Case 23 Cardiology

Dyspnea and Hypoxemia

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

Clue 1

A man undergoes biopsy and plate/screw placement for a pathologic hip fracture and returns to the floor with new dyspnea and hypoxemia. Hypoxemia can be intimidating. Unless you have a system. Let’s go through the case.

Clue 2

The first thing we want to know is the A-a gradient. The difference between partial pressure of oxygen in the alveolar space (A) and arterial space (a).

Clue 3

Here is our patient’s ABG on room air.

Clue 4

PAO2 = 0.21(713) – 17/0.8 = 129 mm Hg.

PaO2 = 53 mm Hg

A-a gradient = 129 – 53 = 76. It’s elevated.

This narrows our differential considerably. We know we’re not dealing with hypoventilation from anesthesia. And now we can focus on the causes of elevated A-a gradient.

Clue 5

Our patient has clear lungs on exam and on CXR.

Clue 6

The exam narrows our differential even further. Hypoxemia with elevated A-a gradient and clear would be incompatible with most causes of physiologic shunt and impaired diffusion.

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