Blood Gas Mixology and Weaning!

Question 1

VA ECMO is a _______ circuit.

Answer 1

Parallel Circuit

Question 2

VV ECMO is a _______ circuit.

Answer 2

Series Circuit

Question 3

VA Ecmo Circuit

Answer 3

Patient Venous Blood –> Native Heart Lung/Artificial Heart Lung –> Patient Arterial Blood

Question 4

VV ECMO Circuit

Answer 4

patient venous blood –> Artificial Lung –> native lung –> patient arterial blood

Question 5

VA ECMO: Central Cannulation

Answer 5

Typically right atrium to aorta
used for patients with open chests (post-CPB)
ideal for high-flow ecmo

Question 6

VA ECMO: Peripheral cannulation

Answer 6

TYpically femoral vein to femoral artery
Can be used without opening hte chest
may cause limb ischemia
risk of coronary/brain ischemia

Question 7

Assumption (for now) of VA ECMO

Answer 7

100% patient blood flow is being provided by the ECMO system no blood is traversing hte lungs and being ejected by the heart

Question 8

What can we control? (Arterial blood)

Answer 8

PCO2/pH
pO2
ECMO Blood flow

Question 9

pCO2/pH

Answer 9

PCO2 can be controlled by the sweep (ventilation) rate. increased sweep leads to decreased pCO2 and vice versa

Question 10

pO2

Answer 10

pO2 can be controlled by manipulating hte fraction of inspired oxygen (FiO2). Increased FiO2 leads to increased pO2

Question 11

ECMO Blood Flow

Answer 11

increasing RPM leads to increased flow and therefore increased oxygen delivery

Question 12

Gas:Blood Flow Ratio

Answer 12

For a given sweep rate, changing the blood flow has an affect on the amount of co2 removed by the oxygenator

as the blood flow is decresaed, the blood has a prolonged exposure to the oxygenator’s fibers, resulting in more CO2 being “blown off”; the reverse is true as well

Question 13

how can a low venous saturation be managed?

Answer 13

Increase oxygen delivery

Decrease metabolism

Question 14

Increase oxygen delivery

Answer 14

increase oxygenation (increase ventilatior or ECMO settings?)
Increase ECMO blood flow
RBC transfusion

Question 15

Decrease metabolism

Answer 15

hypothermia

sedatives/paralytics

Question 16

Mixology refers to…

Answer 16

concept of “dual circulations”
impact of cannulation site of blood mixing
impact of cardiac function and ECMO blood flow on the Mixing cloud and regional blood gases

Question 17

Location of hte “mixing cloud” depends on

Answer 17

cannulation site
rate of ECMO blood flow
cardiac contractility
ECMO mode (VA vs VV)

Question 18

When would ECMO ABG = Patient ABG

Answer 18

If the aortic valve is not opening, no blood is being ejected form the heart therefore all arterial blood flow is being provided by the ECMO system

Question 19

With __________ cannulation, blood will generally be uniform throughout the body even if the aortic valve is opening and the heart is ejecting.

Answer 19

Central cannulation

Question 20

What are some exceptions of blood being uniform with central cannulation?

Answer 20

Coronaries, poor cannula position

Question 21

With ________ cannulation, the two circulations “compete for space” in the vasculature

Answer 21

femoral (peripheral)

Question 22

Veno-Veno ECMO

Answer 22

No arterial cannulation
Arterial blood is always uniform becuase mixing of ECMO and native blood happens in/near the right atrium
ABGs drawn form ECMO circuit should be considered largely independent of patient ABGs
ECMO ABG does not equal patient ABG

Question 23

ECMO oxygenation will be most effective when…..

Answer 23

ECMO flows are high
Cannula recirculation is low
Amount of blood bypassing hte cannula is low
oxygenator performance in high

Question 24

Weaning- VA ECMO

Answer 24

WEaning from VA ECMO should always be done by decreasing ECMO blood flow (RPM)
there is significant risk of circuit thrombus formation during periods of low (or no ) flow

Question 25

Weaning -VV ECMO

Answer 25

DOne in a number of ways but the proper method is decreasing sweep and FIO2

Question 26

Why is decreasing sweep and FiO2 the best method for weaning VV ECMO?

Answer 26

decreasing sweep/ FiO2 will not negatively effect the patient’s arterial blood gases as long as the lungs are functioning properly
Easy to “trial off”
Decreasing RPM/blood flow = risk of circuit clot

Question 27

VV ECMO- Preweaning

Answer 27

The blood exiting hte artificial lung is poorly oxygenated but this is not problematic as long as the lungs are functioning

Question 28

VV ECMO- Intiial Weaning

Answer 28

The blood exiting the artificial lung is poorly oxygenated, but this is not problematic as long as the lungs are functioning

Question 29

VV ECMO-Further Weaning

Answer 29

The blood exiting hte artificial lung is poorly oxygenated but thie is not problematic as long as the lungs are functioning

Question 30

Weaning- RVAD ECMO

Answer 30

weaning from RVAD ecmo should be done similarly to VV ECMO by decreasing FiO2 and sweep (not blood flow)