Prescribing Oxygen

• All patients needing home oxygen in England and Wales must now be referred to a hospital specialist (eg Chest Physician), for diagnosis and full physiological assessment including blood gases.
• A home oxygen order form (HOOF) is then faxed to the single contractor (Air Products) who decide on the appropriate equipment. GPs will no longer use FP10 prescriptions for pharmacists to provide cylinders through a local supplier.³
• GPs will only be able to order (using a HOOF) short burst oxygen for palliative use or emergency use while awaiting assessment.
• Home Oxygen is now funded from PCT budgets, whether ordered by a GP or hospital. A Home Oxygen Record (HOR) form should be sent to the GP with diagnosis, blood gas measurements (at least 2), flow rate, hours of use per day, use of nasal cannulae or masks and provision of humidifier.
• The aim is to improve quality of life for patients on long term oxygen, and to reduce costs by matching provision to need
• A consent form must be completed by all patients (to permit clinical information from the current supplier to go to the new supplier, (Air Products) and this includes those already using oxygen concentrators but a HOOF will not be needed.

There are now 5 types of oxygen provision:

1. Longterm (LTOT)
2. Ambulatory - new development with light portable cylinders lasting 6 hours
3. Short burst - via a cylinder
4. 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.
5. Emergency oxygen - can be supplied within 4 hours. Enough for 3 days will be arranged prior to specialist assessment. Out of hour arrangements exist - but the emergency doctor may need to carry a supply of HOOF forms to leave with patient or fax to suppliers. A second HOOF form will be required if the patient is to continue oxygen after the emergency period pending assessment.

Oxygen is prescribed for chronically hypoxaemic patients (PaO2 below 7.3 kPa). In addition, LTOT can be prescribed in when the PaO2 is between 7.3 kPa and 8 kPa, together with the presence of one of secondary polycythaemia or clinical and or echocardiographic evidence of pulmonary hypertension.
The concentration depends on the condition being treated.

• 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 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.

Smoking and home oxygen

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

Assessment is important because some breathless patients are not hypoxic and hypoxic (even cyanosed) patients are not always breathless.⁵ Detailed assessment involving structured exercise testing and blood gas measurements may be needed.

Oxygen cylinders

Cylinders with 'medium' (2 litres/minute) and 'high' (4 litres/minute) settings. Portable oxygen cylinders last approximately 2 hours 2 litres/minute. Oxygen concentrators are more economical than cylinders for more than 8 hours a day. Exceptionally, 2 oxygen concentrators can be combined using a 'Y' connection. Accessories include face mask, nasal cannula and humidifier. Masks supply either 24% or 28% oxygen. Nasal cannula allows the patient to talk and eat but the concentration is not controlled and mucosal drying can occur in sensitive individuals. Flow rate is normally 2 l/minute via nasal cannulae, or from a 24% controlled oxygen face mask, aiming for a PaO2 of 8 kPa. If oxygenation is insufficient, the oxygen flow rate should be increased gradually. Some patients may require greater than 4 l/minute and may need an additional oxygen concentrator.

LTOT is used for conditions such as COPD, interstitial lung disease, cystic fibrosis, bronchiectasis, pulmonary hypertension, chronic heart failure or nocturnal hypoventilation due to obesity, neuromuscular disease or sleep apnoea (with CPAP therapy). It 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.
Oxygen should not be started at the time of hospital discharge, when patients are still recovering from an exacerbation. Patients should be seen 5 weeks later to assess blood gases when they are clinically stable, then visited within 4 weeks by a respiratory nurse specialist, reviewed by a specialist after 3 months and have 12 monthly blood gases.

Most patients needing this will be also using LTOT. Housebound patients may benefit from occasional use (eg up to an hour a day). More active patients on LTOT may benefit from ambulatory oxygen for longer, though few need it for longer than 4 hours daily. The same flow rate should be used as for LTOT and further assessment is not essential, unless the flow rate needs re-assessing. The aim is to enable the patient to leave the home to improve quality of life.
Patients not on LTOT but with exercise desaturation (a fall in SaO2 of 4% below 90%) may benefit from ambulatory oxygen to increase exercise capacity. This group needs detailed assessment with walking tests. Ambulatory oxygen should only be prescribed if there is evidence of exercise desaturation and improvement in exercise capacity.

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

Education should cover diagnosis, use of ambulatory oxygen therapy, 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 dangers of smoking and fire risk.

Used to measure SaO2 can be a useful guide:

• To spot exercise desaturation (a drop of at least 4% below 90%)
• To diagnose sleep apnoea
• To monitor ambulatory oxygen flow rate (aim to maintain above 90% during exercise)

• Many children only need oxygen for a limited period.
• Assessment is different to adults due to difficulty of arterial blood sampling, and growth and neuro-development considerations.
• Specific equipment is required to allow for lower oxygen flows.
• Almost all children receiving long term oxygen therapy also require ambulatory oxygen therapy. 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.