Here’s a simple graphic that may help conceptualize what’s going on in the body when we discuss hemodynamics and different patterns associated with certain pathologies:
In reality, its often a rough sketch in the margin of a piece of paper, but that’s the beauty of the thing – it’s a simple-to-draw framework for solving clinical problems:
The basic idea is that we can visualize movement of blood through the heart, body and lungs. We start with what is normal:
From there, we can then add in complications or disruptions to this flow to represent different pathologic processes. For example, let’s consider mitral valve stenosis. First a review of the normal thing:
And then we make that mitral valve stenotic (which decreases efficacy of movement across that valve) and adjust things as so:
Early in the process we see blood flow back up into pulmonary circulation like so:
And then with time we see issues on the right side of the heart also:
This sort of exercise is particularly useful in testing scenarios where hemodynamic values or certain conditions are presented and we must decide what findings are most likely. For example:
Just have the normal ranges memorized or, better yet, have a reference card of some sort readily accessible. Here’s a quick video of working through these questions one by one:
Next point of conversation: what to do with all this academic nonsense in clinical practice. We often have to work with incomplete batches of information and/ or verify that the numbers we have on hand are actually worth accepting as true (and therefore accurate descriptors of patient status). Take, for example, this recent case we had.
Adult male patient, myocardial infarction with Impella placement in cath lab after going into cardiogenic shock on the table. He’s got the Impella in running at P9 or max flow. There’s a single-lumen Cordis at the right internal jugular (IJ) and a pulmonary artery catheter (PAC) in the groin, plus one peripheral line. He’s hypotensive on arrival, as seen on both non-invasive or auto-cuff and the Impella screen (there’s no other arterial line in place), so we give a bolus and start an Epinephrine drip. He’s also got heparin running for anticoagulation, so we keep that going as well. And then we do push-dose sedation and analgesia as needed. Blood pressure/ mean arterial pressure (MAP) responds to initial interventions, so we proceed with things.
Now here’s where troubleshooting and considering all these hemodynamic numbers comes in to play. The only data point we have at the moment is a BP or a MAP, which roughly correlates to cardiac output so long as heart rate is reasonable and constant. And that’s OK for now, but not a ton of information to be gleaned there. We transduce the PAC for both a pulmonary artery pressure (PAP) and also to make sure we don’t inadvertently wedge en route – the PAP sheds a bit more light on the thing. Consider whether it’s high or low and how that might look in our sketch:
And then the next data point we could potentially get is a CVP. We could do that either at the Cordis in the right IJ or and the proximal port on the PAC. While we’re at it, let’s review all of our access and what we can do at each of the various places:
But assuming we do transduce one of the lines for a CVP and have that number available, here’s how the decision matrix of sketches might look:
Now let’s say our PAP is high (which it was in the case presented). Of that list of things on the high PAP side of the matrix there’s only so many things to do in transport, regardless of whether CVP is up or down. We’re probably not going to diurese in flight or give inhaled nitro (but power to the people who do!), we can assess for tamponade and rule that out, we can optimize cardiac function with things like dobutamine or electrolyte replacement (i.e., calcium), and then we can give volume.
The CVP tells us what the preload is and guides the decision of whether we should give fluids or not. But there are other ways to get this piece of information – fluid responsiveness, just waiting for a suction alarm on the Impella and treating reactively, or if you work in the modern age of medicine, get an ultrasound probe on the patient and assess for fluid status that way. This is all to say that we don’t actually need the CVP and can maybe save the headache of transducing a second line in transport to focus on other things.
Another framework for thinking about this would be to do a mental inventory of the interventions on hand and decision points for each. Here’s what a working list might look like:
Fluids – suction alarm, low CVP, fluid responsiveness, or collapsed IVC on ultrasound
Increase epi drip – low MAP
Start dobutamine – refractory low MAP after epi increase, narrowing pulse pressure, evidence of pulmonary edema
Consider other pressors – MAP approaching 50 despite all of the above
Consider ACLS stuff – super low MAP sustained <50
Now that’s a complicated cardiac device case and we recognize that those are super rare and don’t come around all that often, so how about a more likely scenario. Adult patient with pneumonia turned sepsis and ARDS being transferred for higher level of care. Ventilation is trash, we’re acidotic, require high PEEP, are on multiple pressors, quite tachycardic, and the BP drops whenever we give sedation or analgesia. Let’s see it all sketched out:
And then working to fill in the gaps, here’s what we might see in terms of all those other hemodynamic parameters, plus actions to be taken:
Big takeaway from all of this: draw pictures, it helps. Other less important lessons: knowing how different pathologic events affect the flow of blood through the body can help direct interventions, knowing how we can gather specific pieces of information in different ways can help with this process, and piecing together an overall clinical picture with an incomplete set of data points takes practice.
Very last thing that also serves as a public service announcement: if we are transducing lines in transport (as we should any time we have a PAC in place), be sure to review the basics. This is especially true for those of us in the transport setting that don’t do this sort of thing often. Know which ports on which lines get transduced for which pieces of information, do all the normal setup things (inflate your fluid bag, level the transducer where you want it, flush the thing, etc. and reassess along the way), and then after all of that draw the fun pictures and put it together into a clinical pattern.
And there you have it. Next time you come across a tricky question on a test or a complicated clinical case, consider using this sort of graphic to help work through and visualize the changes or expected findings associated with a given pathology.
Personal notes:
Cannot for the life of me recall where I first came across this idea of using graphics like this to work through these types of problems, but I know for sure I didn’t invent the thing…
The photo of test questions is from a recent competency I had to take on the ICU where I work part time. Had to wait until after we released those keys to post this, just in case there were any outstanding tests to be completed (not that any of the folks I work with know I have a blog or will read this…). Also wanted to make sure the answer key matched what I got. It did :) But those questions gave me the idea to write this.
The Impella case came up while I had this drafted, decided to add that and the other case to give some clinical context. Good stroke of luck I think.
And it may seem that I have all this information in my working memory in real time. Not the case. I have the advantage of both hindsight and meticulous notes/ reference materials I’ve made over the years to help with this sort of thing. I use them all of the time and you should too.
Also thanks to Scooby over at SFCEBM for chatting about the initial draft of this. Specifically about reiterating the point that we should always transduce a PAC to monitor for inadvertent wedging and that the introducer for the PAC probably has another line/ point of access for meds – this second bit was something I missed on this transport.
As always and forever, let us know if you’ve got any feedback on the thing.
Reference:
J Larry Jameson. (2020). Harrison’s Manual of Medicine. Mcgraw-Hill Education.