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367CHAPTER 35 Pediatric Cardiopulmonary Bypass to minimize patient hemodilution during CPB, ultimately reduc ing the likelihood of donor blood exposure The same adult cir cuit, with a prime volume of[.]

to minimize patient hemodilution during CPB, ultimately

reduc-ing the likelihood of donor blood exposure The same adult

cir-cuit, with a prime volume of about 1 L, would be approximately

500% of the circulating blood volume in a neonate This

discrep-ancy would seem outrageous considering current circuit options,

but the prime-to-blood volume ratio was even higher before

manufacturers began to release pediatric oxygenators in the

mid-1980s Since the oxygenator is one of the largest volume

compo-nents of the CPB circuit, any significant reduction in size would

result in large prime volume reductions A circuit miniaturization

movement began—the new clinical challenge in pediatric CPB

was to reduce both circuit prime volume and surface area The

goal of circuit prime and surface area reduction is to minimize

hemodilution and the deleterious effects of foreign surface blood

contact activation Strategies such as using smaller diameter and

shorter tubing lengths and incorporating neonatal and pediatric

CPB components have allowed clinicians to reach this goal At

Children’s Health Dallas, the perfusionists have made many

cir-cuit modifications to achieve a static prime volume of

approxi-mately 165 mL in our neonatal circuit This prime volume lowers

the circuit size to approximately 45% of the blood volume of a

3-kg patient (Fig 35.4)

Oxygenators

An oxygenator, the artificial lung of the CPB circuit, might be

considered the most important component of the circuit It is

responsible for oxygen (O2) and carbon dioxide (CO2) gas exchange,

as well as volatile anesthetic administration A heat exchanger, used

for cooling and warming the perfusate—and, hence, the patient—

is housed inside the oxygenator Certain newer models now

inte-grate the arterial filter, to reduce particulate matter, into the

oxy-genator A venous reservoir, which includes both venous line and

cardiotomy suction filters and various ports for drug and fluid

administration, is typically packaged with an oxygenator

Cur-rently, hollow fiber membrane oxygenators, which fully separate

the blood flow from gas flow by a thin polymer membrane, are

used during CPB A brief history of oxygenator development

re-veals much about some of the important engineering solutions

that have allowed for cardiac surgery to be performed more safely

in progressively smaller patients

The first oxygenators used in the early days of cardiac surgery

were hardware units that either used rotating discs or large mesh

screens These oxygenators worked by creating a large surface area

film of blood, either over rotating discs in a pool of venous blood

or trickling over large mesh screens and exposing the film of blood

to an oxygenated atmosphere.25 , 26 Though these units were suc-cessful at oxygenating blood, they required extremely large prim-ing volumes; were not disposable; were difficult to assemble, oper-ate, and clean; and lost significant efficiency during hemodilution

In addition to these disadvantages, these oxygenators were not commercially available to clinicians looking to operate beyond the University of Minnesota and Mayo Clinic

The University of Minnesota team dramatically changed this landscape in the late 1950s by releasing the simple, disposable, inexpensive, and commercially available DeWall-Lillehei bubble oxygenator.27 Though the safety of actively adding bubbles to the blood was debated, the commercial availability of this device con-tributed to a rapid global expansion of cardiac surgery The bubble oxygenator was a distinct improvement over the previous un-wieldy direct blood contact oxygenators, yet it was still limited in that the direct blood-air interface could produce significant blood trauma This trauma accrues over time; thus, the safety margin for longer pump runs was diminished for longer, complex cases The next generation of oxygenators, membrane oxygenators, better mimicked the function of the lungs These microporous, gas-permeable membranes eliminated direct contact between gas and blood, thus, reducing blood trauma.26 The concept of a mi-croporous membrane separating the gas and blood was sound, but

it took decades of research to find a suitable membrane material before these oxygenators could replace bubble oxygenators com-mercially Initial success with silicone membranes was observed with long-term support during ECMO However, in the operat-ing room, these membranes proved to be less efficient and prone

to plasma leakage and thrombus formation.26 , 28 The development and release of polypropylene microporous membranes allowed for efficient gas exchange over a wide range of temperatures and pump flow rates, replacing the bubble oxygenator during CPB in the mid-1980s In these oxygenators, CO2 and O2 flow meters and a gas blender control gas and volatile anesthetic flow through the inside of the hollow polypropylene fibers The gas within the hollow fibers passively diffuses into the blood flowing on the out-side of the fibers

In 1985, Cobe released the popular Variable Prime Cobe Membrane Lung (VPCML) designed for the pediatric market This oxygenator was divided into separate compartments and gave clinicians three maximum blood flow options, 1.3, 2.6, and 4.0 L per minute (LPMs) depending on which compartments were opened.29 The VPCML also tried a new concept with the heat exchanger Once a separate external CPB component, the stain-less-steel heat exchanger was placed inside the venous reservoir The stainless-steel coil wrapped around the inside of the reservoir was not efficient unless a large amount of volume was held in the reservoir This was counter to the efforts to reduce the overall circuit prime volume Despite this shortcoming in the VPCML model, the move toward integration and consolidation of func-tionalities continued These heat exchangers are now integrated within the oxygenator housing Considering that pediatric cardiac surgery is more likely than adult surgery to use moderate to deep hypothermia, these heat exchangers need to be extremely efficient with a small surface area

As technology relentlessly improved, membrane hollow fibers were wrapped into tighter configurations This eventually allowed for a priming volume low enough to release a dedicated neonatal oxygenator In 2006, Dideco released the first neonatal oxygen-ator with a prime volume of 31 mL and maximum rated flow of

700 mL/min.30 The new generation of neonatal and pediatric

• Fig 35.4 ​Sorin​S5​heart-lung​machine​with​mast-mounted​arterial​pump​

and​Terumo​Baby​FX​reservoir​and​oxygenator​at​Children’s​Health​Dallas.

oxygenators achieves much higher maximum flow rates while

keeping prime volumes appropriate for neonates This has allowed

clinical teams to achieve consistent physiologic outcomes after

pump runs in neonates and small infants A modern pediatric

device such as the Terumo Baby FX oxygenator with integrated

arterial filter (Terumo Cardiovascular Group) offers a low total

prime volume and a high maximum blood flow (Fig 35.5) With

arterial filter integration, this oxygenator has a total prime volume

of 43 mL and a maximum rated blood flow of 1.5 LPMs This low

prime oxygenator is suitable for neonates but also accommodates

patients up to approximately 15 kg This wide range of blood flow

and low prime improves the likelihood of bloodless surgery—

wherein an asanguineous prime is used—for the larger patients in

range for this device The Maquet Quadrox-i Neonatal

oxygen-ator (Maquet Holding) is another oxygenoxygen-ator with an integrated

arterial filter that has a 40-mL total prime volume and 1.5-LPMs

maximum flow When considering the additional volume of an

external arterial line filter, this high-efficiency oxygenator with an

integrated filter offers the lowest total prime volume unit on the

market today.31 Current trends in oxygenator design and

develop-ment include integration of the arterial line filter, biocompatible

surface coatings for circuit tubing, decreasing flow resistance, and

more efficient heat exchange

Tubing

The tubing used to connect the various components of the CPB

circuit to the patient is made of a medical-grade polyvinyl

chlo-ride Tubing length and diameter are the two main factors to

consider when designing a circuit Shorter tubing with the

small-est internal diameter will reduce prime volume, but the tubing

must also be large enough to safely manage required blood flows

and line pressures for a given patient In the past, ¼-, 3⁄8-, and

½-inch tubing were the only tubing options, which made circuit

miniaturization a difficult task Currently, a wide range and

selec-tion of pediatric tubing and connector sizes are available Tubing

sizes such as 1⁄8, 3⁄16, and ¼ inch have become the new standards

in pediatrics Changing the internal diameter of tubing affects blood flow resistance and must not impede venous drainage or arterial blood flow At our institution, we select arteriovenous line sizes that accommodate gravity venous drainage and do not ex-ceed an arterial line pressure of 350 mm Hg (Table 35.2) Large reductions in tubing length have been made possible by position-ing the smaller new-generation pump consoles close to the patient and using mast mounted pumps to bring components closer to-gether Also, smaller-diameter venous line tubing may be used to further reduce the prime volume, but vacuum-assisted venous drainage (VAVD) must be used to augment the gravity siphon The bioreactivity of blood coming into contact with artificial surfaces, such as tubing, is known to exacerbate the systemic in-flammatory response and disrupt hemostasis A major advance-ment has been the developadvance-ment of surface coatings that attempt

to mimic the endothelial surface of blood vessels These coatings have been shown to attenuate the increase of cytokines and in-flammatory markers and preserve platelets.32 , 33 When selecting tubing for the pediatric circuit, the goal is to safely achieve maxi-mum blood flows, decrease prime volume, and attenuate blood trauma

Hemoconcentrators

A hemoconcentrator is an ultrafiltration device that consists of semipermeable membrane fibers that remove plasma water and solutes They function similarly to hemodialysis units but are simpler in that they do not require a dialysate solution Blood flows through microporous membrane fibers, and since the hy-drostatic pressure is higher inside the membrane fibers, effluent fluid permeates the membrane and can be removed The mem-brane pore sizes are typically less than 55,000 Da, which preserve plasma proteins such as albumin (65,000 Da) and maintain the colloid oncotic pressure The ultrafiltration rate of a hemoconcen-trator is dependent on the hydrostatic pressure gradient across the membrane, blood flow rate through the membrane fibers, mem-brane pore size, and the hematocrit Ultrafiltration is useful for

• Fig 35.5 ​Terumo​Baby​FX05​pediatric​oxygenator.

TUBING SPECIFICATIONS

CHILDREN’S HEALTH DALLAS PROTOCOL

Internal Diameter (in) mL/ft mL/rev

Maximum Arterial Flow (mL/min)

Maximum Gravity Drainage (mL/min)

TABLE

35.2 Tubing Specifications and Maximum Blood Flow Ranges Tested at Children’s Health Dallas

increasing hematocrit, reducing high potassium levels after

car-dioplegia delivery, and removing harmful inflammatory

media-tors Hemodilution during pediatric CPB is difficult to avoid; a

2004 survey of pediatric cardiac surgery centers reports that 98%

of perfusionists routinely use a hemoconcentrator during CPB.20

Circuit Prime

The CPB circuit is primed with a crystalloid replacement fluid

Common solutions include Plasma-Lyte A, lactated Ringer, and

Normosol-R.34 Lactated Ringer is a replacement fluid that

con-tains 29 mEq/L of lactate but lacks magnesium Plasma-Lyte A

and Normosol-R both closely mimic human physiologic plasma

electrolyte concentrations, osmolality, and pH However, these two

solutions do not contain calcium At Children’s Health Dallas, the

perfusionists use Plasma-Lyte A because it does not contain lactate

or calcium This allows the perfusionists to lower CPB perfusate

calcium levels, which is desirable, as is discussed later

Once the CPB circuit is primed with a crystalloid solution and

cleared of any air, the total prime volume of the circuit is estimated

The perfusionist must then choose between initiating CPB with or

without adding heterologous blood Unlike the adult patient

popu-lation, blood products are often added to the neonatal and pediatric

CPB circuits due to the small patient blood volume-to-circuit

prime volume ratio The dilutional effect of the crystalloid prime is

determined by calculating the patient resultant hematocrit (HCTr)

The HCTr formula, HCTr 5 (Patient blood volume 3 HCT)/

(Patient blood volume 1 Circuit prime volume), is calculated once

the patient hematocrit value is measured in the operating room

before surgery The institutional protocol at Children’s Health

Dal-las is to maintain a CPB HCTr above 30% If that value cannot be

reached, then packed red blood cells (PRBCs) are added to the

circuit The institutional protocol also directs that a half unit of

fresh-frozen plasma, approximately 100 mL, will be added to the

circuit prime for all patients less than 6 kg

The pre-CPB circuit prime drug additives at our institution

include heparin (1000 U/mL), 8.4% sodium bicarbonate,

20% mannitol, furosemide (10 mg/mL), methylprednisolone,

tranexamic acid, and 25% albumin (Table 35.3) The ideal prime

solution should be “physiologic” and attempt to attenuate the adverse response to artificially supporting a patient with an extra-corporeal circuit

Anticoagulation

Due to the foreign surface contact and resultant intrinsic activa-tion of the coagulaactiva-tion cascade, the patient must be anticoagu-lated before CPB Heparin is the most widely used anticoagulant during CPB It acts by super-activating antithrombin III (ATIII), which then inactivates thrombin and other proteases involved in coagulation Heparin is used because it is fast-acting, and antico-agulation reversal can easily be achieved by administering prot-amine Anticoagulation helps prevent circuit thrombus formation and avoid the devastating effects of potential arterial thromboem-bolism Heparin was the anticoagulant used during Dr Gibbon’s first successful cardiac surgery in 1953; its use during CPB has continued for more than 60 years Before heparin administration and dosing protocols were available, anticoagulation methods were cumbersome and unsafe The dosing was empiric, and the only methods for testing heparinization were lengthy laboratory heparin concentration tests Fortunately, the activated clotting time (ACT) test was introduced in 1966—this bedside whole blood test became the foundation of how heparinization is moni-tored in the cardiac operating room today.35 Traditional laboratory tests such as partial thromboplastin time (PTT) and prothrombin time (PT) are sensitive to low doses of heparin and therefore are not useful during CPB The ACT test is a point-of-care test that measures the time (in seconds) needed for activated whole blood

to form thrombin In 1975, Bull et al.36 reported a heparin man-agement approach using the ACT test, and the technique quickly became universally accepted The report describes the heparin dose-response curve technique and suggests an optimal ACT range of 480 seconds during CPB In this technique, ACT tests are run on various whole blood samples containing different heparin concentrations and results are plotted versus the heparin concentration The heparin dose-response curve, commonly

re-ferred to as the Bull curve, demonstrates the individualized ACT

response to different levels of heparinization and is a useful tool

in estimating the concentration of heparin necessary to achieve an ACT of 480 seconds (Fig 35.6) Maintaining ACT results of at least 480 seconds during CPB remains the standard of care today Though most clinicians will agree that 480 seconds is acceptable during CPB, there is debate regarding whether that value should

be universally applied considering that not all ACT analyzers operate and activate blood in the same manner

Pediatric patients undergoing cardiac repair suffer dispropor-tionate postoperative bleeding complications after CPB, likely be-cause of their size and immature coagulation system Contributing factors to postoperative bleeding are dilution of coagulation factors during CPB, induction of the systemic inflammatory response, hematologic changes in cyanotic patients, hypothermia, and nu-merous coagulation factor deficiencies All these situations can inhibit adequate anticoagulation with heparin and ultimately lead

to the generation of thrombin It has been shown that prolonged ACT results of pediatric patients poorly correlate with the plasma levels of heparin during CPB.37 Reports have shown that pediatric patients require higher plasma heparin concentrations than adults because they metabolize heparin faster, have a larger blood volume-to-body weight ratio, and have lower ATIII levels.38 , 39 Therefore, weight-based heparin doses and ACT monitoring used with adult patients are not recommended for use in pediatric patients

TABLE

35.3

Heparin Anticoagulant Calculated by

Medtronic HMS and varies per patient Sodium bicarbonate Buffer Achieve pH 7.40

Mannitol Osmotic diuretic;

oxygen radical scavenger

0.5 mg/kg; 12.5 g maximum dose

Furosemide Loop diuretic 0.25 mg/kg; 20 mg

maximum dose Methylprednisolone Corticosteroid 30 mg/kg; 1 g

maximum dose 25% Albumin Plasma protein 10% circuit prime

volume Tranexamic acid Antifibrinolytic 20 mg/kg; 20 g

maximum dose

Cardiopulmonary Bypass Circuit Prime Drugs

The potential variability of a pediatric patient’s response to

heparin necessitates an individual dosing regimen and the use of

different coagulation tests A useful bedside hemostasis

manage-ment tool in pediatric cardiac surgery is the Hepcon HMS PLUS

(Medtronic Inc.) The Hepcon HMS PLUS is fully automated and

is used to run the following tests: ACT, heparin dose response (HDR)

to identify individual heparin needs, and heparin-protamine

titration (HPT) to verify heparin concentration A baseline

sample is collected from the arterial line before heparinization and

is used to test the HDR The HDR test determines the baseline

ACT and patient response to increasing amounts of heparin

Re-sults are used to identify heparin-resistant or heparin-sensitive

patients and determine the patient heparin concentration needed

to achieve appropriate anticoagulation To test the blood heparin

concentration with the HPT test, blood is added to tubes

con-taining different mg/mL concentrations of protamine Heparin

and protamine bind in a 1:1 ratio; thus, the tube that produces a

clot can be used to determine the unit/mL heparin concentration

The HPT test is used frequently during CPB to maintain heparin

concentrations suggested by the HDR and is run post-CPB to

verify proper heparin reversal after protamine administration

Without heparinization, hemodilution and the degree of

hypo-thermia alone could extend the ACT beyond 480 seconds; this

effect is amplified in the pediatric patient Administering heparin

to maintain a patient heparin concentration calculated by the

HDR, despite an ACT greater than 480 seconds, will help to

re-duce consumptive coagulopathy, thrombin generation,

fibrinoly-sis, neutrophil activation, and the need for transfusions.40 , 41

Once the patient is ready to be cannulated for CPB, a heparin

bolus is administered to the patient by the anesthesiologist into an

intravenous line or by the surgeon directly into the right atrium

In general, the patient receives a 400 U/kg dose of heparin

min-utes before arterial cannulation Once the heparin has circulated

within the patient for approximately 5 minutes, a blood sample

from an arterial or intravenous line is used to run an ACT and HPT If the ACT reaches 480 seconds or the HPT confirms an adequate heparin concentration, cardiotomy pump suction may

be used, and CPB may be initiated when the surgeon inserts the arterial and venous cannulas ACT and HPT tests are run every

30 minutes during CPB, and heparin is administered if the ACT falls below 480 seconds or the heparin concentration falls below the maintenance value calculated by the HDR If a parameter is low, the Hepcon HMS PLUS uses a formula based on the HDR, blood volume of the patient, and circuit prime volume to calcu-late the amount of heparin needed to adequately raise the ACT

or HPT

Cannulation

Cannulation refers to the process in which the surgeon attaches the venous limb of the CPB circuit to the systemic venous circula-tion of the patient while attaching the arterial limb to the systemic arterial system of the patient This is most commonly accom-plished by placing an arterial cannula in the distal ascending aorta and venous cannulas in the SVC and IVC, respectively The can-nulas are inserted through appropriately sized purse-string sutures and secured with tourniquets This bicaval configuration allows for the achievement of “total” CPB; the vast majority of cardiac repairs can be accomplished using this technique In pediatric cardiac programs, patients ranging in weight from approximately

1000 g up to adulthood are placed on CPB Therefore, a wide range of cannula sizes must be kept in stock Arterial cannulas range from as small as 8 Fr (2.67 mm) in diameter up to over 20 Fr Venous cannulas for CPB are available in straight and angled varieties and range down to as small as 10 Fr Inserting these cannulas into the diminutive aorta and venae cavae of neonates is

a taxing technical exercise that must be accomplished without complication in order to appropriately support the patient during the repair and leave the patient with undamaged vessels at the cannulation sites postoperatively

Exceptions to standard bicaval cannulation are frequently seen

in pediatric practice First, patients can have anomalies of systemic venous return, such as bilateral SVCs, ipsilateral hepatic veins, or

an interrupted IVC with azygous continuation to the SVC All these anomalies have to be assessed, and an appropriate venous cannulation strategy must be devised Occasionally, if these anom-alies are prohibitive for selective cannulation or the overall patient size is so small that the venae cavae are too small to cannulate, the right atrial appendage is cannulated in isolation and periods of circulatory arrest, wherein venous return is not required, are used

to accomplish intracardiac portions of the repair

Alternatives to standard ascending aortic cannulation are also used In order to accomplish aortic arch reconstructions without resorting to circulatory arrest, a small prosthetic vascular tube graft is anastomosed to the innominate artery and the arterial can-nula is inserted into this “chimney” graft Alternatively, if the pa-tient is large enough, the innominate artery can be cannulated directly These innominate artery cannulation techniques allow the brain to be perfused up the right carotid artery while the aor-tic arch is being repaired

Reoperations are common in congenital heart surgery A num-ber of these patients have pulmonary outflow conduits that are densely adherent to the sternum Patients with transposition of the great arteries have an abnormally anteriorly located ascending aorta that can also be adherent to the chest wall in the midline Peripheral cannulation via a femoral artery is sometimes necessary

600

100

300

200

D

D C

C

B

A

400

500

0

Heparin dose (U/kg)

• Fig 35.6 ​An​ example​ of​ a​ heparin​ dose-response​ curve​ wherein​ the​

patient’s​ baseline​ activated​ clotting​ time​ (ACT)​ is​ shown​ at​ point​ A.​ An​

initial​heparin​dose​of​200​U/kg​resulted​in​an​ACT​shown​at​point​B.​A​

linear​ extension​ of​ points​ A​ and​ B​ is​ drawn​ with​ an​ intersection​ at​ 400​

(point​C)​and​480​seconds​(point D).​These​target​intersects​can​be​used​

to​estimate​further​heparin​doses​to​administer​to​the​patient.​(From​Bull​

BS,​Huse​WM,​Brauer​FS,​Korpman​RA.​Heparin​therapy​during​extracor-poreal​ circulation.​ II.​ The​ use​ of​ a​ dose-response​ curve​ to​ individualize​

heparin​and​protamine​dosage.​J Thorac Cardiovasc Surg.​1975;69:685–

689.)

much greater This relatively greater exposure to nonendothelial-ized surfaces can lead to an increased inflammatory response and damage the formed elements of blood Another important contrast between pediatric and adult support involves calcium management The immature myocardium is susceptible to exacer-bated postischemic injury due to overly rapid calcium loading at reperfusion.42 , 43 Because of this, at Children’s Health Dallas, a perfusate that is relatively depleted of calcium is used until well after cross-clamp removal Calcium is restored in a stepwise fash-ion before weaning from the circuit The coagulatfash-ion system of neonates and infants also differs from adults in that they have quantitative deficiencies of coagulation factors at baseline These deficiencies of the immature coagulation system coupled with hemodilution discussed earlier result in significant postoperative coagulopathies and anemia that must be addressed with blood products much more commonly than in adult cases

Initiation of Cardiopulmonary Bypass

Before starting a planned operation, the surgical team will discuss the procedure and form a detailed management plan for each team member The perfusionist must understand the type and complexity of the surgery and discuss the proper cannula section, degree of hypothermia, myocardial protection technique, and any other unique patient variables that might affect perfusion man-agement The fundamental concepts of managing CPB for con-genital patients are similar to adults, but anatomic variations and physiologic extremes complicate the approach Once the surgical plan is established, the patient is prepped and draped for the skin incision and sternotomy With the chest open, the surgeon ex-poses the heart and major vessels and then directs the anesthesi-ologist to administer heparin before cannulation Alternatively, the surgeon can administer the heparin directly to the right atrium Next, the arterial and venous cannulas are inserted, but before it is safe to initiate CPB, it is important to confirm an ad-equate anticoagulation level by obtaining an ACT and heparin concentration and that the arterial cannula is unobstructed Con-genital patients, especially cyanotic patients, often demonstrate variable dose responses to heparin In addition, it cannot be as-sumed that the CPB dose of heparin is circulating in the patient,

as intravenous line malfunction can occur Initiating CPB on a pediatric patient with an obstructed aortic cannula could quickly exsanguinate the patient, as venous drainage commences without return of this blood to the patient and could cause severe hypo-tension Once these two safety checks are complete, the patient is ready for CPB

The venous line is unclamped to gravity siphon deoxygenated blood from the patient, and the arterial flow is slowly increased as the heart begins to empty Bicaval cannulation is often used in congenital surgery, but it is common to initiate CPB with only one cannula This is done to verify adequate drainage from one cannula, as it would be difficult diagnose poor drainage from a single cannula if both were open Once both cannulas are open, adequate venous drainage is confirmed when the central venous pressure (CVP) falls to zero and the SVC, IVC, and right atrium

are collapsed Total (also termed full or complete) CPB is achieved

when all the systemic venous blood is being diverted to the heart-lung machine and full arterial flow can be achieved In the rare occurrence that venous anomalies prohibit inserting appropriately sized venous cannulas, VAVD may be used to enhance return to the venous reservoir and achieve full-flow CPB However, VAVD has been reported to induce blood trauma, exacerbate gaseous

in these instances Peripheral arterial cannulation in children

should be performed only when absolutely necessary and

con-verted to the ascending aorta as soon as possible The obturation

of the femoral artery by the cannula almost always causes

hypo-perfusion of the lower extremity With longer cannulation times,

the leg can be at significant risk for ischemic complications

Cardiopulmonary Bypass

Pediatric vs Adult Considerations

Although many of the management techniques governing pediatric

and adult CPB are similar, several differences do exist (Table 35.4)

The small size of the pediatric patient and nature of the surgical

repair often expose these patients to moderate or deep

hypother-mic temperatures, wide ranges of perfusion flow rates, and

hemo-dilution These management techniques represent extreme shifts

from normal physiologic parameters, and the harmful effects are

potentially more pronounced in these small patients Low-flow

perfusion or circulatory arrest at deep hypothermia (15–20°C) is

often required because of the complexity of the repair, significant

aortopulmonary collateral blood flow returning to the operative

field from the pulmonary veins, or simply because position of the

perfusion cannulas interferes with access to the surgical site

Compared with adults, hemodilution of the pediatric patient

during CPB has a larger impact on the concentration of blood

components and the blood-to-foreign surface area exposure is

TABLE

35.4

Parameter Adult Pediatric

Hypothermic

temperature Rarely below 25°C–32°C Commonly 15°C–20°C

Use of circulatory

Pump Prime

Dilution effects on

Additional additives Blood, albumin

Perfusion pressures 50–80 mm Hg 25–50 mm Hg

Influence of a-stat

versus pH-stat

management strategy

Minimal at moderate hypothermia Marked at deep hypothermia

Measured Pa co 2

differences 30–45 mm Hg 20–80 mm Hg

Glucose Regulation

Hypoglycemia Rare—requires

significant hepatic injury

Common—

reduced hepatic glycogen stores Hyperglycemia Frequent—

generally easily controlled with insulin

Less common—

rebound hypoglycemia may occur

Pa co 2, Partial pressure of arterial carbon dioxide.

Differences Between Adult and Pediatric

Cardiopulmonary Bypass

From Greely WJ, Cripe CC, Nathan AT Anesthesia for pediatric cardiac surgery In: Miller RD,

Cohen NH, Eriksson LI, et al Miller’s Anesthesia 8th ed Philadelphia: Elsevier; 2015:2820.