When should a nasal cannula be used to deliver oxygen?
Nasal cannulas are used to deliver oxygen when a low flow, low or medium concentration is required, and the patient is in a stable state.
They deliver oxygen in a variable manner; this means the amount of oxygen inspired depends on the patient’s breathing rate and pattern. For this reason they are not suitable for use in the acute phase of illness with patients who need controlled oxygen therapy. This includes patients with acute exacerbations of chronic obstructive pulmonary disease (COPD); these patients retain carbon dioxide and require a Venturi oxygen mask.
In other acute situations patients may need a higher concentration of oxygen and a non-rebreathe mask or simple oxygen mask is often used.
Flow rates of 1-4 litres per minute are used with nasal cannulas, equating to a concentration of approximately 24-40% oxygen. Flow rates of up to 6 litres can be given but this will often cause nasal dryness and can be uncomfortable for patients (British Thoracic Society, 2008).
The advantages of nasal cannulas for patients who have chronic stable respiratory problems is that it is possible to eat, drink and talk while using them; they also reduce the risk of carbon dioxide rebreathing. Dry nasal passages can be a problem initially but with continued use this usually resolves itself.
Author Carol Kelly is senior lecturer/programme lead at the Faculty of Health, Edge Hill University
British Thoracic Society and Scottish Intercollegiate Network (2009) The British Guideline on the Management of Asthma
British Thoracic Society (2008) Guidelines for Emergency Oxygen use in Adult Patients: Executive Summary