Asthma

Overview

Asthma is a chronic inflammatory airway disease characterised by variable, reversible airflow obstruction, airway hyperresponsiveness, and eosinophilic (Th2-mediated) inflammation causing bronchospasm, mucosal oedema, and mucus plugging.

Presentation

•Classic triad - episodic breathlessness, wheeze, and cough; worse at night and early morning

•Expiratory wheeze - polyphonic and diffuse; may disappear as severity increases (silent chest = near-fatal)

•Chest tightness, tachypnoea (RR >25 = severe), accessory muscle use, hyperinflated chest

•Triggers - allergens, viral URTI, cold air, exercise, NSAIDs

•Increasing reliever use with diminishing response over recent days - key warning sign

•Cough-variant asthma - cough may be the sole symptom, often nocturnal

•Atopy history (eczema, hay fever) commonly present

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Occupational asthma - consider in all adults with new-onset asthma. A 2-week improvement on holiday away from the workplace is a classic clue. Sensitisers include isocyanates (spray paint), flour dust, and latex.

Investigations

•Diagnosis (outpatient):

•First-line: spirometry with bronchodilator reversibility - FEV1/FVC <0.7 with ≥12% and ≥200 mL improvement in FEV1 post-bronchodilator confirms reversible obstruction

•PEF variability diary - ≥20% diurnal variability on ≥3 days/week over 2 weeks supports diagnosis

•FeNO - ≥40 ppb = high probability eosinophilic asthma; 25-39 ppb borderline; <25 ppb makes asthma less likely

•Gold standard: methacholine or mannitol bronchial challenge - demonstrates airway hyperresponsiveness when diagnosis uncertain

•Acute setting:

•PEFR - compare to personal best; classify severity and monitor response

•Pulse oximetry - SpO2 <92% = life-threatening

•ABG - expected: low PaCO2 (hyperventilation) and respiratory alkalosis; normal or rising PaCO2 = near-fatal sign (respiratory muscle fatigue, impending arrest)

•CXR - not routine; only if pneumothorax, pneumonia, or pneumomediastinum suspected

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A normal PaCO2 (4.5-6 kPa) in a breathless asthmatic is not reassuring - it means the patient was previously hypocapnic and is now tiring. A rising PaCO2 demands immediate escalation to HDU/ITU.

Differential diagnosis

•COPD - >35 years, smoking history, fixed (irreversible) obstruction; may coexist (ACOS)

•Vocal cord dysfunction - inspiratory stridor rather than expiratory wheeze; flattened inspiratory loop on spirometry

•Cardiac failure ('cardiac asthma') - bilateral crackles, raised JVP, oedema, elevated BNP; responds to diuretics

•Pneumothorax - sudden unilateral pleuritic pain, absent breath sounds unilaterally; may complicate acute asthma

•Anaphylaxis - urticaria, angioedema, hypotension; known allergen exposure

Complications

•Pneumothorax - high intrapleural pressures during severe bronchoconstriction; sudden unilateral deterioration

•Respiratory failure and death - ~1,200 deaths/year in UK; most preventable (NRAD 2014: >90% potentially preventable - inadequate preventer therapy, failure to seek help, poor follow-up)

•Irreversible airway remodelling - chronic poorly controlled asthma → fixed airflow limitation (subepithelial fibrosis, smooth muscle hypertrophy)

•ICS side effects - oral candidiasis (advise mouth rinsing after use), dysphonia; systemic absorption at high doses: adrenal suppression, reduced bone mineral density

Acute severity classification

BTS/SIGN acute asthma severity classification

Feature	Moderate	Severe	Life-threatening
PEFR	50-75% best/predicted	33-50% best/predicted	<33% best/predicted
SpO2	≥92%	≥92%	<92%
Speech	Normal sentences	Cannot complete sentences	Cannot speak
RR / HR	Normal	RR >25, HR >110	Silent chest, cyanosis, bradycardia, altered consciousness

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When signs span two severity categories, always assign the more severe. A silent chest is not reassuring - it means airflow is so severely reduced that no wheeze is generated.

Management - chronic stepwise

Step 1 · All patients

1. 1Salbutamol 100-200 micrograms inhaled PRN (SABA reliever) - all patients regardless of step

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Step 2 · Add preventer

1. 1Low-dose ICS - e.g. beclometasone 200-400 micrograms/day; cornerstone of preventer therapy, reduces eosinophilic inflammation

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Step 3 · Uncontrolled on low-dose ICS

1. 1Add LABA - e.g. salmeterol or formoterol; combination ICS/LABA inhalers (e.g. fluticasone/salmeterol, budesonide/formoterol) improve adherence

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Step 4 · Further add-on

1. 1Increase ICS to medium dose, or add LTRA - montelukast 10 mg daily (useful for aspirin-exacerbated and exercise-induced asthma)
2. 2Consider LAMA - tiotropium as add-on if uncontrolled on ICS/LABA

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Step 5 · Specialist/severe

1. 1High-dose ICS/LABA, oral theophylline, or biologic therapy
2. 2Mepolizumab - severe eosinophilic asthma; omalizumab - severe allergic asthma

Management - acute exacerbation

Immediate · All acute exacerbations

1. 1High-flow oxygen - target SpO2 94-98%
2. 2Back-to-back nebulised salbutamol 2.5-5 mg driven by oxygen
3. 3Oral prednisolone 40-50 mg daily (IV if cannot swallow) for 5 days

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Severe/life-threatening · Add

1. 1Nebulised ipratropium bromide 0.5 mg 4-6 hourly (add-on anticholinergic)
2. 2IV magnesium sulphate 2 g over 20 minutes - single dose for severe/life-threatening not responding to initial therapy

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Improving

Step down nebulisers to inhaler, continue oral prednisolone, review preventer therapy, arrange GP follow-up within 2 days

Not improving / rising PaCO2

Early senior and ITU involvement; consider non-invasive or invasive ventilation; HDU/ITU admission

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Avoid NSAIDs and beta-blockers in all patients with known asthma. In pregnancy, treat asthma as actively as in non-pregnant patients - all regular inhalers (SABA, ICS, LABA) are safe; undertreated asthma poses greater risk to the fetus than inhaled medication.