Asthma Diagnosis and Management
Section snippets
Epidemiology
Asthma is one of the most common chronic diseases in adults, affecting 300 million people worldwide.1 Asthma affects 7% to 8% of people in North America,2, 3, 4 including more than 24 million Americans4 and 3 million Canadians.2, 3 The prevalence of asthma in older adults is 6% to 10%.4, 5 The number of elderly patients will increase in the future as this segment of the population continues to grow. Currently, the highest prevalence of asthma is seen in English-language countries and Latin
Pathophysiology
Asthma is a chronic inflammatory disorder that is characterized by bronchial hyperresponsiveness and airway obstruction.20 Bronchospasm is the key feature of asthma, and is triggered by allergens or other stimuli. Mast cells are activated through immunoglobulin E receptors to release inflammatory mediators that directly target bronchial smooth muscle.21, 22 Bronchodilators are usually effective in reversing these symptoms, and are the recommended first-line treatment of asthma.20, 23, 24
History and physical examination
The classic triad of asthma includes chronic cough, wheeze, and dyspnea. However, patients often present with only 1 of these symptoms, which can make diagnosis challenging. In studies of patients presenting solely with wheeze, chronic cough, or dyspnea, only 24% to 35% were eventually diagnosed with asthma.25, 34, 35 Symptoms of asthma are typically worse at night or early in the morning. A personal history of atopy and family history of asthma favor the diagnosis.
Asthma symptoms are typically
Differential diagnosis
Wheezing is characteristic of asthma, but can be a presentation of many different diseases. Physicians should be aware that “all that wheezes is not asthma; all that wheezes is not obstruction.” The clinical diagnosis of asthma should be confirmed by quantitative measurements of lung function.20 Spirometry is the preferred diagnostic test, and can be done in pulmonary function laboratories, or alternatively in the primary care office. Spirometry measures the forced vital capacity (FVC; the
ED evaluation
Asthma exacerbations are characterized by obstruction to expiratory airflow, and can be assessed by quantitative tests of lung function. These measurements include PEF and spirometry, and are more reliable indicators of the severity of acute asthma than clinical symptoms alone.20 PEF is the most commonly used test in the ED to assess the degree of obstruction. PEF readings are safe, quick, and cost-effective. They can be used to monitor a patient’s response to treatment over time. Normal PEF
Treatment
Early recognition and treatment of the asthma exacerbation is essential for success in overall management. Patients presenting to the ED with acute asthma should be quickly evaluated for the adequacy of airway, breathing, and circulation. This evaluation should include a complete set of vital signs, pulse oximetry, respiratory rate, and an assessment of respiratory effort. Treatment should be started immediately.
Current recommendations are outlined in the 2007 National Asthma and Education and
β2-Agonists
β2-Agonists are potent bronchodilators that act on β receptors to quickly and effectively relax bronchial smooth muscle. Short-acting β-agonists are the recommended first-line therapy for the acute asthma exacerbation.20 Albuterol is the most commonly used β2-agonist for acute asthma.
β2-Agonists can be administered in multiple forms, including MDI, nebulizer, subcutaneous injection, and intravenous injection. Traditionally, aerosolized bronchodilators have been administered by continuous-flow
Anticholinergics
Anticholinergics block the action of acetylcholine on the parasympathetic autonomic system. They decrease vagally mediated smooth muscle contraction in the airways, leading to bronchodilation. Anticholinergics are recommended for the treatment of severe asthma, in combination with short-acting β-agonists.20, 78 The synergistic effects of these 2 agents decrease hospitalization rates and improve lung function.78, 79, 80 Ipratropium bromide is the most commonly used anticholinergic agent for the
Corticosteroids
Acute asthma is characterized by airway edema, mucus hypersecretion, and cellular infiltration, in addition to bronchospasm. This inflammatory reaction can lead to persistent airway obstruction, and is the target of corticosteroids. Corticosteroids are the most potent and effective antiinflammatory agents available for the treatment of asthma. Their onset of action can take up to 6 hours to become clinically apparent.83
Early systemic corticosteroids in the ED are recommended for moderate or
Magnesium sulfate
There is evidence that magnesium inhibits the influx of calcium into smooth muscle cells, causing bronchodilation.91 In addition, magnesium acts on neutrophils to decrease inflammation.92 A 2009 Cochrane Review found that intravenous magnesium sulfate significantly improved pulmonary function and decreased hospital admission rates in patients suffering from severe asthma. There was no significant effect noted for all asthmatics in general.93 Side effects of intravenous magnesium were minimal.
Heliox
Heliox is a blend of 70% to 80% helium and 20% to 30% oxygen, which has a lower gas density than air. Heliox can potentially decrease resistance to airflow and enhance delivery of nebulized bronchodilators.95, 96 The role of heliox in asthma management remains unclear. Currently, it is not recommended as an initial treatment of asthma.20, 97 There have been few controlled studies and the optimal duration of heliox treatment is unknown. Current guidelines recommend that heliox-driven albuterol
Leukotriene modifiers
Leukotrienes are potent inflammatory mediators. Leukotriene modifiers improve lung function and decrease asthma exacerbations.103, 104 Three leukotriene modifiers are currently available for long-term therapy for asthma: montelukast, zafirlukast, and zileuton. However, many studies have found that overall efficacy of inhaled corticosteroids is superior to that of leukotriene modifiers for the long-term control of asthma.103, 104 Leukotriene modifiers are an alternative chronic treatment of
Immunotherapy
Immunotherapy is an emerging area of asthma treatment that targets allergen triggers of asthma. It is the only treatment modality that modifies the underlying disease process. Immunotherapy has no role in the acute management of asthma but can be used for long-term maintenance therapy. Injection immunotherapy should be considered when the allergic component is well documented, and when asthma control remains inadequate.23, 24, 107
Methylxanthines
Theophylline and aminophylline are widely prescribed for asthma worldwide, and have been used for more than 50 years. However, current evidence shows that this medication class does not produce additional bronchodilation when combined with standard β-agonist therapy, and results in more adverse effects.108 Currently, the methylxanthines are not recommended as therapy for the acute exacerbation of asthma. Sustained-release theophylline can be considered for the treatment of mild persistent
Cromolyn sodium and nedocromil
Cromolyn sodium and nedocromil are alternative treatments for mild persistent asthma. These medications block chloride channels and modulate mast cell mediator release.109 They can be used as preventive treatment before exercise or allergen exposure.20 These agents have no role in the acute management of asthma.
Management of status asthmaticus
Status asthmaticus is an acute, severe exacerbation of asthma that does not respond to conventional treatment. It can progress to respiratory failure and death. All patients presenting to the ED with severe asthma should be started on early intensive therapy. This therapy includes β2-agonists, anticholinergics, and systemic corticosteroids. If patients fail to respond to initial therapy, they should be moved to a more closely monitored setting.
Heliox-driven nebulization of bronchodilators and
Noninvasive ventilation
Noninvasive ventilation is a promising area of acute asthma treatment. The goal of this modality is to support and reduce the patient’s respiratory effort, giving enough time to allow other treatments to take effect and possibly avoid intubation.116 Small studies have supported its use for acute asthma.117, 118 Noninvasive ventilation can be considered for the stable asthmatic who is tiring from the high respiratory demand, and who is expected to recover in the next few hours.116 A recent
Intubation and mechanical ventilation
A minority of severe asthmatics require invasive ventilation in a critical care setting. Endotracheal intubation should be considered in the patient with impending respiratory failure, despite maximal medical therapy. Risk factors for death from asthma include previous intubations or intensive care admissions, or recent history of poorly controlled asthma.123, 124, 125, 126, 127 Four percent of patients hospitalized for asthma require endotracheal intubation and mechanical ventilation.128
Asthma and pregnancy
Asthma affects 3% to 8% of pregnant women and has a variable clinical course.134, 135, 136, 137 Clinical symptoms improve in one-third of pregnancies, worsen in one-third, and remain unchanged in one-third.133, 138 Clinical severity of asthma during pregnancy seems to follow severity before pregnancy.139, 140 Asthma exacerbations occur in 20% to 36% of pregnancies, most frequently between weeks 14 and 24. Poorly controlled asthma during pregnancy has been linked with increased risk of
Disposition
The goal for discharge from the ED is an FEV1 or PEF greater than or equal to 70% of predicted, and a response that is sustained for 60 minutes after last treatment. Patient education is a key component to successful asthma management, and should be initiated in the ED.20 Medications and inhaler techniques should be reviewed. A written asthma action plan that describes early recognition and self-management of exacerbations should be started or reviewed.20 Patients should be counseled to avoid
Summary
Asthma is a chronic inflammatory disease that is commonly encountered in the ED. Early signs of worsening asthma should be recognized and immediate treatment given. β-Agonists, anticholinergics, and corticosteroids are mainstays of treatment of the asthma exacerbation. Magnesium sulfate, epinephrine, and heliox can be considered for life-threatening presentations of asthma. Control of environmental triggers, improvements in daily maintenance therapy for asthma, and increasing patient education
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The authors have nothing to disclose.