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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