Author: Bryan Boling

I'm a critical care nurse practitioner and co-director of the Critical Care APP Fellowship Program at the University of Kentucky. I split my clinical time between the Neurocritical Care Service, the Surgical Critical Care Service, and the ECMO Service. I'm also an Adjunct Faculty Member in the Acute Care Nurse Practitioner Program at Georgetown University. I have a passion for education and #FOAM.

Aortic Dissection

We classify aortic dissection as ascending and descending, but there are actually classification schemes with slightly more nuance. The two main classifications are Stanford and DeBakey. Stanford is broken into A (ascending) and B (descending). DeBakey into I (all the way from the ascending down the arch as well), II (ascending only), and III (descending only). Understanding these classifications makes it easier to visualize what’s going on when the CT surgeon calls to admit a patient to the ICU. Sometimes these are surgical emergencies (most commonly Stanford A or DeBakey I and II) but a lot of the time they can be managed conservatively. Conservative management is mainly with impulse control, by keeping the heart rate and blood pressure down. Blood pressure control makes intuitive sense, reduced pressure means less force on the wall of the aorta weakened by the dissection. Heart rate control is a little less obvious, but if you’ve ever seen a heart beating in an open chest, you know that with every beat, the heart twists slightly. This leads to shearing forces that can exacerbate the dissection.

Impulse control may be accomplished by an infusion of esmolol, but increasingly, drips like nicardipine are added for blood pressure control, as esmolol typically doesn’t really control profound hypertension all that well. Esmolol commonly requires a larger volume of fluid because of the dosing and way the drip is made. So, nicardipine in combination with intermittent dosing of metoprolol may be beneficial in patients who can’t tolerate the larger IV volumes.

Count Backwards from 10, has this nice graphic to sum up aortic dissection classification.

Sinus Tachycardia

We see lots of arrhythmias in the ICU, but one that often comes up that isn’t really an arrhythmia is sinus tachycardia. Sinus tach often makes us nervous, and not without good reason, as this echo from Dr Obiajulu Anozie demonstrates. As the heart rate goes up, stroke volume may decrease. Likewise, tachycardia may often be in response to decreased stroke volume as the body attempts to compensate and maintain adequate cardiac output. Sinus tach can often be in response to pain or agitation as well. What do we do about sinus tach? Well, start off by treating potential causes. Pain. Agitation. Hypovolemia. But we very rarely need to treat tachycardia itself. There are cases (as with patients on VV ECMO) where beta blockade is indicated to reduce heart rate, but typically once the potential causes are addressed, nothing else needs to be done. In some cases (as demonstrated below), the tachycardia may in fact be compensatory and by slowing it down, we actually cause harm.

Circle of Willis

Neurovascular anatomy is important to understand, both for neurocritical care as well as vascular. The Circle of Willis is an important anatomical structure, deep in the center of the brain. Blood flow enters the brain via the carotid arteries and then is distributed via the Circle to the rest of the brain. The Circle of Willis allows blood from the left carotid artery to supply the right side of the brain and vice versa. This means that stenosis or blockage of the carotid artery is better tolerated if the Circle is intact. In this illustration from The Radiologist Page, you can see how decreased flow in one carotid artery can be compensated if blood is able to flow through the Circle of Willis. Overall flow may be diminished, but it won’t be absent on one side.

From a neurocritical care standpoint, you can see how the various cerebral arteries, the source of most acute ischemic strokes, disseminate out from the center. The Circle of Willis is also the location of most aneurysmal subarachnoid hemorrhages.

Lobes of the Brain

The various lobes of the brain all have slightly different functions and control different aspects of our lives. It’s good for the ICU provider to have a basic understanding of what is controlled where because it informs how any kind of brain injury will impact the patient. Whether it is acute ischemic stroke, intracerebral hemorrhage, or traumatic brain injury, damage to specific areas of the brain will result in somewhat predictable deficits. Maybe not predicting the degree of impact, but you can be aware of the possible types of problems your patient is likely to experience long-term.

This illustration from the Instagram account, @medical_guidelines, nicely summarizes what the various lobes of the brain control, and thus, what functions may be affected by an injury depending on location.

Norepinephrine

Earlier, we discussed epinephrine. Now, Rishi Kumar has another great post about another vasopressor, norepinephrine. When I was first starting out as a nurse, norepi had quite the reputation, and not in a good way. Known by the brand name Levophed, it was often called “Leave-em-dead.” These days, norepi is the go-to pressor for just about any type of shock except cardiogenic. It’s a good all around drug, causing mainly vasoconstriction, but also having some positive inotropic/chronotropic effects as well.

Epinephrine

Epinephrine is a drug that we use frequently in the ICU as a vasopressor/inotrope. It’s my go to drug when a patient has hypotension that is related to poor contractility. It’s a great drug to start for cardiogenic shock. But, as Rishi Kumar points out here, it’s a super versatile drug.

IV Bicarb: Is There Any Value?

IV Bicarbonate used to be all the rage in critical care. It was included in the ACLS algorithms. It was used, in drips or in pushes, to treat all kinds of problems. I’ll admit, there are still times that I use it when the indication is…shaky, often when my back is against the wall and I need something to buy some time. But, is there any real use for it in ICU practice? In a recent episode of The Elective Rotation, Pharmacy Joe recently took a look at when IV bicarb should be avoided (often) and when it is helpful (a lot less often).

Often, IV bicarb is used as a band-aid. This is ok to a point. If it helps buy you some time, ok. But using it without addressing the underlying issues (like I remember doing a lot in the old days) is fraught with problems. There are a handful of scenarios where we should avoid using bicarb because it’s been shown to be of no value. ACLS has removed it from the algorithms and generally avoids against its use in cardiac arrest, for example. But there are some specific times when it is helpful and should be considered.

Diagnostic Reasoning in Critical Care

When I was a nurse practitioner student, I wanted to do as many procedures as I could so that I could be proficient. My advisor told me, “I don’t care if you do a single procedure in school. I want you to focus on learning to think through a problem, formulate a differential diagnosis, and develop a treatment plan. I wasn’t really happy about that, as I really loved procedures and thought that’s where my focus should be. Making a diagnosis and formulating a treatment plan was easy. I thought.

Now, I teach ACNP students and find myself saying the same thing! I don’t care about students learning procedures. That’s one of the easiest parts of critical care to be honest. Of course it takes repetition to get good at procedures, but the critical thinking, that’s the tricky part. (Sure, there’s no reason that you can’t develop procedural skills and critical thinking.)

In fact, the really tricky part is making the diagnosis. You can look up treatment plans in UpToDate and at least get an idea of what to do. But making the diagnosis, that’s hard.

Recently, we had Andre Mansoor on the Critical Care Scenarios podcast to discuss the art of diagnostic reasoning. Dr Mansoor is the author of a great book on the subject, Frameworks for Internal Medicine. It is the best guide to diagnostic reasoning and differential diagnosis formation that I’ve read. I use it when I teach my ACNP students and when I create scenarios for simulation. In the podcast, Dr Mansoor goes through his thought process when approaching a patient and beginning to formulate a differential diagnosis. The book goes into even more detail, taking common presenting complaints, breaking them down and helping the practitioner narrow the list of possible problems based on the evidence collected in the history and physical exam, and then adding in other diagnostic studies.

The ROX Index, and “How Much Flow?”

I love high flow nasal cannula (HFNC) oxygenation. It’s a great and simple tool to improve oxygenation, ventilation, and work of breathing in people who are struggling but may not need intubation. It’s also a great tool to use when you extubate someone who is a little marginal. We’ve all that experience of the patient who technically meets the criteria for extubation but your gut tells you they may have a hard time. Extubation to HFNC can help them fly following removal of the tube. It can also be used to prevent intubation in someone who is on the fence. But, how do you know who it will work for?

Dr Eddy Joe Gutierrez has a nice post regarding the ROX (Respiratory rate-OXygenation) Index. It’s a simple calculation that can be used to predict who will benefit from HFNC to reduce work of breathing and impending respiratory failure vs who just needs to get intubated. To get the ROX Index, just divide the ratio of SpO2/FiO2 by the respiratory rate. The SpO2/FiO2 ratio is similar to the PF ratio, but using the pulseox instead of having to grab and ABG. Eddy Joe points out that you’ll want to actually count the respiratory rate and not use the number that all to often gets erroneously charted. MDCalc has a calculator here to make it easier. ROX ≥ 4.88 is a good indicator of HFNC success. Lower than that, there is risk that HFNC will fail and you’ll need to intubate anyway. See Eddy Joe’s whole post for more details.

Another thing that this post addresses is the question, “how much flow should I start my patient on?” This is often an issue when providers have little experience with HFNC. When we first started using it, I would frequently find patients on 100% FiO2 and 10lpm of flow. This is the exact wrong way to use HFNC. The real benefit is the flow, not the FiO2. Eddy Joe points out that he typically starts with 50lpm, and this is roughly where I usually start as well. Some people won’t tolerate that much flow, but starting high gives you some wiggle room. If they are uncomfortable with 50, drop down to 40. Odds are, by comparison, this will be more pleasant and you’ll have a little great success than if you start low and go up. Eddy Joe shared a study on Twitter the other day that found that 30-40lpm is the optimal flow rate to use. So, it’s nice to have data to back up what my experience/gut had showed me. Read the entire study here.

So, if you’re not using HFNC, you should. If you are, try the ROX index to guide you. Also, start your flow high. Remember, the real benefit is in the flow and for that you need high rates, at least 30lpm.

Simulation in Critical Care Education

Simulation is a great tool for training in critical care. It allows us to practice performing procedures and dealing with high-risk situations in a safe place without exposing patients to harm. But, it offers so much more than that. I’ve been interested in simulation training for years. In fact, I did my doctoral project on simulation training in critical care.

Studies show that simulation is as good or better at training than actual clinical experience. In one study of medicine residents, 1st year residents without ICU experience outperformed 3rd year residents with ICU experience in clinical scenarios. The difference? The 1st years had a simulation course whereas the 3rd years had only real-world experience.

But, a lot of us in critical care training only scratch the surface of what sim can do. Although beneficial for the high-risk, low-frequency events, sim offers much higher yield in the more everyday scenarios. This includes things like teamwork and communication, but also the concept of “practice like you play.”

“Practice like you play” is the idea that if you practice common situations and scenarios enough, then when you’re confronted with them in real life, they will be automatic. This is the same concept that makes experienced providers generally better than novices. When someone has been practicing critical care for years, that experience allows them to pick up on things that novices miss. It also allows certain things to be automatic. You don’t have to sit and think through all the steps in working up a given condition, they’re automatic.

The Emergency Mind Podcast recently did a great episode on using simulation training. Drs Victoria Brazil and Andrea Austin joined host Dan Dworkis to discuss all the ways we can use simulation. They talk about “practice like you play,” creating psychological safety, in situ simulation, low-fidelity simulation, and much more. Give it a listen.

There are several websites out there where you can download premade simulation scenarios. This is fantastic because building scenarios is the hardest part of developing a simulation curriculum. But, the problem is, these scenarios tend to be fairly algorithmic. “If this, then that” situations are ideal for sim because they are straightforward cases to build. But, what if you want to teach your learners more critical thinking? This is an aspect of simulation that isn’t as well explored. Don’t get me wrong, there is lots of value in the first type of cases. If you do enough a-fib with RVR scenarios in the sim lab, when it happens in the ICU, you’re on autopilot. But, that’s also the problem. How do we use sim to teach nuanced thinking? That requires more detailed scenarios.

I’m not sure I have the answer. Scratch that, I know I don’t have the answer. But, this is where we’re going. In our Critical Care APP Fellowship, our fellows spend a significant amount of time in the sim lab. We do a dedicated sim lab day every month, but mostly, the scenarios are the “if this, then that” type. We’re in the process of redesigning our simulation curriculum to include more scenarios on leadership, communication, teamwork, and critical thinking.

There are lots of great things out there in the world of simulation. Are you using sim in your training program? How are you using it? Have you had any success with new and innovative methods? Tweet @CritCareNotes and let me know what you’re doing. Let’s share these successes and help all of us become better educators.