Case 12 Pulmonology

Hypoxemia

Work it one clue at a time. The diagnosis stays hidden until you reveal it.

Clue 1

A young woman presents with progressive dyspnea. You walk into the room and this is what you see. What finding is present?

Clue 2

Central cyanosis indicates the presence of hypoxemia. SPO2 by pulse oximetry is 80%. ABG on room air shows PaO2 of 40 mm Hg and PaCO2 of 30 mm Hg. We reference our framework for hypoxemia to begin the process of narrowing our differential diagnosis.

Clue 3

The first thing we want to know is the A-a gradient. A (from the alveolar gas equation) = 112 mm Hg a (from the ABG) = 40 mm Hg A-a = 112 – 40 = 72 mm Hg. Elevated

Clue 4

Next we revisit the physical examination for more clues. There is profound peripheral cyanosis. But what else do you notice? If you don’t specifically look for this finding you might never notice it. “The eyes can’t see what the mind doesn’t know.”

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