Oxygen therapy.

Oxygen therapy is common in many clinical areas where there is evidence or a likelihood of deficiency in the normal oxygen delivery pathway. It is a fundamental component of management for patients with type-1 respiratory failure and may be used in the treatment of type-2 respiratory failure.

- Type-1 respiratory failure can be described as hypoxaemic respiratory failure in the presence of a low or normal carbon dioxide level in the arterial blood.

- Type-2 respiratory failure can be described as ventilatory failure with evidence of hypercapnoea due to alveolar hypoventilation. Hypoxaemia may coexist.

- Oxygen therapy is aimed at supplementing the inspired oxygen concentration to prevent tissue hypoxia and resultant cellular dysfunction. However, cellular oxygen delivery is not only dependent on inspired oxygen - it also relies on the concentration of haemoglobin and its ability to saturate with oxygen, as well as oxygen delivery to the cells by cardiac output.

- Oxygen is a drug and must be prescribed by an appropriately qualified practitioner (Jamieson et al, 2002). In some clinical settings local agreement or patient care directives may exist for nurses to initiate therapy independently. In cardiopulmonary arrest ventilatory support with high concentrations of oxygen must be delivered without delay.

Available oxygen systems
Variable performance (low-rate)

These systems deliver gas flow at a low rate (Fig 1). If the patient's inspiratory flow rate (the speed at which gas is taken into the lungs) exceeds the flow of oxygen, air will be absorbed from the atmosphere via holes in the side of the mask. This will dilute the actual inspired oxygen concentration. These systems should not be used in patients who have high oxygen requirements or a high peak inspiratory flow rate.

Variable performance systems include simple face masks and nasal devices, which connect directly to an oxygen flow meter via standard 'bubble' tubing. Nasal devices are thought to be well tolerated by patients (Doughety and Lister, 2004).

Fixed performance (high-flow, oxygen enrichment devices)

Fixed performance systems (Fig 2) use the Venturi principle and deliver a high flow rate of gas enriched with oxygen. This is achieved by passing oxygen through a narrow inlet, entraining atmospheric air as it does so. The delivered concentration of oxygen is dependent on the flow of oxygen via the inlet and the size of the holes through which air is entrained. The total gas flow generated can exceed the peak inspiratory flow rate generated by the patient, thus making the system appropriate for patients with high oxygen requirements, and those who require an accurate oxygen concentration.

Oxygen delivered using these devices predominantly uses face masks or masks that sit over a tracheostomy tube. The high gas flow requires humidification, which may be achieved with warm or cold water systems.

Commencing oxygen therapy
If it is not an emergency, ensure oxygen therapy has been prescribed by an appropriately qualified practitioner and in accordance with the NMC guidelines (2004) for drug administration.

- Using the prescription and taking into account the patient's clinical condition and their preference, select the most appropriate delivery system.

- Obtain informed consent and attempt to allay any anxieties.

- Set the prescribed flow rate/oxygen concentration according to the prescription and the device instructions (Fig 3).

- Administer oxygen, provide assurance and make sure the patient is comfortable (Fig 4).

- Assess the effectiveness of the treatment as needed (Fig 5).

- Document the procedure in line with local policy (Fig 6).

Complications/hazards
Oxygen is combustible, so direct contact with oil, grease and alcohol should be avoided. Smoking must also not be allowed within the vicinity of the oxygen delivery system.

A small number of patients with chronic lung disease processes do not respond to changes in the blood level of carbon dioxide as a stimulus to breathing, and may respond to a low blood oxygen level. If this is suspected, care should be taken that the administration of oxygen does not inhibit this drive, so causing carbon dioxide retention/narcosis. Advice should be sought from experienced clinicians.

However, oxygen will almost always be required for acutely ill patients whose condition is deteriorating.

Professional responsibilities
All nurses who administer oxygen must have received approved training and undertaken supervised practice in drug and oxygen administration. The onus is also on the individual to ensure her or his knowledge and skills are maintained from both a theoretical and practical perspective. Nurses should also undertake this role in accordance with their organisation's protocols, policies and guidelines. This article has been double-blind peer-reviewed.

For related articles on this subject and links to relevant websites see www.nursingtimes.net

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