Asthma

Author: Prof Paul Cullinan, Professor in Occupational and Environmental Respiratory Disease and Honorary Consultant Physician, National Heart and Lung Institute (Imperial College London)

Date: November 2012.

 

These guidelines were prepared for the Fire and Rescue Services.

 

Asthma is a disease characterised by variable constriction of the airways causing an increased resistance to air flow leading to reductions in ventilation and hyperinflation of the lungs.  A diagnosis of asthma is common in United Kingdom populations.  Findings from the Health Survey for England in 2001 (Department of Health, 2003), suggest that about one quarter of men and women aged between 16 and 24 years have at some point been diagnosed with the disease; the proportions are generally lower in older persons (see Figure 1), probably reflecting a birth cohort effect, and at all adult ages are higher in women.  Since a characteristic of asthma is its tendency to remit (and relapse) and since its symptoms are not specific, none of these figures necessarily reflects the age-specific prevalence of current disease.

 

 

 

 

 

 

 

 

 

The incidence of asthma is highest in the first years of life but approximately two thirds of children with asthma will be asymptomatic by the age of 15.  Remission is more common in males, in those whose asthma started after the age of 5, in those without accompanying rhinitis or eczema and in those with no family history of asthma.  About a third of those whose childhood asthma has remitted will have a relapse before the age of 35 but this is seldom severe and is usually controlled with reliever medication alone.

A proportion – probably small - of those with remitted childhood asthma will have asymptomatic bronchial hyper-reactivity in adulthood. This can be detected using a variety of non-specific provocation tests.  There is limited evidence that persisting hyper-reactivity increases the risk of subsequent symptomatic relapse.

The symptoms of asthma are not entirely specific and the disease has no unambiguous or universally accepted definition.  Thus diagnoses, and reports of diagnoses, will include alternative respiratory conditions; most authorities, however, consider a doctor’s diagnosis to be more specific than otherwise self-reported disease.  Conversely, a diagnosis of asthma may not be recalled, especially when it was made in early childhood and the disease has since remitted.  Treatments used in asthma are also used for other respiratory diseases, commonly for infection-related wheeze at any age and, later in life, for chronic obstructive pulmonary disease; reports of such treatment are not necessarily confirmation of asthma

The symptoms of asthma vary from a dry cough to an audible wheeze with shortness of breath.  The disease is characterised by variability and by the provocation of symptoms in response to environmental triggers.  Most asthma arising in childhood is accompanied by atopy, a tendency to develop immediate-type sensitivity to environmental aeroallergens which frequently persists; around half of adults with asthma report symptoms that are provoked by specific allergens (Figure 2).  Other common triggers include respiratory infections, cigarette smoke, exercise and cold air.  Around one in ten adults with asthma recognise no specific provoking factor(s). 

Most UK adults with asthma have disease that requires treatment with only an as-needed ß2 agonist or a regular inhaled corticosteroid at low doses.  Each year about 10% of them will have an exacerbation that will require treatment with prednisolone (Cullinan, 2011), usually provoked by a respiratory infection.  Severe, unpredictable attacks of asthma are rare and are generally reported only by those with a history of such.  Current treatments for asthma are, if used properly, very effective in maintaining disease stability and, in most individuals, freedom from symptoms for most of the time.  Poor asthma control often reflects under-treatment, frequently from poor adherence.

The intra-individual variability in asthma is far smaller than the variation between adults with the disease; thus while the prevalence of the condition is high among professional athletes, others (albeit few) with the disease are severely disabled by breathlessness and it is plain that a diagnosis of ‘asthma’ covers both a spectrum of severities and a variety of phenotypes. This has two important consequences.  First, it is essential that individuals with asthma are assessed on a case-by-case basis; and second, the best predictor of future performance is provided by consideration of the recent past (Cullinan, 2011).

Given the above, it is clear that the needs of recruits with a history of asthma (current or past) should be considered individually with a focus on the severity, stability and predictability of the disease.  Most of the necessary information can be collected through a simple history of current and recent symptoms, recent exacerbations and current treatment use.  While the last of these is commonly used as a measure of asthma severity this may not be appropriate and a distinction between treatment ‘use’ and treatment ‘requirement’ needs to be made.  Spirometry will detect airflow obstruction but is often normal in young adults with well-controlled asthma and in any case is a poor predictor of functional ability.  Measurement of residual bronchial hyperreactivity through non-specific provocation testing in a hospital laboratory may be helpful in determining the likely response to respiratory irritants and the probability of a relapse in the future.

Bronchoconstriction after exercise is common in those with inadequately treated asthma; but rarely severe in those whose disease is mild and treated appropriately, and unusual in those with a history of childhood disease that is in remission. Exercise-induced asthma can be identified through a clinical history and confirmed through formal exercise testing although the test is difficult to standardise and may not reflect working conditions well.

Recruits with a clear history of severe or moderate asthma with inadequate symptom control and frequent exacerbations – especially when these are unpredictable – should not be routinely exposed to irritant or volatile vapours or fumes (including smoke) or strenuous exertion.  Those whose disease is more mild and requires treatment only during periods of respiratory infection, or is well-controlled by the use of a regular inhaled corticosteroid at low doses with no or rare need for treatment with as-needed ß2 agonist, are likely to have few difficulties with active firefighting.  This includes the use of breathing apparatus.

Guidance for Fire and Rescue Services:

  1. There should be no bar to employment based on the diagnosis of asthma alone.Recruits with a history of asthma, past or current, require individual assessment.

  2. Assessment should include a careful history that focusses on current symptoms and treatment requirements; triggering factors including exercise and irritant exposures; and the frequency and history of exacerbations.

  3. Recruits with a history of childhood asthma that was never severe and responded well to treatment with a ß2 agonist with or without an inhaled corticosteroid, who have been symptom free in recent years and who have passed their standard fitness tests without difficulty can be employed in all fire-fighting roles.There is no bar to their using breathing apparatus.

  4. Recruits with current asthma that is controlled by the use of a ß2 agonist with or without an inhaled corticosteroid and in whom any symptoms are mild, predictable and provoked by factors unrelated to the work environment, and exacerbations provoked by infection or seasonal allergy are infrequent can be employed in all fire-fighting roles.  There is no bar to their using breathing apparatus.

  5. Recruits whose asthma causes symptoms with exercise or exposure to common irritants such as cold air, smoke or fumes (ie triggers that are likely to be encountered at work) irrespective of the treatment they are using, and those with frequent exacerbations provoked by infection or seasonal allergy should not be employed in active fire-fighting roles. They may benefit from a specialist review of their current treatment.

  6. Specialist respiratory assessment is required in doubtful cases.Such assessment should include, as appropriate, direct (usually with inhaled histamine, mannitol or metacholine) or indirect (most suitably with exercise) tests of bronchial hyperreactivity.

Adult Onset Asthma

Asthma with an onset in adulthood is, in general, uncommon and more often it reflects a history of childhood disease that has been forgotten.  True adult onset should raise the question of ‘occupational’ asthma arising from new sensitisation to an airborne biological or chemical agent in the workplace or, more rarely, as a result of a single, high-dose exposure to an irritant fume (Reactive Airways Dysfunction Syndrome, or RADS).  The diagnosis of occupational asthma is complex and warrants careful investigation; referral to a respiratory physician with a special interest in occupation is advised.  Occupational asthma that reflects a specific sensitisation is usually managed through exposure control which often requires redeployment.  RADS is managed in the same way as other forms of adult asthma although it may be relatively resistant to standard pharmacological therapies. Serving uniformed fire personnel with severe RADS should not be exposed to smoke or fumes, so the development of this condition in a firefighter may necessitate redeployment.

Department of Health, 2003. Health Survey for England 2001. The Stationery Office, Norwich.  Available from: URL: http://www.archive2.official-documents.co.uk/document/deps/doh/survey01/hse01.htm

Cullinan P., 2011. Evidence-­‐based guidance for the assessment of new employees with asthma; a report to the British Occupational Health Research Foundation. http://www.bohrf.org.uk/downloads/Evidence_based_guidance_for_the_assessment_of_new_employees_with_asthma.pdf