Status Asthmaticus

Severe asthma exacerbation that does not respond to initial treatment with bronchodilators and systemic corticosteroids within 1 to 2 hours (or after three doses of nebulised bronchodilator). It includes acute severe, life threatening and near fatal asthma.

• Hospital mortality is about 0.1 to 0.5% overall, but about 5 to 10% in mechanically ventilated patients. Most deaths happen before arrival at hospital, from delay in recognition and treatment.
• Mechanism: airway smooth muscle spasm, mucosal oedema, mucus plugging and inflammation produce severe airflow obstruction, dynamic hyperinflation with auto positive end expiratory pressure, rising work of breathing, falling venous return and hypercapnic respiratory failure.
• Risk factors: previous near fatal episode, previous intubation, repeated admissions, heavy reliever use, poor adherence, food allergy, psychosocial problems, substance misuse, and delayed presentation.

• Extreme breathlessness, inability to speak, accessory muscle use, paradoxical chest and abdominal movement, tachycardia, pulsus paradoxus, sweating, agitation then exhaustion, drowsiness, confusion.
• Ominous signs: silent chest, cyanosis, bradycardia, arrhythmia, hypotension, poor respiratory effort, normal or high PaCO2.
• Differential diagnosis: tension pneumothorax, pulmonary oedema, anaphylaxis, pulmonary embolism, upper airway obstruction (foreign body, epiglottitis, vocal cord dysfunction), COPD exacerbation, tracheal compression.
• Complications: respiratory arrest, pneumothorax, pneumomediastinum, hypotension from auto positive end expiratory pressure, lactic acidosis, hypokalaemia, arrhythmia, myopathy from steroids and neuromuscular blockers, hypoxic brain injury, and death.

• Clinical diagnosis. Do not delay treatment for investigations.
• Pulse oximetry, ECG monitoring, arterial blood gas (PaCO2 greater than 6 kPa or pH less than 7.35 means impending failure), chest X-ray (pneumothorax, pneumomediastinum, consolidation), potassium, lactate, glucose, full blood count, theophylline level if relevant. Peak flow is not measured in the sickest patients.

• Resuscitation in a monitored area, with early intensive care input.
• Oxygen to SpO2 93 to 95% (94 to 98% in children), IV access, continuous monitoring.
• Bronchodilators:
  • Continuous nebulised salbutamol 10 to 15 mg/h (children 0.5 mg/kg/h, maximum 20 mg/h), or 5 mg every 15 to 20 minutes.
  • Ipratropium 500 micrograms nebulised every 20 minutes for 3 doses, then every 4 to 6 hours (250 micrograms in children under 12).
  • Salbutamol IV 250 micrograms slowly over 10 minutes then 3 to 20 micrograms/min; check lactate and potassium regularly.
• Corticosteroids: hydrocortisone 100 mg IV every 6 hours, or methylprednisolone 60 to 125 mg IV every 6 to 8 hours (1 to 2 mg/kg/day in children), converting to prednisolone 40 to 50 mg daily orally for 5 to 10 days.
• Adjuncts for refractory disease:
  • Magnesium sulfate 2 g IV over 20 minutes (children 40 mg/kg, maximum 2 g); a single dose only; repeat doses are not recommended outside specialist intensive care.
  • Aminophylline 5 mg/kg IV over 20 minutes (omit if on theophylline) then 0.5 to 0.7 mg/kg/h, target level 10 to 20 mg/L.
  • Ketamine as a bronchodilator and sedative: 0.1 to 0.5 mg/kg IV bolus then 0.5 to 2 mg/kg/h (evidence is limited).
  • Adrenaline 0.3 to 0.5 mg IM, or adrenaline infusion 0.05 to 0.5 micrograms/kg/min, in the peri arrest patient or when nebulised treatment cannot be delivered.
  • Helium and oxygen mixture (70:30) to improve gas flow (evidence is limited).
  • Non-invasive ventilation (inspiratory pressure 8 to 12 cmH2O, expiratory pressure 3 to 5 cmH2O) can be used in a monitored setting for a short period in cooperative patients; do not delay intubation if there is no improvement within 30 to 60 minutes.
• Intubation for exhaustion, coma, cardiorespiratory arrest, refractory hypoxaemia, or rising PaCO2 with acidosis despite treatment:
  • Perform with the most experienced operator: pre-oxygenate, give ketamine 1 to 2 mg/kg IV, and rocuronium 1.0 to 1.2 mg/kg (or suxamethonium 1 to 1.5 mg/kg); give fluids 500 mL to 1 L beforehand because induction and positive pressure drop venous return.
  • Ventilator settings: respiratory rate 8 to 12 per minute, tidal volume 6 to 8 mL/kg predicted body weight, inspiratory time short (inspiratory to expiratory ratio 1:4 to 1:5), positive end expiratory pressure 0 to 5 cmH2O, plateau pressure less than 30 cmH2O, accept permissive hypercapnia to a pH greater than 7.2.
  • For a sudden fall in blood pressure or oxygenation: disconnect the circuit and compress the chest to release trapped air, then exclude tension pneumothorax and tube displacement.
  • Sedation with ketamine or propofol; paralysis for the shortest possible time; inhaled sevoflurane or isoflurane in refractory cases (evidence is limited); venovenous or venoarterial ECMO for refractory hypoxaemia and acidosis.
  • Treat bronchial plugging with mucolytic lavage by bronchoscopy when the airway is blocked.
• Supportive: correct hypokalaemia (potassium 4.0 to 5.0 mmol/L), correct acidosis by improving ventilation, give fluids to correct dehydration, thromboprophylaxis with enoxaparin 40 mg SC daily, stress ulcer prophylaxis while ventilated and on high dose steroids, and antibiotics only for proven bacterial infection.
• Special groups:
  • Children: salbutamol, ipratropium, hydrocortisone 4 mg/kg (maximum 100 mg) and magnesium sulfate 40 mg/kg (maximum 2 g) dosed by weight; early senior and paediatric intensive care involvement; ketamine 1 to 2 mg/kg for intubation.
  • Pregnancy: maintain PaO2 greater than 70 mmHg and SpO2 greater than 95%, left lateral tilt, and give salbutamol, ipratropium, hydrocortisone 100 mg IV every 6 hours and magnesium sulfate 2 g IV; steroids and salbutamol are safe.
  • Elderly or cardiac disease: caution with salbutamol infusion and aminophylline (arrhythmia).
  • Aspirin exacerbated and anaphylactic triggers: stop the trigger; adrenaline IM.
• Red flags: silent chest, drowsiness, hypotension, bradycardia, rising PaCO2, lactate greater than 4 mmol/L, pneumothorax.
• Follow up: step down in a high dependency unit; discharge only when peak flow is 75% or more and the patient has been stable for 24 hours on usual treatment; respiratory specialist review within 2 weeks; written action plan; assess adherence, psychosocial factors and triggers; consider biologic therapy for severe eosinophilic or allergic phenotypes (for example omalizumab 150 to 375 mg SC every 2 to 4 weeks by weight and IgE, mepolizumab 100 mg SC every 4 weeks, benralizumab 30 mg SC every 4 weeks for 3 doses then every 8 weeks, dupilumab 300 mg SC every 2 weeks).