pediatric perfusion gerald mikesell, ccp childrens national medical center washington dc
TRANSCRIPT
Pediatric Perfusion
Gerald Mikesell, CCPChildrens 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 Remove unwanted byproducts of
metabolism Minimize the deleterious effects of
bypass
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 medications
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.
Cardiopulmonary BypassGeneralized inflammatory reaction
Capillary Leak Cardiac dysfunction Organ dysfunction/MSOF Mortality
CPB Deleterious Effects Coagulopathy
Systemic heparinization Hemodilution of factors Platelet dysfunction/ consumption Coagulation factor consumption
Cellular destruction/Hemolysis Mechanical stress
Inflammatory Activation Mechanical stress Non-endothelial exposure Complement activation Cytokine and leukocyte activation White cell activation
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 repair
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, hemodilution
Venous Saturation Measurement Though looked to as a standard of
perfusion adequacy, there are limitations Cooling causes left shift of oxyhemoglobin
dissociation curve Cooling causes increase of pH
Alkaline blood also causes left shift of oxyhemoglobin curve
Fetal Hemoglobin in neonates Left shift of curve
Lower levels of 2,3DPG in bank blood also cause left shift
Therefore, 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 demand
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 return
Collaterals to pulmonary veins to LA across unrepaired ASD,VSD to venous cannula
Differental return flow from SVC vs IVC Warm 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 fine
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:
TemperaturepHHematocritPerfusion flow
Temperature
Advantage: Reduce Metabolic Rate
Tissue preservation Myocardial preservation Allows flow variation to improve surgical
access Flexibility in cannulation
Decreased inflammatory response to CPB
Decreases Complement activation and release of vaso-active substance
Decreases white cell activation
Temperature
Disadvantages: Prolongs bypass Increases probability of post-operative
bleeding Possible prolonged post-operative
recovery Especially in adults
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.
Techniques of Hypothermia
Currently, two surgical techniques commonly used in congenital heart surgery, namely,
Deep hypothermic circulatory arrest (DHCA)
Hypothermic low-flow bypass (HLFB)
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.
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.
Deep Hypothermic Circulatory Arrest
Late 1980’s study out of Boston Childrens looking at DHCA vs low flow in arterial switch patients Both groups with deep hypothermia and
hematocrit of 20% One group had circulatory arrest, the other
group a low flow of 50 mL/kg/min Patients have now been followed for 20+ years
CA 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.
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.
Effect of pH
pH and pCO2 have strong systemic and cerebral vasodilatory effects
Effects are opposite with pulmonary circulation Shift in pH or pCO2 can cause a marked
shift in blood flow between pulmonary and systemic beds
A-P collaterals or systemic to pulmonary shunts (B-T shunt for example) need to be considered
Effect of pH
Perfusionist important to acid-base control during CPB Flow rate Dilution Hypothermia
As temperature drops, pH of H2O increases
Effect of pH
Alpha Stat vs pH Stat: First studies in the 1980s Alpha Stat
Maintains optimal intracellular enzyme activity
Maintains cerebral auto-regulation and the coupling of flow and metabolism at low temperatures
In adults, showed improved cognitive outcome
Possibly related to reduced number of micro-emboli
pH Stat: Loss of cerebral auto-regulation as
temperature drops Cerebral flow is pressure dependent, could
cause “luxuriant” flow with the potential for increased micro-emboli
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 impact
With alpha stat patients, there were 19 cases of choreoathetosis in 4 years/ With pH stat, there were none
In lab studies with piglets, found that cerebral micro-circulation was better in pH stat piglets vs alpha stat
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 arrest
pH stat: Decreased post-op acidosis (p=0.02) pH stat: Decreased post-op hypotension
(p=0.05)
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 requirement
pH stat: A trend to better developmental scores at 1 yr of age
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 temperatureVery important in early cooling period
when blood is cold but brain still warm
Improved developmental outcome
pO2 and Bypass Historically feeling that hyperoxia was
responsible for microemboli associated mobidity post CPB A problem with bubble oxygenators, especially
without arterial filters Two studies in piglets at Boston Childrens
in 1999 looked at this issue Compared bubble oxygenator vs membrane
oxygenator with arterial filter Compared normoxia with hyperoxia and DHCA Compared free radical production Compared histological injury of normoxic vs
hyperoxic
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 hyperoxia
Reasoned that nitrogen was less soluble in the blood than oxygen as the temperature dropped
Looking 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 C
An interesting observation was that temperture gradient both cooling and warming had no effect on microemboi
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/m²
Potential for hypoxic injury
Bypass and Optimal Flow
Flow considerations for bypass: What is the metabloic demand for different temperatures Normal thermia
Mild hypothermia: temperature greater than 30ºC
Moderate hypothermia: temperature 25-28º C
Deep hypothermia: temperature less than 18ºC
CPB Flows
• 2.4 -3.0 l/m2 at 37o
• 1.6 l/ m2 at 28o
• 1.2 – 1.6 l/m2 at 25o
• 1.0 – 1.6 l/m2 at 20o
• 0.5 – 1.0 l/m2 at 15o
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 drops Causes a drop in O2 delivery
blood volumeprime volume
Adult
blood volumeprime volume
Pediatric
blood volumeprime volume
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%
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 output
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
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 piglets Lower hematocrit, more alkaline pH and
longer circulatory arrest were predictive of neurological damage
Hematocrit: 30% showed distinct advantage to neuroprotection vs 20%
pH stat was more neuro-protective with lower histological injury vs alpha stat
A temperature of 15ºC was more neuro-protective than a temperature of 25ºC
Study looked at circulatory arrest times of 60, 80 and 100 min
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% hematocrit
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 Infants 147 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 groups
Baley 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 Index
Showed that a hemodilution practice thought to be safe was associated with adverse perioperative and developmental outcomes in infants
Hemodilution and Bypass
Hemoconcentration During bypass
Conventional
Modified Ultrafiltration
MUF
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 bypass We like to come off with hct of 30-35 or even 35-40
with single ventricle repairs
Modified Ultra-Filtration (MUF) Hemoconcentration of patients circulating
blood volume along with remaining volume in circuit
Improvement with CO and blood pressure Disadvantages are the need to maintain
heparinization and cannulation for extended time and…
Complexity of circuit and risk of air around arterial cannula
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
hypothermia the 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)
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
extracellular intracellular
blood cardioplegia. These solutions are administered most
frequently under hypothermic conditions.
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, proteins
Cardioplegia Delivery
Antegrade
Retrograde
Directly to coronary
Cases CNMCCardioplegia Delivery
2-3o CConducer Recirculation System
Plegisol (Oxygenated)First dose 20 ml/kgFollowing doses10 ml/kgAbove 50 kg 1000 mlWith 500 ml second dose
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/LLow K: 10 mEq/L
First dose is high K then switch to low K for redosing
Hemodilution and Prime
1985 study by Haneda et al, compared crystalloid prime vs blood and plasma prime in pediatrics Crystalloid prime patients had a +63 mL/kg
fluid balance vs + 16 mL/kg with blood/plasma
Blood/plasma prime group had a lower mortality and 50% reduction in ICU time compared with the crystalloid group
There is a general consensus that prime for children should not include lactate or dextrose. Hyperglycemia is associated with a worse neurological outcome.
Prime used at Childrens National Medical Center
Circuit primed with Plasma-lyte A, excess drained off
Packed Cells between 3-7 da old Try to maximize 2,3-DPG and have lower K+ Units are leuco-depleted in the blood bank Primary unit of RBC is divided, half for
perfusion for prime and half for anesthesia to use post bypass so donor exposure can be reduced
FFP: Same donor as RBC when possible We 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% Albumin
CNMC Prime
Cefazolin: 25 mg/kg, (1 gm maximum dose)
Lasix: 0.25 mg/kg Feel 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 properties Add to prime, some also give a second dose on
release of cross clamp Heparin Sodium Bicarbonate 84% Solumedrol: 30 mg/kg
Patients ˂ 1 week and DHCA patients
CNMC Bypass
Magnesium Sulfate: 50 mg/kg (1 gm maximum) Given immediately after cross clamp release Has significantly reduced incidence of
junctional ectopic tachycardia ( JET) Calcium Gluconate: 500 mg-1 gm
Given 5 minutes after release of cross clamp
Current PrimesCNMC
250-300 Neonates
300-400Infants
400-600 Toddlers
Blood product use for CPB
Hemodilution from pump prime
Volume expansion Treatment of iatrogenic
or concomitant coagulopathies
Surgical blood loss
Descending order of
incidence
PRBC Transfusion
Hematocrit On CPB < 27% Post CPB < 27% This is patient dependent: size and
lesion Oxygenation
SVO2 < 65% at maximal flow on bypass Hemodynamics
Acute blood loss
FFP Transfusion
Coagulopathies Obvious non surgical bleeding
Long pump runs Hemodilution Preexisting conditions
Heparin resistance Inadequate ACT despite 2X normal
Heparin Dose “Fast” easy source of ATIII
Platelet Transfusion Triggers
Coagulopathies Obvious non surgical bleeding
Long pump runs Hemodilution Preexisting conditions DHCA patients
Low platelet count < 70,000
How do we achieve low prime circuits
Get mind set Look at circuit as separate
components Be willing to use different
venders Must modify perfusion
techniques Must be adaptable Constantly update equipment &
techniques
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 bypass
Tubing 2/32" I.D. 0.6ml/ft.
3/32" I.D. 1.8ml/ft.
1/8" I.D. 3.5ml/revolution(2.5 ml/ft.)
5/32" I.D. 5ml/revolution(3.7 ml/ft.)
3/16" I.D. 7ml/revolution(5 ml/ft.)
1/4" I.D. 13ml/revolution(9.65 ml/ft.)
5/16" I.D. 18ml/revolution(13.5 ml/ft.)
3/8" I.D. 27ml/revolution(21.71 ml/ft.)
7/16" I.D. 38ml/revolution(28.5 ml/ft.)
1/2" I.D. 45ml/revolution(38.61 ml/ft.)
5/8" I.D. 65ml/revolution(55.77 ml/ft.)
Arterial Lines
3/16” 1200 ml/min
1/4” 2500 ml/min
3/8” 7000 ml/min
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/min
A-V LOOPSCNMC
Flows 0-1 L/min 3/16 x 1/4
Flows 1 – 1.5 L/min 1/4 x 1/4
Flows 1.5 – 2.5 L/min 1/4 x 3/8
Flows 2.5 – 4.0 L/min 3/8 x 3/8
Flows > 4.0 L/min 3/8 x 1/2
Oxygenators
New Oxygenators specific for infants and pediatrics Reduced volume Arterial flilters incorporated in design
Reduces prime of circuit (??) Improved flow dynamics
Reduced pressure drop Improved reservoir design with improved
drainage and volume handling VAVD capable
Most common
Maquet
Terumo
Medtronic
Sorin
Medos
VENOUS RESERVOIR
Two types of venous reservoirs hardshell venous
reservoir “open” system
collapsible bag venous reservoir
“closed” system
VENOUS RESERVOIRSHARDSHELL VS. BAG
Arterial Blood Gas Control
Blender and Gas Flowmeter Carbon Dioxide Anesthesia - Forane
Arterial Blood Gas ControlAnesthesia: Forane
CDI500
On-line arterial blood gas, hemoglobin/hematocrit, K+ and venous saturation
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 cold
Ease of insertion
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 opened
vena caval cannulation one cannula through the RA appendage into
the IVC a second cannula through the RA wall into
the SVC used when the heart IS going to be opened
a tie encircling the IVC and SVC is secured
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 procedure
Cannulation 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 defect
Right angle vs straight Develop flow tables for cannulas ( and for each
surgeon)
Cannulas
Venous Drain blood
from the body 2 stage Bicaval Femoral Arterial
Return blood to the body
Aortic Femoral
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 microns open system: cardiotomy integral with
venous reservoir closed system: cardiotomy is separate
from venous reservoir blood, priming fluids, blood components
VENT (or sump) SYSTEM Purpose = evacuate LV blood
sources of LV blood right atrium escaping the venous
cannula bronchial venous blood non-coronary collateral blood
Usually ¼” I.D. tubing Usually requires an occluded
roller pump requires a negative pressure
relief valve This blood directed to the
cardiotomy reservoir
SAFETY SYSTEMS
Reservoir level detection Air bubble detection
(arterial line) Arterial line pressure
Safety Systems
Flow Meter: Distal to all shunts to give more accurate flow delivery to the patient
Safety Systems
Level and air sensors
Safety Systems
Arterial line pressure
Cardioplegia delivery pressure
Pressure Monitoring
Cardiopulmonary bypass…
Do you ever wonder….How does it affect your patient?