인제대 일산 백병원 장우익

 Systemic embolism affecting the brain  Both from CPB and underlying cardiovascular disease of the patients  Central nervous dysfunction  Major stroke - > macroembolism  Neuropsychologic problems -> microembolism

 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

 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

 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.

 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

 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

 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

 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

 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.

 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

 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

 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

 Clark et al  117 CABG pt  >60 emboli rate of neurologic dysfunction 35%  emboli 4.2%  <30 emboli 2.4%

 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

 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 um range

 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)

 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

 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.

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

 CO 2 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  CO 2 potent cerebral vasodilator  Hypocapnia (PaCO mmHg) ; reduce cerebral blood flow and embolization  No significant difference btw hypocarbic gr and normocarbic gr  Potential disadvantage of cerebral hypoperfusion

 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

 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 mL/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)

 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.

 ? 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.

 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

 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.

 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

 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

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

 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