Acute Asthma Exacerbation In Children

An acute asthma exacerbation is an episode of progressively worsening cough, wheeze, breathlessness and chest tightness with reduced expiratory airflow, caused by bronchial smooth muscle constriction, mucosal oedema and mucus plugging.

It is among the commonest reasons for paediatric emergency visits and admission. Most episodes are triggered by viral respiratory infections (rhinovirus above all; also respiratory syncytial virus and influenza).

Other triggers: allergen exposure, cold air, exercise, tobacco smoke, air pollution, thunderstorms, poor adherence to controller therapy, and emotional stress.

Risk factors for severe or fatal asthma: previous near fatal asthma (intubation or intensive care), more than one hospital admission or three or more emergency visits in the past year, overuse of short acting beta agonists (more than one canister per month), poor adherence to inhaled corticosteroids, food allergy, psychosocial problems, adolescence and low socioeconomic status.

Preschool wheeze should be distinguished: children under 5 years with viral induced wheeze may not be asthmatic, but acute episodes are treated the same way.

Severity assessment (children aged 5 to 12 years; thresholds for younger children differ slightly):

• Moderate: speaks in sentences, SpO2 94% or above, peak expiratory flow (PEF) above 50% of best or predicted, no features of severe disease

• Severe: SpO2 below 92%, too breathless to talk or feed, heart rate above 125/min (over 5 years) or above 140/min (2 to 5 years), respiratory rate above 30/min (over 5 years) or above 40/min (2 to 5 years), accessory muscle use, PEF 33 to 50% of best or predicted

• Life threatening: SpO2 below 92% with any of silent chest, cyanosis, poor respiratory effort, exhaustion, hypotension, altered consciousness or confusion, PEF below 33%, or normal or rising PaCO2

• Symptoms: breathlessness, cough (often worse at night), wheeze, chest tightness, difficulty speaking or feeding, and sometimes abdominal pain or vomiting in younger children
• Signs: tachypnoea, tachycardia, subcostal, intercostal and suprasternal recession, nasal flaring, tracheal tug, prolonged expiration, widespread polyphonic wheeze, hyperinflation, pulsus paradoxus in severe attacks, reduced air entry
• Ominous signs: silent chest, cyanosis, inability to speak, bradycardia, exhaustion, drowsiness or agitation (hypoxia and hypercapnia), paradoxical thoraco abdominal movement
• Wheeze can disappear in very severe obstruction, so absent wheeze with distress is dangerous

Look for triggers, adherence and technique, previous severity, and alternative or complicating diagnoses: pneumonia, pneumothorax, foreign body aspiration, anaphylaxis, bronchiolitis (under 12 months), croup, vocal cord dysfunction, cardiac failure and anxiety with hyperventilation.

The diagnosis is clinical. Assess severity at presentation by heart rate, respiratory rate, SpO2 in air, work of breathing, ability to speak, and PEF in those who can perform it. A validated score such as the Paediatric Respiratory Assessment Measure helps.

Investigations are not needed in most children and must not delay treatment:

• Chest radiograph only with focal signs, suspected pneumothorax or pneumomediastinum, suspected foreign body, life threatening features, or failure to respond
• Venous or arterial blood gas for children not improving or with life threatening features; a normal or rising PaCO2 in severe asthma warns of exhaustion and impending respiratory failure
• Electrolytes (potassium falls with high dose beta agonists), glucose and lactate
• Infection screen (respiratory virus PCR, cultures) if febrile and unwell

Oxygen. By mask or nasal cannulae to keep SpO2 94 to 98%. A hypoxic child receives oxygen before and during bronchodilators.

Salbutamol.

• Metered dose inhaler with spacer (and face mask under 3 years): 100 microgram puffs given one at a time with 5 tidal breaths per puff. Mild to moderate: 4 to 6 puffs (2 to 4 puffs under 5 years); severe: 10 puffs. Repeat every 20 minutes for the first hour, then every 1 to 4 hours as required
• Nebulised salbutamol 2.5 mg (under 5 years) or 5 mg (5 years or above), oxygen driven, every 20 minutes for 3 doses in severe attacks, then every 1 to 4 hours as required; or continuous nebulisation (0.15 to 0.5 mg/kg/hour, maximum 15 to 20 mg/hour) in severe refractory disease with cardiac monitoring
• Spacer therapy is as effective as nebulisation in mild to moderate attacks with fewer side effects (tachycardia, tremor, hypokalaemia)

Ipratropium bromide. Add for severe or poorly responding attacks: 250 micrograms nebulised (500 micrograms from age 12), or 20 micrograms per puff by inhaler, 4 to 8 puffs, every 20 minutes for the first hour, then every 4 to 6 hours. It reduces admission in severe asthma, and offers no benefit after the first 24 hours of admission.

Systemic corticosteroids. Give within the first hour to every child with a moderate to severe exacerbation or an inadequate response to bronchodilators.

• Prednisolone 1 to 2 mg/kg orally once daily (maximum 40 mg; commonly 20 mg for ages 2 to 5 years and 30 to 40 mg from age 5) for 3 to 5 days; no taper for courses under 10 to 14 days
• Dexamethasone 0.6 mg/kg orally as a single dose (maximum 16 mg), repeated once at 24 to 48 hours if needed: equivalent, better tolerated and less often vomited
• If vomiting or unable to take oral medication: hydrocortisone 4 mg/kg IV every 6 hours (maximum 100 mg per dose) or methylprednisolone 1 mg/kg IV every 6 hours (maximum 60 mg)
• Inhaled corticosteroids are not a substitute

Second line treatment for severe and life threatening asthma (inadequate response after 1 hour of intensive therapy).

1. IV magnesium sulfate 40 to 50 mg/kg (maximum 2 g) over 20 minutes as a single bolus; reduces admission in severe attacks; monitor blood pressure (flushing, hypotension, nausea). Nebulised isotonic magnesium sulfate 150 mg is an adjunct
2. IV salbutamol: 15 micrograms/kg bolus over 10 minutes (maximum 250 micrograms), then 1 to 2 micrograms/kg/minute (up to 5 micrograms/kg/minute in some centres) under high dependency monitoring; watch for lactic acidosis, hypokalaemia and tachycardia
3. IV aminophylline: loading 5 mg/kg over 20 minutes (omit if already on oral theophylline), then 1 mg/kg/hour (0.5 to 0.7 mg/kg/hour in younger children), with level monitoring (target 10 to 20 mg/L); risks are arrhythmia, seizures and vomiting; used when other agents fail
4. Heliox (70:30 or 80:20) through a tight fitting mask in refractory cases (requires FiO2 below 30%)
5. Intramuscular adrenaline 0.01 mg/kg (1 mg/mL, maximum 0.5 mg) or subcutaneous terbutaline 0.01 mg/kg (maximum 0.4 mg) when inhaled therapy cannot be delivered, in near arrest, or if anaphylaxis is suspected
6. High flow nasal cannula oxygen or non-invasive ventilation in impending respiratory failure in a cooperative child, in the paediatric intensive care unit

Intubation and ventilation. For respiratory arrest, severe hypoxia despite maximal therapy, coma and exhaustion; use the most experienced operator. Induction: ketamine 1 to 2 mg/kg IV (bronchodilator effect) with rocuronium 1 to 1.2 mg/kg.

Ventilation: low respiratory rate, long expiratory time (I:E 1:4 to 1:5), tidal volume 6 to 8 mL/kg, permissive hypercapnia (pH above 7.2), PEEP 0 to 5 cmH2O, and monitoring for dynamic hyperinflation, pneumothorax and hypotension (disconnect and allow passive exhalation if hypotension occurs). Continue bronchodilators, steroids and magnesium, and consider ECMO for refractory cases.

Monitoring. Continuous pulse oximetry, heart rate and respiratory rate in severe attacks; repeat blood gases and potassium; chest radiograph if deterioration (pneumothorax, collapse). Avoid over hydration, treat dehydration, and note that antidiuretic hormone secretion is often raised. Antibiotics only for proven bacterial infection (for example amoxicillin or azithromycin for focal pneumonia).

Discharge criteria and planning. The child is stable on bronchodilators every 3 to 4 hours or less, SpO2 94% or above in air, minimal recession, PEF above 75% of best where measurable, and inhaler technique is checked. Provide:

• A written asthma action plan, spacer and inhaler technique training, trigger avoidance and smoking cessation support for caregivers
• Prednisolone to complete 3 to 5 days
• Salbutamol 2 to 4 puffs every 4 hours as needed, tapering over 1 to 2 weeks, then as required
• A review of preventive therapy: step up inhaled corticosteroid (for example budesonide 200 to 400 micrograms twice daily or fluticasone propionate 50 to 100 micrograms twice daily), or start low dose budesonide formoterol maintenance and reliever therapy from age 6 (100/6 micrograms, one inhalation twice daily plus one as needed, up to 8 inhalations daily at ages 6 to 11); a leukotriene receptor antagonist (montelukast 4 mg for ages 2 to 5, 5 mg for ages 6 to 14, once nightly; watch for neuropsychiatric effects) for allergic or preschool wheeze
• Primary care review within 48 hours and specialist review at 4 to 6 weeks (earlier if admitted), covering adherence, allergic rhinitis, eczema, obesity, reflux and psychosocial factors
• Specialist consideration of biologics (omalizumab, mepolizumab, dupilumab, tezepelumab) for severe allergic or eosinophilic asthma uncontrolled on high dose inhaled steroid plus a second controller
• Influenza and pneumococcal vaccination

Prognosis and prevention. Most children recover within days; severe attacks need 2 to 4 days in hospital. Prevention rests on good controller adherence (the main modifiable cause), trigger avoidance, treatment of allergies, and early action plans at the onset of viral symptoms.