In medical school, the pulsus was a Step 1 concept that I learned to associate with tamponade. But now that I’ve seen a couple of cases, I think it’s helpful to have a reminder of how to measure a pulsus and create a differential for when you do hear one.
First: what causes a pulsus?
We often measure the pulsus if we’re worried about tamponade physiology but a very important learning point is that there are many things that can cause pulsus! Pulsus paradoxus is created when there is markedly less left ventricular volume, which can be caused either by lower LV and/or RV volume–as in asthma, myocardial infarction, shock, or PE. Even profound hypovolemia can cause pulsus. So really, it’s only “pulsus paradoxus” in the concerning sense if the variation in systolic blood pressure with inspiration is >10 mm Hg lower than it is with expiration.
Next: how to measure a pulsus.
By knowing how to take a blood pressure, you’re already halfway there! It can be confusing if you’ve never identified a pulsus paradoxus before, or if you feel uncertain because there’s no one else listening along to confirm your diagnosis. My tip is to practice on patients who you know do NOT have cardiac tamponade. Get familiar with when a normal patient’s Korotkoff sounds go away and come back. Let the air out of the cuff slowly. You will learn that you don’t even have to look to see when they’re breathing in and out. Then, when you have a patient who you ARE concerned about, you will be able to identify that point/systolic reading at which the Korotkoff sound remains constant and strong despite their breathing in and out, and calculate what their pulsus is.
Example: go to this Australian EMS Spot Diagnosis! link (video #3 is probably most revealing). Observe that the systolic blood pressures on the arterial tracing go from 100 to 50 in time with respiration.
Example: the ubiquitous and well-done Stanford 25 video (skip to 1:10 for the actual blood pressure-taking part).