PATHOPHYSIOLOGY OF EMBOLIC EVENTS Flashcards
Incidence of clinically obvious strokes post CPB is
1-5%
MRI suggests could be new cerebral infarcts in
~30% of those same patients.
Source of strokes is not necessarily from CPB
• Patient is
a major contributor
percentage of CABG patients experienced cerebral infarct prior to surgery
50%. sub clinical and hard to detect
Types of Emboli
- Biologic (bloodborne)
- Foreign material • Circuit
- Manufacturing • Gaseous
micro vessels diameter
3 to 500 m in diameter
Greatest period of risk for emboli
- 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
Biologic Emboli
- Fibrin / fibrinogen microthrombi • Fat or lipids • Protein • Cold-reacting antibodies
- Calcium fragments • Bone fragments • Muscle fragments • Platelet aggregates • Neutrophil aggregates • RBC aggregates
Formation of Biologic Emboli
• Homologous transfused blood • Increase
with storage time
Formation of Biologic Emboli
• Inadequate anticoagulation • Contact with foreign surface
• Areas at Risk
Minimal flow • Stagnant areas • Turbulence • Cavitation • Rough Surfaces
areas of the circuit most at risk of forming biological emboli from inadequate anticoagulation
• Connectors
• Bubble Oxygenators • Arterial line filters • Cardiotomy (venous)
reservoir • Intraluminal projections
how does fat emboli occur
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
2/3 fat/lipid emboli within a circuit come from
cardiotomy suction. Large particles 4-200 microns
fat emboli is found in these organs post bypass
Kidney, lungs, heart, brain, liver, spleen
biological emboli come from activation of
immune response . neutrophils/ platelets
Platelet count drops_____with initiation of bypass
30-50%. Also drop in # of functional platelets
drop in platelets causes
Post op bleeding, neurologic dysfunction, release of histamine (membrane permeability), release of serotonin/ thromboxane (vasoconstriction)``
neutrophils cause
aggregation, interaction with endothelial cells, change permeability`
Foreign Particle Emboli
Cotton fibers • Plastic particles • Filter material • Tubing fragments (spallation) • Metal • Talc • Thread • Bone wax • Microfibrillar collagen • Silicone antifoam
Formation of Gaseous Microemboli
• Bubble oxygenator
• 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
how does surgical air emboli happen
Heart contracts before chambers completely de- aired
• Surgeon cuts into chamber of beating heart • Placement of arterial, venous or LV vent cannulae
Air present in heart_______ post bypass
30 to 40
flush heart with CO2 to remove
86% bubbles gone within 1 minute
Pump Air happens by
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
Blood-Bubble Interactions
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
Safety Devices
- 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
How Do You Minimize Biologic Emboli Formation?
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
How Do You Minimize Introduction of Foreign Particle Emboli?
- 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
How Do You Minimize Formation of Gaseous Microemboli?
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
