test 6 embolic events

Question 1

embolic events background

Answer 1

• CPB is not the sole source of emboli
• Patient is a major contributor
  * ~ 50% of CABG patients experienced a cerebral infarct prior to surgery
• Obvious stroke post CPB
  * ~ 1 – 5%
  * MRI suggests there could be new cerebral infarcts in up to ~ 30% of patients post CPB

Question 2

What is an Embolus?

Answer 2

• Deformable or non-deformable particle carried by blood and occludes some part of the vascular system
  * Deformable (conformal): GME or fat
  * Change shape to stick and slip as progresses through the vessel
  * Non-deformable: bone chip or calcific particle
  * Travel until its width exceeds the vessel’s ability to deform
• Both can cause ischemia

Question 3

Sources of Emboli

Answer 3

• Circuit components
• Prime solutions/drugs
• Blood/surface interactions
• Perfusionists/surgeons
- Emboli remains a major cause of morbidity even though the efforts to decrease it

Question 4

Types of Emboli

Answer 4

• Foreign material
• Gaseous
• Biologic (blood borne)

Question 5

Foreign Material

Answer 5

• Cotton fibers
• Plastic particles
• Filter material
• Tubing fragments
• Talc
• Surgical thread
• metal
• Bone wax
• Silicone antifoam

Question 6

Gaseous Emboli

Answer 6

• Placement of arterial, aortic root, and cardioplegia cannulas
• Cardiac contraction before de-airing is complete
• Reversal of LV vent
• Low reservoir levels
• Damaged circuit components
• Perfusion interventions (drug administration)
• Vacuum-assisted venous drainage
• Tubing disconnection
• Air left in venous cannula
• Cardiac chambers open to atmosphere
  * Valve replacements, ASD and VSD repairs
• Inattention to reservoir level
• Pressurized cardiotomy reservoir
• Retrograde flow through centrifugal pump
• Cardiotomy suction
• Inadequate debubbling of arterial filter
• Oxygenator and reservoir
  * Ability to handle air

Question 7

Biologic Emboli

Answer 7

• Thrombin
• Platelet aggregates
• Neutrophil aggregates
• Red cell aggregates
• Denatured proteins
• Cold-agglutinin antibodies
• Fibrin/fibrinogen
• Calcium particles
• Bone fragments
• Muscle fragments
• Fat or lipids

Question 8

Formation of Biologic Emboli

Answer 8

• Inadequate anticoagulation

* Contact with foreign surface

Question 9

Areas at risk for Formation of Biologic Emboli

Answer 9

• Low flow areas
• Stagnant areas
• Turbulence
• Cavitation
• Rough surfaces

Question 10

Areas of the circuit at risk for Formation of Biologic Emboli

Answer 10

• Connectors
• Oxygenators
• Arterial line filters
• Cardiotomy (venous) reservoir

Question 11

Greatest period of risk for Embolic Events

Answer 11

• Insertion arterial cannula
• Initiation of bypass
• Cross-clamp application / removal
  * Manipulation of aorta

Question 12

Organ at greatest risk for Embolic Events

Answer 12

BRAIN

Question 13

Opportunity for Embolic Events

Answer 13

• Patient anatomy plays an important role in outcome

* 15 – 20% of population are born with incomplete Circle of Willis

Question 14

How to Prevent Biologic Emboli

Answer 14

• Use transfusion filters
  * Emboli in stored blood increases with time
• Adequate anticoagulation
• Minimize surface area of circuit
• Use leukocyte-depleting filters
• Minimize complement and immune activation
• Minimize platelet and neutrophil activation

Question 15

How to Prevent Foreign Material Emboli

Answer 15

• Choose appropriate circuit components
• Circulate crystalloid solution through entire circuit
• Use prebypass filters
• Use medical grade tubing
• Use venous and cardiotomy filters

Question 16

How to Prevent Gaseous Emboli

Answer 16

• Check all equipment for proper operation
• Ensure all tubing and component connections are secure
• Flush circuit with CO2 prior to priming
• Careful priming of arterial filter
  * Retrograde prime
• 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 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
• Use of LV and PA vents
• Flood field with CO2
• Lung expansion to clear pulmonary veins of air
• Trendelenburg position when take cross clamp off
• Single clamp technique
• Alternative cannulation site if calcified aorta
• Use of TEE for arterial cannula placement
• Proper use of suction
• Use TEE for de-airing

Question 17

Type of aortic cross-clamp to use to decrease gaseous emboli

Answer 17

• Bahnson is best

- Fogarty

Question 18

Safety Devices

Answer 18

• Low level alarm
• Air bubble detector
• Arterial line filter
• Cardiotomy filter
• One-way valve in 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 19

Treatment of Massive Air Emboli

Answer 19

• Retrograde cerebral perfusion with induced hypothermia
• Hyperbaric chambers
  * Most effective
  * Limited access
• Have a protocol in place

Question 20

Take Home Message

Answer 20

•Preventing embolic events remains our best hope for improving neurologic outcomes following cardiac surgery