A 72-year-old man with a 15-year history of COPD (baseline FEV1 28% predicted) presents to the emergency department with acute dyspnea and pleuritic chest pain that began 2 hours ago. He denies fever, sputum production, or leg swelling. Vital signs: BP 138/82 mmHg, HR 110/min, RR 28/min, SpO2 88% on his home oxygen (2L/min), temperature 37.2°C. Physical examination is unremarkable except for prolonged expiration. Chest X-ray shows chronic hyperinflation without acute infiltrates, pleural effusion, or pneumothorax. Troponin and BNP are both normal. An arterial blood gas on 2L oxygen shows: pH 7.42, PaCO2 38 mmHg, PaO2 58 mmHg, HCO3- 24 mEq/L. Which of the following ABG findings would be MOST consistent with acute pulmonary embolism rather than an acute exacerbation of his underlying COPD?

1. A)Hypercapnia (PaCO2 >50 mmHg) with respiratory acidosis
2. B)Hypoxemia with an elevated alveolar-arterial (A-a) gradient despite relatively preserved alveolar ventilationGABARITO
3. C)Hypocapnia with metabolic alkalosis and a normal A-a gradient
4. D)Respiratory acidosis with PaCO2 >55 mmHg and PaO2 <50 mmHg
5. E)Hypoxemia with a normal A-a gradient and normal PaCO2