Classification of Asthma Exacerbations
Asthma exacerbations are classified into four severity categories—mild, moderate, severe, or life-threatening—based primarily on percent predicted FEV₁ or peak expiratory flow (PEF), with additional assessment of symptoms, physical examination findings, and oxygen saturation. 1
Primary Classification System
The severity classification uses a multi-parameter approach where the primary determinant is lung function measured as percent predicted FEV₁ or PEF 1:
Severity Categories Based on Lung Function
- Mild exacerbation: PEF 70-90% of predicted or personal best, can usually be managed at home 1, 2
- Moderate exacerbation: PEF 50-79% of predicted or personal best, may require emergency department evaluation 1, 2
- Severe exacerbation: PEF <50% of predicted or personal best, requires emergency department treatment and possible hospitalization 1, 2
- Life-threatening exacerbation: Marked by severe respiratory distress, altered mental status, or inability to speak in phrases 1
Supporting Clinical Parameters
Beyond lung function, the classification incorporates 1:
- Symptoms: Breathlessness, coughing, wheezing, and chest tightness intensity 1
- Physical examination: Agitation, increased respiratory rate and pulse, use of accessory muscles, inability to speak in complete sentences 1
- Oxygen saturation: SaO₂ levels and arterial blood gas measurements (PaO₂, PaCO₂) 1
Critical Distinction: Exacerbation vs. Chronic Severity
An important advance in the NAEPP Expert Panel Report 3 guidelines is the creation of different spirometry cut points for assessing acute asthma exacerbations versus chronic asthma severity 1. This distinction is crucial because:
- Exacerbations represent acute or subacute episodes of progressively worsening symptoms 1
- Unlike poor chronic asthma control, diurnal variability in airflow may not change during an exacerbation 1
- Patients at any baseline severity level (intermittent through severe persistent) can experience severe exacerbations 3
High-Risk Populations Requiring Special Attention
Certain patients warrant heightened vigilance during exacerbations 1, 3:
- Previous severe exacerbation (intubation or ICU admission) 1, 3
- Two or more hospitalizations for asthma in the past year 1, 3
- Three or more ED visits for asthma in the past year 1, 3
- Recent hospitalization or ED visit within the past month 1, 3
- Excessive SABA use (>2 canisters per month) 1, 3
- Difficulty perceiving symptoms or exacerbation severity 1, 3
- Lack of written asthma action plan 1, 3
- Infants, who are at inherently greater risk 1
Treatment Implications Based on Severity
The exacerbation severity directly determines treatment intensity and location of care 1:
- Mild exacerbations: Home management with up to two treatments of 2-6 inhalations of short-acting β₂-agonists 20 minutes apart, followed by reassessment 2
- Moderate to severe exacerbations: Emergency department evaluation with goals of correcting hypoxemia, rapidly reversing airflow obstruction, and reducing relapse risk 2
- Systemic corticosteroids should be administered within one hour of ED presentation for moderate to severe cases, as this decreases hospitalization need 2
Common Pitfalls to Avoid
- The most dangerous clinical error is underestimating exacerbation severity or assuming well-controlled baseline asthma protects against severe exacerbations 3
- Relying solely on symptoms without objective lung function measurement can lead to misclassification 4
- Failing to recognize that patients with any baseline severity level can experience life-threatening exacerbations 3
- Not identifying high-risk patients who require more aggressive monitoring and intervention 1, 3