A conversation about plethysmography

“What’s that?” asks a student on another ambulance, pointing to my cardiac monitor.

“It is the plethysmograph” I replied, most likely butchering the pronunciation.

“What’s it for?”


After dropping my patient off, I made my way back to the EMS room where I found the student. It turned out he is a paramedic student, just finishing up his intern rides. He has a few weeks to go before he takes his exam. He has been an EMT for roughly 4 years, and by all accounts, is a good student, and a fast learner.

The fact that he asked a paramedic whom he didn’t know bodes well for him. He is engaged, and wants to learn.

We spent the next 15 minutes or so discussing the plethysmograph and its usefulness in assessing patients. What struck me most about our conversation was the fact that he had no idea whatsoever that there was even such a thing, much less that it could be used to assess patients.

We talked about how vasoconstriction can cause an increase in amplitude, and what could cause vasoconstriction. We talked about how vasodilation would cause a decrease in amplitude, and the causes of vasodilation.

We discussed how waveforms would change in a hypertensive patient with chest pain to whom we were administering nitroglycerin. The mechanism of nitro’s action, in decreasing systemic vascular resistance through causing vasodilation. It seemed to make sense how waveforms would change, and how that was directly related to afterload.

My patient happened to be septic, and I could show him how plethysmography could help confirm that diagnosis. My patient was an infirm older woman who had a mildly altered mental status, hypotension, and some mild tachycardia. The fact that she had a chronic Foley catheter with cloudy urine in the bag made the diagnosis of a UTI fairly easy, but the plethysmograph showed a very deep, prominent dicrotic notch.

He asked, appropriately, how the waveform would help me in my assessment, and I explained that the deep dicrotic notch showed me a low SVR, and there was no need to assess orthostatic vital signs.

He was receptive, inquisitive, and it was a refreshing conversation.


I’m just a regular paramedic, and nothing special. I only learned about this stuff because I asked and because I wanted to learn. I enjoy showing students, and other EMS personnel, things that I have learned along the way, and I enjoy learning from others. Our education doesn’t stop when we get that paramedic patch, it begins.

What is disheartening is the fact that a paramedic student, only weeks away from testing to become a paramedic, had never heard of a plethysmograph, a dicrotic notch, and did not understand the relationship between waveforms and vascular resistance.

We have a very, very long way to go in the education of our paramedic students.



  1. Flash Larry says:

    I had a refreshing episode last week. I was doing KSA assessment on paramedics being considered for employment by my service. One of them was a tall, nice looking kid with a country accent from the middle part of my state. He looks like a big country boy who drives a jacked-up pickup truck.

    Well, my assessment of him was wrong. He breezed through all the skills stations and since I add a lot of questions while I’m testing that are not on the list, much to the frustration of the HR people, I take twice as long to assess these candidates as they are used to – they being the candidate and/or the HR people.

    But in talking to him about a cardiac case, he readily understood all my arcane electrocardiology, answered all my questions, and asked me some more.

    “I just love cardiology. It’s the most interesting part of EMS. I fell in love with it in EMT school. “Trauma. Oh well, trauma is pretty easy to manage. I really like the challenging stuff, like cardiology.”

    23 years old. Not particularly interested in trauma. Loves the medical challenge.

    He’ll show up on here before long.


    • Flash Larry says:

      You know, I’m going to turn off all the editing functions on everything that I use. It really gets tedious seeing absolutely mystifying changes to the things I write.

      Let’s try to get this sentence through as I actually wrote it, “My assessment of him was a little longer than I had planned.”

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