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Asthma 

Chapter:
Asthma
Author(s):

A.J. Newman Taylor

and Paul Cullinan

DOI:
10.1093/med/9780199204854.003.1807

A relevant case history from Oxford Case Histories in Respiratory Medicine has been added to this chapter.

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date: 30 March 2017

Asthma is a chronic inflammatory disease of the bronchial airways that is characterized pathologically by a desquamative eosinophilic bronchitis and clinically by reversible airway narrowing and increased airway responsiveness to nonspecific provocative stimuli. The condition is common, frequently disabling, and can cause death. In the Western world it now affects more than 10% of children and more than 5% of adults, and in England and Wales it is the cause of more than 100 000 hospital admissions and is the certified cause of death of 1500 to 2000 people each year.

Asthma triggers

The risk of developing asthma is increased in atopic individuals, and in asthmatics natural allergen exposure induces asthma and airway hyper-responsiveness. Viral infections, most commonly with rhinoviruses, cause 80 to 85% of exacerbations of asthma in children and 50 to 75% in adults.

Occupational asthma—agents inhaled at work can be the primary cause (induce) or can exacerbate (provoke) asthma. Such occupational asthma may be due to inhalation of irritant chemicals (‘irritant induced asthma’) or substances that induce an allergic reaction (‘hypersensitivity induced asthma’).

Drugs—some can exacerbate asthma, with β‎-blockers and nonsteroidal anti-inflammatory drugs (NSAIDs) being the most important.

Clinical features

History—symptoms are nonspecific, typically shortness of breath, wheezing, chest tightness and cough. They are usually variable in severity over short periods of time, but can be persistent, and are typically worse at night. Because occupational causes are potentially avoidable, all cases of asthma that have occurred or recurred in adult life should be questioned about symptomatic improvement when away from work, and, if present, enquiry made about potential causes of asthma in the workplace.

Clinical examination—outside the context of an acute exacerbation (see below), the physical signs of mild or moderate asthma may be limited to expiratory wheezes audible over the lungs. Because of the variable nature of airway narrowing some patients have normal lung sounds, but this would not be expected in those with persistent symptomatic asthma.

Diagnosis

Asthma needs to be differentiated from localized airways obstruction, other causes of generalized airways obstruction, and other causes of intermittent breathlessness.

Demonstration of airflow limitation—asthma is most typically diagnosed by the demonstration that this varies spontaneously over short periods of time, or improves after inhalation of a short acting β‎-agonist or, over a more prolonged period of time, use of a corticosteroid either by inhalation or by mouth. The most clinically useful measurements of airflow limitation are (1) forced expiratory volume in 1 s (FEV1), which may be expressed as a proportion of the forced vital capacity (FVC) as FEV1/FVC%, and (2) peak expiratory flow rate (PEF).

Occupational asthma—(1) in irritant-induced asthma the association of the onset of asthma with inhalation of a toxic chemical is usually clear; (2) in hypersensitivity-induced asthma the diagnosis depends on (a) exposure to a sensitizing agent at work; (b) a characteristic history of onset of asthma after an initial symptom-free period of exposure, with deterioration in symptoms during periods at work and improvements during absence from work; and (c) the results of objective investigations—lung function tests, immunological tests, and inhalation tests.

Classification—patients with asthma can be categorized, at any one time, by whether their symptoms are intermittent or persistent, and by the severity of their symptoms and underlying airway narrowing (measured by lung function tests).

Management—general aims

The aims of treating patients with intermittent or persistent asthma are to: (1) educate the patient about their disease and the objectives of its management; (2) minimize or eliminate asthma symptoms; (3) achieve best possible lung function and prevent an accelerated decline in lung function; (4) prevent exacerbations of asthma; (5) achieve these objectives with fewest drugs, keeping short-term and long-term adverse effects to a minimum.

The objectives for effective asthma control in individual patients are to: (1) allow normal daytime activities as well as the ability to enjoy physically demanding activities; (2) permit sleeping through night, without being awoken by respiratory symptoms; (3) achieve a situation where use of ‘rescue’ medication with inhaled β‎2 agonists is needed less than once per day; (4) achieve normal or near normal PEF and FEV1 with less than 20% variability between best and worst values; (5) to avoid drug side effects.

The ‘stepped’ approach to treatment

Education—there is clear evidence that patient education to enable adults to manage their asthma can reduce the frequency of unscheduled visits to general practitioners, hospital admissions, and time off work. The four important components of effective patient education are (1) information, (2) self-monitoring, (3) regular medical review, and (4) having a written action plan.

Avoidance of precipitants—the identification and, where feasible, the avoidance of relevant allergens at home or at work is an essential part of the management of asthma.

A ‘stepped’ approach to treatment is the basis of current guidelines for asthma management:

Step 1—mild intermittent asthma controlled by the use of an inhaled shorter-acting β‎2-agonist (e.g. salbutamol or terbutaline) less than once a day. Requirement for more regular treatment implies the need for regular anti-inflammatory treatment (i.e. a higher step).

Step 2—mild persistent or intermittent asthma that is of sufficient frequency to require regular anti-inflammatory treatment. Treatment with an inhaled corticosteroid should be started at a dose of beclometasone 400 µg twice daily (or equivalent) in adults and continued for at least 3 months, before reducing the dose to the minimum required to maintain good control. Short-acting β‎2-agonists are used as required for symptomatic relief.

Step 3—moderate persistent asthma that is not controlled by Step 1 and Step 2. The treatment of choice is the addition of a long-acting β‎2-agonist. If it provides benefit but asthma remains inadequately controlled, the dose of inhaled corticosteroid should be doubled. If it provides no benefit it should be discontinued and the inhaled steroid dose doubled, and if this does not provide adequate control a trial of other treatments such as a slow-release theophylline or leukotriene antagonist should be instituted.

Step 4—asthma control remains poor despite the measures recommended in Step 3. Consideration should be given to further increasing the dose of the inhaled corticosteroid to the equivalent of beclometasone 2000 μ‎g/day or to the addition of a fourth drug, e.g. slow-release theophylline, a leukotriene antagonist, or an oral β‎2-agonist.

Step 5—failure to respond to combinations of Step 4 treatments requires the addition of an oral corticosteroid while continuing high-dose inhaled corticosteroid treatment.

Acute exacerbations of asthma

Asthma exacerbations are episodes of progressively worsening airway narrowing that can vary in severity from those that patients are able to manage themselves by following an agreed treatment plan, to severe attacks which at their most dramatic develop rapidly and become life threatening within minutes or hours.

Fatal or near fatal attacks—these are associated with (1) patients who have previously required hospital admission for severe asthma and who require regular oral steroid treatment; (2) failure to recognize severity of asthma by the patient; (3) failure to recognize the severity of asthma by the doctor; (4) undertreatment or inappropriate treatment, with failure to use oral corticosteroids in adequate doses early in an exacerbation probably being the single commonest remediable factor.

Clinical features—in acute severe asthma the patient is usually extremely short of breath, sitting up or leaning forward to use their accessory muscles of respiration, with impaired speech and increasingly prolonged expiration alternating with short inspiratory gasps. Tachycardia and pulsus paradoxus are often found. Airway narrowing may become sufficiently severe for no wheeze to be audible and gas exchange sufficiently impaired to cause detectable cyanosis, when the patient will be distressed, anxious, apprehensive and confused. Exhaustion ultimately leads to inadequate ventilation and a rising Pco2, the two cardinal features that indicate the need for transfer to an intensive care unit in the event that assisted ventilation is required. A value of PEF of less than 50% of predicted or of the recent best value in an adult aged less than 50 years usually indicates severe asthma; a value of less than 33% indicates a potentially life-threatening attack.

Management—initial treatment of a severe attack of asthma should be with (1) oxygen (60% FiO2); (2) β‎2-agonist—nebulized salbutamol 2.5 to 5 mg or terbutaline 5 to 10 mg driven by oxygen; (3) steroid—oral prednisolone 30 to 60 mg or intravenous hydrocortisone 200 mg. If there is a poor response to initial treatment after 15 to 30 min, then (1) continue oxygen; (2) repeat nebulized salbutamol 5 mg after 15 min; (3) add ipatropium 0.5 mg to nebulized β‎2-agonist; (4) give intravenous hydrocortisone 200 mg 4 hourly; (5) consider intravenous magnesium sulphate 1.2 to 2 g over 20 min.

Investigations—chest radiograph to exclude pneumothorax; arterial blood gases to assess oxygenation and ventilation; monitor serum K+ (risk of hypokalaemia with high-dose β‎2-agonist).

The patient in extremis—indications for transfer to intensive care and for consideration of intermittent positive-pressure ventilation (IPPV) are (1) hypoxia (PaO2 <8 kPa) despite FiO2 60%; (2) hypercapnoea (PaCO2 > 6 kPa); (3) exhaustion with feeble respiration; (4) confusion or drowsiness; (5) unconsciousness; (6) respiratory arrest.

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