Respiratory · Year 1 · from Respiratory
Case 1: Acute Severe Asthma Exacerbation
Clinical Image
Source: Wikimedia Commons - COPD - CC BY-SA 4.0
Case Presentation
A 24-year-old woman with a history of asthma presents to the emergency department with severe dyspnea and wheezing that has worsened despite using her albuterol inhaler repeatedly over the past 6 hours. She reports a recent upper respiratory infection. She appears anxious and is unable to speak in full sentences. Vital signs show heart rate 125 bpm, blood pressure 145/90 mmHg, respiratory rate 32/min, and oxygen saturation 88% on room air.
On examination, she is sitting upright, using accessory muscles of respiration, with audible wheezing. Lung auscultation reveals diffuse bilateral expiratory wheezes with prolonged expiratory phase. Peak expiratory flow is 120 L/min (personal best 450 L/min, 27% of personal best). Arterial blood gas on room air shows pH 7.38, PaCO2 42 mmHg, PaO2 58 mmHg.
The normal PaCO2 in this severely dyspneic patient is concerning. In a typical asthma exacerbation, hyperventilation from hypoxemia and dyspnea causes hypocapnia (low PaCO2). A "normal" PaCO2 in the setting of severe respiratory distress indicates respiratory muscle fatigue and impending respiratory failure - the patient can no longer maintain the hyperventilation needed to compensate.
The pathophysiology involves bronchospasm from smooth muscle contraction, mucosal edema, and mucus plugging, all causing severe airway obstruction. The obstructed airways cause air trapping (unable to fully exhale before next inspiration begins), leading to dynamic hyperinflation that further compromises respiratory mechanics.
The patient receives continuous nebulized albuterol, IV magnesium sulfate (smooth muscle relaxant), IV methylprednisolone (reduces inflammation), and supplemental oxygen. She is closely monitored for deterioration requiring intubation. Over 4 hours, her peak flow improves to 280 L/min, PaCO2 decreases to 32 mmHg (indicating improved ventilatory capacity), and she is admitted to a monitored bed. She is discharged 3 days later on inhaled corticosteroids with a rescue inhaler and an asthma action plan.
Key Learning Points
- In acute asthma, a "normal" PaCO2 is a warning sign of impending respiratory failure
- Peak expiratory flow less than 25% of personal best indicates severe exacerbation
- Dynamic hyperinflation from air trapping increases work of breathing
- Accessory muscle use, inability to speak in sentences, and declining PaCO2 indicate severity
- Treatment includes beta-agonists, corticosteroids, and ipratropium; magnesium sulfate for severe cases