Prescribing oxygen

Oxygen therapy is used to treat hypoxia. The concentration of oxygen required depends on the condition being treated. Inappropriate concentrations of oxygen may cause very serious problems for the patient - even death.

The NHS oxygen contract

Types of oxygen therapy

There are now five types of home oxygen provision³:

• Long-term oxygen therapy (LTOT).

• Ambulatory - new development with light portable cylinders lasting six hours.

• Short-burst - via a cylinder.

• Nocturnal oxygen therapy.

• Palliative oxygen therapy.

Travel - usually portable cylinders. For holidays in the UK, the usual contractor will make reciprocal arrangements with another contractor to supply oxygen at the holiday destination.

Emergency oxygen - can be supplied within four hours. Enough for three days will be arranged prior to specialist assessment. Arrangements for out of hours exist - but the emergency doctor may need to carry a supply of HOOFs to leave with the patient or fax to suppliers. A second HOOF will be required if the patient is to continue oxygen after the emergency period pending assessment.

Indications for long-term oxygen therapy³

High-concentration oxygen, up to 60%, is safe in conditions such as pneumonia, pulmonary thromboembolism and fibrosing alveolitis. Low-concentration oxygen (of 24-28%) is used in patients with chronic obstructive pulmonary disease (COPD) or other conditions causing underventilation and CO₂ retention. 24-28% oxygen significantly increases haemoglobin saturation, without risking further underventilation and a rising pCO₂, which can cause coma and death. Repeated blood gas measurements are required to assess the correct oxygen concentration.

Patients with a resting stable oxygen saturation of ≤92% should be referred for a blood gas assessment in order to assess eligibility for LTOT.

British Thoracic Society guideline

NIV should be the treatment of choice for patients with chest wall or neuromuscular disease causing type 2 respiratory failure. Additional LTOT may be required in case of hypoxaemia not corrected with NIV.

Nocturnal oxygen therapy (NOT) is not recommended in patients with COPD who have nocturnal hypoxaemia but who fail to meet the criteria for LTOT. Other causes of nocturnal desaturation in COPD should be considered, such as obesity hypoventilation, respiratory muscle weakness or obstructive sleep apnoea (OSA). Patients with OSA, obesity hypoventilation syndrome or overlap syndrome should not have NOT alone ordered. It can be considered in patients with evidence of established ventilatory failure, where it should be given with NIV support.

See also the separate Use of Oxygen Therapy in COPD article.

Smoking and home oxygen

Patients should be made aware of the dangers of continuing to smoke in the presence of home oxygen therapy³.

Assessment

Assessment is important because some breathless patients are not hypoxic and hypoxic (even cyanosed) patients are not always breathless. Detailed assessment involving structured exercise testing and blood gas measurements may be needed.

Equipment

Oxygen cylinders⁶

Oxygen may be supplied under the NHS as oxygen cylinders. Oxygen flow can be adjusted using an oxygen flow meter with 'medium' (2 litres/minute) and 'high' (4 litres/minute) settings.

A concentrator is recommended if oxygen is required for more than eight hours a day (or 21 cylinders per month). Occasionally, if a higher concentration of oxygen is required, the output of two oxygen concentrators can be combined using a 'Y' connection.

A nasal cannula is usually preferred for long-term oxygen therapy from an oxygen concentrator. However, it may cause dermatitis and mucosal drying. Also the concentration of oxygen is not controlled and so a nasal cannula may not be appropriate for acute respiratory failure.

When oxygen is given through a nasal cannula at a rate of 1-2 litres/minute, the inspiratory oxygen concentration is usually low; however, it varies with ventilation and can be high if the patient is hypoventilating.

Oxygen concentrators are more economical for patients who require oxygen for long periods and can be ordered on the NHS in England and Wales on a regional tendering basis (contact details are available in the British National Formulary). Arrangements for oxygen supply are different in Scotland and Northern Ireland⁶:

• In Scotland, patients should be referred for assessment by a respiratory consultant. If the need for a concentrator is confirmed, the consultant will arrange for the provision of a concentrator through the Common Services Agency. A Scottish Home Oxygen Order Form (SHOOF) should be completed and emailed to Health Facilities Scotland. They will arrange for oxygen to be supplied by their contractor.

• In Northern Ireland, oxygen concentrators and cylinders should be prescribed on form HS21. Oxygen concentrators are supplied by a local contractor. Prescriptions for oxygen cylinders and accessories can be dispensed by pharmacists contracted to provide domiciliary oxygen services.
  

Arranging supply of oxygen⁶

The type of oxygen service (or combination of services) should be ordered on a home oxygen form appropriate to the country (see above). The amount of oxygen required (hours per day) and flow rate should be specified. Special needs or preferences should be specified on the form.

Patients must provide consent for their details to be passed on to the supplier, the fire brigade and any other relevant organisations. The supplier will contact the patient to make arrangements for delivery, installation and maintenance of the equipment. The supplier will also train the patient to use the equipment.

The supplier will continue to provide the service until a revised form is received or until notified that the patient no longer requires the home oxygen service.

Long-term oxygen therapy³

LTOT prolongs survival in COPD if given for at least 15 hours daily to include night time (arterial hypoxaemia is worse at night), to raise oxygen tension above 8 kPa.

Patients should undergo formal assessment for LTOT after a period of stability of at least eight weeks from their last acute exacerbation.

Ambulatory oxygen therapy³

Ambulatory oxygen therapy (AOT) should not be routinely offered to patients who are on LTOT. Even then, patients on LTOT should only be assessed for AOT if they are mobile outdoors. A particular group who may benefit are patients exercising in a pulmonary rehabilitation programme or other forms of exercise programme. In such cases, a formal assessment demonstrating improvement in exercise endurance should be conducted.

Short-burst oxygen therapy³

Short-burst therapy (eg, for 10-20 minutes) is indicated to relieve dyspnoea in palliative care or episodic breathlessness, not relieved by other treatments in severe COPD, interstitial lung disease or heart failure. Review annually and repeat assessment in the event of clinical deterioration.

Traditionally, short-burst oxygen therapy has been offered to COPD patients prior to exercise or to relieve dyspnoea after exercise. The BTS guidelines advise that this practice is not effective, irrespective of whether the patient has hypoxaemia.

The National Institute for Health and Care Excellence (NICE) advises against the use of short-burst oxygen therapy in mild-to-moderate COPD⁷.

Patient education

Education should cover diagnosis, use of AOT, principles of treatment, maintenance of portable equipment, servicing arrangements and electricity reimbursement, use of nasal cannulae or masks, requirement for humidifier, contact telephone number and advice on travel. Further education is provided by the engineer at the time of delivery. A family member or carer should attend the education sessions.

NB: the patient should be made aware of the dangers of smoking and fire risk.

People should know that there are a few side-effects of oxygen therapy. These include a dry or bloody nose, skin irritation from the face mask or nasal prongs, tiredness and morning headaches. If these happen, they should be encouraged to let their clinician know, as they may be able to change the prescription to ease the patient's problems.

Pulse oximetry

Used to measure SaO₂, this can be a useful guide to spot exercise desaturation (a drop of at least 4% below 90%), to diagnose sleep apnoea and to monitor ambulatory oxygen flow rate (aim to maintain above 90% during exercise).

However, patients potentially requiring LTOT should not be assessed using pulse oximetry alone³.

Oxygen for children⁸

Many children only need oxygen for a limited period. Assessment is different to that of adults, due to difficulty of arterial blood sampling and growth and neuro-developmental considerations. Specific equipment is required to allow for lower oxygen flows.

Almost all children receiving LTOT also require AOT. Many children require LTOT overnight only (less than the 15 hours that forms part of the adult LTOT definition). Provision of oxygen may be necessary at school. All children require supervision from a parent/carer.

The American Thoracic Society (ATS) based their guidelines on the British version but acknowledge they have not been revised since 2009. There is a surprising lack of evidence in this area, and the ATS recommends large-scale trials, particularly the areas of home oxygen use and the methods used to wean children off oxygen⁹.