Acute Exacerbation of Asthma

Episode of progressive increase in breathlessness, cough, wheeze or chest tightness with a fall in expiratory airflow. Most episodes follow viral respiratory infection (about 50 to 80%), allergen exposure, air pollution, tobacco smoke, non-adherence to inhaled corticosteroid, drugs (beta blockers, aspirin and other NSAIDs) or emotional stress. Thunderstorm asthma occurs in pollen season.

• Asthma affects about 1 to 18% of the population by region; about 5 to 10% have severe disease. Hospital admission rates are about 10 to 20 per 100,000 per year in adults. Asthma deaths are largely preventable and are linked to delayed treatment, undertreatment with corticosteroids, over reliance on short acting beta agonists and failure to recognise severity.
• Severity (peak expiratory flow as a percentage of best or predicted):
  • Moderate: increasing symptoms, peak flow 50 to 75%, no features of severe disease.
  • Acute severe: peak flow 33 to 50%, respiratory rate 25 or more, heart rate 110 or more, inability to complete sentences in one breath.
  • Life threatening: peak flow less than 33%, SpO2 less than 92%, PaO2 less than 8 kPa, normal PaCO2 (4.6 to 6.0 kPa), silent chest, cyanosis, poor respiratory effort, arrhythmia, hypotension, exhaustion, confusion or coma.
  • Near fatal: raised PaCO2 or need for mechanical ventilation.
• Risk factors for fatal asthma: previous near fatal episode, previous intubation or intensive care admission, two or more admissions or three or more emergency visits in the past year, heavy use of reliever (more than one canister a month), poor adherence, psychiatric illness, food allergy, and low socioeconomic status.

• Breathlessness, wheeze, cough (often nocturnal), chest tightness, difficulty speaking. Accessory muscle use, tachypnoea, tachycardia, pulsus paradoxus (greater than 15 to 25 mmHg), hyperinflation, sweating, agitation.
• Warning signs of impending arrest: silent chest, cyanosis, bradycardia, exhaustion, confusion, hypotension, inability to lie flat.
• Differential diagnosis: COPD exacerbation, pulmonary oedema (cardiac asthma), pulmonary embolism, pneumothorax, anaphylaxis, vocal cord dysfunction, foreign body or upper airway obstruction, bronchiolitis in infants, pneumonia, panic attack, eosinophilic granulomatosis with polyangiitis.
• Complications: respiratory failure and arrest, pneumothorax, pneumomediastinum, lactic acidosis (salbutamol), hypokalaemia, arrhythmia, hypoxic brain injury, and death.

• Measure peak expiratory flow (not in life threatening disease), SpO2, heart rate, respiratory rate, pulsus paradoxus, ability to speak.
• Arterial blood gas if SpO2 is less than 92% or the patient is severely ill: a normal or rising PaCO2 signals fatigue.
• Chest X-ray only if pneumothorax, pneumonia or other complication is suspected, or life threatening disease. Blood tests: potassium, glucose, lactate (high with salbutamol), full blood count, theophylline level if on theophylline, ECG for arrhythmia. Look for precipitants (infection, drugs, allergens).

• Treat at once; do not wait for tests. Sit the patient up, give oxygen to keep SpO2 93 to 95% in adults and 94 to 98% in children.
• Bronchodilators (first hour):
  • Salbutamol 5 mg nebulised every 20 minutes for 3 doses (children under 5: 2.5 mg), or continuous nebulisation 5 to 10 mg/h in severe disease; or salbutamol 100 micrograms per puff, 4 to 10 puffs via spacer every 20 minutes for 1 hour.
  • Add ipratropium bromide 500 micrograms nebulised (250 micrograms in children under 12) every 20 minutes for 3 doses, then every 4 to 6 hours, in acute severe and life threatening disease.
  • Oxygen driven nebulisers; in hypercapnic patients use air driven nebulisation with supplemental oxygen by nasal cannulae.
• Corticosteroids within 1 hour:
  • Prednisolone 40 to 50 mg orally daily for 5 to 7 days (children 1 mg/kg, maximum 40 mg, for 3 to 5 days); no taper is needed for courses of 10 days or less.
  • Hydrocortisone 100 mg IV every 6 hours (children 4 mg/kg, maximum 100 mg) when oral therapy is not possible.
• Escalation for acute severe or life threatening disease not responding after 1 hour:
  • Magnesium sulfate 2 g IV over 20 minutes (children 40 mg/kg, maximum 2 g); a single dose only.
  • Salbutamol IV 250 micrograms slowly over 10 minutes then 3 to 20 micrograms/min (monitor potassium and lactate).
  • Aminophylline 5 mg/kg IV over 20 minutes (omit the loading dose if already taking theophylline), then 0.5 to 0.7 mg/kg/h; target level 10 to 20 mg/L (55 to 110 micromol/L); watch for arrhythmia and seizures.
  • Adrenaline 0.5 mg (0.5 mL of 1 in 1000) IM, or terbutaline 0.25 mg SC, when nebulised therapy is impossible or anaphylaxis is suspected (evidence is limited).
  • Seek intensive care input early. Avoid sedatives.
• Monitor: SpO2, heart rate, peak flow every 15 to 30 minutes until improving, then every 4 to 6 hours; potassium (hypokalaemia from salbutamol), blood gas repeated within 1 to 2 hours if abnormal.
• Intubation and ventilation for exhaustion, coma, cardiorespiratory arrest, rising PaCO2 with acidosis despite treatment, or refractory hypoxaemia (ketamine 1 to 2 mg/kg IV with rocuronium 1.0 to 1.2 mg/kg; use low respiratory rate, tidal volume 6 to 8 mL/kg, long expiratory time, and permit hypercapnia to a pH greater than 7.2; use a respiratory rate of 8 to 12 per minute, plateau pressure less than 30 cmH2O, and disconnect the circuit and compress the chest if blood pressure or oxygenation suddenly falls).
• Antibiotics only for clinical evidence of bacterial infection.
• Discharge when peak flow is 75% or more of best, symptoms are controlled, and the patient has been stable on usual treatment for 12 to 24 hours:
  • Prednisolone to complete the course; inhaled corticosteroid with formoterol: budesonide formoterol 160/4.5 micrograms, 1 to 2 puffs as needed and 2 puffs twice daily as maintenance (reduces further exacerbations); or a corticosteroid inhaler plus salbutamol reliever.
  • Written action plan, inhaler technique check, trigger avoidance, smoking cessation, vaccination (influenza, pneumococcal), and review within 2 days and again at 4 to 6 weeks.
• Special groups:
  • Children: salbutamol 2.5 mg nebulised (under 5 years), prednisolone 1 mg/kg (maximum 40 mg) and magnesium sulfate 40 mg/kg (maximum 2 g); oral dexamethasone 0.6 mg/kg (maximum 16 mg) once or twice is an alternative to prednisolone; oxygen to SpO2 94 to 98%.
  • Pregnancy: give salbutamol, ipratropium, prednisolone 40 to 50 mg daily (or hydrocortisone 100 mg IV every 6 hours) and magnesium sulfate 2 g IV when needed, keep SpO2 greater than 95%, avoid aggravating hypoxia; prednisolone and salbutamol are safe.
  • Elderly: lower threshold for admission; watch for cardiac disease and drug interactions with theophylline.
  • Aspirin exacerbated and beta blocker induced asthma: stop the drug; add ipratropium and consider glucagon 1 to 5 mg IV for beta blocker induced bronchospasm.
• Red flags: silent chest, SpO2 less than 92%, normal or rising PaCO2, exhaustion, confusion, cyanosis, bradycardia, hypotension, failure to improve after 1 hour.
• Follow up: review within 48 hours and at 4 to 6 weeks; step up preventive therapy (inhaled corticosteroid dose increase, add long acting beta agonist or long acting muscarinic antagonist, consider biologic therapy for severe eosinophilic or allergic asthma).