Review Question - QID 100823

The patient in this vignette most likely has a pulmonary embolism (PE) secondary to a deep vein thrombosis (DVT). Classically, a PE results in a hypoxic, respiratory alkalosis.

Advanced age, immobilization, and a pelvic fracture are all risk factors for development of a deep vein thrombosis in this patient. Symptoms of PE include sudden-onset dyspnea, pleuritic chest pain, low-grade fever, cough, anxiety, and (rarely) hemoptysis. Physical exam can show tachypnea, tachycardia and hypoxia. Signs of DVT include an erythematous, swollen, and warm lower extremity. Characteristically, a PE will increase dead space resulting in a ventilation-perfusion mismatch (V/Q = infinity).

Wilbur and Shian describe pulmonary embolism in the context of DVT. A PE is typically a consequence of DVT. CT angiography is the diagnostic test of choice when available and not contraindicated. D-dimer has a high negative predictive value, but in a post-surgical patient (as in this case) is almost universally elevated.

Burrowes KD et al. describe the pathophysiology of acute pulmonary embolism. They report that this condition causes redistribution of blood in the lungs, which impairs ventilation-perfusion matching and gas exchange. As a result, pulmonary vascular resistance increases, elevating pulmonary arterial pressure.

Illustration A shows a PE on CT. Note the filling defect in the pulmonary arteries and branches.
Illustration B shows a PE on EKG. Note the S1Q3T3 pattern.

Incorrect Answers:
Answer 2: Low pH with a low PaCO2 is more consistent with metabolic acidosis with respiratory compensation.
Answer 3: High pH with a high PaCO2 is more consistent with a metabolic alkalosis with respiratory compensation.
Answer 4: Low pH with a high PaCO2 is more consistent with a respiratory acidosis.
Answer 5: Normal pH with normal CO2 is not physiologically possible with low PaO2.