About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Wheeze is a sign, not a diagnosis. Asthma and COPD are common, but anaphylaxis, foreign body, heart failure, PE, and central airway obstruction can also wheeze
- Asthma: variable symptoms, triggers, atopy, night/early morning symptoms, reversible airflow obstruction. COPD: age >40, smoking/biomass exposure, chronic progressive dyspnoea, post-bronchodilator obstruction
- Severe asthma red flags: silent chest, inability to speak, exhaustion, drowsiness, SpO2 <92%, peak flow <50% predicted/personal best, rising CO2
- Canadian Thoracic Society asthma care emphasises inhaled corticosteroid-containing therapy and avoiding SABA-only reliance in many patients
- COPD pharmacotherapy is symptom/exacerbation-driven; confirm diagnosis with post-bronchodilator spirometry before long-term labelling whenever feasible
Approach to the Presentation
Wheezing is caused by airflow through narrowed intrathoracic airways. The first distinction is acute dangerous wheeze versus chronic/recurrent wheeze. In acute wheeze, assess ABCs, oxygenation, work of breathing, speech, mental status, and exposure history. In recurrent wheeze, determine whether the pattern is variable and reversible (asthma), fixed and exposure-related (COPD), episodic with allergen/food/drug exposure (anaphylaxis), cardiac (pulmonary oedema), or focal/monophonic (foreign body or airway tumour). The MCCQE1 often tests the next best step: acute treatment is clinical and should not wait for spirometry; chronic diagnosis should be confirmed with objective lung function.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Life-Threatening Asthma Exacerbation | must-not-miss | Severe dyspnoea, inability to speak, accessory muscle use, silent chest, agitation/drowsiness, prior ICU/intubation, poor response to salbutamol | Clinical severity; peak flow if safe; VBG/ABG for CO2 retention/acidosis; do not delay treatment for tests |
| Anaphylaxis | must-not-miss | Wheeze with urticaria, angio-oedema, hypotension, GI symptoms after allergen/food/drug/insect sting. May have stridor from upper airway oedema | Clinical diagnosis; response to IM epinephrine. Tryptase later if diagnostic uncertainty |
| Foreign Body Aspiration | must-not-miss | Sudden cough/wheeze/choking episode, unilateral or monophonic wheeze, child or older adult, persistent symptoms despite bronchodilator | Inspiratory/expiratory CXR may show air trapping; bronchoscopy definitive |
| Acute Heart Failure / Cardiac Asthma | must-not-miss | Wheeze with orthopnoea, PND, crackles, elevated JVP, S3, oedema, hypertension, older patient, cardiac history | BNP/NT-proBNP, CXR pulmonary oedema, bedside ultrasound B-lines, echocardiography |
| Asthma | common | Variable wheeze, cough, chest tightness, dyspnoea; worse at night/early morning; triggers: allergens, exercise, cold air, viral infection; personal/family atopy | Spirometry showing obstruction with bronchodilator reversibility; peak flow variability; methacholine challenge if needed |
| COPD | common | Age >40, smoking/vaping/biomass/occupational exposure, chronic progressive dyspnoea, cough/sputum, frequent winter bronchitis, reduced exercise tolerance | Post-bronchodilator spirometry FEV1/FVC below lower limit of normal or <0.70 in many clinical pathways |
| Viral-Induced Wheeze / Bronchiolitis | common | Infant/young child with viral prodrome, tachypnoea, wheeze/crackles, feeding difficulty; bronchiolitis usually <2 years | Clinical; avoid routine CXR/labs in typical bronchiolitis without severe features |
| Pulmonary Embolism | less common | Dyspnoea, pleuritic pain, tachycardia, hypoxia, VTE risks; wheeze can occur from bronchoconstriction around embolic/infarcted regions | Pre-test probability + D-dimer/CTPA pathway |
| Vocal Cord Dysfunction / Inducible Laryngeal Obstruction | less common | Episodic dyspnoea/noisy breathing, throat tightness, inspiratory component, triggered by exercise/stress/irritants; poor response to asthma therapy | Laryngoscopy during symptoms; flow-volume loop may show inspiratory flattening |
| Central Airway Tumour or Tracheal Stenosis | rare | Fixed or monophonic wheeze, stridor, haemoptysis, recurrent pneumonia, smoking or prior intubation/tracheostomy; symptoms not variable | CT neck/chest and bronchoscopy |
Red Flags & Key History
Symptoms
Inability to complete sentences, exhaustion, drowsiness, confusion, or previous intubation for asthma/COPD
Silent chest — airflow is too poor to generate wheeze
Wheeze with urticaria, swelling, hypotension, vomiting/diarrhoea after exposure — anaphylaxis
Sudden choking episode or unilateral wheeze — foreign body
Orthopnoea, PND, oedema, cardiac history — cardiac asthma/heart failure
Nocturnal/early-morning cough or wheeze, triggers, atopy — asthma pattern
Progressive exertional dyspnoea with chronic sputum and smoking/exposure history — COPD pattern
Signs
SpO2 <92% in asthma or <88% in known CO2 retainer
Peak expiratory flow <50% predicted/personal best or inability to perform due to distress
Pulsus paradoxus, accessory muscle use, tripod posture
Crackles, elevated JVP, S3 — heart failure rather than simple bronchospasm
Focal monophonic wheeze — obstruction in a single airway
Approach to Investigation
First-line
Pulse oximetry + severity assessmentSpeech, mental status, respiratory rate, accessory muscle use, prior ICU/intubation, response to bronchodilator
Peak expiratory flow (if safe)Useful in asthma to grade severity and response; do not force it in a crashing patient
CXRNot routine for straightforward mild asthma. Obtain if fever/focal signs, suspected pneumothorax, pneumonia, foreign body, heart failure, malignancy, or poor response
VBG/ABGIf severe, drowsy, hypoxic, suspected hypercapnia, COPD exacerbation, or poor response. Normal or rising CO2 in severe asthma is ominous
Second-line
Spirometry pre/post bronchodilatorConfirms asthma/COPD after acute episode stabilises. Asthma: reversibility/variability. COPD: persistent post-bronchodilator obstruction
CBC/eosinophils, IgE/allergy testing where relevantPhenotyping asthma and identifying triggers; not needed for simple acute exacerbation decisions
BNP/ECG/troponinIf cardiac wheeze, older patient, chest pain, pulmonary oedema, or cardiac risk factors
Specialist
Methacholine challengeWhen asthma suspected but spirometry normal and diagnosis remains uncertain
LaryngoscopyFor suspected inducible laryngeal obstruction/vocal cord dysfunction
BronchoscopyForeign body, focal wheeze, suspected airway lesion, or unexplained fixed obstruction
Management Principles
Canadian Thoracic Society 2021 Asthma Guideline Update + 2023 CTS COPD Pharmacotherapy Guideline1
Acute asthma exacerbation
- Oxygen to maintain SpO2 generally 92-96%
- Inhaled salbutamol by MDI/spacer or nebuliser; add ipratropium for moderate-severe exacerbation
- Systemic corticosteroid early: prednisone/prednisolone orally if able, IV methylprednisolone if unable or severe
- IV magnesium sulfate for severe exacerbation or poor response to initial therapy
- Prepare ICU/intubation support if exhaustion, drowsiness, silent chest, worsening acidosis, or rising CO2
2
Acute COPD exacerbation
- Controlled oxygen target 88-92% if chronic CO2 retention is possible
- Short-acting bronchodilators: salbutamol + ipratropium
- Prednisone 40 mg daily for approximately 5 days is commonly used
- Antibiotics if increased sputum purulence plus increased volume/dyspnoea, or if ventilatory support is required
- Non-invasive ventilation if acute hypercapnic respiratory failure with acidosis and no contraindication
3
Long-term asthma vs COPD distinction
- Asthma: avoid SABA-only reliance; use inhaled corticosteroid-containing controller strategy according to severity and risk
- COPD: smoking cessation, vaccination, pulmonary rehabilitation; maintenance bronchodilator therapy with LAMA/LABA based on symptoms and exacerbation risk; ICS reserved for exacerbation-prone/eosinophilic phenotypes or asthma overlap
- Check inhaler technique and adherence before escalating therapy
4
Mimics
- Anaphylaxis: IM epinephrine first, airway readiness, adjunct antihistamines/bronchodilators after epinephrine
- Foreign body/focal obstruction: urgent bronchoscopy referral
- Heart failure: nitrates/diuresis/non-invasive ventilation based on presentation rather than repeated bronchodilator escalation
Complications & Pitfalls
- Silent chest: Severe asthma may have less wheeze, not more; this is pre-arrest physiology.
- SABA-only trap: Repeated salbutamol without anti-inflammatory therapy increases risk in asthma; controller therapy matters.
- Oxygen overcorrection in COPD: Excess oxygen can worsen hypercapnia; target 88-92% if CO2 retention risk.
- Mislabelled COPD: Do not diagnose COPD without objective obstruction unless spirometry is genuinely unavailable and the clinical picture is compelling.
- Missing anaphylaxis: Wheeze plus skin/GI/circulatory features after exposure requires IM epinephrine, not just salbutamol.
MCCQE1 Exam Tips
- 1Asthma = variable/reversible; COPD = persistent obstruction and exposure history. MCC stems often give these clues deliberately
- 2In severe asthma, a normal PaCO2 is not reassuring — patients should be hypocapnic from hyperventilation; normal/rising CO2 means fatigue
- 3Silent chest, drowsiness, or exhaustion = ICU/intubation preparation while continuing aggressive therapy
- 4COPD exacerbation with pH <7.35 and high PaCO2 = non-invasive ventilation if no contraindication
- 5Wheeze after food/drug/sting exposure with hypotension or urticaria = IM epinephrine first
- 6Focal monophonic wheeze or sudden choking = foreign body/airway lesion, not asthma escalation
- 7CanMEDS collaborator: inhaler teaching by pharmacist/respiratory educator and written asthma action plan are part of high-quality care
practicetest your knowledge on wheezingApply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — respiratory and beyond.
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