Key Facts

Acute asthma exacerbations are one of the most common medical emergencies in the UK. Deaths from asthma are largely preventable and are associated with underestimation of severity, inadequate treatment, and poor follow-up. BTS/SIGN guidelines provide a structured approach.

Epidemiology

Asthma affects approximately 5.4 million people in the UK. There are approximately 77,000 hospital admissions for asthma annually. Approximately 1,400 people die from asthma each year in the UK. The UK has one of the highest asthma mortality rates in Europe.

Aetiology

Acute exacerbations are triggered by:

• Viral infections (most common trigger, especially rhinovirus)
• Allergen exposure: Pollen, dust mite, animal dander
• Exercise, cold air, emotional stress
• Non-adherence to preventer inhalers (most common modifiable factor)
• Drugs: NSAIDs, beta-blockers, aspirin
• Occupational exposures

Pathophysiology

Acute asthma involves bronchospasm (smooth muscle contraction), airway inflammation (oedema, cellular infiltration), and mucus hypersecretion. This causes progressive airway obstruction, hyperinflation, and ventilation-perfusion mismatch. In severe cases, respiratory muscle fatigue leads to hypoventilation, CO2 retention, and respiratory arrest.

Severity Classification (BTS/SIGN)

Moderate acute asthma:

• Increasing symptoms, PEF 50-75% best/predicted
• No features of acute severe asthma

Acute severe asthma (any one of):

• PEF 33-50% best/predicted
• Respiratory rate ≥25/min
• Heart rate ≥110/min
• Inability to complete sentences in one breath

Life-threatening (any one of):

• PEF <33% best/predicted
• SpO2 <92% or PaO2 <8 kPa
• Normal or raised PaCO2 (>4.6 kPa) — indicates exhaustion
• Silent chest, cyanosis
• Poor respiratory effort, altered consciousness
• Hypotension, arrhythmia

Near-fatal:

• Raised PaCO2 requiring mechanical ventilation

Red Flags

• Normal/rising CO2 in acute asthma — indicates respiratory failure (NOT reassuring)
• Silent chest — severe bronchospasm with minimal air entry
• Altered consciousness — imminent respiratory arrest
• Previous ICU admission for asthma — high-risk patient

Bedside

• PEF: Essential — correlate with best/predicted; repeat after treatment
• SpO2: Continuous monitoring
• ABG/VBG: If SpO2 <92% or life-threatening features — assess PaCO2

Bloods

• ABG: If severe/life-threatening — PaCO2, PaO2, pH, lactate
• FBC: Neutrophilia (infection), eosinophilia (allergic component)
• U&Es: If IV aminophylline considered; K⁺ monitoring (salbutamol causes hypokalaemia)
• CRP: If infection suspected
• Theophylline level: If on maintenance theophylline before aminophylline loading

Imaging

• CXR: If first episode, diagnostic uncertainty, life-threatening features, failure to respond (exclude pneumothorax, infection, foreign body)

Special Tests

• Blood/sputum eosinophil count: Guide biologic therapy eligibility in recurrent exacerbators
• FeNO: When stable — assess eosinophilic airway inflammation

Non-pharmacological

• Position: Sit patient upright
• High-flow oxygen: 15L/min via non-rebreather to maintain SpO2 94-98%
• Reassess frequently: PEF, SpO2, clinical status at 15-30 min intervals

Pharmacological

Immediate treatment (all acute severe):

• Salbutamol 5mg nebulised (driven by O2 at 6-8 L/min) — repeat every 15-30 min or back-to-back if life-threatening
• Ipratropium bromide 500mcg nebulised — add for severe/life-threatening
• Prednisolone 40-50mg PO (or hydrocortisone 100mg IV if unable to swallow) — continue for at least 5 days

If life-threatening or poor response:

• IV magnesium sulphate 1.2-2g (50% solution) over 20 minutes — single dose
• IV aminophylline loading dose 5mg/kg over 20 min (NOT if on oral theophylline) — then maintenance 0.5-0.7mg/kg/hr
• IV salbutamol 250mcg slow IV bolus — if nebulisation ineffective

If near-fatal/failing treatment:

• ICU referral: Intubation and mechanical ventilation
• Ketamine: May be used as bronchodilator at induction
• Volatile anaesthetic agents: Sevoflurane/isoflurane provide bronchodilation

Surgical/Interventional

• Intubation and ventilation: Last resort — high risk of dynamic hyperinflation and cardiac arrest
• Chest drain: If pneumothorax complicates acute asthma

Referral Criteria

• Life-threatening features — immediate ICU referral
• Poor response to initial treatment (PEF not improving >15 min) — senior review
• Previous near-fatal asthma — low threshold for ICU
• All patients — GP follow-up within 48 hours; respiratory specialist review within 4 weeks of hospital admission

• Hospital mortality for acute asthma: <1% overall; higher in life-threatening/near-fatal
• Risk factors for fatal asthma: Previous ICU admission, ≥3 ED attendances/year, poor adherence to treatment, psychosocial factors, brittle asthma
• Post-discharge: 30% readmission rate within 12 months if no structured follow-up
• Structured discharge planning: Reduces readmission by 30-40%
• The UK has one of the highest asthma mortality rates in Europe — the National Review of Asthma Deaths (NRAD) found most deaths were preventable

BTS/SIGN Acute Asthma Treatment Ladder

Discharge Checklist (BTS/SIGN)