Gerald Mikesell CCP Childrens National Medical Center Washington DC Fundamental Goals of CPB To facilitate a surgical intervention Provide a motionless field Provide a bloodless field Supply adequate substrate for the metabolism of all tissues ID: 553313
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Slide1
Pediatric Perfusion
Gerald
Mikesell
, CCP
Childrens
National Medical Center
Washington DC Slide2
Fundamental Goals of CPB
To facilitate a surgical intervention
Provide a motionless field
Provide a bloodless field
Supply adequate substrate for the metabolism of all tissues
Remove unwanted byproducts of metabolism
Minimize the deleterious effects of bypassSlide3
The Cardiovascular Perfusionist
The perfusionist controls the patients blood flow, blood pressure, and gas exchange as well as monitoring and delivering anticoagulation and protective heart medicationsSlide4
Differences Between Adult and
Pediatric
Cardiopulmonary Bypass
Major differences exist between adult and pediatric cardiopulmonary bypass (CPB), stemming from anatomic, metabolic, and physiologic differences in these 2 groups of patients. Slide5
Cardiopulmonary Bypass
Generalized inflammatory reaction
Capillary Leak
Cardiac dysfunction
Organ dysfunction/MSOF
MortalitySlide6
CPB Deleterious Effects
Coagulopathy
Systemic
heparinization
Hemodilution
of factorsPlatelet dysfunction/ consumption Coagulation factor consumptionCellular destruction/HemolysisMechanical stressInflammatory Activation
Mechanical stressNon-endothelial exposureComplement activationCytokine and leukocyte activation
White cell activationSlide7
Effects of CPB
All the discussed effects of bypass are related to exposure to our circuits and the mechanical devices used to allow bypass to
procede
Total bypass time continually emerges as a risk factor for morbidity and mortality
Optimal outcome is benefited by surgeons operating accurately and rapidly, using efficient sequencing of repairSlide8
Bypass Management
No perfect means to measure level of support
Normal monitoring: EKG, NIRS, Saturations and Pressures are designed for non-bypass monitoring
With bypass, loss of normal physiologic homeostatic control, loss of
pulsatility, change of oxygen supply, hemodilutionSlide9
Venous Saturation Measurement
Though looked to as a standard of perfusion adequacy, there are limitations
Cooling causes left shift of
oxyhemoglobin
dissociation curveCooling causes increase of pH
Alkaline blood also causes left shift of oxyhemoglobin curveFetal Hemoglobin in neonates Left shift of curve Lower levels of 2,3DPG in bank blood also cause left shiftTherefore, as temperature of blood drops, venous saturation will rise but brain and tissues are still warm and not receiving the O2 needed to meet metabolic demandSlide10
Venous Saturation Measurements
Left Heart Return and collateral steal
Dangerous to assume all flow pumped into patient is going where planned.
Colleteral
development with some lesions can steal up to 50% of flow and return directly to venous returnCollaterals to pulmonary veins to LA across unrepaired ASD,VSD to venous cannula
Differental return flow from SVC vs IVCWarm brain uses lots of O2 and SVC with low sat but Systemic blood colder, IVC with higher sat, blood mixes in venous line and sat monitor reading appears fineSlide11
Bypass Management
We do things to exert control of the patient on CPB and work to maintain a margin of safety for the patient even if all parameters aren’t perfectly controlled.
The important decisions that we can control:
Temperature
pH
Hematocrit Perfusion flow Slide12
Temperature
Advantage:
Reduce Metabolic Rate
Tissue preservation
Myocardial preservationAllows flow variation to improve surgical access
Flexibility in cannulationDecreased inflammatory response to CPBDecreases Complement activation and release of vaso-active substanceDecreases white cell activationSlide13
Temperature
Disadvantages:
Prolongs bypass
Increases probability of post-operative bleeding
Possible prolonged post-operative recoveryEspecially in adultsSlide14
Use of Hypothermia
Effect on Central Nervous System
The effect of hypothermia on the nervous system is multifactorial. In addition to decreasing the metabolic rate, hypothermia has been demonstrated to decrease the release of glutamate, which is involved in CNS injury during CPB.
A negative effect of hypothermia on brain function is the loss of autoregulation at extreme temperatures, which makes the blood flow highly dependent on extracorporal perfusion. Slide15
Techniques of Hypothermia
Currently, two surgical techniques commonly used in congenital heart surgery, namely,
Deep hypothermic circulatory arrest (DHCA)
Hypothermic low-flow bypass (HLFB) Slide16
Deep Hypothermic Circulatory Arrest
DHCA provides excellent surgical exposure by eliminating the need for multiple cannulas within the surgical field. Normally use arterial cannula and a single venous cannula in the right atrium.
Surgical technique
Initiate the cooling phase prior to institution of CPB by simple cooling of the operating room environment and begin surface cooling the patient After systemic heparinization and cannulation, initiate CPB. Monitor body temperature via esophageal, tympanic, and rectal routes.Have also seen less edema.Slide17
Deep Hypothermic Circulatory Arrest
Disadvantages:
Time constraints on the surgical team. Must be highly organized with the repair and efficient with technique. Precise and accurate repairs must be completed in limited time.Slide18
Deep Hypothermic Circulatory Arrest
Late 1980’s study out of Boston
Childrens
looking at DHCA
vs
low flow in arterial switch patientsBoth groups with deep hypothermia and hematocrit of 20%One group had circulatory arrest, the other group a low flow of 50 mL/kg/minPatients have now been followed for 20+ yearsCA patients had lower verbal and development scores until age 4. Caught up with developmental scores by age 4 and by age 8 caught up with verbal.Both groups were below mean controls.If longer periods of arrest are anticipated, may be advantageous to apply ancillary procedures such as intermittent reperfusion.Slide19
Deep Hypothermic Circulatory Arrest
Mechanical Problems
Arterial cannula misplacement can occur. If the cannula inadvertently slips beyond the takeoff of the right innominate artery, preferential perfusion to the left side of the brain can be observed.
Presence of any anomalous systemic-to-pulmonary shunts can lead to shunting of blood away from the systemic circulation, through the pulmonary circuit, and then through the venous cannula returning to the CPB circuit.
Thus, the systemic perfusion is shunted away from the body in a futile circuit back to the CPB circuit. Anatomic lesions where such shunting can occur include an unrecognized patent
ductus arteriosus and large aortopulmonary collaterals as found in pulmonary atresia. Slide20
Effect of pH
pH and pCO2 have strong systemic and cerebral
vasodilatory
effects
Effects are opposite with pulmonary circulationShift in pH or pCO2 can cause a marked shift in blood flow between pulmonary and systemic bedsA-P collaterals or systemic to pulmonary shunts (B-T shunt for example) need to be consideredSlide21
Effect of pH
Perfusionist important to acid-base control during CPB
Flow rate
Dilution
HypothermiaAs temperature drops, pH of H2O increasesSlide22
Effect of pH
Alpha Stat
vs
pH Stat: First studies in the 1980s
Alpha StatMaintains optimal intracellular enzyme activity
Maintains cerebral auto-regulation and the coupling of flow and metabolism at low temperaturesIn adults, showed improved cognitive outcome Possibly related to reduced number of micro-embolipH Stat:Loss of cerebral auto-regulation as temperature dropsCerebral flow is pressure dependent, could cause “luxuriant” flow with the potential for increased micro-emboliSlide23
Effects of pH
Boston
Childrens
Hospital did multiple studies, both clinical and animal, in the late 1980’s
Alpha stat patients had worse developmental outcome during cooling than pH stat. There was strong correlation during cooling of pCO2 and developmental outcome
The circulatory attest time of 35-60 minutes had no impactWith alpha stat patients, there were 19 cases of choreoathetosis in 4 years/ With pH stat, there were noneIn lab studies with piglets, found that cerebral micro-circulation was better in pH stat piglets vs alpha statSlide24
Effect of pH
In 1990’s Boston
Childrens
completed two randomized clinical studies which both showed better outcomes with pH stat
pH stat had lower mortality (p=0.058)pH stat, with continuous EEG monitoring during surgery and 48 hours post bypass, show lower rate of post-op seizures
pH stat: First EEG activity returned faster after circulatory arrestpH stat: Decreased post-op acidosis (p=0.02)pH stat: Decreased post-op hypotension (p=0.05)Slide25
Effect of pH
Boston pH
vs
Alpha stat clinical studies (
Cont)
pH stat: Shorter mechanical ventilation time and ICU stay (p=0.01)pH stat: in d-TGA sub-group, higher cardiac index with lower inotrope requirementpH stat: A trend to better developmental scores at 1 yr of ageSlide26
Effect of pH
Boston study:
Conclusion was pH stat:
Suppresses cerebral metabolism and lengthens safe duration of DHCA for a given temperature and hematocrit
Improves oxygen availability by counteracting the oxy-hemoglobin curve’s leftward shift with dropping temperature
Very important in early cooling period when blood is cold but brain still warmImproved developmental outcomeSlide27
pO2 and Bypass
Historically feeling that
hyperoxia
was responsible for
microemboli associated mobidity
post CPBA problem with bubble oxygenators, especially without arterial filtersTwo studies in piglets at Boston Childrens in 1999 looked at this issueCompared bubble oxygenator vs membrane oxygenator with arterial filterCompared normoxia with hyperoxia and DHCACompared free radical productionCompared histological injury of normoxic vs hyperoxicSlide28
pO2 and Bypass
Study Results:
At cold temperatures there was increased
microemboli
with bubble oxygenator vs membrane oxygenator with filter
As temperature was dropping, there were more microemboli with normoxia vs hyperoxiaReasoned that nitrogen was less soluble in the blood than oxygen as the temperature droppedLooking at histological injury, there was significantly more injury in the brains of normoxic animals vs hyperoxic animals after 120 minutes of arrest at 15 deg CAn interesting observation was that temperture gradient both cooling and warming had no effect on microemboiSlide29
Bypass and Optimal Flow
The standard bypass flow target has always been 2.4 L/min/m²
Must weigh all the options:
Normal may be as much as 3.5-4 L/min/m²
Hemodilution can add up to 3-4 times greater flow demand to meet O2 demand
Add aorto-pulmonary collaterals with 50% of pump flow returning directly to the pump. Leaves an effective flow of 1.2 L/min/m²Potential for hypoxic injurySlide30
Bypass and Optimal Flow
Flow considerations for bypass: What is the
metabloic
demand for different temperatures
Normal thermia
Mild hypothermia: temperature greater than 30ºCModerate hypothermia: temperature 25-28º CDeep hypothermia: temperature less than 18ºCSlide31
CPB Flows
2.4 -3.0 l/m
2
at 37
o
1.6 l/ m2 at 28
o1.2 – 1.6 l/m2 at 25
o1.0 – 1.6 l/m2 at 20
o
0.5 – 1.0 l/m
2
at 15
oSlide32
Hemodilution
Decreased concentration of cells & solids in the blood
RBC’s
, WBC’s, Platelets,
Plasma Proteins, Clotting factors, Lytes (
Ca,Mg)Is hemodilution bad?May allow better perfusion as temperature dropsCauses a drop in O2 deliverySlide33
Adult
Pediatric
Infant
Prime Volumes
30% of blood volume
23% of total volume
Hct 35%
27%
50% of blood volume
33% of total volume
Hct 35%
23%
176% of blood volume
63% of total volume
Hct 40%
14%Slide34
Hemodilution
On bypass and before cooling, O2 demand still high flow not compensated
Thought to be related to drop in perfusion pressure
Perfusion pressure change in direct proportion to change of viscosity with
hemodilution
If hemodilution not on bypass, body compensates by increasing cardiac outputSlide35
Hemodilution
vs
Cerebral Protection
1996 study by
Shinoka et al, in JTCVS. Working with piglets looked at 3 levels of hematocrit, 10,20 and 30%; went on bypass and cooled to 15ºC and arrested for 60 minutes.Low hematocrit piglets had worse neurological outcome, both physiologically and histologically.Lowest hematocrit piglets showed hypoxic stress during cooling and before arrest Slide36
Hemodilution
vs
Cerebral Protection
2001 Study by Sakamoto et al looked at the interaction of hematocrit (20 and 30%), pH (alpha stat
vs pH stat) and temperature on the neurological impact of pigletsLower hematocrit, more alkaline pH and longer circulatory arrest were predictive of neurological damageHematocrit: 30% showed distinct advantage to neuroprotection vs 20%pH stat was more neuro-protective with lower histological injury vs alpha statA temperature of 15ºC was more neuro-protective than a temperature of 25ºCStudy looked at circulatory arrest times of 60, 80 and 100 minSlide37
Hemodilution
vs
Cerebral Protection
2001 a companion study by
Duebener et al looked at microcirculation (capillary blood flow) and at tissue oxygenation with hematocrits of 30% vs 10%.30% was associated with improved re-perfusion (functional capillary density) vs 10%There was no evidence of capillary plugging or white cell activation with the higher viscosity level of the 30% hematocritSlide38
Hemodilution
vs
Cerebral Protection
2002 Study by Jonas et al, JTCVS. The Influence of
Hemodilution on Outcome After Hypothermic CPB: Results of a Randomized Trial in Infants147 patients randomized to a hematocrit of 21 (74) or 27 (73)Hematocrit 21: post-operative serum lactate was higher, cardiac index was lower and had greater total body water at POD1. Blood product usage was the same for both groupsBaley Scales of Infant Development: at 1 year the high hematocrit group had higher Psycomotor Development Index (low hct group was 2 SD below normal populations) , there was no difference in Mental Development IndexShowed that a hemodilution practice thought to be safe was associated with adverse perioperative and developmental outcomes in infantsSlide39
Hemodilution
and Bypass
Hemoconcentration
During bypass
Conventional
Modified UltrafiltrationMUFSlide40
Hemodilution
and
Hemoconcentration
Conventional
Removes free water, dissolved ion and small molecules
Remove byproducts of bypass and excess volume, i.e. cardioplegia after delivery Maximize hematocrit before termination of bypassWe like to come off with hct of 30-35 or even 35-40 with single ventricle repairsModified Ultra-Filtration (MUF)Hemoconcentration of patients circulating blood volume along with remaining volume in circuitImprovement with CO and blood pressureDisadvantages are the need to maintain heparinization and cannulation for extended time and…Complexity of circuit and risk of air around arterial cannulaSlide41
Myocardial Protection Strategies
Myocardial Protection
The term "myocardial protection" refers to strategies and methodologies used either to attenuate or to prevent
postischemic myocardial dysfunction that occurs during and after heart surgery. Principles of Myocardial Protection The main principles of myocardial protection are the reduction of metabolic activity by hypothermiathe therapeutic arrest of the contractile apparatus and all electrical activity of the myocytes by administering cardioplegic solution (e.g. depolarizing of the membrane potential by high potassium crystalloid or blood cardioplegia) Slide42
CARDIOPLEGIC TECHNIQUES
Cardioplegic solutions contain a variety of chemical agents that are designed to
arrest the heart rapidly in diastole,
create a quiescent operating field, and
provide reliable protection against ischemia/reperfusion injury.
There are two types of cardioplegic solutions:crystalloid cardioplegia extracellularintracellularblood cardioplegia. These solutions are administered most frequently under hypothermic conditions. Slide43
CARDIOPLEGIA DELIVERY SYSTEM
Purpose = arrest and preservation
Two types of delivery
crystalloid cardioplegia: no blood added
blood cardioplegia: blood is mixed with crystalloid)proposed advantages: oxygen, buffers, proteinsSlide44
Cardioplegia
Delivery
Antegrade
Retrograde
Directly to coronarySlide45
Cases CNMC
Cardioplegia
Delivery
2-3
o
CConducer Recirculation SystemPlegisol (Oxygenated)First dose 20 ml/kgFollowing doses 10 ml/kgAbove 50 kg 1000 ml
With 500 ml second doseSlide46
Blood Cardioplegia at CNMC
Use a modified Plegisol recipe. Potassium is added with a high K and low K formulation. Cardioplegia is delivered 4:1 blood:crystalloid.
High K: 20 mEq/L
Low K: 10 mEq/L
First dose is high K then switch to low K for redosingSlide47
Hemodilution
and Prime
1985 study by
Haneda
et al, compared crystalloid prime vs blood and plasma prime in pediatricsCrystalloid prime patients had a +63 mL/kg fluid balance
vs + 16 mL/kg with blood/plasmaBlood/plasma prime group had a lower mortality and 50% reduction in ICU time compared with the crystalloid groupThere is a general consensus that prime for children should not include lactate or dextrose. Hyperglycemia is associated with a worse neurological outcome.Slide48
Prime used at
Childrens
National Medical Center
Circuit primed with Plasma-
lyte A, excess drained off
Packed Cells between 3-7 da oldTry to maximize 2,3-DPG and have lower K+Units are leuco-depleted in the blood bankPrimary unit of RBC is divided, half for perfusion for prime and half for anesthesia to use post bypass so donor exposure can be reducedFFP: Same donor as RBC when possibleWe use some of the unit in the prime, add some to the circuit while rewarming and any remaining goes to anesthesia post CPB. If using clear prime, will add 100-300 mL 25% AlbuminSlide49
CNMC Prime
Cefazolin
: 25 mg/kg, (1
gm
maximum dose)Lasix: 0.25 mg/kgFeel a loop diuretic is helpful to maintain renal function
Mannitol 25%: 0.5 gm/kg (12.5 gm maximum dose)Potent osmotic diuretic with free radical scavenger propertiesAdd to prime, some also give a second dose on release of cross clampHeparinSodium Bicarbonate 84%Solumedrol: 30 mg/kgPatients ˂ 1 week and DHCA patientsSlide50
CNMC Bypass
Magnesium Sulfate: 50 mg/kg (1
gm
maximum)
Given immediately after cross clamp releaseHas significantly reduced incidence of junctional
ectopic tachycardia ( JET)Calcium Gluconate: 500 mg-1 gmGiven 5 minutes after release of cross clampSlide51
Current Primes
CNMC
250-300 Neonates
300-400Infants
400-600 ToddlersSlide52
Blood product use for CPB
Hemodilution
from pump prime
Volume expansion
Treatment of iatrogenic or concomitant coagulopathiesSurgical blood loss
Descending order of incidenceSlide53
PRBC Transfusion
Hematocrit
On CPB < 27%
Post CPB < 27%
This is patient dependent: size and lesionOxygenation
SVO2 < 65% at maximal flow on bypassHemodynamicsAcute blood lossSlide54
FFP Transfusion
Coagulopathies
Obvious non surgical bleeding
Long pump runs
HemodilutionPreexisting conditions
Heparin resistanceInadequate ACT despite 2X normal Heparin Dose“Fast” easy source of ATIIISlide55
Platelet Transfusion Triggers
Coagulopathies
Obvious non surgical bleeding
Long pump runs
HemodilutionPreexisting conditions
DHCA patientsLow platelet count< 70,000Slide56
How do we achieve low
prime circuits
Get mind set
Look at circuit as separate components
Be willing to use different vendersMust modify perfusion techniquesMust be adaptable
Constantly update equipment & techniquesSlide57
Our goal with bypass is reduce the surface area of exposure of the patient’s blood to our circuits. We can accomplish this goal through our selection of circuit components and cannulae and the use of techniques such as bio-passive circuit coatings to attenuate the response of our patients to bypassSlide58
TubingSlide59
Arterial Lines
3/16”
1200 ml/min
1/4”
2500 ml/min
3/8”
7000 ml/minSlide60
Venous Lines
3/16”
600 ml/min
1/4”
1500 ml/min
5/16”
2200 ml/min
3/8”
4000 ml/min
1/2”
>7000 ml/minSlide61
A-V LOOPS
CNMC
Flows 0-1 L/min
3/16 x 1/4
Flows 1 – 1.5 L/min
1/4 x 1/4Flows 1.5 – 2.5 L/min1/4 x 3/8Flows 2.5 – 4.0 L/min3/8 x 3/8Flows > 4.0 L/min3/8 x 1/2Slide62
Oxygenators
New Oxygenators specific for infants and pediatrics
Reduced volume
Arterial
flilters
incorporated in designReduces prime of circuit (??)Improved flow dynamicsReduced pressure dropImproved reservoir design with improved drainage and volume handlingVAVD capableSlide63
Most common
Maquet
Terumo
Medtronic
Sorin
MedosSlide64
VENOUS RESERVOIR
Two types of venous reservoirs
hardshell venous reservoir
“open” system
collapsible bag venous reservoir“closed” systemSlide65
VENOUS RESERVOIRS
HARDSHELL VS. BAGSlide66
Arterial Blood Gas Control
Blender and Gas
Flowmeter
Carbon Dioxide
Anesthesia -
ForaneSlide67Slide68
Arterial Blood Gas Control
Anesthesia:
ForaneSlide69
CDI500
On-line arterial blood gas, hemoglobin/hematocrit, K+ and venous saturationSlide70
Cannula Selection
Arterial
Important component of the circuit as it’s a point of narrowing in the pressurized limb of the bypass circuit
A point of increased flow velocity and potential high sheer stress and increased hemolysis
Want largest cannula possible for expected flow but not large enough to obstruct vessel lumen preventing retrograde flow around the cannula
Other factors include: thin wall, tolerate temperature variations without kinking or stressing aorta when coldEase of insertionSlide71
VENOUS CANNULA
Two types of venous cannulation procedures
right atrial cannulation
single RA cannula: through the RA appendage; tip in body of the RA
cavo-atrial cannula (or two-stage cannula): through the RA appendage; tip in the IVC and “basket” in the body of the RA
used when the heart IS NOT going to be openedvena caval cannulationone cannula through the RA appendage into the IVCa second cannula through the RA wall into the SVCused when the heart IS going to be openeda tie encircling the IVC and SVC is securedSlide72
Cannula Selection
Venous
Essential for surgeon to have a
cannulation
plan based on the defect to allow for optimal venous return and perfusion of the entire body throughout the procedureCannulation must not interfere with appropriate sequencing of operative steps
A balance of a size large enough to meet flow demands and small enough to be accommodated with a particular defectRight angle vs straightDevelop flow tables for cannulas ( and for each surgeon)Slide73
Cannulas
Venous
Drain blood from the body
2 stage
BicavalFemoral
ArterialReturn blood to the bodyAorticFemoralSlide74
THE SUCTION SYSTEM
Purpose = evacuate shed blood
Usually ¼” I.D. tubing
Requires an occluded roller pump
This blood directed to the cardiotomy reservoir
filters any fluid to 19-35 micronsopen system: cardiotomy integral with venous reservoirclosed system: cardiotomy is separate from venous reservoirblood, priming fluids, blood componentsSlide75
VENT (or sump) SYSTEM
Purpose = evacuate LV blood
sources of LV blood
right atrium escaping the venous cannula
bronchial venous blood
non-coronary collateral bloodUsually ¼” I.D. tubingUsually requires an occluded roller pumprequires a negative pressure relief valveThis blood directed to the cardiotomy reservoirSlide76Slide77
SAFETY SYSTEMS
Reservoir level detection
Air bubble detection (arterial line)
Arterial line pressureSlide78
Safety Systems
Flow Meter: Distal to all shunts to give more accurate flow delivery to the patientSlide79
Safety Systems
Level and air sensorsSlide80
Safety Systems
Arterial line pressure
Cardioplegia delivery pressure
Pressure MonitoringSlide81
Cardiopulmonary bypass…
Do you ever wonder….How does it affect your patient?