Long term oxygen therapy (McDonald 2016)
Initiating oxygen therapy
- Before introducing oxygen therapy, ensure optimal treatment of the pulmonary disorder while monitoring improvement with objective tests such as FEV1 and FVC. Treatment may include maximum therapy for airway obstruction, attention to nutrition and bodyweight, an exercise rehabilitation program, control of infection, and treatment of cor pulmonale.
- In patients selected for oxygen therapy, assess the adequacy of relief of hypoxaemia (PaO2 > 60 mmHg, or 8 kPa; SpO2 > 90%) and/or improvement in exercise capacity or nocturnal arterial oxygen saturation while using a practical oxygen delivery system.
What the patient needs to know
- Patients receiving oxygen therapy in the home, and their carers, should have the use clearly explained. That is, hours of use and flow rate, and any need to vary flow rates at given times. The equipment and its care, including how to obtain servicing or replacements, needs to be explained. The dangers of open flames (especially cigarettes, gas heaters and cookers) need to be emphasised.
- Flow should be set at the lowest rate needed to maintain a resting PaO2 of 60 mmHg (8kPa) or SpO2 > 88%. For patients with COPD, 0.5-2.0 L/min is usually sufficient. Flow rate should be increased by 1 L/min during exercise.
- Humidifiers are generally not needed at oxygen flow rates below 4 L/min.
- Extrasoft nasal prongs are recommended for continuous oxygen use, but may become uncomfortable at flow rates over 2-3 L/min and in the long term. Facemasks may be preferred for at least some of the time, although there are dangers of rebreathing exhaled CO2 at flow rates below 4 L/min.
- Reassess 4-8 weeks after starting continuous or nocturnal oxygen therapy, both clinically and by measurement of PaO2 and PaCO2, with and without supplementary oxygen. A decision can then be made as to whether the treatment has been properly applied and whether it should be continued or abandoned.
- Patients on intermittent oxygen therapy should also be reassessed periodically. The review can be undertaken by appropriately trained staff using a pulse oximeter to confirm hypoxaemia (SpO2 < 88%) at rest or during daily activities. They should also check compliance with therapy and smoking status.
- Review at least annually, or more often according to the clinical situation.
- Supplementary oxygen in patients with increased arterial PaCO2 may depress ventilation, increase physiological dead space, and further increase arterial PaCO2. This is suggested by the development of somnolence, headache and disorientation.
- In long-term oxygen therapy, the increase in arterial PaCO2 is usually small and well tolerated. However, serious hypercapnia may occasionally develop, making continued oxygen therapy impractical. Risk appears greater during exacerbations of disease or if the flow of oxygen is increased inappropriately.
- Sedatives (particularly benzodiazepines), narcotics, alcohol and other drugs that impair the central regulation of breathing should not be used in patients with hypercapnia receiving oxygen therapy.
Choosing the right method (see Adult Domiciliary Oxygen therapy Clinical Practice Guideline for further details)
Domiciliary oxygen therapy can be delivered via the following systems:
- Stationary oxygen concentrators: These floor-standing electrically driven devices work by extracting the nitrogen from room air by means of molecular sieves and deliver a continuous flow of oxygen at the outlet. The percentage of oxygen is around 90 to 95% depending on the model used. A back-up standard D-size oxygen cylinder is often supplied in case of concentrator breakdown or power failure. Users may claim a rebate on their electricity account.
- Portable oxygen concentrators: These are small, lightweight portable oxygen concentrators (POC) that are powered by the household electrical supply or via a car battery or rechargeable battery which makes them suitable for ambulatory use. Some models have been approved by some of the commercial airlines. Two types are available, those that are only capable of delivering pulsed oxygen (these are generally smaller and lighter in weight) and those that can deliver both pulsed and continuous flow oxygen. The performance specifications of the different models of POCs vary considerably and for patients with high oxygen needs, some POCs may not achieve a sufficient concentration of inspired oxygen to meet the patient’s needs during exercise.
- Cylinders: These contain compressed oxygen gas and deliver 100% oxygen at the outlet. Portable lightweight cylinders are available. Electronic conservation devices are often supplied to deliver oxygen predominantly during inspiration and therefore avoid wastage. Demand flow devices are the most common and deliver a pre-set volume or bolus of oxygen in early inspiration. Use of such devices results in up to a fourfold reduction in oxygen consumption. Reservoir-style conservers (i.e. nasal cannulae with an integrated pendant shaped reservoir) are a cost-effective alternative.
The prescription should always specify:
- the source of supplemental oxygen;
- method of delivery;
- duration of use; and
- flow rate at rest, during exercise and during sleep.
There is no significant difference in the quality of oxygen delivery among the above methods. However:
- Concentrators are cheaper than cylinders if use is equivalent to or more than three E-size cylinders per month.
- Concentrators can be wheeled around the home but are heavy (about 2126 kg) and are difficult to move up stairs and in and out of cars.
- Concentrators cannot be used for nebulisation, as the pressure delivered is too low (3563 kPa, compared with 140 kPa for nebuliser pumps).
- If the anticipated need is for longer than three years, it is cheaper to buy than to rent a unit. The units usually have a five-year guarantee. However, public funding is available for pensioners and Health Care Card holders, subject to means testing.