1. The Physiology and Mechanics of Extracorporeal Life Support (ECLS)
Over the next few minutes, I hope to share with you a basics in the physiology and mechanics of ECMO.

2. What is ECMO or ECLS? Extra Extra Corporeal Corporeal Membrane Life
Oxygenation
Extra
Corporeal
Life
Support
It’s science, but not rocket science…Simply put, ECMO is a life-support mechanism that allows the native heart and/or lungs to rest, while providing gas exchange for the body, outside of the body……before we get too far into specifics, let’s review a comparison of our native bodies to the extra-corporeal system.

3. ECMO Systems Centrifugal Roller-Head
ECMO is broken down into 2 sub sets. The roller head pump is for our infant and neonates where as the newer centrifugal system is currently for the pediatric and adult populations.

4. Extra-Corporeal to Corporeal Comparisons
Tubing =
Vasculature
The ecmo tubing is simply the pathway or route to shunt the blood from and back to the body

5. Extra-Corporeal to Corporeal Comparisons
Pump Head =
Heart
The pump head is the work horse of the system. It is the driving force of the blood thru the system and back to the patient either to the vein for pulmonary support or to an artery to provide the cardiac output.

6. Extra-Corporeal to Corporeal Comparisons
Oxygenator =
Lungs
The oxygenators work by diffusive properties and are as much as 6 times more efficient as our native lung!

7. Extra-Corporeal to Corporeal Comparisons
Sweep =
Ventilator
Sometimes the we get lost in the terminology of “sweep”. The sweep is simply the fashion in which we ventilate or assist in gas exchange thru our oxygenator. The increasing and decreasing sweep flow and FiO2 ….

8. Extra-Corporeal to Corporeal Comparisons
Hemofilter/Prismaflex =
Kidneys
Via a shunt within our system, we implement a hemofilter which consists of a tube-like structure with many hollow-fiber micro straws stretched lengthwise of the housing allowing convection or ultrafiltration to take place (simply the movement of solution by a pressure gradient, from higher to lower)

9. ECMO Anatomy Veno-Venous Cannulation
When you walk up to the BS of an ECMO patient, it all looks relatively the same…so you have to know where the cannulae are placed in order to understand whether the patient is actually on VA or VV.
In this slide the VV cannulation is represented and placed in either the RIJ or Femoral vein

10. ECMO Anatomy Veno-Arterial Cannulation
Venous Cannula
In VA, the venous access is the same as mentioned before with the addition of an intra-atrial site and the arterial cannulae is placed in either the Aortic arch, RCCA, or Femoral. (Expand on position for types of patients)
So now that we’ve quickly reviewed some of the mechanical portion of ECMO, lets attempt the physiology side…

11. Poor Oxygenation and / or Poor Delivery
The Problem
Poor Oxygenation
and / or
Poor Delivery
So if a patient has found themselves needing ECMO, they’re simply because they can’t get enough oxygen to the tissues on their own…and …we as health care professionals were also unable to appropriately assist them by conventional means…i.e. chemical support, conventional or oscillatory ventilation, or Nitric Oxide.

12. The Goal Oxygen Delivery to the Tissues
…and that’s where ECMO comes in!
The venous blood is drained from the right side of the body, CO2 removed, the blood is hyper-oxygenated, and then return the blood back to the vein for lung rest or to an artery for heart and lung rest….either way, it’s goal again is to oxygenate the blood outside of the body and then deliver it back to the tissues!

13. Cardiopulmonary physiology
Oxygen Content
O2 delivery (DO2)
O2 consumption (VO2)
CO2 production/removal
It’s all about supply and demand !
O2 content is how well the hemoglobin is saturated with O2 is simply measured at the bedside by the patients PaO2 and hemoglobin saturation
O2 Delivery is The amount of O2 delivered to the peripheral tissues each minute

14. Systemic Oxygen Delivery
The amount of O2 delivered to the peripheral tissues each minute
Major influences on DO2
cardiac output
Hemoglobin
FiO2
Minor influence on DO2
O2 dissolved in plasma
these 3 factors are all influenced at the BS by the BP, both the native cardiac output and extracorporeal ECMO flow, the patients hematocrit, and the FiO2 (by both the vent and ECMO sweep)

15. Systemic O2 Consumption
How much O2 the body is using?
The difference between what is delivered (DO2) and taken up by the tissues and what returns to the right side of the heart
DO2 = 4-5 times the amount of VO2 (5:1)
SVO2 = 75%
ECMO’s BS measurement of the patients O2 consumption is the SvO2, an SvO2 of 75% reflects a consumption of 25%.
When you get closer to a 2:1 ratio of delivery to consumption, the patient will go into anaerobic metabolism….which means the patients consumption is greater than the delivery

16. Systemic O2 Consumption
VO2 is controlled by tissue metabolism and decreased by
VO2 is controlled by tissue metabolism and increased by
Rest
Sedation & Paralysis
Hypothermia
Muscular activity
Infection
Hyperthermia
The main goal of ECMO is simply to rest the body
The pts temp can be controlled or regulated by ECMO’s abilities thru our heat exchanger.

17. Carbon Dioxide Production
Amount of CO2 produced during systemic metabolism (VCO2)
VCO2/VO2 = respiratory quotient
CO2 excretion not affected by Hb or blood flow
Very sensitive to changes in ventilation
CO2 production is the waste product of aerobic metabolism and interestingly, the amount of CO2 produced is roughly equivalent to the amount of O2 consumption. Even during severe lung dysfunction, normal CO2 levels can typically be easily maintained.

18. Blood O2 in the Membrane Lung
Gas exchange in ECLS
Blood O2 in the Membrane Lung
Function and geometry of the Oxygenator
Sweep FiO2
Residence time of red cells in gas exchange area
Hematocrit
Inlet saturation (functions as SvO2)

19. Rated Flow
The amount of normal venous blood that can be raised from 75% to 95% saturation in a given period.
DO2 via ECMO circuit is controlled by
Blood flow
O2 uptake capacity of the membrane
O2 uptake of the native lung
Native Cardiac Output
As long as ECMO blood flow thru the oxygenator is less than rated flow, blood leaving the oxygenator will be fully saturated and the O2 content will be sufficient

20. CO2 removal Membrane lung’s geometry Material Surface area Blood PCO2
Blood flow
Sweep flow
CO2 removed by ECMO is dependent on…
Usually ventilation gas contains no CO2 so there’s a Large gradient between blood /membrane lung. The Major determinants of CO2 elimination are the Total surface area of the oxygenator and the Flow rate of sweep gas delivered across the lung

21. V-A ECMO Provides excellent D02 Right Atrial Drainage
Arterial / Aortic return
Alters / Sustains Normal Hemodynamics
Oxygenated Blood Bypasses Pulmonary and Coronary Arteries
Bypass the lungs natural filtering properties
Maintain the vent FiO2 at levels of atleast 40% to ensure coronary perfusion.
That’s why our bubble detector and bridge are so important to our system.

22. Veno-arterial bypass (VA)
Blood is drained from the Right Heart
Perfusate blood mixes in the aorta with LV blood (from the lungs)
The content of arterial oxygen and carbon dioxide is a combination of both sources
Systemic blood flow (SBL) = extracorporeal flow (EF) + corporeal flow (CF)
In V-A, functions of both the heart and lungs are directly supported or temporarily replaced by extracorporeal organs.
From UMHS Internet Site

23. Physiologic Principles and Management
Circuit should be planned for total support
ECMO flow rates
cc/kg/min newborn
75-100cc/kg/min children
50-75cc/kg/min adult
Higher flows during V-V may be necessary to maintain adequate oxygen delivery.

24. Hemodynamics Non-Pulsatile Flow
ECMO pump creates flow that is non-pulsatile
Systemic arterial pulse contour flattens with reduction of pulse pressure
Unless myocardial stun present, VA ECLS can run at 80% normal cardiac output
As long as the flow is > 100 cc/kg/min, there’s no significant difference between non-pulsatile and pulsatile perfusion.
If during low-flow periods, DO2 must be countered with and supported by adequate BP and ventilator settings.

25. Hemodynamics ECMO flow increases  systemic pulse pressure decreases.
There are 2 main reasons you could see cardiac stun on VA ECMO: as a result in off-loading right heart, decreasing pre-load ( decreased circulating volume thru the heart) and the pump assumes more responsibility of the total cardiac output! , As long as the total blood flow is adequate, the presence of a discernable pulse contour is not physiologically important in gas exchange..….if you see this picture in VV, we have problems! Code your patient as you would if ECMO wasn’t even in the room.

26. Left Ventricular Function
Hemodynamics
Left Ventricular Function
Myocardial stun
Severe malfunction
Left sided heart can be come distended
Resulting in myocardial damage
Pulmonary edema

27. Left Ventricular Function
Hemodynamics
Left Ventricular Function
Treatment:
Left side decompression
LA or LV Vent
PDA
Atrial septostomy
The left heart will over-fill and distend from an under-functioning left ventricle. If there’s not a PDA or surgically enhanced pop-off already in place, pressure can be relieved by performing a balloon septostomy or cannulating the left heart with a vent for decompression and true resting of the left heart.

28. Venovenous bypass (VV)
Venous blood is drained from the right heart
Perfusate blood returns to the venous circulation
Raising the O2, lowering CO2 content in RA blood
Mixes with venous blood coming from systemic organs
Arterial content of O2 and CO2 are represented by left ventricular blood
SBF = CO
Acceptable SpO2’s during VV could be in the low to mid 80’s…Again just providing enough lung rest from ventilator induced trauma and ensuring sufficient oxygen delivery.

29. Venovenous bypass (VV)
From a blood flow standpoint:
Volume removed = volume re-infused
No net effect on CVP, right or left ventricular filling or hemodynamics
A percentage goes to the right ventricle---lungs---systemic circulation
Some of the mixed blood is returned to the ECMO circuit (recirculation)
We’ve essentially created a large shunt outside of the body. The hematocrit and flow required to maintain the same oxygen delivery during V-V ECMO may need to be higher than the flow used during V-A to provide the same DO2

30. Cardiac Effects Veno-Arterial Veno-Venous Decreased Preload
Increased Afterload
Low to variable pulse pressure
Coronary Perfusion ?
Requires Native Cardiac Output
Indirect improvement on Cardiac Output
No change in Pulse Pressure
No change in Preload or Afterload
What is the effect we have on our patients when either form of ECMO is provided?
For VA we commonly see a decreased preload…..
VV is again just providing pulmonary support and has minimal direct cardiac effects….

31. Safety Veno-Venous Veno-Arterial Native Lung Filter Normal pressure
Normal Flows
Quicker Cannulation
Embolization
Reperfusion Injury
Slower cannulation
OF the 2 types, VV is by far the quickest and safest method of support that we can provide: VV allows the use of the native lungs to filter out any particulate matter, and since the patients native cardiac output is what perfuses the body, the patient doesn’t see the fluctuation of high flows and pressures as you would in VA.
In VA the

32. ECMO adequacy How do we evaluate effectiveness? Hemodynamics
How does the patient look?
Color
Cap refill
Renal Function
Labs
ABG
Lactate
Don’t forget about what you are supporting…always look at your patient and use your bedside assessment!

33. Questions?
Thank You!