Hanna Knauss MD
@HKnaussMD
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PGY2 Resident @BIDMC_IM via @ohiou & @UToledoMed l Aspiring Cardiologist, Medical Educator l Part-time Runner & Amateur Plant Mom l Views are my own.
Joined June 2023
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🚨 You're in the ICU when the 📟 en route page arrives for a patient on VA-ECMO.
What framework do you use for approaching VA-ECMO?
It's ⏰ for a
@CardioNerds
thread in the Devices in a Dash VA-ECMO Series! Follow along with Video 1 here:
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You walk in the room of your patient on VA-ECMO & see the following pump display.
How do you interpret those values?
It's ⏰ for our next
@CardioNerds
thread in the VA-ECMO series of Devices in a Dash! Follow along with the video here:
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Thanks for following along! See the infographic below ⬇️ for a summary of 🗝️ take-home points.
Check out the Devices in a Dash VA-ECMO series: Video 2 to go along with this thread, linked here:
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First, let's review the VA-ECMO circuit.
VA-ECMO is a continuous pump. The circuit (below) drains via venous cannula ➡️ pump & oxygenator ➡️ arterial cannula to return blood retrograde up the abdominal aorta and increases afterload to the 🫀.
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When is VA-ECMO used?
- When the native heart 🫀 function + pressors, inotropes, and/or mechanical circulatory support fails to provide enough perfusion and/or oxygenation to vital organs.
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Why a RIGHT upper extremity line?
🧠 Recall the mixing cloud ☁️ from Video 1. As 🫀 function recovers, proximal aortic branches are perfused by poorly oxygenated native contractility rather than oxygen-rich blood from peripheral VA ECMO cannulation.
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Again, it takes a village. Thank you
@CardioNerds
@KatieV_MD
@AmitGoyalMD
@WilsonGrandinMD
for the edits, inspiration, & support! Shout out to my Digital Education Track leaders
@ShreyaTrivediMD
@AdamRodmanMD
for the encouragement & lessons.
@BIDMCVFellows
@BIDMC_IM
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Thus, there may be a discrepancy in O2 saturation in the right vs left upper extremities. The right side is preferred to better detect poor perfusion.
This phenomenon is called "North South" or "Harlequin" syndrome.
We will cover this more in a later video!
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2⃣ P2 is the pressure measured after the oxygenator. The oxygenator has some resistance, so P2 < P1.
Oxygenator resistance (🔺P), aka trans-oxygenator pressure = P1 - P2.
🥅 Goal 🔺P varies based on type of oxygenator & flow rates. Generally, goal 🔺P = 10-40 mmHg.
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Next, the pulmonary artery catheter (PAC).
Patients on VA-ECMO require a PAC to monitor PA pressures.
🥅 Goal PA diastolic pressure is <20 mmHg (typically 8-15 mmHg).
🚨 Note: If RV does not contract ➡️ no pulsatility in the PAC tracing!
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The SvO2 is used to estimate CO via the Fick principle. Thus, it can assess if the patient is receiving adequate blood flow.
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In the absence of an impella unloading the LV (aka EC-Pella), pulsatility goal 🥅 on VA-ECMO is >/= 10 mmHg.
This prevents over-distension of chambers & clot formation!
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All patients on VA-ECMO require invasive hemodynamic monitoring with:
🩸 Arterial line
🩸 Pulmonary artery catheter
We will discuss the arterial line pressure tracings first ⬇️
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What about the MAP goal?
🥅 MAP goal is 65-80 mmHg. This allows for perfusion of organs while preventing ⬆️ afterload that would limit ECMO flow and LV ejection.
🩸 Typically monitored via RIGHT upper extremity arterial line.
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🚨 Remember: The VA-ECMO circuit is continuous, NOT pulsatile. Because the LV creates pulsatile flow from intermittently pumping blood, the degree of pulsatility in the A-line tracing is dependent on LV function.
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Remember to check out the Devices in a Dash VA-ECMO Series: Video 1 to go along with this thread (linked here: )
Check out our next thread & video to learn more about VA-ECMO hemodynamic parameters, circuit pressures, & monitoring!
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Before we talk about management, let's take a step back 🔙 and understand:
🧠 What is VA-ECMO?
🧠 What are components of the circuit?
🧠 What are some indications and contraindications?
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If 🔺P rises, this could represent clot or fibrin in the circuit. This may result in hemolysis due to shear stress and poor gas exchange.
Below is an oxygen console with P1 (left), P2 (right), and 🔺P (center) values circled in green.
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In addition to arterial and PA pressures, the mixed venous O2 saturation (SvO2) is another parameter to measure VA-ECMO function.
🧠 Recall that SvO2 is the percentage of O2 bound to hemoglobin returning to the right side of the heart 🫀.
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It takes a village. Thank you
@CardioNerds
@KatieV_MD
@AmitGoyalMD
@WilsonGrandinMD
for the edits, inspiration, & support! Shout out to my Digital Education Track leaders
@ShreyaTrivediMD
@AdamRodmanMD
for the encouragement & lessons.
@BIDMCVFellows
@BIDMC_IM
@tony_breu
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6 L/min! ECMO can provide complete biventricular circulatory support in cardiogenic shock.
The circuit contains an oxygenator as well for respiratory failure. Think of this as an artificial "lung" to manage gas exchange. Thus, it can also be used for respiratory failure.
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What is the goal SvO2?
🧠 Recall that SvO2 is influenced by hemoglobin levels.
🥅 Goal SvO2 % with normal Hb: 60-70s
🥅 Goal SvO2 % with ⬇️ Hb (i.e. 7-10 g/dL): 50-60s
In general, aim for SvO2 > 55%.
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No! Recall our goals:
🥅 MAP 65-80 mmHg
🥅 PA diastolic pressure < 20
🥅 Pulsatility >/= 10 mmHg
This tracing shows PA distolic pressure is ⬆️ 20 mmHg.
🚨 Disclaimer: We are discussing absolute values but you should follow patient trends & clinical status.
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Now that we've covered indications and mechanics, what are contraindications to VA-ECMO?
🧠 Another way to approach this: What patients would not qualify for a bypass circuit with large cannulas and systemic A/C?
🧠 Are the organs too sick to be supported?
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The circuit flow is measured by a sensor in the arterial return cannula.
🥅 Flow goal rate: 3.5-5 L/min
The operating range of RPMs varies amongst manufacturers, however 3500-5500 RPMs is typically needed to provide complete circulatory support.
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Lastly, let's discussion circuit pressures. There are few pressures we monitor in the VA-ECMO circuit:
1⃣ P1 is measured after the pump & before the oxygenator. It is the ➕ pressure generated by the pump to push blood through the circuit.
🥅 Goal P1: ~150-350 mmHg
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Let's test our knowledge on the hemodynamic targets discussed so far. Does the monitor below meet our pulsatility, MAP, and PA diastolic pressure goals for VA-ECMO?
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Thanks for following along! In summary, VA-EMCO is a complex decision that should be made amongst a multidisciplinary team.
Recall 🗝️ points we discussed:
🗝️ Indications and contraindications for VA-ECMO.
🗝️ Basic circuit components and flow.
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Finally, let's discuss A/C. VA-ECMO is prothrombotic! Measures to mitigate clot risk:
🩸 Systemic A/C (check your institutional guidelines!).
🩸 Heparin-coated cannulas.
🩸 High flow rates (>2.5L/min) are maintained, with higher rates (>3.5L/min) in patients not on A/C.
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Let's 🛑 and reflect on this concept: If the LV has no contractile function, what would you expect the A-line pressure tracing to look like from the VA-ECMO circuit alone?
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Flat
353
Minimal Pulsatility
130
Moderate Pulsatility
5
High Pulsatility
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Let's move on to flow within the VA-ECMO circuit.
There is only 1 parameter we set in the continuous flow pump: revolutions per minute (RPMs).
⬆️ Increasing the RPMs ⬆️ increases circuit flow.
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SvO2 is monitored with an in-line censor built into the circuit.
Based on what we learned from our prior thread on circuit components, where in the circuit would the most deoxygenated blood appear?
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Arterial return cannula
9
Venous drainage cannula
87
In the centrifugal pump
6
Right before oxygenator
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First, what is VA-ECMO?
Venoarterial (VA) extracorporeal membrane oxygenation (ECMO) is a partial cardiopulmonary bypass system.
Think of it as an external circuit with a pump and gas exchange to support the heart and lungs 🫀🫁 in circulatory shock.
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VA-ECMO can be used as a bridge to recovery or to transplant:
🌉 Recovery: Goal is to wean VA-ECMO as the cardiopulmonary system heals.
🌉 Advanced therapies: Temporizing organ function while awaiting more permanent heart replacement therapy (i.e. LVAD or transplant).
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Right before the oxygenator!
Since most of the venous drainage is diverted from native circulation through the VA-ECMO circuit, the SvO2 is measured via a continuous sensor just proximal to or within the oxygenator.
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Time to 🛑 pause and recap:
🗝️ VA-ECMO is an external heart-lung system used in cardiogenic shock with or without respiratory failure.
🗝️ VA-ECMO can be used as a bridge 🌉 to recovery or a 🌉 to advanced therapies, such as LVAD or transplant.
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The tracing would be flat! Similar to that pictured below ⬇️
Without pulsatile flow from the LV 🫀, all that would be seen is the continuous flow from the VA-ECMO circuit. You would not see a systolic & diastolic pressure difference.
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The cannulas can be placed either central or peripheral:
🩸 Central cannulation: Often used in post-cardiac surgery patients.
🩸 Peripheral cannulation: Most often used in the CCU or cath lab.
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Let's 🛑 and consider: What is the maximum blood flow rate VA-ECMO can provide?
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4 L/ min
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6 L/min
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8 L/min
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The location of the ☁️ varies and holds important implications to be covered in another Devices in a Dash thread and video!
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➡️ The venous cannula connects to a continuous centrifugal pump, which creates ➖ pressure to "pull" blood from the body.
The pump then uses ➕ pressure to push 🫸 blood through the oxygenator.
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➡️ Oxygenated blood flows to the arterial return cannula and returns and disperses to the body in a retrograde fashion in the aorta.
Compared to the venous cannula, the arterial cannula is shorter, 15-19F, & only has 1 end hole.
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This means there are 2 pumps to consider: the native heart AND the VA-ECMO circuit.
In this tale of 2 pumps, blood from native circulation and the ECMO circuit meet in a location termed the "mixing cloud" ☁️.
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🚨 Be aware! The peripheral arterial cannula can impede blood flow to the leg on the side of arterial cannula insertion.
A small, distal perfusion cannula can be placed in the superficial femoral artery to improve ipsilateral limb perfusion.
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Recall: The 🫀 maintains some contractile function, so a portion of blood travels through native circulation instead of the ECMO circuit.
🩸 Blood pumped by the heart travels anterograde down the aorta to "mix" with retrograde flow from the ECMO circuit.
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Let's explore the VA-ECMO circuit...what are the components & how does blood flow?
1⃣ Deoxygenated blood drains from venous circulation,
2⃣ Travels to continuous flow pump,
3⃣ Traverses oxygenator (artificial lung) and
4⃣ Oxygenated blood returns to arterial circulation.
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Let's break down venous cannulation even further.
The venous cannula (typically 25F) inserts via the femoral (or other peripheral) vein up through the IVC to the RA and SVC. It contains multiple side holes and an end hole for blood drainage.
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🚨 Oxygenation: Adjusting the fraction of delivered oxygen (FDO2) changes the proportion of oxygen delivered, similar to FiO2.
🚨 Ventilation: The sweep gas flow rate, or the rate of gas flow through the oxygenator, can be ⬆️ to ⬆️ CO2 clearance.
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➡️ Deoxygenated blood traverses the oxygenator and becomes oxygenated. Additionally, CO2 is removed.
🚨 Note: We can control the oxygenation and ventilation settings, similar to mechanical ventilation.
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@ShreyaTrivediMD
@AdamRodmanMD
@Mjfernaturizo
@anugupta327
@alingg25
@natelong_11
@RatiVani7
@ccsmith269
@BIDMC_Education
@BIDMC_IM
Looking forward to learning and growing with this amazing group!
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