Sh!t I Learned This Week 2019.03.12

It’s halfway through the month and I have flown precisely 0 patients this week. I’ve been part of a few conversations lately about how hard it can be to stay fresh clinically in the environment that we work. The conditions are a perfect storm for clinical complacency; relatively low volume, objectively high confidence, and mostly flying from scenes. We simply don’t see many of the situations that would allow us the necessary repetition to maintain our critical care skillset.

What can we do about it? I don’t know, but I have a few ideas for myself. In part, I want to make a public commitment to you guys that, I hope, will keep my nose in the books and feet on the ground, so to speak.

  • The first half of that commitment is to share what I learned each week. I figure that if I didn’t learn one thing worth sharing over the span of an entire week, then I should probably consider that week a failure.
  • The second half is to write one paper. That’s it. One measley paper on something. Physiology, pathology, procedure, something. They say that if you can’t explain it to a 5 year old, then you don’t truly understand it. It’s my goal to be able to explain everything that we do well enough that I could explain it to a 5 year old.

So! Here it is. Week numero uno of Sh!t I Learned This Week.

Peripheral Perfusion Index

Starting off exciting, I know. Yayyyy Pulse Oximetry! If there is one thing on our aircraft that probably doesn’t get the love it deserves, it’s probably our pulse oximetry, but maybe there are a few things you didn’t know about it, like myself!

  • Starting off simple with what you probably already know. If you can’t get a waveform, it’s not the pulse oximetry’s fault. It’s either placement (try rotating 90 degrees or prepping if nail polish is an issue), light interfering (wrap the probe to block out external light), or the patient isn’t perfusing to the site enough for the probe to read. If the probe works on you, but not on the patient, the problem is your patient, not the probe. Don’t write this off! The body shunts due to shock long before the patient’s BP drops. If only there was a way to objectively measure the shunting to give us a clue….
  • As it turns out, the amplitude (height) of the pulse ox waveform is directly correlated with the amount of perfusion wherever your probe is placed; more perfusion = more waveform. Makes sense, right? Let’s take it one step further. If shock is lack of end organ perfusion, and the skin is an organ, and we just learned to measure skin perfusion, then we now have a tool to actually measure shock. This is where it gets really cool. It turns out that the pulse oximetry machine tells you exactly how much it has to stretch the waveform to fill your screen, it’s called a Peripheral Perfusion Index (PFI) or simply the Perfusion Index (PI). The PI is a 1-10 scale that is different from manufacturer to manufacturer. There is only a small amount of research on this at the moment, but there is some evidence to show that a PI below approximately 1.4 is correlated with a state of shock, just as peripheral temperature, delayed capillary refill time, and mottling are all documented signs to assess for shock. It’s not enough to diagnose shock on it’s own per se, but it’s one more piece of the puzzle. If you tie that piece of the puzzle in with your other signs of shock such as increased HR, increased ETCO2, and increased respiratory rate to paint a picture that your patient is already in a severe shock state, then you can begin to aggressively treating the patient before the BP tanks, which is one of the last signs of shock to appear. For some data to support the above idea, check out this study and this second study as well, which are both fully available in the links.
  • On the Zoll X series, you can easily turn on PI by selecting the pulse oximetry box and turning on “PI Monitoring” in the menu that appears. Here are some frustratingly blurry photos I took this morning after checking off the aircraft. You’ll be glad to hear that despite the recent time change, I was not in shock when I applied the pulse ox to myself. Thanks for sticking with me!
Select the Pulse Ox
Turn on “PI Monitoring”
Profit!