A 63-year-old man presents to the clinic for evaluation of symptoms of shortness of breath. The symptoms are worse on exertion, but there is no chest discomfort, cough, or sputum production.His physical examination is completely normal. Investigations include a normal CXR, and on the arterial blood gas the PO2 is 74 mm Hg, and PCO2 is 60 mm Hg. Which of the following mechanisms is the most likely cause for the elevated PCO2?
Correct Answer: hypoventilation
Description: Hypoventilation always causes both hypoxemia and hypercapnia. If the hypoventilation syndrome is caused exclusively by impaired respiratory drive (e.g., drug overdose), then the alveolar-arterial PaO2 gradient remains normal. Often, hypoventilation results from more than one disorder in the respiratory system (e.g., COPD plus metabolic alkalosis secondary to diuretics and glucocorticoids).
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