treat" a high PaCO2 was common practice.

• It was common practice to use simple face masks at 2 litres per minute if the patient had COPD.

There are many false beliefs about oxygen and the result is that many patients are incorrectly treated. Yet oxygen is a drug with a correct concentration and side effects.

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