Life-threatening asthma with a normal CO2
Mr D is a 22-year-old student with asthma since childhood. He has had a viral upper respiratory infection for four days and has used a salbutamol inhaler every two hours, with little relief. Paramedics have given three back-to-back nebulised salbutamol and ipratropium and oral prednisolone 40 mg. On arrival he is drowsy but rousable, respiratory rate 34/min, heart rate 128/min, SpO2 89% on air, peak flow 25% of predicted. His chest is quiet with minimal wheeze. Arterial blood gas on air: pH 7.32, PaCO2 5.7 kPa, PaO2 8.1 kPa, bicarbonate 22 mmol/L. He has never been admitted to intensive care and says he 'hates hospitals'. The emergency department is busy and the respiratory ward has no beds. He weighs 70 kg and is on regular beclometasone 200 mcg twice daily but admits he stopped it two months ago.
1. How would you categorise the severity and what are your immediate actions and escalation?
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Severity. This is life-threatening asthma: drowsiness, silent chest, SpO2 <92%, PEF <33%, and a normal PaCO2 in a tachypnoeic patient, which signals fatigue rather than improvement. A normal or rising CO2 in acute asthma is an ominous sign.
Immediate actions.
- Call for senior emergency and critical care help immediately; move to resus.
- Oxygen to target SpO2 94–98%; continuous nebulised salbutamol 5–10 mg with ipratropium 0.5 mg; IV hydrocortisone 100 mg or oral prednisolone 40 mg (already given).
- IV magnesium sulfate 1.2–2 g over 20 minutes.
- Correct hypokalaemia; monitor ECG; continuous SpO2, capnography if available.
- Do not sedate. Prepare for intubation with a senior anaesthetist and ketamine/rocuronium; anticipate hypotension and auto-PEEP.
Reasoning. The common error is to be reassured by a 'normal' CO2 or to send him to a ward because he is young. He needs a critical care decision now.
2. Discuss the role of magnesium, intravenous bronchodilators, NIV and intubation in this situation.
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Magnesium: recommended for severe/life-threatening asthma not responding to initial therapy; 1.2–2 g IV over 20 minutes, monitor BP and reflexes.
IV bronchodilators: IV salbutamol or aminophylline can be considered by a senior clinician, but evidence is limited and side effects (arrhythmia, hypokalaemia) are real. Do not delay intubation to try them.
NIV: not recommended in acute severe asthma; it can worsen air trapping and delay intubation. It may be used only in a specialist setting as a bridge.
Intubation: indicated for exhaustion, altered consciousness, silent chest with rising CO2, hypoxia despite maximal therapy, or cardiac arrest. Use a small tidal volume, low respiratory rate, permissive hypercapnia, and watch for hypotension. Ventilation is high-risk; the decision should be made before collapse.
3. What would you tell him and his family about the need for critical care, and how would you document a decision if he refuses?
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Communication. Explain that he is exhausted and that his breathing could stop; the machine is to support him while the drugs work. Avoid blaming him for stopping his inhaler. Ask about his fears and involve his family with his consent. Use clear language and check understanding.
Refusal. If he refuses, assess capacity. If he has capacity, respect his decision but continue all treatment, explain the risk of death, involve senior/legal advice and document. If he lacks capacity, treat in his best interests, using the least restrictive option. Do not use sedation solely to facilitate intubation without a best-interests decision. Record the discussion, who was present, and the plan for review. Afterwards, refer to respiratory for adherence support and an asthma action plan.