Embolic problems in Cardiac Surgery - CPB view point

1. Embolic problems in Cardiac Surgery- CPB view point 인제대 일산 백병원 장우익

2. Embolic problems during cardiopulmonary bypass • Systemic embolism affecting the brain • Both from CPB and underlying cardiovascular disease of the patients • Central nervous dysfunction • Major stroke - > macroembolism • Neuropsychologic problems -> microembolism

3. Interventions to reduce embolism • Surgical technique • Avoidance of major embolism of air, intracardiac thrombus, and calcific debris from diseased heart valves. • Avoidance of atheroembolism from the ascending aorta • CPB • Membrane oxygenators better than bubble oxygenators • Arterial line filter • Hemocompatible circuits • The most important embolic hazard of cardiac surgery is atheroembolism from manipulation of the ascending aorta

4. Macroemboli & Microemboli • Macroemboli ; occluding flow >200um artery -> single macroembolus might result hemiplegia • Microemboli ; smaller arteries, arterioles, and capillaries. Single microembolus, no clinical effect. Numerous emboli can result diffuse pattern of CNS injury • Except perfusion accidents, macroemboli are unlikely to rise from the extracorporeal circuits, but rather from heart and aorta

5. Type of emboli and tissue effects • Gas bubbles • Air, anesthetic gas(esp, nitrous oxide) • Dynamic equilibrium with the same gas dissolved in the plasma • Grow or shrink, dependent on temperature. • Small bubbles collapse when less than 10um • Biologic aggregates • Thrombus, platelet aggregates, fat • Inorganic debris • Fragment of polyvinyl chloride tubing, silicone antifoam, reduced currently.

6. Mechanism of microbubble tissue damage • Mechanical – compression against vessel wall, gap formation, fluid leakage, muscle hypertrophy • Inflammatory – neutrophil sequestration around bubble, increased permeability, radical species production, clot deposition • Complement – increased levels of C3a and C5a triggering PMNs, histamine release, prostaglandins, leukotriene synthesis • Clotting activation – platelet aggregation, thrombin production, thrombus generation

7. Entrapment of air into the arterial circulation • Events at the bypass machine • Not properly de-aired prior to bypass • Inattention to the reservoir level • Ruptured arterial pump-head tubing • Arterial line separation • Unnoticed rotation of the arterial pump head • Runaway pump head • Reversal of pump-head rotation • Reversal of tubing connected to the ventricular vent • Inadvertent detachment of oxygenator during CPB • Air transmitted through the membrane oxygenator by an occluded scavenger line • Clotted oxygenator • Pressurized cardiotomy reservoir

8. Entrapment of air into the arterial circulation • Events on the operative field • Unexpected resumption of heartbeat • Opening of beating heart • Aortic root air during cardioplegic solution administration • Aortic root air accumulation secondary to suction for returning retrograde cardioplegic solution • Inadequate de-airing after cardiotomy • High flow suction deep in pulmonary artery • Use of an intraaortic blood pump while aorta is open • Rupture of pulsatile assist device • Difficult insertion of a vent line

9. Perfusion safety survey - trend

10. Increase in the safety of pefusion • Increased use of safety devices • Arterial line filter, air bubble detectors, activated clotting time devices, one-way vent valves • Blood level sensors • One-way vent valves • Prebypass checklists, written protocols • Membrane oxygenators – downstream from the systemic pump, another device to trap/delay passage of air emboli • Centrifugal pump – added safety, deprime and prevent transmission of massive air embolism • Backflow from aorta, recommended use of a one-way flow valve in the arterial line

11. Adverse neurologic outcomes • Vary widely, due to multiple other factors, such as cerebral blood flow, systemic inflammation, patient co-morbidities • Cognitive decline, such as memory deterioration ; 60% one week, 25-30% from 2 months to one year postop.

12. Relationship btw microembolism and adverse neurologic outcomes • Higher incidence of poor neurologic functions. • Pugsley et al • Compared 50 pts bubble oxygenators with and without arterial filter • TCD monitor • More microemboli, more neuropsychologic deficts at 8days and 8weeks in unfiltered group

13. Microembolism and neurocognitive functions • Comparisons between OPCAG and on-pump CABG • Slight tendency toward decreased performance in neurocognitive tests in the on-pump group. Decreased as the time after surgery increased. • Comparisons between valve and CABG • Increased rate of emboli in valve surgery • But no significant difference in neurocognitive test scores

14. Microembolism and neurocognitive functions • Barbut et al 1997 • 82 pt CABG, TCD in MCA • With stroke (4 pts) 449 emboli • Without stroke (78 pts) 169 emboli • Increased emboli results increased hospital stay

15. Microembolism and neurocognitive functions • Clark et al • 117 CABG pt • >60 emboli rate of neurologic dysfunction 35% • 30-59 emboli 4.2% • <30 emboli 2.4%

16. Detection and quantification of microembolism -ultrasound • Doppler mode – transcranial doppler • Limitations • Counts ; signals depends on software programming • Unclear whether increase in signal amplitude reflects increase in number of size of emboli • Quantification error ; attenuation of the signal by blood component on the surface, scattering of signals from clusters of bubbles, shielding of bubbles by others

17. Microemboli detection • Arterial filter is not 100% effective in blocking microemboli (even larger emboli) • Riley et al • 10 adult arterial line filter • Small pore size filter generally are more effective • 60-94% efficient in the removal of emboli in the 20-25 um range

18. Perfusionist interventions • Borger et al • 34 pts • 75% of all emboli detected during perfusionist interventions (drug injection and blood sampling) • Emboli count more higher during perfusion intervention (6.9/min) than during surgical intervention(1.5/min) or during baseline(0.4/min)

19. Perfusionist interventions • Rodriquez et al • Emboli detected in MCA • 534 perfusionist interventions in 90 pts • Blood sampling and bolus injection higher than infusion • Repetitive purging of the syringe increase counts • Reservoir volume less than 800mL increased counts during blood sampling

20. Gaseous microemboli • Perfusion intervention ; during drug injection into the venous reservoir. • Air in the syringe, source of microemboli • Venous line air ; traversed membrane oxygenator and arterial line filter, possibly d/t bubble deformation or coalescence within or after the filter.

21. Vacuum assisted venous drainage • Augment drainage of venous blood • Smaller venous cannulae • Favor formation of gaseous microemboli • > -40 mmHg and high blood flow(6 L/min) ; increased GME

22. CO2 • CO2 flooding of the op site • High solubility compared to room air • Disadvantage ; hypercarbia and respiratory acidosis • CO2 flooding only during the period of de-airing of the heart • CO2 potent cerebral vasodilator • Hypocapnia (PaCO2 30-32mmHg) ; reduce cerebral blood flow and embolization • No significant difference btw hypocarbic gr and normocarbic gr • Potential disadvantage of cerebral hypoperfusion

23. Steep trendelenburg position • Rationale ; buoyancy effects will cause bubbles to rise and minimize cerebral embolization • Study ; did not decrease the cerebral embolic load • GME in flowing blood ejected from the heart respond more as an emulsion not subject to normal buoyancy effects as would be larger bubbles

24. Dynamic bubble trap • Rotating stream that forced GME to the center of the flow -> passively vented out to the reservoir by a small tube located midstream and near the exit of the bubble trap. • Volume diverted 400-450mL/min • Reduction in the number of bubbles detected in the range 11-40um in MCA • Greater efficiency of removal by the bubble trap for the larger-sized GME ( >96% for bubbles >31um)

25. Dynamic bubble trap

26. Oxygenators – capability of trapping air • Oxygenator design that provided for rapid blood contact with the membrane material, increased bubble/membrane contact time, avoidance of high blood flow velocities and low pressure drop, and membrane bundle geometry all favored entrapment of GME • Capability of CPB circuits to remove entrained venous air. • Five type oxygenators • Air detected after arterial filter in all • Statistical different results among different manufactures • Contributing factors ; Residence time for blood and bubbles within the membrane oxygenator, pressure drop, turbulence in the flowing blood • Avoidance of venous air whenever it is observed.

27. Cannula type or excessive blood flow velocities • ? Increased number of microemboli • High blood velocity could contribute to particulate release fron the aortic wall • Theoretically possible for GME to be produced by high blood flow velocities or abrupt pressure differences at cannula tips • Banaroia et al ; • 32 elective CABG pt • No correlation between blood velocities or type of cannula and the presence of TCD-detected emboli • Conventional cannula under conventional CPB, systemic flow was not important.

28. Newer circuits • Minimizing prime volumes • Reducing reservoir volumes -> lessen perfusionist reaction time in the events • Without venous reservoir • CPB tubing smaller and shorter ->increased blood flow velocities thru the circuit. • Blood transit time is reduced -> decreased opportunity for GME to be removed prior to its return to the patients

29. Deairing of the venous drainage-reduction of arterial microbubbles • Deairing ; double clamp and saline filling • Connecting venous line without deairing of the venous line ; incorporation of 15cc air into the circuit • Entrapped air in the venous line is microfragmented while passing through the ECC with subsequent microbubble formation • Microbubbles detected after arterial filter ; once saturated they release captured gas bubbles.

30. Deairing of the venous drainage-reduction of arterial microbubbles

31. Gross air bubbles - Massive air embolism • Accident that can occur during cardiac surgery • Almost eliminated • 1/2500 in 1970s, 1/30000 in 1990s • Fatal / Permanent neurologic defect • Air bubble detectors, reservoir blood level sensors, arterial line filter, prebypass checklists

32. Cause • Sudden reduction in the blood level in the venous reservoir that is not noticed by the perfusionist • Inadvertent pressurization of the reservoir. • Air from the cardiac chamber • Runaway pump head • Inversion of left-sided heart vent • Reversal of pump head • Inadvertent detachment of oxygenator during bypass • Cardiotomy suction wedged deep into the pulmonary artery

33. Treatment • Stop the circulation • Steep trendelenburg position • De-air the entire pump line • Retrograde SVC perfusion • Hypothermia • Barbiturate and corticosteroid • Hyperbaric oxygen therapy

34. Conclusion Embolic problems during cardiopulmonary bypass • Brain most susceptible. • Cause of stroke is mostly from underlying disease. • Especially from atherosclerosis of the aorta. • Current CPB circuits itself – low embolic risk • Microembolism • Clinical effect ; difficult to notice but has potential risk • Efforts to reduce it!! • Gross air – rare incidence but fatal • Prevention !!! • Prebypass checklist, education, drill • Rapid reaction if occurs