Use of oxygen therapy in COPD

See also the separate articles: Chronic obstructive pulmonary disease, Diagnosing COPD, Management of stable COPD and Acute exacerbations of COPD.

General points about oxygen therapy in chronic obstructive pulmonary disease

• There is strong evidence of survival benefit of long-term oxygen therapy (LTOT) in patients with COPD and severe chronic hypoxaemia when used for at least 15 hours daily.

• Therefore, oxygen therapy in COPD must be used with care in the acute setting but it can have distinct benefits in the long term. Chronic hypoxaemia causes slowly progressive pulmonary hypertension with the development of right ventricular hypertrophy and possible cor pulmonale with secondary polycythaemia. Secondary polycythaemia increases blood viscosity and hence resistance to flow. There is also sludging and a tendency to thrombosis.

• Whilst long-term domiciliary oxygen has been proven to be beneficial in severe hypoxaemia, its value in lesser degrees of hypoxaemia requires further research.¹

• Studies from burns units suggest a strong association between burns injuries and smoking whilst using oxygen therapy. Ongoing education and a circumspect approach to prescribing home oxygen therapy to known smokers is encouraged.²

Oxygen therapy in the acute setting (in hospital)³

• For most COPD patients, you should be aiming for an SaO₂ of 88-92%, (compared with 94-98% for most acutely ill patients NOT at risk of hypercapnic respiratory failure). Mark the target saturation clearly on the drug chart.

• The aim of (controlled) oxygen therapy is to raise the PaO₂ without worsening the acidosis. Therefore, give oxygen at 24% (via a Venturi mask) at 2-3 L/minute or at 28% (via Venturi mask, 4 L/minute) or nasal cannula at 1-2 L/minute. Aim for oxygen saturation 88-92% for patients with a history of COPD until arterial blood gases (ABGs) have been checked .

• Treat patients aged over 50 with possible COPD in the same way (eg, long-term smokers with a history of chronic breathlessness) and get ABGs urgently.
  

  It is particularly important to check ABGs promptly if the patient has been brought in as emergency by an ambulance: ambulance crews have to give high-flow oxygen if a patient is hypoxic, regardless of previous history.

• Measure ABGs within 30-60 minutes of starting supplemental oxygen or changing its concentration. If PaCO₂ normal, concentration of the supplemental oxygen may be increased to 94-98%.

• It is worth noting that a large-scale systematic review questioned the benefits of raising the SaO₂ above 96% in acutely ill adults.⁴ The British Thoracic Society (BTS) has responded that the main thrust of their advice is to provide target rather than liberal oxygen therapy. It feels therefore that its guidelines need not be changed at this stage.

• Oxygen therapy will have to be complemented with other interventions for any acute exacerbation of COPD.

• The risk of respiratory acidosis in patients with hypercapnic respiratory failure is increased if the PaO₂ is above 10.0 kPa due to previous excessive oxygen use. If acidosis develops (falling pH) with a rising PaCO₂, other therapeutic interventions need to be discussed with the acute medical team; the intensive treatment unit (ITU) may need to be involved and decisions regarding ceiling of care have to take place at this point. Non-invasive positive pressure ventilation (NIPPV) and targeted oxygen therapy should be considered.

• Oxygen therapy should be stopped once a patient is clinically stable on low-concentration oxygen. Oxygen saturation on air should be monitored for 5 minutes after stopping oxygen therapy. If it remains in the desired range, it should be rechecked at 1 hour.

Long-term oxygen therapy⁵⁶

Assessments for long-term oxygen therapy for COPD are performed specialist teams, ie community respiratory teams or secondary care services, and initiated and monitored by those services.

Once this is started, LTOT is likely to be lifelong. It is usually given over a minimum of 15 hours a day, including overnight when arterial hypoxaemia worsens during sleep (some advocate 18 or even 24 hours a day). See also the separate Prescribing oxygen article.

• Assess the need for oxygen therapy in people with any of the following:
  

  • Very severe airflow obstruction - forced expiratory volume in one second (FEV₁) less than 30% predicted.

  • Cyanosis.

  • Polycythaemia.

  • Peripheral oedema.

  • Raised jugular venous pressure.

  • Oxygen saturation 92% or below when breathing air.

• Consider assessment for people with severe airflow obstruction (FEV₁ 30-49% predicted).

• Assess by measuring ABGs on two occasions at least three weeks apart in people with confirmed stable COPD who are receiving optimum medical management. Obtaining ABGs in the community can be difficult and may require a visit to the local hospital or involvement of the specialist respiratory nurse.

• Offer LTOT to people with PaO₂ less than 7.3 kPa when stable (or less than 8 kPa when stable and with peripheral oedema, polycythaemia (haematocrit ≥55%) or pulmonary hypertension).

• Be aware that inappropriate oxygen therapy in people with COPD may cause respiratory depression.

• Consider whether the risk of falling over oxygen delivery equipment outweighs the benefits of LTOT.

• All healthcare settings should have a pulse oximeter to ensure all people needing LTOT are identified and to review people receiving LTOT at least once a year.

• People receiving LTOT should breathe supplemental oxygen for at least 15 hours a day. If they smoke or live with someone who smokes, warn them about the risk of fire and explosion. Offer smoking cessation advice where appropriate.

• Use oxygen concentrators to provide the fixed supply for LTOT at home.

• Refer people who are hypercapnic or acidotic on LTOT to a specialist centre for consideration of long-term non-invasive ventilation (NIV).

• NIV should be used as the treatment of choice for persistent hypercapnic ventilatory failure during exacerbations not responding to medical therapy.

Ambulatory oxygen therapy⁶

• Offer ambulatory oxygen therapy (AOT) to people already on LTOT who want to use oxygen outside the home, following assessment by a specialist.

• Consider it in motivated individuals who have exercise desaturation and PaO₂ less than or equal to 7.3 kPa and whose exercise capacity and/or breathlessness improve with oxygen.

The BTS recommends:⁵

• AOT should not be routinely offered to patients who are not eligible for LTOT.

• AOT should not be routinely offered to patients already on LTOT.

• AOT assessment should only be offered to patients already on LTOT if they are mobile outdoors.

• AOT should be offered to patients for use during exercise in a pulmonary rehabilitation programme or during an exercise programme following a formal assessment demonstrating improvement in exercise endurance.

Short-burst oxygen therapy

• Short-burst oxygen therapy (SBOT) is typically given to patients for the relief of breathlessness not relieved by any other treatments.

• It is used intermittently at home for short periods - for example, 10-20 minutes at a time.

• Oxygen used in this way has traditionally been ordered for non-hypoxaemic patients and used for subjective relief of dyspnoea prior to exercise for oxygenation or after exercise for relief of dyspnoea and recovery from exertion. However, the BTS guidelines specifically advise against SBOT in COPD with or without hypoxaemia in this scenario.

• The National Institute for Health and Care Excellence (NICE) advises that SBOT should not be used to manage breathlessness in people with mild-to-moderate COPD.⁶

Prescription⁷

See the separate related Prescribing oxygen article for full details but some aspects are repeated here.

• Patients need to be assessed first by a specialist team before a GP can make the prescription.

• The supply of home oxygen has been transferred from community pharmacies to regional oxygen supply companies.⁸ These companies are responsible for supplying cylinders, concentrators and liquid oxygen as part of an integrated service.

• Oxygen should be ordered directly from one of four regional supply companies via the Home Oxygen Order Form (HOOF).⁹ This has replaced prescribing of oxygen on FP10 prescriptions.

• Form completion notes are on the back - ensure you specify all the details (notably, the oxygen concentration).

• Regular orders should take three days; emergency ones should be delivered in four hours.

• The NHS home oxygen service is available throughout the UK. However, delivery is different in Scotland and Northern Ireland:

  • 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. Prescribers should complete a Scottish Home Oxygen Order Form (SHOOF) and email it to Health Facilities Scotland. Health Facilities Scotland will then liaise with their contractor to arrange the supply of oxygen.

  • In Northern Ireland oxygen concentrators and cylinders should be prescribed on form HS21. Oxygen concentrators are supplied by a local contractor.

  • In Northern Ireland prescriptions for oxygen cylinders and accessories can be dispensed by pharmacists contracted to provide domiciliary oxygen services.

Maximising benefit

• As a general rule, it is more economical to use an oxygen concentrator rather than cylinders if oxygen is required for more than eight hours per day or if prescriptions exceed 21 cylinders per month. Use nasal prongs at 2-4 L/minute (depending on ABGs).

• There is no benefit from LTOT for less than 15 hours a day.

• Smokers should stop smoking or benefit is unlikely. There is a very significant risk of burns and fire.

• Get optimum benefit from other forms of therapy, including inhalers.

Monitoring

• The patient's ABGs need to be monitored. Simply measuring SaO₂ is not enough, as assessment of hypercapnia and its response to oxygen therapy is required.

• ABGs can be radial, femoral or from the earlobe. Collect a sample when the patient has been breathing air for at least 30 minutes after having received any prior supplemental oxygen.

• Once therapy has started, measure ABGs with oxygen therapy (for at least 30 minutes on therapy, using the same equipment as at home if possible), to assess response and ensure pO₂ is >8.0 kPa without unacceptable hypercapnia.

• Subsequently, measure ABGs when the patient is clinically stable and on optimal therapy on two occasions at least three weeks apart.

• All patients should be visited at home within four weeks of prescription by a specialist nurse, physiotherapist or technician (depending on local arrangements), experienced in the provision of domiciliary oxygen therapy. The aim is to provide education and support and to measure the SaO₂ with oximetry both on air and with therapy. This should be 92% or above with therapy. This should be followed by visits at three months and then 6-12 months by a respiratory health worker.

Travel

Travel by land or sea presents a few potential problems:

• Reduced pO₂ in airline cabins will increase hypoxia in those patients with hypoxia at sea level.

• The BTS states that commercial air travel is contra-indicated for patients with usual oxygen requirement at sea level at a flow rate exceeding 4 L/minute.¹⁰

• Most major airlines can provide supplemental inflight oxygen and assistance with embarkation if arranged in advance.

• It is usually possible to arrange temporary provision of LTOT from a local chemist during a holiday but many patients can manage well without LTOT for several days.