Dyspnea: Approach and Management for MCCQE1

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.

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.

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

Clinical Approach: The MCCQE1 Framework

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

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

• A. Intravenous furosemide
• B. Oral azithromycin alone
• C. Inhaled salbutamol/ipratropium and oral prednisone
• D. Inhaled salbutamol/ipratropium, oral prednisone, and oral antibiotics
• E. Intravenous tissue plasminogen activator (tPA)

Explanation

The correct answer is:

• D. Inhaled salbutamol/ipratropium, oral prednisone, and oral antibiotics

Detailed Analysis: This patient is presenting with an Acute Exacerbation of COPD (AECOPD).

• Diagnosis: She meets the Anthonisen criteria for a severe exacerbation (Type 1): Increased dyspnea, increased sputum volume (implied by productive cough), and increased sputum purulence (green sputum).
• Canadian Thoracic Society (CTS) Guidelines:
  • Bronchodilators: Increase frequency of short-acting bronchodilators (SABA/SAMA) is the first step (part of C and D).
  • Systemic Corticosteroids: Indicated for moderate to severe exacerbations to improve lung function (FEV1) and reduce hospital length of stay (part of C and D).
  • Antibiotics: Indicated in AECOPD if the patient has increased sputum purulence plus at least one other cardinal symptom (dyspnea or volume). This patient has purulence and dyspnea. Therefore, antibiotics are required.

Why other options are incorrect:

• A. Intravenous furosemide: This treats heart failure. While she has HTN, her exam lacks JVD, edema, or S3, and CXR shows hyperinflation rather than pulmonary edema.
• B. Oral azithromycin alone: Insufficient. Bronchodilators and steroids are crucial for resolving the obstruction and inflammation.
• C. Inhaled salbutamol/ipratropium and oral prednisone: Incorrect because it omits antibiotics, which are indicated due to the purulent sputum (CTS Guidelines).
• E. tPA: This is for massive PE or stroke. While PE is a differential, the clinical picture strongly fits AECOPD, and she is not hemodynamically unstable to warrant thrombolysis without confirmation.

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/