Near-Fatal Asthma

Near fatal asthma is an acute attack with a raised arterial carbon dioxide tension (PaCO2 over 6.0 kPa or 45 mmHg), or an attack needing mechanical ventilation with raised inflation pressures. It is the stage before respiratory arrest.

Epidemiology. Fewer than 1 in 10 patients admitted with severe asthma reach this stage, but those who do have a high risk of death. Most asthma deaths occur out of hospital and after delay in seeking or receiving treatment.

Risk factors. Previous intubation or intensive care admission, repeated admissions, heavy reliance on short acting beta agonists, low use of inhaled corticosteroid, poor adherence, psychiatric illness, substance misuse, food allergy and a poor perception of breathlessness.

Pathophysiology. Airway smooth muscle spasm, mucosal oedema and mucus plugging cause severe airflow obstruction. Gas trapping produces dynamic hyperinflation and intrinsic positive end expiratory pressure (auto-PEEP), which reduces venous return and cardiac output. Hypercapnia, acidosis and exhaustion follow.

Presentation is silent chest, cyanosis, exhaustion, poor respiratory effort, bradycardia, hypotension, confusion or coma. Peak expiratory flow is under 33% of best or predicted, and oxygen saturation is under 92%. Look for pneumothorax, pneumomediastinum, anaphylaxis and pneumonia.

Red flags.

• Inability to speak, silent chest, cyanosis or altered consciousness.
• Normal or rising PaCO2 in a breathless patient.
• Bradycardia or hypotension.

Diagnosis is clinical, and treatment must not wait for tests. Obtain an arterial blood gas (a normal or high PaCO2 is a warning), chest radiograph (pneumothorax, consolidation), potassium, glucose and lactate, and ECG. Peak flow is not attempted in extremis.

Differential diagnosis. Anaphylaxis, upper airway obstruction, foreign body, vocal cord dysfunction, pulmonary oedema, pulmonary embolism, tension pneumothorax and COPD exacerbation.

Give high flow oxygen to keep saturation at 94 to 98%, and monitor continuously in resuscitation or intensive care.

Bronchodilators.

• Salbutamol 5 mg nebulised, repeated every 15 to 20 minutes or given continuously at 10 to 15 mg/h. Oxygen driven nebulisation is usual. Monitor potassium, lactate (a rise is common and is not a sign of hypoxia) and heart rate.
• Ipratropium 500 microgram nebulised every 20 minutes for 3 doses, then every 4 to 6 hours.

Corticosteroid. Prednisolone 40 to 50 mg orally, or hydrocortisone 100 mg IV every 6 hours when oral intake is impossible. Continue for 5 to 7 days.

Magnesium. Magnesium sulphate 2 g IV over 20 minutes, single dose. Reduce in renal impairment and monitor reflexes and blood pressure.

Intravenous options (specialist use).

• Salbutamol 250 microgram IV slowly over 10 minutes, then 5 to 20 microgram/min. Monitor potassium, lactate and arrhythmia.
• Aminophylline 5 mg/kg IV over 20 minutes (omit the load if already taking theophylline), then 0.5 mg/kg/h with level monitoring. Avoid in older adults, liver disease and heart failure without level checks.
• Adrenaline 0.5 mg IM (0.5 mL of 1 in 1000) if anaphylaxis is possible, or when no other option exists.

Non-invasive support. High flow nasal oxygen or NIV may be tried in cooperative patients under close observation in intensive care, with early intubation if there is no improvement within 1 hour.

Intubation. Indications are coma, respiratory arrest, exhaustion, rising PaCO2 with acidosis and failure of treatment. Use the most experienced operator, a large tube (8.0 mm or more), ketamine 1 to 2 mg/kg IV with rocuronium 1.2 mg/kg IV, and give fluid before induction to offset the fall in blood pressure.

Ventilation. Set a respiratory rate of 8 to 10 breaths/min, tidal volume 6 to 8 mL/kg predicted body weight, inspiratory flow 80 to 100 L/min, an inspiratory to expiratory ratio of 1 to 4 or longer, and low PEEP. Accept permissive hypercapnia (pH over 7.2). Keep plateau pressure under 30 cmH2O.

Post-intubation hypotension. Disconnect the ventilator for 30 to 60 seconds with chest compression to release trapped gas, give fluid and treat pneumothorax.

Sedation. Ketamine infusion 0.5 to 2 mg/kg/h, or propofol, with a paralytic if needed to reduce dyssynchrony. Avoid prolonged paralysis with high dose corticosteroid because of myopathy.

Rescue therapy. Inhaled anaesthetic (sevoflurane or isoflurane) and extracorporeal membrane oxygenation for refractory cases.

Monitoring. Continuous ECG, oximetry, arterial gas every 1 to 2 hours, potassium, lactate, airway pressures and auto-PEEP.

Referral and escalation. Contact intensive care at once for any near fatal feature or failure to improve within 15 to 30 minutes. Review in a specialist asthma service before discharge.

Special groups. In pregnancy, give the same drugs and keep saturation over 95% for foetal oxygenation. In children, salbutamol 2.5 to 5 mg nebulised, ipratropium 250 microgram, prednisolone 1 to 2 mg/kg (maximum 40 mg) and magnesium sulphate 40 mg/kg IV (maximum 2 g).