Pulmonology

Asthma: Diagnostics

History/Symptoms

1. Dyspnea
2. Cough, chest tightness, anxiety, diaphoresis
3. Exacerbating factors (often worser at night)
   • Exercise
   • Allergies
   • Cold
4. Historical questions
   • Medication use, recent illness, precipitants
   • Nocturnal awakenings, peak flow best
   • ED visits, steroid use, intubations, hospital/ICU admits
   • Hx of tobacco use, CAD, COPD, SLE/Sarcoid
   • Hx of atopy/atopic dermatitis, allergies, pets, eczema, hay fever
5. Lack of response to corticosteroids
   • Indicates rapid decline

Physical Exam/Signs

1. Dependent on patient experience acute exacerbation or not
   • Tachycardia, tachypnea, HTN
   • Assess
     • Accessory muscle use
     • Ability to speak
     • Alertness
     • Nasal flaring
     • Cyanosis
     • Ability to lie flat
     • Assumption of tripod position
   • Wheezing
     • Absence may signify impending respiratory failure
   • Pulsus paradoxus
   • Increased I:E ratio (1:2 or even 1:4)
     • Due to prolonged expiration
   • Fine tremor in hands due to salbutamol use
   • Respiratory distress
     • Patient sitting forward to splint open their airways
     • Auscultation
       • Bilateral, expiratory wheeze
   • Life-threatening asthma
     • Does not respond to systemic steroids and beta 2 agonist nebulization
     • Peak expiratory flow < 33% of personal best
     • O2 saturation < 92%
     • Normal partial pressure of CO2
     • Silent chest
     • Cyanosis
     • Feeble respiratory effort
     • Bradycardia
     • Arrhythmias
     • Hypotension
     • Confusion, coma
     • Exhaustion
   • Near-fatal asthma
     • Partial pressure of CO2 is raised or
     • Mechanical ventilation required w/ raised inflation pressures

Labs/Tests

1. ABGs:
   • May not be needed in patients with mild/moderate symptoms
   • PaCO2 ≥ 42 mmHg sign of impending resp failure
   • Low CO2 due to hyperventilation (prolonged attack)
2. BUN/Cr, urea, electrolytes (hypokalemia due to beta adrenergics)
3. CBC
   • Not routinely needed
   • Leukocytosis, eosinophilia
4. Sputum eosinophils
   • Eosinophilia common but not specific for asthma
5. Theophylline levels
   • Rule out toxicity if patient taking theophylline (rare)
6. BNP
   • Rule out "cardiac asthma" (CHF), especially in older patients

Imaging

1. CXR
   • Rule out pneumothorax/mediastinum, infiltrate, foreign body
   • CXR abnormal in < 33% of cases
2. Bronchoscopy
   • May be useful with mucous plug removal (View Video)
   • With bronchoalveolar lavage (BAL) to count eosinophils
     • High counts of airway eosinophils predict exacerbations and loss of lung function
3. Chest CT
   • Performed in patients w/ recurrent symptoms
   • Do not respond to therapy

Other Tests/Criteria

1. Calcs
   • Prevention and Incidence of Asthma and Mite Allergy (PIAMA) Risk Score (Open Calc)
   • Asthma Impairment and Risk Questionnaire (Open Calc)
   • Pregnancy Asthma Control Test (Open Calc)
2. ECG
   • STach common
   • Rule out dysrhythmias (toxicity)
3. PFTs:
   • Before/after Tx (View Video)
   • FEV1 < 25% is a sign of impending respiratory failure
4. Spirometry
   • Diagnostic method of choice will show an obstructive pattern
     • Partially or completely resolved by salbutamol
   • Perform prior to treatment to determine severity of disorder
   • Reduced ratio of FEV1 to FVC is indicative of airway obstruction
     • Reversible w/ treatment
   • Reversibility testing
     • Patient is given inhaled short-acting beta 2 agonist, then
     • Spirometry test is repeated
     • If 12% or 200 ml improvement in EV1 from previous value
       • Shows reversibility and diagnostic for bronchial asthma
   • Peak expiratory flow measurement
     • Common test performed today
     • Allows documentation of one aspect for response to therapy
     • Limitation is that it is effort dependent
5. Exercise spirometry
   • Helps identify patients w/ exercise-induced bronchoconstriction
6. Staging
   • Chronic asthma
     • Intermittent
     • Mild persistent
     • Moderate persistent
     • Severe persistent
   • Acute asthma
     • Acute severe asthma
     • Life-threatening asthma
     • Near-fatal asthma

Differential Diagnosis

1. Acute heart failure
2. Congestive heart failure
3. Upper airway obstruction
4. Interstitial lung disease
5. Pulmonary embolism
6. Foreign body aspiration
7. GERD
8. Endobronchial lesions
9. Laryngeal obstruction
10. Vocal cord dysfunction

Related Topics

• Asthma: Pathophysiology
• Asthma: Stepwise Treatment Algorithm
• Asthma: Treatment Modalities
• Asthma: Disposition
• Asthma: NAEPP Stepwise Guide and Long Term Drug Dosing Guide

References

1. National Heart, Lung, and Blood Institute. Expert panel report 3: guidelines for the diagnosis and management of asthma- full report 2007. Available at: https://www.nhlbi.nih.gov/health-topics/guidelines-for-diagnosis-management-of-asthma. [Accessed May 2024]
2. CDC. Asthma. Available at: https://www.cdc.gov/asthma/management.html. [Accessed May 2024]
3. Tintinalli JE, Stapczynski JS, Ma OJ, Yealy DM, Meckler GD, Cline DM. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 8th ed, McGraw-Hill Education, 2016;Chapter 69
4. Asthma. StatPearls [Internet]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK430901/. [Accessed May 2024]

Contributor(s)

1. Justice, Jordan, MD
2. Huang, Christine, MD
3. Singh, Ajaydeep, MD

Updated/Reviewed: May 2024