Broad Strokes in Clinical Problem Solving: The Simpler, the Better

Nan was huffing and puffing after walking into the other room to get her medicine bottles. Her oxygen saturation wasn’t bad, but, of course, she had her nasal oxygen running at 2 liters per minute, 24/7.

So I told her about the three possible reasons for being short of breath:

An air problem

A blood problem

A heart problem

That’s pretty much covers it. As clinicians we get in trouble when we fail to think of one of those very large categories and zero in too quickly on the one we think is the root of the problem. For example, the air problem could be bad lungs, air pollution, or somebody standing on your belly while you’re trying to sleep. (Because you can’t push your diaphragm down into a compressed abdominal cavity and the lungs are suddenly having to pretend to be smaller than their original size.)

The heart problem could be heart failure, a bad valve, an abnormal heart rate or rhythm, a pericardial effusion (fluid collection betweeen the heart and its covering membrane), inadequate coronary blood flow , thickening of the heart muscle and many other things.

The blood problem could be not enough hemoglobin, usually caused by anemia from bleeding, but sometimes from iron deficiency for other reasons or B12 deficiency, for example. Blood cancers, leukemias, can cause anemia too. I still remember one time when I completely forgot anemia as a cause of shortness of breath. I only arrived at the correct diagnosis after both heart and lung imaging. Boy, did I feel stupid!

So my whole point with this little reflection is to not try to consider differential diagnoses as a myriad of random possibilities but to start with the big groups of disease mechanisms and then dig deeper. Within each big category you first consider the most common things and the better your patient looks in any one of those categories, the more likely the answer is in one of the others.