Perfusion – A Holistic Approach

It’s time we talk about perfusion.

The basic paramedic understanding of perfusion has generally followed this principle in pretty much every textbook and degree I’ve seen: pipes, pump, fluid- vessels, heart, blood. It’s a fairly functional but also somewhat limited understanding, and I wonder if it’s time we just overhaul the concept entirely.

It promotes perfusion as predominately about blood flow. And perfusion is about flow, to be fair, but it’s not just the flow, it’s what’s in the blood. And there’s a lot in the blood that you need to mention, such as oxygen and glucose. The blood can flow all day, every day, to every part of the body, but it’s entirely useless if it’s not carrying oxygen or glucose. This is how we end up with people going “Hmm, oxygen sats are fine, and systolic BP is still 110, no need for oxygen!” in a patient who is anaemic and compensating for all they’re worth.

It almost entirely ignores the respiratory system’s input. The old maxim “Air goes in and out, blood goes round and round” is true. So why do we rarely integrate respiratory function with perfusion? If we’re not well ventilated or oxygenated, perfusion is bad, irrespective of the pipes, pump, or fluid. Granted, some books will mention that blood needs to be “well oxygenated” but watch how many people forget that point once they glance at the SpO2 monitor and see it reading somewhere over 95%. Case in point: hypotensive right ventricular infarct with a ruined preload, but an SpO2 of 96%. Any idiot can tell you they’re poorly perfused, but how many will remember that they also need oxygen because that 96% saturation of poorly perfusing blood is absolutely useless? By linking the concepts of the respiratory and cardiovascular systems, you get a much better understanding of the fact that what’s in the blood is just as important as where that blood is going.

It ignores the importance of glucose. Some books make mention of the fact that cells need glucose… and then never mention it again until it’s time to talk about diabetes mellitus. And yet a patient who has very little circulating glucose, or who can’t make use of said circulating glucose, is ultimately not well perfused. The nutrients in the blood are just as important as the blood itself – and if there’s no glucose, it doesn’t matter how much oxygen they have, the cells are doing to starve and die. Along with ignoring the role of glucose, it ignores the input that the liver and pancreas have, and how they too can affect perfusion. The liver in particular has a major effect on perfusion, not just with glucose management but also clotting factors.

It ignores the increasing importance of the inflammatory process. Go back a few years and inflammation was mentioned as a passing comment in most books. Today it lies at the very heart of many pathophysiological concepts, and shock is really no different. Very few paramedic textbooks ever mention the role of inflammation, either as part of disease processes or its effect on shock. This represents a fundamental problem with the way paramedic textbooks are written – and perhaps another reason why it’s time to abandon the “all in one” approach adopted by the US programs.

 

How do we fix it?

There are two ways I see that we can improve the base understanding of perfusion.

  1. Overhaul the pathophysiology section of paramedic textbooks to have a more comprehensive, integrated discussion on the concept of perfusion, at least integrating respiratory and cardiovascular function. This probably means tossing out a lot of concepts that are better left to an anatomy and physiology textbook. Start linking it with vital signs. Get rid of these “classes of shock” which have little to no clinical correlation.
  2. Scrap it entirely and get a good pathophysiology textbook… but given that they divide things into systems, this isn’t much of a solution either.

Mistovich’s Prehospital Emergency Care has a section that does integrate respiratory and cardiovascular systems into the concept of perfusion, as well as linking patient presentation/vital signs to compensatory responses. It’s limited, given that it’s aimed at EMTs, but it’s surprisingly good at explaining the basic concepts. Paramedic textbooks probably need to adopt a similar approach – rather than presenting a confused, limited set of facts, they need to deliver something that readers can relate with clinical presentations. The confused, overlong “pathophysiology” chapters are getting to the point where they’re a chore to read through and end up confusing too many people – they show no real clinical relevance, because that’s all fallen by the wayside in pursuit of trying to cram more concepts in there.

At this point it’s tempting to just scrap the paramedic textbook, rely on a basic EMT book like Prehospital Emergency Care for your fundamentals, and start using a medical textbook like Tintinalli’s Emergency Medicine in conjunction with a good pathophysiology textbook – such is the state of paramedic textbooks. I still have hope that we’ll turn away from these overly long, somewhat confusing books… but so far, the industry seems intent on proving me wrong.

So how can you improve your own understanding of perfusion? If you’ve only ever relied on your paramedic textbook, get a good pathophysiology textbook and start reading. You may need an anatomy/physiology textbook first to help with your understanding, although there are a few decent pathophysiology books that also cover anatomy and physiology to a sufficient depth. This provides a much better understanding than any paramedic textbook of how the body works and breaks. Start to integrate respiratory function with perfusion – remember the importance of the stuff in the blood, not just the blood itself. Revise early signs of shock and how they relate to the compensatory responses. It’s largely up to us as clinicians to integrate this knowledge, and then to pass it on to our students. By moving away from isolated systems and into a holistic, integrated approach, we’ll deliver better patient care. We just need to explain it to the new medics who are so focused on PIPESPUMPFLUID that they forget the patient is anaemic and carrying bugger all oxygen.

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