- Clinical science
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.
- 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
Epidemiological data refers to the US, unless otherwise specified.
The following factors can act as initial triggers of asthma or exacerbate an existing condition:
Allergic asthma (extrinsic asthma)
- Cardinal risk factor:
- Environmental allergens: pollen (seasonal), dust mites, domestic animals; , mold spores
- Allergic occupational asthma: from exposure to allergens in the workplace (e.g., flour dust)
Nonallergic asthma (intrinsic asthma)
- Cold air
- Physical exertion (exercise-induced asthma)
- (GERD): often exists concurrently with asthma
- Chronic sinusitis or rhinitis
- Medication: aspirin/NSAIDS (), beta blockers
- Viral respiratory tract infections
- Irritant-induced asthma; (e.g., from exposure to solvents, ozone, tobacco or wood smoke, cleaning agents)
Childhood exposure to second-hand smoke increases the risk of developing asthma!
Asthma is generally characterized by the following three processes:
- Bronchial hyperresponsiveness
- 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.
- Endobronchial obstruction caused by:
Some forms of asthma have specific pathophysiologies:
- Allergic asthma: IgE-mediated type 1 hypersensitivity to a specific allergen; ; characterized by mast cell degranulation; and release of histamine after a prior phase of sensitization
- Nonallergic asthma
- Mild to moderate symptoms
- Severe dyspnea
- Increased risk of pulmonary infection (in chronic asthma)
- Cough variant asthma
- Definition: acute, reversible episode of lower airway obstruction that may be life-threatening
|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|
|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%|
- Auscultation (characteristic findings are usually only present during acute attacks)
- Hyperresonant sound
- Inferior displacement and poor movement of the diaphragm
- In severe attacks
- Altered level of consciousness
Characteristic examination findings may not be present between episodes of asthma exacerbation!
Evaluation of pulmonary function
- (bronchoprovocation test)
- Chest x-ray
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 =
- ↓ pO2 and ↑ pCO2 =
- 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|
|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%|
|Age at diagnosis|| || |
|Etiology|| || |
|Clinical presentation|| || |
|Obstruction|| || |
| || |
- dyspnea due to left heart failure and pulmonary venous obstruction :
- with sudden-onset dyspnea
- (Tension) with sudden-onset dyspnea
The differential diagnoses listed here are not exhaustive.
- Avoid triggers (see “Etiology” above)
- Early hyposensitization in allergic asthma
- Early treatment of infections in infection-triggered asthma
- If GERD is suspected: proton pump inhibitors
Overview of asthma medication
|Commonly used drugs for asthma management|
|β2-agonists|| || |
|Inhaled corticosteroids|| || |
|Leukotriene pathway modifiers|| |
|Biological agents|| || |
|Methylxanthines|| || |
|Mast-cell stabilizers|| || |
- For mild symptoms: short-acting beta agonist
- For exercise-induced asthma: short-acting beta agonist prior to exercise
- For severe asthma exacerbations, see “Treatment” in .
- 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|
|First-line treatment|| || |
Inhaled corticosteroids do not take full effect until they have been used for approx. 1 week!
- Definition: extreme asthma exacerbation that does not respond to initial treatment with bronchodilators
- Clinical features
- 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!
We list the most important complications. The selection is not exhaustive.
- Pregnant women
- 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.