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Difficulty: EasyPulmonary and Critical Care

A 26-year-old pregnant woman at 28 weeks gestation is brought to the emergency department for severe shortness of breath that has worsened over the past 12 hours. She has a history of poorly controlled asthma. On arrival, she is lethargic, diaphoretic, and can only speak in single syllables. Her temperature is 37.0°C (98.6°F), blood pressure is 110/70 mmHg, pulse is 132/min, and respiratory rate is 36/min. Pulse oximetry shows an oxygen saturation of 86% on room air. Physical examination reveals a gravid uterus, profound accessory muscle use, and a "quiet chest" with minimal air movement bilaterally. An arterial blood gas analysis on room air demonstrates:

pH: 7.32
PaCO2PaCO_2: 48 mmHg
PaO2PaO_2: 55 mmHg

Which of the following is the most appropriate next step in management?

  1. Endotracheal intubation and mechanical ventilationAnswer
  2. B
    Administer intravenous furosemide
  3. C
    Administer broad-spectrum intravenous antibiotics
  4. D
    Administer intravenous sodium bicarbonate
  5. E
    Reassure the patient that her blood gas values are normal for pregnancy

Answer

Endotracheal intubation and mechanical ventilation
The correct answer is endotracheal intubation and mechanical ventilation. This patient is experiencing a severe asthma exacerbation leading to impending respiratory failure. Classic signs of impending respiratory arrest in asthma include an altered level of consciousness (lethargy), a 'quiet' or 'silent' chest on auscultation (indicating airflow is too poor to even generate wheezing), and a normalizing or elevated PaCO2PaCO_2. During an acute asthma attack, patients typically hyperventilate, leading to a respiratory alkalosis (low PaCO2PaCO_2). When the respiratory muscles fatigue, ventilation decreases, and the PaCO2PaCO_2 begins to rise. A PaCO2PaCO_2 of 48 mmHg in a severely dyspneic asthmatic patient is an absolute indication for immediate intubation and mechanical ventilation. Furthermore, because normal pregnancy is associated with a chronic respiratory alkalosis (PaCO2PaCO_2 normally 28-32 mmHg), a level of 48 mmHg is exceptionally dangerous in this context.

Step-by-Step Solution

1
Evaluate the patient's clinical presentation for signs of impending respiratory failure.
The patient exhibits lethargy, inability to speak in full sentences, and a 'quiet chest' indicating minimal air movement, all of which point to exhaustion and severe airflow obstruction.
Recognizing clinical signs of fatigue is critical in determining the urgency of airway intervention.
2
Interpret the arterial blood gas (ABG) in the context of an acute asthma exacerbation and pregnancy.
The ABG shows acidemia (pH 7.32) and hypercapnia (PaCO2PaCO_2 48 mmHg). In a normal asthma attack, hyperventilation causes respiratory alkalosis (low PaCO2PaCO_2). A normal or elevated PaCO2PaCO_2 signifies respiratory muscle fatigue.
An elevated PaCO2PaCO_2 in an acute asthma exacerbation is a classic red flag for impending respiratory arrest.
3
Determine the appropriate intervention based on the clinical and objective findings.
The patient requires immediate endotracheal intubation and mechanical ventilation to secure the airway and ensure adequate gas exchange.
When a patient with severe asthma tires out and loses the ability to ventilate (hypercapnia, lethargy, quiet chest), definitive airway management is life-saving.

Key Concept

Impending respiratory failure in severe asthma exacerbation
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Topics

Pulmonary and Critical Care

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