PATHOPHYSIOLOGY OF EMBOLIC EVENTS

Question 1

Incidence of clinically obvious strokes post CPB is

Answer 1

1-5%

Question 2

MRI suggests could be new cerebral infarcts in

Answer 2

~30% of those same patients.

Question 3

Source of strokes is not necessarily from CPB

• Patient is

Answer 3

a major contributor

Question 4

percentage of CABG patients experienced cerebral infarct prior to surgery

Answer 4

50%. sub clinical and hard to detect

Question 5

Types of Emboli

Answer 5

• Biologic (bloodborne)
• Foreign material • Circuit
• Manufacturing • Gaseous

Question 6

micro vessels diameter

Answer 6

3 to 500 m in diameter

Question 7

Greatest period of risk for emboli

Answer 7

• Insertion arterial cannula
• Initiation of bypass • Hypotension • Most circuit “junk”
• Cross-clamp application / removal • Manipulation of aorta
• Trauma to aorta can contribute to brain infarctions for up to 1 month • Use of centrifugal pump
• Any time you have to decrease blood flow

Question 8

Biologic Emboli

Answer 8

• Fibrin / fibrinogen microthrombi • Fat or lipids • Protein • Cold-reacting antibodies
• Calcium fragments • Bone fragments • Muscle fragments • Platelet aggregates • Neutrophil aggregates • RBC aggregates

Question 9

Formation of Biologic Emboli

• Homologous transfused blood • Increase

Answer 9

with storage time

Question 10

Formation of Biologic Emboli
• Inadequate anticoagulation • Contact with foreign surface
• Areas at Risk

Answer 10

Minimal flow • Stagnant areas • Turbulence • Cavitation • Rough Surfaces

Question 11

areas of the circuit most at risk of forming biological emboli from inadequate anticoagulation

Answer 11

• Connectors
• Bubble Oxygenators • Arterial line filters • Cardiotomy (venous)
reservoir • Intraluminal projections

Question 12

how does fat emboli occur

Answer 12

Trauma to fat cells of epicardium and trauma to tissue of the surgical wound
• Do not need bypass to produce fat emboli • Median sternotomy • Thoracotomy

Question 13

2/3 fat/lipid emboli within a circuit come from

Answer 13

cardiotomy suction. Large particles 4-200 microns

Question 14

fat emboli is found in these organs post bypass

Answer 14

Kidney, lungs, heart, brain, liver, spleen

Question 15

biological emboli come from activation of

Answer 15

immune response . neutrophils/ platelets

Question 16

Platelet count drops_____with initiation of bypass

Answer 16

30-50%. Also drop in # of functional platelets

Question 17

drop in platelets causes

Answer 17

Post op bleeding, neurologic dysfunction, release of histamine (membrane permeability), release of serotonin/ thromboxane (vasoconstriction)``

Question 18

neutrophils cause

Answer 18

aggregation, interaction with endothelial cells, change permeability`

Question 19

Foreign Particle Emboli

Answer 19

Cotton fibers • Plastic particles • Filter material • Tubing fragments (spallation) • Metal • Talc • Thread • Bone wax • Microfibrillar collagen • Silicone antifoam

Question 20

Formation of Gaseous Microemboli

• Bubble oxygenator

Answer 20

• Bubble oxygenator • bubbles in 35 to 40 m size associated with CPB mortality and
morbidity • Mainly oxygen • Transitioned to membrane oxygenators
• Temperature gradients • Surgical air • Pump / Circuit problems

Question 21

how does surgical air emboli happen

Answer 21

Heart contracts before chambers completely de- aired

• Surgeon cuts into chamber of beating heart • Placement of arterial, venous or LV vent cannulae

Question 22

Air present in heart_______ post bypass

Answer 22

30 to 40

Question 23

flush heart with CO2 to remove

Answer 23

86% bubbles gone within 1 minute

Question 24

Pump Air happens by

Answer 24

Inattention to level in venous reservoir
• Vortexing of blood in venous reservoir at low volume levels
• Reversed roller pump
• Leak / kink in tubing on negative side of roller pump
• Cavitation
• Pressurized cardiotomy reservoir
• Retrograde flow through centrifugal pump
• Runaway pump
• Disconnection / breakage / detachment of oxygenator, tubing or other components
• Inattention while transfusing volume to patient post bypass • Drug injections into circuit and perfusion interventions • Mechanical jarring of circuit components • Inadequate debubbling – especially arterial filter
• Pulsatile flow through microporous membrane oxygenator • Over occluded arterial pump head • Tubing reversed in roller head
Slide 15

Question 25

Blood-Bubble Interactions

Answer 25

Adsorption / denaturation plasma proteins • Adsorption phospholipids • Adsorption fibrinogen • Complement activation
• Clumping red blood cells • Leukocyte activation / adherence • Lipid peroxidation • Microthrombi production • Platelet activation / adherence • Thrombin activation • Phospholipase activation • Endothelial wall damage

Question 26

Safety Devices

Answer 26

• Low level alarm
• Air bubble detector
• Arterial line filter • cardiotomy filter
• One-way purge line from arterial line filter to cardiotomy reservoir
• One-way valve in vent line • One-way valve in arterial line • Clear lines of communication • Use of protocols, policies and procedures • Use of prebypass checklist

Question 27

How Do You Minimize Biologic Emboli Formation?

Answer 27

Use of transfusion filters • Adequate anticoagulation • Design of circuit components • Minimize surface area of circuit • Use membrane oxygenator • Minimize complement / immune activation • Minimize platelet activation • Minimize neutrophil activation

Question 28

How Do You Minimize Introduction of Foreign Particle Emboli?

Answer 28

• Component design and manufacturing
• Circulate crystalloid solution through entire circuit
• Flush circuit with crystalloid solution in conjunction with a pre-bypass filter in AV loop
• Don’t use silicone tubing in arterial pump head • Use medical grade tubing

Question 29

How Do You Minimize Formation of Gaseous Microemboli?

Answer 29

Check all equipment for proper operation
• Ensure all tubing / component connections are secure
• Flush circuit with CO2 prior to priming
• Careful priming of arterial filter
• Warm prime – then let it cool
• Check circuit for proper alignment of tubing and components
• Check proper placement of tubing in roller pump raceway
• Proper use of all safety devices
• Open one-way purge line from arterial filter to cardiotomy reservoir
• Use of pressure relief valve on venous reservoir when using VAVD
• Test vent line prior to attachment to vent catheter
• Continual circuit scan while on bypass
• Continual monitoring of centrifugal pump flow and RPM – ensure forward flow at all times
• Avoid air in venous line