Pediatric Perfusion - PowerPoint Presentation

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 -

ForaneSlide67
Slide68

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 reservoirSlide76
Slide77

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?