Harlequin Syndrome in ECMO

One of the big complications of VA ECMO is something called Harlequin Syndrome, also known as North-South Syndrome. It happens when the oxygenated blood being returned from the ECMO circuit mixes with the deoxygenated blood being ejected from the heart (there was a big reason the patient was put on ECMO, remember?). This is actually sometimes a good sign, because it means the heart is able to pump (you were on VA because of heart problems). But, the lungs haven’t really recovered yet, hence the deoxygenated blood being ejected. And so, despite the good news of better heart function, the patient still may end up in life-threatening hypoxia from this mixing.

As usual, countbackwardsfrom10 is our go-to for all things cardiac surgery, and he has a nice Instagram post explaining this phenomenon and what to do about it.

Chest CT

I always have lots of students interested to learn to read radiology studies. In class, we typically only cover CXR. I occasionally do some special lectures on head CT, but it takes a lot of practice to really be able to read your own imaging studies. We don’t spend a whole lot of time in NP school teaching it. It’s something that is really better spent on the job. The fact is, with the exception of CXR, actually reading your own radiology studies is going to be highly dependent on the area in which you work.

But, I think it’s always good to be able to understand the basics. So, Dr Naveen Sharma (known on Instagram as theRadiologist) has some great posts to help. This is a really good one detailing the basic anatomy of the chest CT. Chest CT is a study that is used not infrequently in critical care, whether to evaluate for PE, look for pneumonia, or more advanced lung disease. So, check out this post with some really great teaching on the basics of reading chest CTs.

Ultrasound Case: PE

Bedside echo can be very helpful in the diagnosis of pulmonary embolism. There are a number of things to look for including septal bowing, right-heart strain in the form of increased RV size and decreased RV function, McConnell’s sign, and the always exciting clot in transit. Sarah Wolochatiuk is a PGY-4 in Emergency Medicine at the University of Cincinnati just up the road from me. She has a great case presentation on the UC EM blog Taming of the SRU that covers all of this with some great echo images as well.

Waveform Capnography

While we’ve used colorimetric capnography for years to confirm ETT placement, not all ICU providers are as familiar with waveform capnography. It offers significant benefits to the intubated and non-intubated patient alike.

Using waveform capnography to confirm ETT placement offers a benefit over colorimetric confirmation. during the peri-intubation period, while the patient is being ventilated via BVM, there can be an accumulation of CO2 in the stomach so that it is possible to get color change on an esophageal intubation. The use of waveform capnography prevents this. As carbon dioxide is not manufactured in the stomach, eventually the levels will fall. So, by trending the waveform over a few breaths, you should see a steady decrease in end-tidal CO2 over the course of a few breaths.

In addition to ETT positioning, ETCO2 has a number of other benefits including detecting displaced ETTs, monitoring effectiveness of ventilation in non-intubated patients, assessing ROSC during CPR, and much more. But essential to its use is understanding how to interpret the waveform and not just read the number. In this video, Obiajulu Anozie (@icuexplained) does a great job of explaining what the waveform means and how to use it in the ICU.

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.

Ventilator Dyssynchrony

Dyssynchrony with the mechanical ventilator is a common problem in the ICU. Often, we treat this with increased sedation, but that’s not always what is needed. In fact, it’s usually not what’s needed. Matt Siuba has a nice summary of common dyssynchronies on Instagram. Take a look at them to better understand why patients are dyssynchronous and what to do about them. We did an episode of the Critical Care Scenarios podcast covering this as well. Give it a listen here.

Bivalirudin vs Heparin for ECMO

ECMO is a therapy that’s becoming more and more common, particularly during the COVID-19 pandemic, as it’s often the only support therapy that will get some of these patients through when all conventional ARDS treatments have failed. ECMO involves the use of lots of plastic, catheters, pumps, oxygenators, etc. Blood traditionally doesn’t really like plastic, it often forms clots. So, typically, ECMO patients require some sort of systemic anticoagulation while they’re on the circuit.*

Unfractionated heparin as a continuous infusion has long been the mainstay of ECMO anticoagulation, but there are other options, including bivalirudin. Bivalirudin is a direct thrombin inhibitor (similar to dabigatran) that works by preventing the conversion of fibrinogen to fibrin (you knew that, I’m sure you have the clotting cascade memorized still, right?). It has a rapid plasma clearance, small volume of distribution, and elimination half-life of about 30 mins. All that means that it’s easy to titrate and you can usually just shut it off if there are bleeding problems. Also, it can’t cause heparin induced thrombocytopenia (HIT).

So, should we be using bivalirudin to anticoagulate all our ECMO patients? Well, in the interest of full disclosure, I’m a little biased. We use bivalirudin on all ECMO patients in our center.** We made that decision based on the overall safety of bivalirudin as compared to heparin, but another factor influenced that decision as well, COVID (doesn’t everything seem to come back to COVID these days?). In this case, our average ECMO run for patients who are COVID + is over 30 days. That amount of time presents lots of opportunities for bleeding issues and lots of opportunities for clotting issues (especially given the hypercoagulability of COVID patients). Ordinarily, if an ECMO patient develops clots in their circuit or oxygenator, while not ideal, it’s not the end of the world. You simply cut out the section of clotted circuit or exchange the oxygenator. However, with most patients with COVID, even a 30 second oxygenator exchange can see rapid desaturation, bradycardia, and peri-arrest (or actual arrest). So, it is a good idea to minimize the need for those. Additionally, the long ECMO runs require a lot of exposure to heparin, which increases the risk of developing HIT. HIT isn’t necessarily common, even in ECMO patients, but again, when it happens, it’s BAD.

The podcast ED ECMO, recently discussed this controversy with Ryan Rivosecchi, a pharmacist at University of Pittsburgh and lead author of a new study comparing heparin to bivalirudin. (You can read the original study here) They found a significant decrease in ECMO circuit events as well as decreased incidence of major bleeding in ECMO patients on bivalirudin as compared to heparin. They also discuss the potential cost differences in bivalirudin vs heparin, and, like lots of these things, it’s not as straightforward are the cost of one drug vs the other.

*Not all ECMO patients technically require systemic anticoagulation. Theoretically, if your flow rate is >5lpm on VV ECMO, the risk of significant clotting is low. At our center, we used to run VV ECMO quite frequently with no systemic anticoagulation. Also, shorter runs typically can avoid anticoagulation. VA ECMO can avoid this as well, but the stakes are higher. If a clot forms on VV and it embolizes, it’s going to get caught in the lungs, and well, you’re already on ECMO. But if a clot embolizes on VA, that’s a stroke. That’s bad. In the ED ECMO podcast linked above, Rivosecchi discusses this concept of “dry” ECMO and mentions an upcoming study at University Health Network in Toronto examining the feasibility of an “anticoagulation-free strategy” for VV ECMO.

**Again, not ALL. We have done a few short runs of ECMO with no anticoagulation even recently. However, these were done in patients without COVID and the associated hypercoagulability and in patients for whom systemic anticoagulation was contraindicated for some other reason.

Hampton’s Hump

We all know that CTA is the way to diagnose PE in a patient, but this requires a trip to CT and a large dose of IV contrast. So, there are ways to narrow things down in patients for whom PE is suspected. Most of us are familiar with evaluating right heart strain on bedside echo, and lots of us know that you can identify certain characteristic ECG changes. But, somewhat less well known is the radiographic sign known as Hampton’s Hump. This is a dome-shaped opacification that is most commonly associated with PE, but also can be a sign of pulmonary infarction due to other causes, such as angioinvasive aspergillosis. PE causes a wedge shaped infarct with sparing of the apex due to collateral circulation in the bronchial arteries. This leads to the characteristic rounded shape.

New England Journal of Medicine’s Images in Clinical Medicine series recently featured a nice example of this. This requires a free NEJM Online account to view the entire post (but the free account is well worth your time).

Return of the Live Journal Club!

Back by popular demand, live Twitter journal club! But I’ve chosen a new time that should allow a lot more people to participate. Wednesday, November 3 @ 4:00pm Eastern (GMT-5). We’ll be discussing a big new study that has a potential impact on not only how we treat COVID, but possibly ARDS in general.

The COVID Steroid 2 trial compared 2 different dosing strategies for steroids in COVID-19 infection and had some…interesting results. You can get the paper here. We’ll be discussing the trial itself, the findings, and what you think they mean for COVID steroid treatment and if you think this will have any impact on steroids in ARDS or other lung diseases.

So, you’ve got almost a week to read the paper (if you haven’t read it already) and get ready to discuss. Hope you’ll join us on Twitter (@CritCareNotes) on Wednesday, November 4 @ 4:00pm Eastern/GMT -5. See you then!