Pulmonary Disease Processes and the Dyspnea Differential

Pulmonary Disease Processes and the Dyspnea Differential

1. Four Ways a Lung Can Fail

A patient who can't breathe is failing at one of four jobs. Air has to get in. Oxygen has to cross into the blood. Blood has to move through the lung to pick it up. And the drive to breathe has to match what the body actually needs.

So every dyspnea call sorts into one of four buckets:

• Obstruction — air can't move in and out. Asthma, COPD.
• Alveolar filling — the air sacs fill with fluid, pus, or inflammatory debris instead of air. Pulmonary edema, pneumonia, ARDS.
• Perfusion failure — the air moves fine, but blood flow to part of the lung is blocked. Pulmonary embolism.
• Demand and compensation — the lungs are fine. The body is breathing fast for a reason that has nothing to do with the lungs. DKA, sepsis, salicylate toxicity.

That last bucket is the one that gets missed, because it looks exactly like a respiratory emergency. Hold onto it. We'll come back to it.

Your differential is built from onset, lung sounds, jugular veins, temperature, leg findings, and capnography. Then you narrow it by how the patient responds to what you do. Treat the mechanism you've identified, reassess, and change your impression when the response doesn't match it.