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[.]
CHAPTER 35 Pediatric Cardiopulmonary Bypass • 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 to minimize patient hemodilution during CPB, ultimately reducing the likelihood of donor blood exposure The same adult circuit, with a prime volume of about L, would be approximately 500% of the circulating blood volume in a neonate This discrepancy 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 mid1980s Since the oxygenator is one of the largest volume components 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 circuit modifications to achieve a static prime volume of approximately 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 integrate the arterial filter, to reduce particulate matter, into the oxygenator 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 Currently, 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 reveals 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 367 or trickling over large mesh screens and exposing the film of blood to an oxygenated atmosphere.25,26 Though these units were successful at oxygenating blood, they required extremely large priming volumes; were not disposable; were difficult to assemble, operate, 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 contributed to a rapid global expansion of cardiac surgery The bubble oxygenator was a distinct improvement over the previous unwieldy 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 microporous 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 commercially Initial success with silicone membranes was observed with long-term support during ECMO However, in the operating 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 outside 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 stainless-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 functionalities 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 oxygenator with a prime volume of 31 mL and maximum rated flow of 700 mL/min.30 The new generation of neonatal and pediatric 368 S E C T I O N I V Pediatric Critical Care: Cardiovascular TABLE Tubing Specifications and Maximum Blood Flow 35.2 Ranges Tested at Children’s Health Dallas TUBING SPECIFICATIONS Internal Diameter (in) CHILDREN’S HEALTH DALLAS PROTOCOL Maximum Gravity Drainage (mL/min) mL/ft mL/rev Maximum Arterial Flow (mL/min) 18 ⁄ 2.5 3.5 ,450 ⁄ 3.7 5 ,750 ⁄ 7 ,1300 500–650 ⁄ 9.65 13 ,3000 1300–1500 32 16 14 ⁄ 13.5 18 ,5500 2000–2200 ⁄ 21.71 27 5000 4000–4500 16 38 ⁄ 28.5 38 5000–5500 12 ⁄ 38.61 45 5000 ⁄ 55.77 65 16 58 • Fig 35.5 Terumo Baby FX05 pediatric oxygenator 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 oxygenator (Maquet Holding) is another oxygenator 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 development include integration of the arterial line filter, biocompatible surface coatings for circuit tubing, decreasing flow resistance, and more efficient heat exchange 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 not exceed an arterial line pressure of 350 mm Hg (Table 35.2) Large reductions in tubing length have been made possible by positioning the smaller new-generation pump consoles close to the patient and using mast mounted pumps to bring components closer together 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 inflammatory response and disrupt hemostasis A major advancement has been the development 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 inflammatory markers and preserve platelets.32,33 When selecting tubing for the pediatric circuit, the goal is to safely achieve maximum blood flows, decrease prime volume, and attenuate blood trauma Tubing 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 not require a dialysate solution Blood flows through microporous membrane fibers, and since the hydrostatic pressure is higher inside the membrane fibers, effluent fluid permeates the membrane and can be removed The membrane 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 hemoconcentrator is dependent on the hydrostatic pressure gradient across the membrane, blood flow rate through the membrane fibers, membrane pore size, and the hematocrit Ultrafiltration is useful for The tubing used to connect the various components of the CPB circuit to the patient is made of a medical-grade polyvinyl chloride Tubing length and diameter are the two main factors to consider when designing a circuit Shorter tubing with the smallest 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, ẳ-, 38-, and ẵ-inch tubing were the only tubing options, which made circuit miniaturization a difficult task Currently, a wide range and selection of pediatric tubing and connector sizes are available Tubing sizes such as 1⁄8, 3⁄16, and ¼ inch have become the new standards Hemoconcentrators CHAPTER 35 Pediatric Cardiopulmonary Bypass 369 increasing hematocrit, reducing high potassium levels after cardioplegia delivery, and removing harmful inflammatory mediators 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 solution should be “physiologic” and attempt to attenuate the adverse response to artificially supporting a patient with an extracorporeal circuit Circuit Prime Due to the foreign surface contact and resultant intrinsic activation of the coagulation cascade, the patient must be anticoagulated 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 anticoagulation reversal can easily be achieved by administering protamine Anticoagulation helps prevent circuit thrombus formation and avoid the devastating effects of potential arterial thromboembolism 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 monitored 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 management 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 referred 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 disproportionate postoperative bleeding complications after CPB, likely because 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 numerous 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 volumeto-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 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 contains 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 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 population, 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 (Patient blood volume HCT)/ (Patient blood volume 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 Dallas 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 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 TABLE Cardiopulmonary Bypass Circuit Prime Drugs 35.3 Drug Action Prime Dose 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; g maximum dose 25% Albumin Plasma protein 10% circuit prime volume Tranexamic acid Antifibrinolytic 20 mg/kg; 20 g maximum dose Anticoagulation 370 S E C T I O N I V Pediatric Critical Care: Cardiovascular 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 calculate the amount of heparin needed to adequately raise the ACT or HPT 600 D 500 C ACT (sec) 400 B 300 200 D A 100 C 0 100 200 300 Heparin dose (U/kg) 400 • 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 extracorporeal circulation II The use of a dose-response curve to individualize heparin and protamine dosage J Thorac Cardiovasc Surg 1975;69:685– 689.) 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 management 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 Results 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 containing 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 hypothermia 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 reduce consumptive coagulopathy, thrombin generation, fibrinolysis, 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 minutes before arterial cannulation Once the heparin has circulated within the patient for approximately minutes, a blood sample Cannulation Cannulation refers to the process in which the surgeon attaches the venous limb of the CPB circuit to the systemic venous circulation of the patient while attaching the arterial limb to the systemic arterial system of the patient This is most commonly accomplished by placing an arterial cannula in the distal ascending aorta and venous cannulas in the SVC and IVC, respectively The cannulas 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 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 anomalies 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 cannula is inserted into this “chimney” graft Alternatively, if the patient 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 aortic arch is being repaired Reoperations are common in congenital heart surgery A number 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 CHAPTER 35 Pediatric Cardiopulmonary Bypass in these instances Peripheral arterial cannulation in children should be performed only when absolutely necessary and converted to the ascending aorta as soon as possible The obturation of the femoral artery by the cannula almost always causes hypoperfusion 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 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 hypothermic temperatures, wide ranges of perfusion flow rates, and hemodilution 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 Differences Between Adult and Pediatric 35.4 Cardiopulmonary Bypass Parameter Adult Pediatric Hypothermic temperature Rarely below 25°C–32°C Commonly 15°C–20°C Use of circulatory arrest Rare Common 25%–33% 150%–300% Pump Prime Dilution effects on blood volume 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 Paco2 differences 30–45 mm Hg 20–80 mm Hg Hypoglycemia Rare—requires significant hepatic injury Common— reduced hepatic glycogen stores Hyperglycemia Frequent— generally easily controlled with insulin Less common— rebound hypoglycemia may occur Glucose Regulation Paco2, Partial pressure of arterial carbon dioxide 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 371 much greater This relatively greater exposure to nonendothelialized 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 exacerbated 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 fashion before weaning from the circuit The coagulation 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 management The fundamental concepts of managing CPB for congenital 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 exposes the heart and major vessels and then directs the anesthesiologist 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 adequate anticoagulation level by obtaining an ACT and heparin concentration and that the arterial cannula is unobstructed Congenital patients, especially cyanotic patients, often demonstrate variable dose responses to heparin In addition, it cannot be assumed 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 hypotension 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 heartlung 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 ... 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... 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... 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