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Difficulty: MediumPulmonary and Critical Care

Emergency medical services transport a 2424-year-old man to the acute care bay for profound respiratory distress. He has a history of poorly controlled asthma and ran out of his fluticasone inhaler two weeks ago. Upon arrival, the patient is extremely agitated and diaphoretic, using prominent accessory muscles of respiration. Auscultation of the lungs reveals loud, diffuse expiratory wheezing bilaterally. He is immediately treated with continuous nebulized albuterol, ipratropium, and intravenous methylprednisolone. Reassessment one hour later reveals a somnolent patient who is difficult to arouse. His temperature is 37.1∘C37.1^{\circ}\text{C} (98.8∘F98.8^{\circ}\text{F}), blood pressure is 118/72118/72 mm Hg, pulse is 124124/min, and respirations are 1414/min. Oxygen saturation is 88%88\% on a 1515 L/min non-rebreather mask. Pulmonary examination now demonstrates markedly diminished breath sounds bilaterally with minimal wheezing. Arterial blood gas analysis on the current oxygen setting shows:

Laboratory TestResult
pH7.267.26
PaCO2_25858 mm Hg
PaO2_25656 mm Hg
HCO3−_3^-2424 mEq/L

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

  1. Perform endotracheal intubationAnswer
  2. B
    Administer intravenous furosemide
  3. C
    Initiate intravenous piperacillin-tazobactam
  4. D
    Calculate expected respiratory compensation using Winter's formula
  5. E
    Administer intravenous sodium bicarbonate

Answer

The most appropriate next step is to perform endotracheal intubation.
This patient is exhibiting classic signs of impending respiratory failure due to a severe asthma exacerbation. Initially, asthma exacerbations cause hyperventilation, which typically leads to respiratory alkalosis and a low PaCO2. However, as the patient fatigues, the respiratory rate inevitably decreases, leading to dangerous carbon dioxide retention. This is evidenced by the ABG showing a respiratory acidosis with a PaCO2 of 58 mm Hg. The transition from agitation to somnolence, combined with a 'silent chest' (diminished breath sounds indicating critically low airflow) and an elevated PaCO2, are absolute clinical indicators for immediate endotracheal intubation and mechanical ventilation to prevent cardiopulmonary arrest.

Step-by-Step Solution

1
Analyze the patient's clinical progression and vital signs.
The patient transitioned from agitated and tachypneic to somnolent with a decreased respiratory rate.
A falling respiratory rate and altered mental status in a patient with a severe asthma exacerbation indicates muscle fatigue and impending respiratory failure.
2
Interpret the arterial blood gas (ABG) values in the clinical context.
The ABG shows a primary respiratory acidosis (pH 7.267.26, PaCO 2_2 5858 mm Hg) with severe hypoxemia.
Early in an asthma attack, patients hyperventilate and exhibit respiratory alkalosis (low PaCO 2_2). A normal or elevated PaCO 2_2 signifies a critical inability to maintain adequate ventilation.
3
Determine the necessary clinical intervention.
Immediate airway protection and mechanical support are required.
The triad of somnolence, a 'silent chest' indicating minimal airflow, and respiratory acidosis requires endotracheal intubation to prevent imminent cardiopulmonary arrest.

Key Concept

In a patient with a severe asthma exacerbation, the development of altered mental status, a 'silent chest', and a normal or elevated PaCO2 indicates impending respiratory failure requiring immediate endotracheal intubation.
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Topics

Pulmonary and Critical Care

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