Preparatory Mindset
Asthma is a chronic inflammatory airway disease defined by variable and reversible airflow obstruction — the contrast to COPD's fixed obstruction is the single most-tested distinction (know the "asthma vs COPD" comparison table). The exam skills: (1) diagnose — episodic wheeze/cough/dyspnoea with documented reversibility (post-bronchodilator FEV₁ ↑ ≥12% and ≥200 mL; PEF diurnal variability >20% adults/>10%; methacholine challenge for equivocal cases), (2) classify severity (intermittent → persistent, STEP 1–4), and (3) manage — the modern GINA paradigm is ICS-based (never SABA monotherapy), stepwise escalation, and for acute exacerbations a clear moderate/severe/life-threatening triage (life-threatening = drowsy, confused, silent chest) with O₂ to 93–95%, repeated salbutamol, early corticosteroids, and ICU for life-threatening features. The HKHA Adult Acute Asthma + long-term management sections are LMCHK priorities.
Core Concepts
Definition & epidemiology
- Bronchial asthma = chronic inflammatory disease of the airways characterised by variable airflow obstruction, airway hyperresponsiveness, and symptoms of wheeze, dyspnoea, chest tightness and cough (worse at night/early morning), with reversible bronchoconstriction.
- Global Asthma Network: ~334 million people affected; higher prevalence in developed countries/urban areas; China prevalence ~1–4% (rising with urbanisation).
- Strong genetic component: heritability ~48–79%; one parent asthmatic → child risk ~25%; both parents → higher.
Etiology & risk factors
- Host: genetic predisposition (atopy), airway hyperresponsiveness, gender/age.
- Environmental triggers: allergens (house-dust mite, pollen, animal dander, mould), respiratory viral infections (RSV, rhinovirus), exercise (EIA), cold air, emotional stress, occupational sensitisers, drugs (NSAIDs/aspirin — aspirin-exacerbated respiratory disease; β-blockers), tobacco smoke/air pollution.
- Pathophysiology: TH2-type inflammation — mast cells, eosinophils, CD4+ T cells; IgE; mediators (leukotrienes, histamine, PGD₂) → bronchoconstriction, mucus hypersecretion, oedema, smooth-muscle hypertrophy; airway remodelling with chronic disease.
Clinical manifestations
- Episodic wheeze, dyspnoea, cough (often nocturnal), chest tightness; worse at night/early morning and with triggers; symptom-free intervals.
- Signs during attack: expiratory wheeze, prolonged expiration, tachypnoea, accessory muscle use; silent chest = life-threatening (no air entry).
- Diurnal variability of symptoms/PEF is characteristic; family/atopy history supportive.
- Physical exam between attacks may be normal.
Diagnosis
Objective confirmation of variable airflow obstruction (reversibility/variability):
| Test | Diagnostic cut-off (adults) |
|---|---|
| Bronchodilator reversibility | Post-bronchodilator FEV₁ ↑ ≥12% and ≥200 mL (10–15 min after 200–400 mcg salbutamol) |
| PEF diurnal variability | Average daily variability >10% (adults); >13% children; >20% between attacks per Chinese classification |
| Bronchial provocation (methacholine/histamine) | Fall in FEV₁ ≥20% from baseline (when baseline normal) |
| Exercise challenge | Fall in FEV₁ >10% and >200 mL (adults) |
- Spirometry at diagnosis: FEV₁/FVC often reduced; improvement confirms reversibility; PEF monitoring at home.
- Asthma vs COPD (key table):
| Asthma | COPD | |
|---|---|---|
| Age of onset | Often young (children) | Usually >40 y |
| Smoking | Not required | Almost always (smoking history) |
| Course | Episodic/variable | Progressive |
| Reversibility | Reversible (marked) | Largely irreversible (fixed) |
| Inflammation | Eosinophilic (TH2) | Neutrophilic (CD8/macrophage) |
| Response to ICS | Excellent | Limited (selected benefit) |
Classification of severity (Chinese curriculum, pre-GINA-stepwise)
- Intermittent: symptoms ≤2×/month, PEF variability <20%, normal between attacks.
- Mild persistent (STEP 2): symptoms >1×/week but not daily; PEF variability 20–30%.
- Moderate persistent (STEP 3): daily symptoms, attacks affect activity/sleep; PEF variability >30%.
- Severe persistent (STEP 4): continuous symptoms, limited physical activity; PEF variability >30%.
Management (long-term)
- Treatment goals: symptom control, prevent exacerbations, maintain normal activity, minimal reliever use, minimal side effects.
- GINA modern paradigm: ICS-based controller therapy for ALL patients — never SABA monotherapy (SABA-only increases severe-exacerbation risk).
- Stepwise approach: step 1–2: low-dose ICS (± as-needed low-dose ICS-formoterol); step 3: ICS-LABA (± LAMA); step 4/5: high-dose ICS-LABA + add-on (LAMA, anti-IgE omalizumab, anti-IL5, anti-IL4R, oral corticosteroids last).
- Non-pharmacology: trigger avoidance, smoking cessation, influenza/pneumococcal vaccination, weight loss, exercise, self-management plan (written action plan), specific immunotherapy/desensitisation for defined allergens (~60% of attacks attributable to specific allergens in sensitised patients).
- Patient education + inhaler technique review; monitor control (ACT, PEF diary).
Acute exacerbation — assessment & management
Definition: acute/subacute worsening of symptoms and lung function from usual status (GINA 2022).
Initial assessment — ABC; identify life-threatening features: drowsiness, confusion, silent chest → consult ICU, prepare for intubation.
| Feature | Mild/Moderate | Severe |
|---|---|---|
| Speech | Talks in phrases | Talks in words |
| Posture | Prefers sitting | Sits hunched forwards |
| Consciousness | Calm | Agitated |
| Respiratory rate | ↑ | RR >30/min |
| Accessory muscles | None | Use of accessory muscles |
| Pulse | 100–120/min | >120/min |
| SpO₂ (room air) | 90–95% | <90% |
| PEF | >50% predicted/best | ≤50% predicted/best |
Management:
- Moderate: controlled O₂ (target SpO₂ 93–95%); salbutamol 4 puffs q4h with spacer + PRN (high dose/more frequent if very symptomatic); oral corticosteroids (prednisolone 30–50 mg daily 5–7 days); ± ipratropium bromide.
- Severe: nebulised salbutamol ± ipratropium; IV corticosteroids; consider IV magnesium sulfate; monitor ABG, electrolytes; CXR to exclude pneumothorax; ICU if life-threatening features or no response; intubation + mechanical ventilation if deteriorating (silent chest, exhaustion, acidosis, altered consciousness).
- Discharge: step up controller, review inhaler technique, written action plan, follow-up.
HKHA Handbook (LMCHK) — Key Points
- Adult Acute Asthma (P 8–9, GINA 2022): exacerbation = acute/subacute worsening of symptoms and lung function from usual status (may be first presentation). Initial ABC + life-threatening features (drowsiness, confusion, silent chest) → ICU consult + prepare intubation. Moderate vs severe grading as table above (words vs phrases, RR >30, accessory muscles, pulse >120, SpO₂ <90%, PEF ≤50%).
- Management: controlled O₂ aiming SpO₂ 93–95%; salbutamol 4 puffs q4h with spacer + PRN (higher dose/frequency for severe); oral corticosteroids ± ipratropium; severe → nebulised SABA, IV steroids, consider IV Mg; monitor PEF/ABG; ICU if life-threatening.
- Long-term management of asthma (P 10–13): ICS-based stepwise therapy — no SABA monotherapy; step-up/down by control; add LABA, LAMA, biologics (anti-IgE/anti-IL5) for uncontrolled disease; written action plan, inhaler technique, treat comorbidities (rhinitis, GERD), smoking cessation.
- Asthma exacerbation vs COPD exacerbation: oxygen target differs — asthma 93–95%, COPD 88–92% — a classic exam trap.
High-Yield Points
- Asthma = variable + reversible airflow obstruction; COPD = fixed.
- Reversibility: FEV₁ ↑ ≥12% and ≥200 mL post-bronchodilator; PEF diurnal >10% (adults); methacholine fall ≥20%.
- GINA: ICS-based for all — never SABA alone.
- Life-threatening: drowsy, confused, silent chest, exhaustion, acidosis → ICU + intubation.
- Moderate: salbutamol 4 puffs q4h + oral steroids + O₂ 93–95%; Severe: nebulised SABA, IV steroids, ± IV Mg.
- PEF ≤50% predicted = severe; SpO₂ <90% = severe.
- Asthma O₂ target 93–95% vs COPD 88–92% (exam trap).
Topic Summary
Asthma is a chronic inflammatory airway disease with variable, reversible airflow obstruction — diagnosed clinically and confirmed by bronchodilator reversibility (FEV₁ ↑≥12% and ≥200 mL), PEF variability, or methacholine challenge, and contrasted with COPD's fixed obstruction. Long-term management follows the GINA ICS-based stepwise paradigm (never SABA monotherapy), with trigger avoidance, action plans and biologics for severe disease. Acute exacerbations are graded moderate/severe/life-threatening (life-threatening = drowsiness, confusion, silent chest), treated with controlled oxygen (SpO₂ 93–95%), repeated salbutamol, early corticosteroids and ICU/intubation for life-threatening features — the HKHA acute-asthma algorithm being an LMCHK priority.