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Understanding difficult-to-control asthma

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VOL: 102, ISSUE: 36, PAGE NO: 44

Debbie A. Campbell, BSc, RGN, is asthma clinical nurse specialist, Royal Brompton and Harefield NHS Trust, London.

Asthma is characterised by airway inflammation, reversible or partially reversible airflow obstruction and an exacerbated bronchoconstrictor response to various inhaled stimuli (also known as bronchial hyper-responsiveness) (British Thoracic Society/Scottish Intercollegiate Guideline Network, 2005). It causes symptoms of breathlessness, wheeze, chest tightness and cough, with occasional sputum production, all of which are usually intermittent and variable (BTS/SIGN, 2005).

Most people with asthma achieve good symptom control with inhaled therapies but approximately 5-10% of these patients in the UK remain symptomatic despite maximal therapy. They have what is described as difficult-to-control asthma (Barnes and Woolcock, 1998). Such patients have an increased risk of death (Wareham et al, 1993), experience greater morbidity, have a reduced quality of life (Barnes and Woolcock,1998) and often have adverse side-effects from drug therapy.

There is no precise definition for difficult-to-control asthma, but it is associated with the number of symptoms patients have and how much treatment they require. The term refers to those patients on step four (persistent poor control) and five (continuous or frequent use of oral corticosteroids) of the British Thoracic Society/Scottish Intercollegiate Guideline Network asthma management guidelines (BTS/SIGN, 2005).

Patients who continue to have uncontrolled symptoms despite standard therapy require referral to a difficult-to-control asthma clinic. The benefit of such a clinic is that a systematic evaluation can take place that may reveal factors contributing to the individual’s symptoms (Heaney et al, 2003; Robinson et al, 2003; Chung, 2000). It can take 6-12 months to establish a diagnosis (Chung et al, 1999).

There is no consensus about what investigations should be performed, but a detailed assessment, including lung-function testing and compliance with therapy is required.

Patterns of difficult-to-control asthma

Assessment of symptoms and exacerbation rates over a period of time can help to establish types of difficult-to-control asthma. Chung et al (1999) have identified the following types of difficult-to-control asthma and the treatment for each:

  • Fatal or near-fatal asthma - usually associated with hypercapnia (high concentrations of carbon dioxide in the arterial circulation) and/or the need for mechanical ventilation despite treatment. These patients often require frequent courses of oral corticosteroids;
  • Brittle asthma type I - there is consistent wide variation in symptoms and lung function tests despite regular medication at high dose;
  • Brittle asthma type II - characterised by severe episodes of airway narrowing that occur rapidly over minutes or hours with no obvious trigger. Patients have a background of normal lung function and/or well-controlled asthma (Ayres, 1998). They often require short periods of mechanical ventilation. This type of asthma is extremely rare; it has been suggested that it accounts for only 0.05% of people with asthma (Ayres et al, 1998).
  • Airway narrowing - patients require continuous low doses of oral corticosteroids with intermittent increases to high doses (from 40-60mg prednisolone/day). These patients are known as steroid-dependent asthmatics;
  • Aspirin-induced asthma - usually associated with rhinitis, sinusitis and nasal polyps (known as Samter’s Triad). These patients are sensitive to non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin (Barnes and Woolcock, 1998); a severe asthma attack can occur within three hours of ingestion of an NSAID (Lee, 2003);
  • Premenstrual asthma - this has a very distinct pattern, with symptoms occurring within two to five days of the onset of the menstrual bleed. Once the bleed has occurred the symptoms disappear and the lung function returns fully to normal. This type of asthma is usually responsive to beta-agonist therapies but the cause is unclear (Barnes and Woolcock, 1998);
  • Adult onset asthma - patients who develop asthma after the age of 21 years often have difficult-to-control asthma (Chung et al, 1999). The reason for this is unknown, but despite high doses of therapy and/or continuous oral corticosteroids they usually remain symptomatic.

It can take time to understand the different types of asthma, but knowing the type experienced by a patient can assist with planning that individual’s management and treatment regimen.

Is the diagnosis correct?

It is important to have a diagnosis of asthma confirmed or to identify whether there is another cause for the patient’s symptoms. A structured history should include details of childhood asthma, allergies, any admissions to intensive care with respiratory problems and past and current treatment.

Detailed lung-function assessment includes the following tests:

  • Spirometry - to measure airflow from the lungs and lung volume;
  • Gas transfer - to measure the ability of the lungs to transfer a trace amount of carbon monoxide into the pulmonary circulation;
  • Airway resistance measurement - a method of determining the patency of the airways during tidal breathing.

Asthma treatment should be withheld before performing lung function investigations; for example, the use of short-acting bronchodilators should be stopped for four hours before a lung function test (BTS/SIGN, 2005). Patients may find this stressful, so it is important that the nurse reassures them that they are safe and that action will be taken if they become symptomatic.

Reversibility testing, which measures whether there is an increase in airflow following the inhalation of short-acting bronchodilator medication, is the most common lung-function test for diagnosing asthma, but patients may also be given a histamine challenge to identify airway hyper-responsiveness (BTS/SIGN, 2005).

Although lung conditions such as bronchiectasis (irreversible dilatation and destruction of the bronchial wall) and chronic bronchitis (chronic inflammation of the mucus membrane of the respiratory tract) may co-exist with asthma, the effect of co-existing lung disease on the severity of asthma and its control is unknown (Chung et al, 1999).

Factors contributing to loss of asthma control

There are a number of medical factors that may contribute to loss of asthma control (Box 1). Some of these are discussed in more detail below.

Psychological factors

Factors such as anxiety, depression, denial of having the disease and the lack of appropriate medical care have all been identified in patients with difficult-to-control asthma (Chung et al, 1999).

Concordance with medication

A recent evaluation of a group of patients with difficult-to-control asthma found that almost 50% did not take their inhaled medication (Gamble et al, 2005). Although adherence to prescribed medicines is notoriously difficult to assess, prescription monitoring, weighing inhaler canisters and taking blood tests for theophylline, prednisolone and cortisol levels are all methods that can be used to obtain a more detailed picture of the extent of patients’ concordance with their prescribed medicines.

Many factors can influence concordance. For example, patients misunderstanding their treatments, denying they have asthma, or their social situation (O’Connor, 2005). Providing patients with information about their treatments, educating them about their disease and building an open and honest relationship can assist in identifying factors that influence an individual patient’s attitudes and beliefs towards their medicines. Discussions concerning concordance must take place during the initial assessment and periodically while the patient is under review.

Conclusion

Patients with difficult-to-control asthma have more hospital admissions, greater morbidity and an increased risk of death than other people with asthma. These patients need to be referred to a difficult-to-control asthma clinic in order to have their diagnosis confirmed and the factors that contribute to their condition identified.

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