1. Asthma is an inflammatory disease of the airways featuring reversible airway obstruction.

2. Asthma exacerbations represent acute or subacute increases in airway obstruction that require a temporary change in treatment to prevent further worsening (moderate exacerbation) or that require urgent action to prevent serious morbidity or mortality (severe exacerbation).

3. Status asthmaticus describes an exacerbation of asthma that fails to improve rapidly (usually within 1 hour) with intensive bronchodilator therapy.

A. Triggers of asthma exacerbations: Common triggers include environmental factors such as viral upper respiratory tract infections, inhaled allergens, air pollutants, smoke exposure, and nonsteroidal anti-inflammatory drugs (NSAIDs).

1. Slow-onset attacks (>6 hours of deterioration) are most common (approximately 90%).

2. Sudden-progression attacks (<6 hours of deterioration) are less common (approximately 10%).

1. Inflammation obstructs the airways by increasing mucus, causing edema and eosinophil infiltration of the airway wall, promoting spasm of smooth muscle, and causing damage to the airway epithelium.

2. Sudden-progression asthma attacks tend to be neutrophil predominate.

1. Increased airway resistance leads to hypoxemia.

a. Ventilation-perfusion inequalities mainly account for hypoxemia.

b. Atelectasis from mucus plugging can cause right-to-left shunt.

2. Severe, increased airway resistance may lead to hypercapnia because of a patient’s inability to sustain the increased work of breathing.

1. Not all wheezing is due to asthma. Obstruction of the airway at any level by any disease process can produce wheezing and dyspnea.

1. Failure to appreciate the severity of obstruction contributes to mortality. The amount of wheezing is a poor way to assess the severity of airway obstruction.

2. History: See Table 41-1 for historical features suggesting the presence of or high risk for severe airway obstruction.

3. Physical examination: See Table 41-1 for findings suggesting severe obstruction.

4. Laboratory.

a. Pulmonary function tests (PFTs).

i. Obtain an objective measure of maximal expiratory airflow to assess the severity of obstruction whenever possible (peak expiratory flow rate [PEFR] or forced expiratory volume in 1 second [FEV1]).

ii. PEFR (or FEV1) <40% of baseline is severe obstruction.