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Internal MedicinePulmonologyDyspnea
Pulmonology5 min readUpdated February 2, 2026

Dyspnea

Dyspnea, commonly known as shortness of breath, is a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity. It is one of the most common reasons for emergency department visits in Canada. For MCCQE1 preparation, understanding the differential diagnosis between cardiac and pulmonary causes, applying the CanMEDS roles (specifically Medical Expert and Communicator), and knowing when to apply Canadian clinical decision rules (e.g., Wells Score, PERC) is essential.

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Definition: The American Thoracic Society defines dyspnea as “a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity.”

Pathophysiology and Classification

Dyspnea arises from interactions among multiple physiological, psychological, social, and environmental factors. It generally results from a mismatch between central respiratory motor output (feed-forward) and incoming afferent information from airways, lungs, and chest wall structures (feedback).

Acute vs. Chronic Dyspnea

Categorizing dyspnea by duration is the first step in the clinical reasoning process for the MCCQE1.

Onset is sudden (minutes to hours). Requires urgent evaluation to rule out life-threatening causes (The “Killer Causes”). Examples: Pulmonary Embolism, Pneumothorax, Acute Asthma, Pulmonary Edema, MI.

Differential Diagnosis

A systems-based approach is crucial for the Medical Council of Canada (MCC) objectives.

The “4 P’s” Mnemonic for Acute Dyspnea

  • Pulmonary (Asthma, COPD, Pneumonia, Pneumothorax)
  • Pump (Heart Failure, MI, Tamponade)
  • Piping (Airway obstruction, PE)
  • Psychogenic/Physiologic (Panic attack, Acidosis, Anemia)

Comparative Table: Cardiac vs. Pulmonary Causes

FeatureCardiac Causes (e.g., CHF)Pulmonary Causes (e.g., COPD/Asthma)
HistoryOrthopnea, PND, history of CAD/HTNSmoking history, cough with sputum, occupational exposure
ExamJVD, S3 gallop, bilateral crackles (wet), peripheral edemaWheezing, barrel chest, decreased breath sounds, prolonged expiration
CXRCardiomegaly, pulmonary venous congestion, Kerley B linesHyperinflation, flattened diaphragm, focal consolidation
BiomarkersElevated BNP or NT-proBNPNormal BNP (usually), Elevated Eosinophils (Asthma)

Clinical Approach: The MCCQE1 Framework

When approaching a patient with dyspnea on the MCCQE1, follow this structured workflow.

Step 1: Assess Stability (ABC)

Check Airway, Breathing, and Circulation.

  • Vitals: Is the patient hypoxic (SpO2 < 92%)? Hypotensive? Tachypneic?
  • Action: If unstable, initiate IV, O2, and Monitors immediately before detailed history.

Step 2: Focused History (OPQRST)

  • Onset: Sudden (PE, Pneumothorax) vs. Gradual (COPD, CHF).
  • Provocation/Palliation: Exertion? Lying flat (Orthopnea)?
  • Quality: “Tightness” (Asthma), “Suffocating” (CHF).
  • Radiation: To jaw/arm (Ischemia).
  • Severity: Interference with ADLs.
  • Timing: Nocturnal?

Step 3: Physical Examination

  • General: Accessory muscle use, tripod position, cyanosis.
  • Lungs: Wheezes, crackles, stridor, percussion dullness vs. hyper-resonance.
  • Cardiovascular: JVD, heart sounds (S3/S4), murmurs, edema.
  • Extremities: Signs of DVT (unilateral swelling).

Step 4: Diagnostic Testing

Order investigations based on pre-test probability.

  • Essential: CBC, Electrolytes, Creatinine, CXR, ECG.
  • Context-Dependent: D-Dimer, Troponin, BNP, ABG, CT-PE, Spirometry.

🚩 Red Flags (Alarm Symptoms)

  • Hypotension (Shock)
  • Altered Level of Consciousness
  • Stridor (Upper airway obstruction)
  • Tracheal Deviation (Tension Pneumothorax)
  • Silent Chest (Severe Asthma)
  • Sudden onset chest pain (PE or MI)

Canadian Guidelines and Management

For the MCCQE1, you must be familiar with guidelines from the Canadian Thoracic Society (CTS) and Canadian Cardiovascular Society (CCS).

1. Pulmonary Embolism (PE)

Use the Wells Score to determine pre-test probability before ordering imaging. This aligns with Choosing Wisely Canada.

  • Low Probability (Wells < 4): Order D-Dimer. If negative, PE is ruled out (high sensitivity).
  • High Probability (Wells > 4): Skip D-Dimer; order CT Pulmonary Angiogram (CTPA).
# Wells Score Criteria (Mnemonic: DON'T DIE)
D - DVT symptoms (3.0)
O - Other diagnosis less likely than PE (3.0)
N - No other choice (Heart rate > 100) (1.5)
T - Three days immobilization or surgery in last 4 weeks (1.5)
D - DVT or PE previous history (1.5)
I - Hemoptysis (1.0)
E - Estrogen/Cancer (Active malignancy) (1.0)

2. COPD Exacerbation (CTS Guidelines)

  • Assessment: Assess for the cardinal symptoms (Anthonisen criteria):
    1. Increased dyspnea
    2. Increased sputum volume
    3. Increased sputum purulence
  • Management:
    • Bronchodilators (SABA/SAMA).
    • Systemic Corticosteroids (Prednisone 30-50mg PO for 5 days).
    • Antibiotics only if increased purulence + one other cardinal symptom.

3. Heart Failure (CCS Guidelines)

  • Diagnosis: If diagnosis is uncertain, measure BNP or NT-proBNP.
  • Acute Management (LMNOP):
    • Lasix (Furosemide)
    • Morphine (Use with caution, rarely first line now) / Monitoring
    • Nitrates (if hypertensive/ischemic)
    • Oxygen (if SpO2 < 90%)
    • Positioning (Upright) / Positive Pressure Ventilation (BiPAP)

Key Points to Remember for MCCQE1

  • Rule out the killer causes first: Tension pneumothorax, PE, MI, Cardiac Tamponade, Upper Airway Obstruction.
  • D-Dimer: High negative predictive value. Useful only to rule out PE in low-risk patients. Do not order on high-risk patients.
  • Silent Chest: In asthma, the disappearance of wheezing without clinical improvement suggests impending respiratory failure (severe obstruction).
  • Oxygen Therapy: In suspected CO2 retainers (chronic COPD), target SpO2 88-92% to avoid blunting the hypoxic drive and causing hypercapnic respiratory failure. For all others, target > 92-94%.
  • Palliative Care: For refractory dyspnea in palliative patients (e.g., advanced cancer), opioids (PO or SC) are the first-line pharmacological treatment to reduce the sensation of breathlessness.

Sample Question

Clinical Scenario A 62-year-old female presents to the Emergency Department with a 2-day history of worsening shortness of breath and a productive cough with green sputum. She has a 40-pack-year smoking history. Her past medical history includes hypertension and COPD.

Vitals:

  • Temp: 37.8°C
  • HR: 98 bpm
  • BP: 145/90 mmHg
  • RR: 24/min
  • SpO2: 89% on room air

Physical Exam:

  • Chest: Diffuse expiratory wheezes and coarse crackles at the bases. No JVD or peripheral edema.
  • Heart: Regular rhythm, no murmurs.

Investigations:

  • CXR: Hyperinflation, no focal consolidation.

Which one of the following is the most appropriate initial pharmacological management?

Options

Choose an answer, then check it against the explanation.

References

  1. Medical Council of Canada. (2023). MCCQE Part I Objectives: Dyspnea.
  2. Canadian Thoracic Society (CTS). (2023). Guideline on the Management of COPD. https://cts-sct.ca/ 
  3. Canadian Cardiovascular Society (CCS). (2021). Comprehensive Update of the CCS Guidelines for the Management of Heart Failure.
  4. Toronto Notes 2024. Respirology & Cardiology Chapters.
  5. Choosing Wisely Canada. Imaging for Pulmonary Embolism. https://choosingwiselycanada.org/ 
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