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LTOT in COPD and the care of patients in the home

Primary care nurses have an increasingly important role in supporting patients on oxygen at home. COPD nurse specialist Steph Reilly discusses the use of oxygen in patients with COPD and the use of pulse oximetry in general practice as a screening tool

Steph Reilly
BN(Hons) RN(Adult) DipCOPD Dip Asthma
Lead COPD Nurse Specialist
Southern Derbyshire COPD Primary Care Service
Chair of Southern Derbyshire COPD Steering Group

Long-term oxygen therapy (LTOT) is indicated in patients with chronic hypoxia, due to conditions such as chronic obstructive pulmonary disease (COPD), interstitial lung disease, severe chronic asthma, bronchiectasis, cystic fibrosis, pulmonary vascular disease, primary pulmonary hypertension, pulmonary malignancy or chronic heart failure. LTOT is also indicated in patients who have nocturnal hypoventilation, such as obstructive sleep apnoea or neuromuscular disorders. It can also be used for palliative use. 

What is COPD?
COPD is a chronic, slowly progressive disease, characterised by airflow obstruction that is progressive, not fully reversible and does not change markedly over several months. Approximately 85-95% of the disease is caused by smoking.(1)
Not all patients with COPD will benefit from oxygen, and before considering the need for oxygen, patients must be optimised on pharmacotherapy and non-pharmacological interventions. As highlighted in the National Institute for Health and Clinical Excellence (NICE) COPD guidelines, it is important to consider the following:(1)

  • Long- and short-acting bronchodilators.
  • Inhaled corticosteroids for patients with frequent exacerbations.
  • Pulmonary rehabilitation if available.
  • Exercise and diet.
  • Vaccination.

Hypoxaemia
Normal respiratory drive is largely initiated by the partial pressure of carbon dioxide (PaCO2), which is the concentration of carbon dioxide in the blood. In chronic respiratory disease, destruction of alveoli and progressive airflow obstruction interfere with gas exchange and will eventually lead to significant hypoxaemia. Clinical signs of chronic hypoxaemia include ankle oedema and cyanosis, but these may not be apparent until the patient is severely hypoxic. Chronic hypoxaemia can also cause slowly progressive pulmonary hypertension with the development of right ventricular hypertrophy and possible cor pulmonale with secondary polycythaemia. Polycythaemia increases blood viscosity and hence increases the resistance to blood flow with a tendency to lead to thrombosis.
Oxygen therapy is used in patients with COPD to prolong and improve quality of life by correcting the hypoxia. Caution must be given to the use of oxygen in patients with COPD. In some patients, due to the chronic hypoxaemia that has occurred, the respiratory driver is the partial pressure of oxygen (PaO2). In these patients, giving oxygen at inappropriate flow rates can cause respiratory depression and hence a build-up of carbon dioxide in the blood leading to a respiratory acidosis.

Pulse oximetry in practice
It is essential that pulse oximeters are available in primary care (see Figure 1). This is a quick and easy screening tool, and while caution must be taken to ensure an accurate reading (see Table 1), pulse oximetry monitoring aids clinical decision-making. Pulse oximetry is a noninvasive measure of oxygen saturation via a finger or ear probe. It works by transcutaneous examination of the colour spectrum of haemoglobin, which changes with its degree of saturation. The oxygen saturation reading is a measure of the percentage of haemoglobin molecules saturated with oxygen. The normal arterial oxygen saturation is approximately 95-98%. A measurement of 92% or below, on more than one occasion, is the criterion for further detailed blood gas analysis and oxygen assessment in
secondary care.

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Indications for considering long-term oxygen therapy
NICE COPD guidelines recommend that the need for LTOT should be assessed six-monthly in patients with:(1)

  • Moderate to severe airflow obstruction (FEV1 less than 50% predicted). FEV1 is the amount of air blown out in the first second of a forced manoeuvre on a spirometry test. It is a measure of the level of severity of the lung function.
  • Cyanosis.
  • Polycythaemia.
  • Peripheral oedema.
  • Raised jugular venous pressure.
  • Oxygen saturations less than or equal to 92% breathing air.
  • Disabling breathlessness due to terminal disease.


Assessment for long-term oxygen therapy (LTOT)
Patients are referred to a specialist centre where the assessment is carried out. The criteria for assessment are as follows: patients with a PaO2 of less than 7.3 kPa when stable or patients with a PaO2 of 7.3-8.0 kPa when stable, with an additional risk feature, such as:

  • Secondary polycythaemia.
  • Nocturnal hypoxaemia.
  • Peripheral oedema.
  • Pulmonary hypertension.

Blood gases are measured using a capillary tube at the earlobe. This is an equivalent measure to that from arterial blood and is easier to obtain and more comfortable for the patient. The blood is measured when the patient is clinically stable and on optimal therapy on at least two occasions three weeks apart. The blood is then taken again once oxygen has been administered to ensure PaO2 is > 8.0 kPa without unacceptable hypercapnia.

Long-term oxygen therapy
For patients who require LTOT, this is best provided with a concentrator for home use via nasal prongs at 2-4 l/min depending on blood gases. 
Concentrators are machines that plug into the mains and convert room air into usable oxygen. Room air contains approximately 79% nitrogen and 21% oxygen. Zeolite inside the concentrator absorbs the nitrogen in the air, and produces oxygen at a concentration of 90%. Patients who have previously been used to cylinders may say the oxygen feels different. This is due to the lower pressure of oxygen from the concentrator.
LTOT is usually given for at least 15 hours per day, but greater benefits are seen if it is given for 20 hours per day. Patients are advised to put on the oxygen in the early evening and use it overnight so they can have a few hours during the daytime when they do not have to be attached to the machine.
It is important to maintain six-monthly follow-up with reassessment for early recognition of problems. The British Thoracic Society recommends domiciliary assessment by a respiratory health worker; however, new oxygen services are not widely in place at present, and community services to support this may not be available.(3)

Ambulatory oxygen therapy
Some patients with normal oxygen saturation at rest can desaturate on exercise and may benefit from ambulatory oxygen. There is not a great deal of evidence for benefit. The need for ambulatory oxygen, as in the case of LTOT, must be formally assessed. However, ambulatory oxygen assessment services are not widely available at present.

Short-burst oxygen
Short-burst oxygen has not been shown to be beneficial in patients with COPD and should not be prescribed unless the indication is for palliative use (see Table 2).

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The primary care nurse's role
Patients with COPD on oxygen therapy should be assessed six monthly. This provides an opportunity to assess and measure the following:

  • Smoking cessation.
  • Spirometry.
  • Pulse oximetry.
  • Inhaler technique and compliance.
  • General education (see Table 3).
  • Body mass index (BMI).
  • Exacerbation frequency.
  • MRC dyspnoea score (see Table 4).
  • lThe patient is caring for their oxygen equipment correctly:
    • Check the filter on the concentrator.
    • Correct use of the tubing, mask or cannulae and ensuring it is changed regularly according to manufacturer's instructions.
    • Ensure there is a full back-up cylinder.

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The new home oxygen service
On 1 February 2006 new changes in oxygen provision were brought in under the new DH guidelines to provide a new integrated oxygen service.4 Oxygen is now ordered using a home oxygen order form (HOOF), which should be completed by the assessing clinician once the formal assessment is carried out in the specialist centre. The type of oxygen required, flow rate and duration, and any other equipment required is ordered on the same form. The patient must also sign a consent form to allow their personal information to be released to the oxygen provider, who passes this information onto the fire service. The companies (see Table 5) provide 24-hour cover for emergencies with trained engineers on hand, and there are nurse advisers who provide training and education to clinical staff.

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The future of oxygen services
To support the new oxygen service, it is vitally important that community services are developed in partnership with secondary care specialist centres to ensure patients are supported and reviewed in accordance with the BTS recommendations. In some areas this is starting to happen either as part of existing respiratory services or as a new initiative. There is now an opportunity to develop services locally to support patients in a more structured way by developing a truly integrated approach between primary and secondary care.

References

  1. NICE. Management of chronic obstructive pulmonary disease in adults in primary and secondary care. London: NICE; 2004.
  2. Nocturnal Oxygen Therapy Trial Group. Continuous or nocturnal oxygen therapy in hypoxaemic chronic obstructive lung disease: a clinical trial. Ann Intern Med 1980;93:391-8.
  3. British Thoracic Society. Working group on home oxygen services. Clinical component for the home oxygen service in England and Wales. London: BTS; 2005.
  4. Department of Health. Home oxygen service. London: DH; 2007. Available from: http://www.dh.gov.uk/en/Policyandguidance/Medicinespharmacyandindustry/P...