Prescribing oxygen

What is oxygen therapy?¹

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.

In most acutely ill patients with a normal or low arterial carbon dioxide (PaCO2), oxygen saturation should be 94–98% oxygen saturation. However, in some clinical situations such as cardiac arrest and carbon monoxide poisoning it is more appropriate to aim for the highest possible oxygen saturation until the patient is stable. A lower target of 88–92% oxygen saturation is indicated for patients at risk of hypercapnic respiratory failure.

Low concentration oxygen therapy is reserved for patients at risk of hypercapnic respiratory failure, which is more likely in those with:

• Chronic obstructive pulmonary disease (COPD). See Use of oxygen therapy in COPD.

• Severe asthma.

• Advanced cystic fibrosis.

• Severe non-cystic fibrosis bronchiectasis.

• Severe kyphoscoliosis or severe ankylosing spondylitis.

• Severe lung scarring caused by tuberculosis.

• Musculoskeletal disorders with respiratory weakness.

• Overdose of opioids, benzodiazepines, or other drugs causing respiratory depression.

Increased respiratory depression is seldom a problem in patients with stable respiratory failure treated with low concentrations of oxygen although it may occur during exacerbations. Patients and relatives should be warned to call for medical help if drowsiness or confusion occur.

Domiciliary oxygen

Oxygen should only be prescribed for use in the home after careful evaluation in hospital by respiratory experts.

Patients should be advised of the risks of continuing to smoke when receiving oxygen therapy, including the risk of fire. Smoking cessation therapy should be recommended before home oxygen prescription. In patients with COPD, domiciliary oxygen should only be provided if the patient has stopped smoking.

The NHS oxygen contract

Types of oxygen therapy

There are now five types of home oxygen provision:³

• 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. Some patients with arterial hypoxaemia require supplementary oxygen for air travel. The patient’s requirement should be discussed with the airline before travel.

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 therapy¹³

Long-term administration of oxygen (usually at least 15 hours daily) improves survival in COPD patients with more severe hypoxaemia. The need for oxygen should be assessed in COPD patients with an FEV1 less than 30% predicted (consider assessment if FEV1 is 30-49%), cyanosis, polycythaemia, peripheral oedema, raised JVP, and when oxygen saturation levels are 92% or less when breathing air.

Assessment for long-term oxygen therapy requires measurement of arterial blood gas tensions. Measurements should be taken on 2 occasions at least 3 weeks apart to demonstrate clinical stability.

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 therapy.³

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 cylinders¹

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 Ireland:¹

• 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 oxygen¹

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) is prescribed for patients on long-term oxygen therapy who need to be away from home on a regular basis. Patients who are not on long-term oxygen therapy can be considered for ambulatory oxygen therapy if there is evidence of exercise-induced oxygen desaturation and of improvement in blood oxygen saturation and exercise capacity with oxygen. Ambulatory oxygen therapy is not recommended for patients with heart failure, COPD with mild or no hypoxaemia at rest, or those who smoke.

Short-burst oxygen therapy³

Short-burst oxygen therapy is occasionally prescribed for short-burst (intermittent) use for episodes of breathlessness not relieved by other treatment in patients with interstitial lung disease, heart failure, and for dyspnoea in palliative care.

Short-burst oxygen therapy can be used to improve exercise capacity and recovery. It should only be continued if there is proven improvement in breathlessness or exercise tolerance. It is not recommended for COPD patients who have mild or no hypoxaemia at rest.

The National Institute for Health and Care Excellence (NICE) advises against the use of short-burst oxygen therapy in mild-to-moderate COPD.⁶

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 alone.³

Oxygen for children⁷

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.