Exhausted Asthmatic With a Silent Chest and Rising PaCO2
A 24-year-old woman with lifelong asthma is brought by her brother after two days of a viral upper respiratory infection. She has used salbutamol every 30 minutes since midnight and now can speak only single words. On arrival she is drowsy but rousable, RR 34, HR 138, BP 108/68, SpO2 89% on a 15 L non-rebreather, temperature 37.8°C. The chest is silent with minimal wheeze and poor air entry bilaterally. Peak flow is unrecordable. She has received three back-to-back salbutamol nebulizers, ipratropium, IV hydrocortisone 200 mg, and magnesium sulfate 2 g over 20 minutes. Arterial blood gas on 15 L oxygen: pH 7.28, PaCO2 48 mmHg, PaO2 62 mmHg, HCO3 22 mmol/L, lactate 3.1 mmol/L. Chest radiograph shows hyperinflation but no pneumothorax. The ED has ketamine, rocuronium, propofol, and norepinephrine; the ICU has one ventilator.
1. Is intubation indicated now, or should you continue medical therapy or attempt non-invasive ventilation?
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Intubation is indicated now. This patient has impending respiratory failure from severe asthma: altered mental status, inability to speak, a silent chest, exhaustion, and a PaCO2 of 48 mmHg with acidosis despite maximal bronchodilators and magnesium. In acute severe asthma, a normal or rising PaCO2 is a late and ominous sign because the patient is no longer able to hyperventilate.
Non-invasive ventilation is not appropriate for an exhausted asthmatic with depressed consciousness. It may delay definitive airway management, and positive pressure can worsen dynamic hyperinflation and gastric insufflation. High-flow nasal oxygen does not treat hypoventilation. More nebulisers are not a substitute for securing the airway.
I would prepare for rapid sequence intubation with ketamine 1–1.5 mg/kg and rocuronium 1.2 mg/kg. Ketamine is preferred because it provides bronchodilation and preserves blood pressure. I would have norepinephrine ready, give a 500 mL crystalloid bolus if she is hypotensive, and call anaesthesia and ICU. The highest-risk period is immediately after intubation, when dynamic hyperinflation and sedative-induced hypotension can cause arrest. This should be an anticipated, prepared-for event, not a surprise.
2. What ventilator strategy will you use immediately after intubation, and why?
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I would use controlled ventilation with settings designed to minimise dynamic hyperinflation and barotrauma:
- Mode: volume-controlled ventilation for reliable tidal volume delivery.
- Respiratory rate: 8–10/min, deliberately lower than her spontaneous rate, to allow full exhalation.
- Tidal volume: 6–8 mL/kg predicted body weight.
- PEEP: start at 5 cmH2O; higher PEEP can worsen air trapping in asthma.
- Inspiratory flow: high, 60–80 L/min, to shorten inspiratory time and lengthen expiration.
- I:E ratio: 1:4 or longer.
- Plateau pressure: keep below 30 cmH2O.
- Permissive hypercapnia: accept PaCO2 up to about 60–70 mmHg if pH remains above 7.15 and the patient is stable.
I would check for auto-PEEP with an expiratory hold. If auto-PEEP is high, I would reduce the respiratory rate, increase expiratory time, and treat agitation or pain. Sedation with ketamine or propofol infusion is appropriate; morphine should be avoided because of histamine release and respiratory depression. I would continue systemic steroids and bronchodilators through the circuit and obtain a chest radiograph to exclude pneumothorax.
3. Ten minutes after intubation her BP falls to 70/40 and the ventilator alarms show high peak pressures. What is your immediate approach?
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This is a peri-intubation crisis, and the most likely cause is dynamic hyperinflation with reduced venous return, followed by tension pneumothorax. I would act immediately rather than order tests first:
- Disconnect the patient from the ventilator for 30–60 seconds and allow full exhalation. Bag manually at a slow rate with an easy squeeze. If the blood pressure improves, auto-PEEP was the cause.
- Check for tension pneumothorax: unilateral breath sounds, tracheal deviation, distended neck veins, and sudden desaturation. If suspected, needle decompress immediately without waiting for a chest radiograph.
- Reduce respiratory rate and minute ventilation to lengthen expiratory time.
- Treat hypotension: start or increase norepinephrine, give a cautious fluid bolus, and check tube position and circuit obstruction.
- Deepen sedation or paralysis if the patient is fighting the ventilator and generating high airway pressures.
I would not simply increase the sedation and walk away. The combination of high peak pressures and hypotension after intubation in asthma is a mechanical problem until proven otherwise. I would also check for oesophageal intubation and mucus plugging.