Status Asthmaticus: When the Carbon Dioxide Goes the Wrong Way
Seven-year-old (22 kg) in the emergency department, hour 4 of status asthmaticus. He has had continuous albuterol with ipratropium, IV methylprednisolone 1 mg/kg, and magnesium 50 mg/kg an hour ago. Now: RR 42, HR 168, SpO2 90% on a 15 L nonrebreather, minimal air movement bilaterally with a silent chest, drowsy but arousable, speaking single words. ABG: pH 7.28, PaCO2 52 mmHg (was 32 mmHg one hour ago), PaO2 62 mmHg, lactate 3.1 mmol/L. The respiratory therapist suggests another round of continuous nebs and asks whether you want to try BiPAP first, since the family is anxious about a breathing tube.
1. Interpret the arterial blood gas trend and the clinical picture together. Why is this not reassuring?
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The rising PaCO2 is the emergency.
- A child in severe asthma hyperventilates: PaCO2 is typically low (his was 32). A PaCO2 that climbs to 52 while the child is still tachypneic at 42 does not mean the asthma is improving - it means he can no longer generate the work of breathing. Fatigue, not resolution.
- pH 7.28 with a normal-ish CO2 is deceptive - the lactate of 3.1 reflects the work of breathing and possible hypoperfusion, and it is masking the respiratory acidosis.
- The physical findings corroborate it: silent chest, minimal air entry, drowsiness, single-word speech. Air movement is disappearing because ventilation is failing, not because bronchospasm has resolved.
- Hypoxemia persists despite a 15 L nonrebreather - a high-oxygen requirement in asthma signals severe ventilation-perfusion mismatch.
Conclusion: this is impending respiratory failure and the patient needs a definitive airway, not another nebulizer.
2. The family is anxious about intubation and the therapist wants to try BiPAP. How do you respond, and how do you prepare for the intubation itself?
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Response to the team
- Address the family's fear directly and briefly - a short, honest statement: "His breathing is tiring out. A breathing tube is how we take over the work so his lungs can rest. We will keep him comfortable." Anxiety is managed with information and presence, not with a delay that costs him the airway.
- Noninvasive ventilation in a drowsy, tiring child with a silent chest is a bridge to nowhere; it can delay intubation until a crash airway. If BiPAP were chosen at all, it would need a PICU team at the bedside with intubation equipment open and a hard 15–20 minute reassessment window. Here, the safer call is to intubate now, in a controlled setting, with the most experienced operator available.
Preparation
- Call anesthesia/attending; move to a resuscitation bay.
- Preoxygenate; have suction, a cuffed tube of appropriate size plus half-size smaller, and a backup plan (LMA, surgical airway) stated out loud.
- Induction: ketamine 1–2 mg/kg (bronchodilator, preserves blood pressure) with rocuronium. Avoid histamine-releasing agents such as morphine and atracurium, and avoid propofol-induced hypotension in a preload-dependent asthmatic.
- Give a fluid bolus before induction and have push-dose epinephrine drawn up; post-induction hypotension is common.
- Ventilate slowly with a long expiratory time during bagging - rapid bagging in asthma stacks breaths, causes air trapping, and precipitates hypotension or arrest.
3. Outline your ventilator and medication strategy for the first 24 hours after intubation, including what you will monitor for.
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Ventilation: control the expiratory time, accept the CO2
- Low rate (roughly 12–16 for 22 kg), tidal volume 6–8 mL/kg, high inspiratory flow, I:E of 1:4 or longer - the goal is complete exhalation.
- Permissive hypercapnia is expected and acceptable: target pH above ~7.20, not a normal PaCO2. Chasing a normal CO2 will cause air trapping.
- Watch peak and plateau pressures; a rising plateau suggests hyperinflation, not just bronchospasm.
The complication to anticipate: sudden hypotension from auto-PEEP. If the blood pressure drops, disconnect from the circuit and let the chest empty (manual compression if needed) before reaching for fluids or pressors.
Medications: continue inhaled bronchodilators via the circuit, IV corticosteroids, magnesium; consider a ketamine infusion for sedation and bronchodilation; deep sedation early to prevent dyssynchrony and breath stacking.
Monitoring: continuous capnography, pulse oximetry, blood pressure, and serial gases. Watch for barotrauma (pneumothorax), myopathy from prolonged paralysis, and rhabdomyolysis from isoproterenol/albuterol. Plan for daily sedation interruption once the wheeze and air trapping improve.