• Clinical science

Asthma

Abstract

Asthma is a chronic inflammatory disease of the respiratory system characterized by bronchial hyperresponsiveness, episodic exacerbations (asthma attacks), and reversible airflow obstruction. Allergic (extrinsic) asthma usually develops during childhood and is triggered by allergens such as pollen, dust mites, and certain foods. Nonallergic (environmental or intrinsic) asthma usually develops in patients over the age of forty and can have various triggers, such as cold air, medication (e.g., aspirin), exercise, and viral infection. The cardinal symptoms are intermittent dyspnea, coughing, and high-pitched expiratory wheezing. Symptoms remit in response to antiasthmatic medication or resolve spontaneously upon removal of the trigger. Confirmation of the diagnosis involves pulmonary function tests, allergy tests, and chest x-ray. First-line treatment consists of inhaled bronchodilators (e.g., short-acting beta2-agonists) for acute exacerbations and inhaled corticosteroids (e.g., budesonide) for long-term asthma control. Patients should be taught the correct usage of inhalers for self-medication and measurement of peak expiratory flow (PEF) to self-monitor disease progression and severity. Severe asthma exacerbation can be life-threatening and may require immediate emergency treatment and/or hospitalization.

Epidemiology

  • Prevalence: 5–10% of the US population; more common in black than white patients
  • Sex: differs depending on age at onset
    • ♂ > ♀ in patients < 18 years
    • ♀ > ♂ in patients > 18 years
  • Age of onset

References:[1][2]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

The following factors can act as initial triggers of asthma or exacerbate an existing condition:

Childhood exposure to second-hand smoke increases the risk of developing asthma!

References:[3][1]

Pathophysiology

Asthma is generally characterized by the following three processes:

  1. Bronchial hyperresponsiveness
  2. Bronchial inflammation
    • Symptoms are primarily caused by inflammation of the terminal bronchioles, which are lined with smooth muscle but lack the cartilage found in larger airways.
    • When an allergen triggers a hypersensitivity reaction, there is bronchial submucosal edema and smooth muscle contraction and the bronchioles collapse (they lack support of cartilage) → symptoms of asthma.
  3. Endobronchial obstruction caused by:

Some forms of asthma have specific pathophysiologies:

References:[1]

Clinical features

Chronic/persistent symptoms

  • Mild to moderate symptoms
    • Persistent, dry cough that worsens at night, with exercise, or on exposure to triggers/irritants (e.g., cold air, allergens, smoke)
    • End-expiratory wheezes
    • Chronic allergic rhinitis with nasal congestion
    • Dyspnea
    • Chest tightness
  • Severe symptoms
  • Cough variant asthma
    • A form of asthma in which the predominant symptom is chronic, dry cough
    • Other characteristic symptoms of asthma (e.g., wheezes, congestion, dyspnea) are absent.

Acute asthma attack

  • Definition: acute, reversible episode of lower airway obstruction that may be life-threatening
Symptoms Mild Moderate Severe
Breathlessness While walking While at rest At rest
Position Can lie down Prefers sitting Hunched over
Ability to speak Sentences Phrases Individual words
Alertness May be agitated Usually agitated Agitated
Signs
Respiratory rate Increased Increased Often > 30/minute
Wheezing Moderate, often only end-expiratory Loud; throughout exhalation Throughout inhalation and exhalation; can also be absent
Use of accessory muscles Rarely Commonly Usually
Pulse/minute < 100 100–120 > 120
Pulsus paradoxus Absent May be present Often present
PCO2 < 42 mm Hg > 42 mm Hg ≥ 42 mm Hg
SaO2 > 95% 90–95% < 90%

Clinical examination

  • Auscultation (characteristic findings are usually only present during acute attacks)
  • Percussion
    • Hyperresonant sound
    • Inferior displacement and poor movement of the diaphragm
  • In severe attacks

Characteristic examination findings may not be present between episodes of asthma exacerbation!

References:[3][4][1][5]

Diagnostics

Evaluation of pulmonary function

  1. Pulmonary function testing (spirometry)
  2. Methacholine challenge test (bronchoprovocation test)
  3. Chest x-ray
    • Usually only indicated in patients with severe asthma to exclude differential diagnoses (e.g., pneumonia, pneumothorax)
    • Normal in mild cases
    • Signs of pulmonary hyperinflation in cases of severe asthma

Laboratory studies and further workup

  • Pulse oximetry and blood gas analysis (ABG)
    • Blood gas analysis should be performed if oxygen saturation (SpO2) is < 94%
    • Findings on ABG
      • ↓ pO2 = type 1 respiratory failure
      • ↓ pO2 and ↑ pCO2 = type 2 respiratory failure
  • In allergic asthma
  • In asthma triggered by infection: elevated inflammatory markers
  • Sputum sample: Curschmann spirals, Charcot-Leyden crystals, and/or Creola bodies

Patients with acute asthma exacerbation generally have ↓ PCO2 and ↑ pH due to tachypnea. If these values begin to normalize, it is a sign of respiratory fatigue and impending respiratory failure!

Classification of asthma severity at initial assessment for children ≥ 12 years and adults

The following table allows for classification of asthma severity in the initial assessment of patients who are not yet taking asthma control medication.

Classification of asthma severity
Intermittent Mild Moderate Severe
Symptoms (e.g., dyspnea, wheezing, cough) ≤ 2 days/week ∼ 2 days/week Most days Daily
Nighttime symptoms (e.g., difficulty falling asleep because of symptoms, nighttime awakenings) Rare 3–4 times/month 1–2 times/week Often (most nights)
FEV1 > 80% > 80% 60–80% < 60%

References:[1][6]

Differential diagnoses

Asthma COPD
Age at diagnosis
  • Often childhood and adolescence, although nonallergic asthma can present after the age of 40
  • Typically > 40 years old
Etiology
  • Allergic and non-allergic (see “Etiology” above)
  • Cigarette consumption (90% of cases)
Clinical presentation
  • Episodic: symptom-free phases, sudden attacks
  • Insidious onset and chronic progression over years
Obstruction
  • Reversible
  • Persistent airflow limitation

Medication
  • Good response to treatment with long-term inhaled corticosteroids

References:[1]

The differential diagnoses listed here are not exhaustive.

Treatment

Causal

Symptomatic

Overview of asthma medication

Commonly used drugs for asthma management
Class Examples Mechanism
β2-agonists
Inhaled corticosteroids
Leukotriene pathway modifiers
  • Inhibits 5-lipoxygenase → ↓ production of leukotrienes
Biological agents
Methylxanthines
Mast-cell stabilizers
  • Prevents release of inflammatory mediators from mast cells

Acute management

Long-term management

  • General principles
    • Reduce number of asthma attacks → Medical therapy is escalated or de-escalated depending on the patient's individual needs.
    • Self-monitoring for patients: use of a peak flow meter to measure peak expiratory flow rate (PEFR)
      • Patients can avoid exacerbations with frequent PEFR measurements: PEFR decreases before symptoms appear → indicates insufficient medication regimen
Management of chronic asthma
Severity
Intermittent Mild Moderate Severe
First-line treatment
  • PRN short-acting β2-agonist
  • No daily medications needed
  • Daily low-dose inhaled corticosteroid
  • PRN short-acting β2-agonist
Alternative treatment

Inhaled corticosteroids do not take full effect until they have been used for approx. 1 week!

References:[3][4][6][7]

Complications

Status asthmaticus

  • Definition: extreme asthma exacerbation that does not respond to initial treatment with bronchodilators
  • Clinical features
    • Initially: orthopnea, tachypnea, tachycardia, hypoxemia and cyanosis, hypercarbia
    • Signs of imminent respiratory arrest
  • Treatment
    • Short-acting beta agonist
    • Inhaled anticholinergics (e.g., ipratropium)
    • Systemic glucocorticoids
    • Supplemental oxygen and/or helium-oxygen mixture (heliox)
    • Intravenous magnesium sulfate
    • Indications for intubation: use of accessory muscles, decreased oxygen saturation, inability to speak in full sentences, inadequate response to initial therapy, normalizing PCO2 or pH (see “Laboratory Studies” under “Diagnostics” above)

Status asthmaticus is a medical emergency, as it can be a life-threatening!

References:[8][9]

We list the most important complications. The selection is not exhaustive.

Special patient groups

  • Pregnant women
  • Children
    • Treatment similar to that for adults, with inhaled corticosteroids as the initial drug of choice
    • Young children (< 5 years) may require nebulizers due to difficulty using other inhalers.

References:[1][10]

last updated 11/28/2018
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