Chapter 20 · Asthma

Causative factors · Pathophysiology · Diagnostic approach · Treatment (stepwise) · Prognosis · Acute severe asthma
📌 Core principles: Asthma = chronic airway inflammation, bronchial hyperresponsiveness, reversible obstruction. Causative factors: atopy, viral infections, pollution, genetics (ADAM33, IL-4, IL-13). Pathophysiology: Th2 inflammation (eosinophils, mast cells), airway remodelling, smooth muscle hypertrophy. Diagnosis: recurrent wheeze, reversible airflow obstruction (FEV1 increase ≥12%), FeNO. Stepwise treatment: SABA (step1), low-dose ICS (step2), ICS+LTRA or ICS+LABA (step3), medium-high dose ICS+LABA (step4), add-on biologics (step5). Acute severe asthma: oxygen, inhaled SABA + ipratropium, systemic corticosteroids, IV magnesium, consider IV salbutamol/aminophylline, ICU if no response.

📖 Asthma – Key Concepts

🌍 Causative factors
Host: atopy (eczema, allergic rhinitis), genetics (ORMDL3, IL33, ADAM33). Environmental: viral infections (RSV, rhinovirus), allergens (dust mite, pollen), tobacco smoke, air pollution, obesity.
🧬 Pathophysiology
Chronic airway inflammation (Th2 cells, eosinophils, mast cells, IL-4, IL-5, IL-13). Bronchial hyperresponsiveness. Airway remodelling (subepithelial fibrosis, smooth muscle hypertrophy, mucus hypersecretion).
🩺 Diagnostic approach
History: episodic wheeze, cough, chest tightness, triggers (exercise, laughter, cold air). Spirometry: FEV1/FVC <0.70, reversible (≥12% increase post-bronchodilator). FeNO ≥35 ppb (eosinophilic). Bronchial challenge (methacholine) if normal spirometry. Allergy testing (skin prick, IgE).
💊 Stepwise treatment (GINA 2024)
Step 1: SABA as needed (salbutamol).
Step 2: low-dose ICS + SABA as needed (or low-dose ICS + formoterol as maintenance and reliever).
Step 3: low-dose ICS + LABA (formoterol) or low-dose ICS + LTRA (montelukast).
Step 4: medium-dose ICS + LABA.
Step 5: add-on tiotropium, anti-IgE (omalizumab), anti-IL5 (mepolizumab), anti-IL4R (dupilumab).
📉 Prognosis
Childhood asthma may remit in adolescence, but persists in many. Poor prognostic factors: severe atopy, early onset, low lung function, exposure to smoke, frequent exacerbations. Adult COPD risk increased.
⚠️ Acute severe asthma
Features: unable to speak, tachypnoea, tachycardia, silent chest, cyanosis, exhaustion. PEF <50% predicted. Management: oxygen (maintain SpO2 94-98%), inhaled SABA + ipratropium bromide via spacer (or nebuliser), systemic corticosteroids (prednisolone 1-2 mg/kg, IV hydrocortisone), IV magnesium sulphate (40 mg/kg) if severe. Consider IV salbutamol or aminophylline in PICU. Noninvasive ventilation (BiPAP) may avoid intubation.

🔎 Symptom-based approach: wheeze, cough, breathlessness

1️⃣
Child with episodic wheeze, triggered by viral infections, exercise, laughing. Normal between episodes. – Asthma. Spirometry (reversible obstruction) or FeNO. Start stepwise treatment.
2️⃣
Infant with recurrent wheeze, atopic dermatitis, family history of asthma. – Likely asthma (viral-induced wheeze). Trial of ICS + SABA as needed; avoid triggers.
3️⃣
Child with persistent nocturnal cough, no wheeze, normal spirometry, elevated FeNO. – Cough variant asthma. Trial of ICS, LTRA (montelukast).
4️⃣
Teenager with exercise-induced bronchoconstriction (EIB), normal baseline spirometry. – EIB. Warm-up, SABA before exercise; if frequent, low-dose ICS.
5️⃣
Child with acute breathlessness, tachypnoea, unable to speak sentences, PEF 40% predicted. – Acute severe asthma. Oxygen, nebulised salbutamol + ipratropium, prednisolone, reassess.
⚠️ Red flags in acute asthma: Silent chest, cyanosis, exhaustion, altered consciousness, PaCO2 normal or elevated (respiratory failure), PEF <33% predicted.

📋 Management algorithms: Stepwise chronic asthma & acute severe asthma

📋
Chronic asthma – GINA stepwise (children 6-11y)
▪️ Step 1: SABA as needed (salbutamol 100-200 mcg).
▪️ Step 2: low-dose ICS (budesonide 100-200 mcg/day) + SABA as needed.
▪️ Step 3: low-dose ICS + LTRA (montelukast) OR low-dose ICS + LABA (formoterol).
▪️ Step 4: medium-dose ICS + LABA.
▪️ Step 5: add-on tiotropium, refer for biologic (omalizumab, mepolizumab, dupilumab).
🚨
Acute severe asthma – emergency protocol
▪️ Assess severity (PEF, SpO2, speech, respiratory rate, heart rate).
▪️ Oxygen via mask (target SpO2 94-98%).
▪️ Inhaled SABA: 10 puffs salbutamol via spacer (repeat every 20-30 min) or nebuliser (2.5-5 mg).
▪️ Add ipratropium bromide (250-500 mcg via spacer or nebuliser) with first SABA dose.
▪️ Systemic corticosteroid: prednisolone 1-2 mg/kg (max 60 mg) oral or IV hydrocortisone 4 mg/kg if vomiting/shock.
▪️ If severe (PEF <50% after initial treatment): IV magnesium sulphate 40 mg/kg (max 2g) over 20 min.
▪️ Consider IV salbutamol (15 mcg/kg bolus then infusion) or aminophylline in PICU.
▪️ BIPAP (noninvasive ventilation) may prevent intubation.
▪️ Intubation if life-threatening features (silent chest, exhaustion, altered mental state, PaCO2 rising).
🩺
Follow-up and monitoring
▪️ Review after 2-6 weeks: assess adherence, inhaler technique, symptom control, exacerbations.
▪️ Step down to lowest effective dose after 3 months good control.
▪️ Annual influenza vaccine, COVID-19 vaccine, consider asthma action plan.

💡 Reflex prompts – Asthma

🌿 A 7-year-old with intermittent wheeze, no interval symptoms. Step 1 treatment?
SABA as needed (salbutamol). No regular controller.
📊 A child with persistent wheeze, FeNO 60 ppb, FEV1/FVC 0.68. Step 2?
Low-dose ICS (budesonide 200 mcg/day) + SABA as needed.
🚨 A 10-year-old in acute asthma, PEF 35% predicted, unable to speak. First drug?
Oxygen + nebulised salbutamol 5 mg + ipratropium 500 mcg.
💊 A child with exercise-induced bronchoconstriction despite SABA before exercise. Next step?
Low-dose daily ICS or LTRA (montelukast).
🧪 Which biologic is indicated for severe allergic asthma (elevated IgE)?
Omalizumab (anti-IgE).
🩺 A child with severe eosinophilic asthma, exacerbations despite high-dose ICS+LABA. Add-on biologic?
Mepolizumab (anti-IL5) or dupilumab (anti-IL4R).
📉 What is the first-line treatment for acute severe asthma after initial bronchodilators and steroids, if poor response?
IV magnesium sulphate 40 mg/kg (single dose).
⚠️ A child with acute asthma, PEF 60% post-nebuliser, but still respiratory distress. Next ICU criteria?
Consider PICU if PEF <50% after adequate treatment, rising CO2, exhaustion, or silent chest.
📊 FeNO level >35 ppb suggests which type of inflammation?
Eosinophilic (steroid-responsive) airway inflammation.
🩺 A 5-year-old with viral-induced wheeze, normal interval, no atopy. Best initial controller?
Low-dose ICS (e.g., budesonide 100 mcg/day) started at onset of viral illness (intermittent ICS).