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 bubblesAir, 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 aggregatesThrombus, platelet aggregates, fat
Inorganic debrisFragment 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 protocolsMembrane 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 CABGIncreased 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%
30-59 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 al10 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
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
CO2 flooding of the op siteHigh solubility compared to room airDisadvantage ; hypercarbia and respiratory acidosisCO2 flooding only during the period of de-airing of
the heart
CO2 potent cerebral vasodilatorHypocapnia (PaCO2 30-32mmHg) ; reduce cerebral
blood flow and embolizationNo significant difference btw hypocarbic gr and
normocarbic grPotential 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 400-450mL/minReduction in the number of bubbles detected
in the range 11-40um in MCAGreater 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, prebypasschecklists
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