A 58-year-old man presents to the emergency department with shortness of breath, chest pain that worsens on inspiration, and diaphoresis for the past 3 hours. Past medical history is significant for hypertension and gout. He works as a truck driver. Vitals signs are temperature 37.0°C (98.6°F), blood pressure 130/100 mmHg, heart rate 109 beats/minute, and respirations 22/minute. Arterial Blood Gas (ABG) shows the following: pH = 7.60, pCO2 = 28 mmHg, pO2 = 68 mmHg, HCO3 = 24 meq/L.
Which of the following is the most likely underlying etiology for this patient’s illness?
The correct answer is:
A) Acute pulmonary thromboembolism
This clinical scenario presents a classic presentation of acute pulmonary thromboembolism (also called pulmonary embolism or PE). The patient's occupation as a truck driver is a risk factor for the development of PE. Patients often develop dead space physiology (normal ventilation with poor perfusion), which may lead to hypoxemia (decreased pO2) and a wide A-a gradient. The tachypnea (decreased pCO2) resulting in respiratory alkalosis is usually from the pleuritic chest pain that a PE can cause. Renal compensation does not occur in the acute setting (i.e., serum HCO3 levels are often within the reference range).
Answer choice B: Atypical pneumonia, is incorrect. The classic presentation of atypical pneumonia (e.g., Mycoplasma pneumoniae, Chlamydophila pneumoniae) includes fever, malaise, dry cough, headache. The chest x-ray does not correspond to the severity of the disease.
Answer choice C: Ethylene glycol poisoning, is incorrect. Ethylene glycol poisoning presents with metabolic acidosis and acute tubular necrosis.
Answer choice D: Obstructive Sleep Apnea (OSA), is incorrect. OSA by itself does not present with respiratory acidosis during sleep. However, obesity hypoventilation syndrome (OHS) does present with a chronic respiratory acidosis with an elevated PaCO2 during and at night.
Answer choice E: Pseudohypoaldosteronism, is incorrect. Pseuhypoaldosteronismis a condition where the organs do not respond to aldosterone (i.e., "aldosterone resistance"). Patients may present with hyponatremia, hyperkalemia, metabolic acidosis, and hypotension.
Answer choice F: Severe salicylate poisoning, is incorrect. Severe salicylate poisoning usually presents with metabolic acidosis. Milder poisoning usually presents with respiratory alkalosis in the acute setting.
Key Learning Point
Acute pulmonary thromboembolism commonly presents with respiratory alkalosis, hypoxemia, and hypocapnia.
