Abstract
There are still many unanswered questions regarding blood management in the critically ill patient. Patients with congenital cardiac disease are further complicated by their variable physiology and subsequent response to persistent hypoxia. This chapter discusses blood management throughout the perioperative time period for a pediatric patient undergoing cardiac surgery. It begins with the preoperative optimization of the patient and potential impact on clinical outcomes. A thorough discussion of the effects of bypass and the methods that are used to minimize and optimize blood product use in the intraoperative period follows. The chapter concludes with an evidence-based evaluation of blood management and utilization in the postoperative time period, including a discussion of the effect of red cell age on clinical outcomes.
Key Words
Preoperative blood optimization, Blood utilization, Blood conservation, Transfusion strategies, Red cell storage
The use of blood products is common in patients who have surgery for congenital heart disease (CHD). Ninety-eight percent of these patients receive at least one red cell transfusion, and greater than 50% receive fresh frozen plasma (FFP) or platelets. Transfusions are given to improve oxygen delivery and to prevent or improve coagulation abnormalities. Pediatric cardiac surgical patients have varying physiologies, and oxygen delivery needs can be different for neonates compared to teenagers and for cyanotic patients compared to acyanotic patients. This variation can complicate a provider’s decision making on when, what, and how much to transfuse.
Transfusions also are not without risks. Immunologic reactions may occur, and the risk of infectious transmission remains despite thorough screening. Blood transfusions also lead to increased risk of infection, ICU and hospital length of stay (LOS), duration of mechanical ventilation, and mortality. The benefits of transfusing a critically ill child and the potential harms must be carefully balanced.
The concepts of blood utilization and blood conservation originated in attempt to optimize the balance of benefit and harm from transfusion. These concepts are similar but focus on two slightly separate components when trying to minimize transfusions. Blood utilization focuses on how and what is transfused; blood conservation attempts to minimize the likelihood or potential need for transfusion. In this chapter we will discuss both concepts throughout the entire perioperative period.
Preoperative
The preoperative period offers the provider a unique opportunity to engage the patient in strategies for blood conservation and utilization that will last throughout the perioperative course. Many of these strategies have been studied and proven in adults, whereas the pediatric literature relies more on institutional experience and case reports. The preoperative strategies can be divided into the following: general strategies, iron replacement for iron deficiency anemia, recombinant human erythropoietin, preoperative autologous donation, and optimization of other blood components
General Strategies
First, it is important to recognize that cell counts are individual to the patient and rely on other factors, including age of the patient, medications, syndromes, and comorbidities. Although it is imperative to obtain a complete blood cell count (CBC) before surgery, attention should be paid to being judicious and thoughtful about preoperative phlebotomy and making sure blood draws are limited to those tests that are absolutely necessary. Furthermore, hemodilution via volume administration should be avoided for any patient admitted preoperatively.
Patients with CHD are often on numerous medications, including those that may affect bleeding. Acetylsalicylic acid (aspirin) is commonly prescribed, and adult literature shows it can have an effect on postoperative bleeding. An analysis of the risks and benefits of continuing aspirin, other nonsteroidal antiinflammatory medications that may affect platelet function, and other anticoagulant and antiplatelet agents should be made with the patient’s surgeon and cardiologist and in consideration of the patient’s comorbidities.
As with the general preoperative evaluation of the pediatric cardiac surgery patient, it is necessary to maximize nutrition in an effort to maintain levels of hemoglobin (Hgb), albumin, and other plasma proteins. Furthermore, although there is concern for increased morbidity with blood transfusion, the clinician must balance this risk with concerns that preoperative anemia may have adverse effects. It is independently associated with adverse outcomes after cardiac surgery in adults and a risk factor for postoperative mortality in both neonates and children undergoing noncardiac surgery. Although the risk of preoperative anemia in pediatric cardiac surgical patients not been studied, it is important to consider that the strategies discussed in the following sections could both conserve blood and treat a potentially modifiable preoperative risk factor.
Iron Replacement
As mentioned previously, nutrition is an important aspect of the preoperative evaluation, particularly with a goal of blood conservation. One modifiable nutritional risk factor that is of particular benefit is iron deficiency anemia (IDA). IDA is a very common pediatric condition that most often affects toddlers and adolescent girls.
The prevalence of IDA is 3% to 7% and is increased in patients with prematurity, Hispanic ethnicity, obesity, and low socioeconomic status. Laboratory workup shows a decreased Hgb, decreased mean corpuscular volume, increased red cell distribution width, decreased serum iron concentration, increased total iron-binding capacity, and decreased transferrin saturation. One can often see low ferritin levels as a surrogate of iron stores. However, in the setting of acute inflammation, ferritin level may be elevated because it is an acute phase reactant. If IDA is suspected, the child can be given enteral iron (premature infant: 2 to 4 mg elemental iron/kg/24 h divided twice a day; child: 3 to 6 mg elemental iron/kg/24 h divided twice a day; adult: 60 to 100 mg elemental iron twice daily), and Hgb values can be reassessed in 4 to 6 weeks.
Recombinant Erythropoietin
Erythropoietin (EPO) is an endogenous hormone that is produced by the kidney and allows for differentiation and proliferation of erythroid precursor cells resulting in increased hemoglobin. Recombinant human EPO (rHuEpo) has been used in pediatrics for anemia related to many conditions such as chronic renal failure, oncologic disease, human immunodeficiency virus, and anemia of prematurity with an established safety profile and dosing. It is important to provide concomitant iron supplementation unless iron stores are already in excess, and the peak effect is seen in 2 to 3 weeks. Perioperatively there has been success in pediatric critical care and pediatric anesthesia in other procedures that have a high risk for bleeding and need for blood transfusion, including patients who are Jehovah’s Witnesses and craniosynostosis repair. In pediatric cardiac surgery there have been reports of the successful use of EPO in the preoperative period, and the dose recommendation is 300 U/kg of EPO 7 days before surgery supplemented with iron. EPO has been proven to be safe, and, although it may increase hematocrit in the pediatric cardiac patient, the effect on outcome and blood utilization in the perioperative period is still questioned. Given the variable response and rare usage in pediatrics, consultation with a pediatric hematologist may be beneficial in select patients.
Autologous Blood Donation
Preoperative autologous blood donation (PAD) has been shown to be safe and efficacious in adult cardiac surgery. It should be noted that differences in adult and pediatric physiology should be taken into consideration when planning for PAD. Adults after PAD are able to benefit from enteral rehydration to replenish the reduction in intravascular volume and increase stroke volume. Older children may have a similar physiologic response; however, pediatric patients less than 4 years of age cannot compensate with increased stroke volume due to differences in myocardial muscle fibers and may be unable to rehydrate with oral fluids and require intravenous fluid replacement. Furthermore, infants and young children, often require sedation or anesthesia during procedures. The strategy of PAD has been shown to safely and effectively minimize homologous blood transfusion in the perioperative period in pediatric cardiac surgery patients older than 5 years. Various protocols have been studied for PAD in smaller children. Masuda et al. showed that autologous donation can be performed in children weighing less than 20 kg through collection of volumes 5 to 10 mL/kg over six PAD sessions in the 50 days before surgery. In this study the patients received no homologous blood donations; however, many of the children did not cooperate with the PAD procedure. Fukahara et al. showed that the lack of cooperation with the donation procedure could be overcome with PAD at the time of preoperative cardiac catheterization. Hibino et al. studied children 6 months to 5 years of age undergoing primary cardiac surgery who underwent PAD via two donations of 5 to 10 mL/kg collected via the femoral vein under general anesthesia at 2 and 3 weeks preoperatively. They found a significant decrease in homologous transfusion with no difference in intraoperative or postoperative Hgb levels. Although there are no randomized trials for PAD, careful patient selection could allow this strategy to be employed for pediatric patients undergoing cardiac surgery. However, one must remember that through PAD the patient will often become anemic and therefore may benefit from adjunctive preoperative EPO and iron. PAD is not without cost to the patient and medical system, and because preoperative autologous blood units are often wasted if not needed in the perioperative period, patient selection is crucial. The blood bank can store the preoperative autologous blood for 3 weeks with citrate phosphate dextrose adenine solution or 6 weeks with cryopreservation.
Other Blood Components
It is important to recognize that perioperative bleeding can be multifactorial, and it is important in the preoperative, intraoperative, and postoperative periods to maximize other factors in the coagulation cascade. Cardiopulmonary bypass–associated platelet dysfunction can contribute to postoperative bleeding. Some studies have suggested that platelet dysfunction diagnosed by thromboelastography (TEG) indicating an increased time to platelet plug formation are at increased risk for intraoperative red blood cells and FFP transfusions. Most pediatric anesthesiologists would agree that for both cardiac and noncardiac surgery platelets should be transfused preoperatively if the platelet count is less than 50,000/µL. Because there are few well-defined preoperative laboratory values that require preoperative transfusion, it is important to have a personalized approach to each patient’s history and comorbidities, which can allow further evaluation with platelet counts, coagulation studies, fibrinogen, bleeding times, and TEG.
Intraoperative
Intraoperative blood conservation and utilization are important components of blood management for a child undergoing cardiac surgery. The focus is on minimizing the amount of blood loss and using various methods of returning the patient’s blood back to the intravascular space while optimizing the benefits when transfusing. Both these methods can be made more complicated by patient factors and variations in physiology during the intraoperative period.
This period of physiologic variability can begin with the transition from negative pressure ventilation to positive pressure ventilation that occurs with intubation. There is also the hemodynamic transition that occurs coming on and off cardiopulmonary bypass (CPB), as well as the physiologic change that occurs with the repair. These transitions can alter oxygen delivery and utilization for each patient and potentially the transfusion thresholds for the practitioner. Furthermore, just the initiation of CPB can involve the use of blood products and/or significant hemodilution. The CPB circuit has numerous deleterious effects on the coagulation cascade and blood product function, as does the process of cooling and rewarming that is required in many pediatric cardiac surgeries. These factors, along with the surgery itself, can make it difficult to know how to treat any bleeding that occurs. A thorough understanding of these transitions, the patient’s physiology, and the surgical repair will better allow one to make an educated decision on transfusion practices during the intraoperative time course.
Blood Conservation
General Strategies.
Minimizing blood loss is not just a component of surgical technique. Laboratory draws, waste, and line insertion are small but not insignificant causes of blood loss especially in children. New technology has allowed for a minimal volume of blood, less than 0.1 mL in the newest blood gas machines, to be drawn and still provide the same information as the older machines. These machines are often used as a point-of-care service, which could potentially increase their overall utilization. Judicious use of blood draws and laboratory tests will minimize blood loss directly and also by reducing the waste that occurs each time that blood is obtained.
Invasive lines are placed in many patients undergoing cardiac surgery. The placement of invasive lines can be difficult due to the size of the vessels, cannulation sites, and the number of previous cannulation attempts. Techniques to minimize blood loss should be used, including holding pressure at the line site, optimizing positioning for line placement, and occluding infusion sites once the line is in the vessel. Some blood loss is inevitable with both line placement and blood draws, but a focus on the details will make this minimal even in the smallest of children.
Acute Normovolemic Hemodilution.
Acute normovolemic hemodilution (ANH) is an excellent method of minimizing actual hemoglobin loss during surgery. Blood is removed from the patient in the operating room, replaced with an equal volume of crystalloid, and stored at room temperature until transfusion is required. The hemoglobin is diluted, and thus hemoglobin loss from the surgery is decreased. Transfusion of whole blood containing all the coagulation factors and platelets may minimize further transfusions. ANH can be difficult in neonates and small children. The amount of blood that must be removed is likely to cause a large drop in hemoglobin and potentially affect oxygen delivery for the patient. There are only small studies of ANH in pediatric patients, and none are in patients with congenital cardiac disease. These studies showed no effect on transfusion requirements, but the theoretical benefits exist and could manifest with larger studies. A recent meta-analysis did find that ANH reduced red blood cell transfusions in adults undergoing cardiac surgery. This may be the best evidence for its use in large children, teenagers, or adults with CHD, though the need for surgery is quite different between the populations.
Cell Salvage/Pump Blood.
There can be a large amount of blood loss during cardiac surgery. The easiest way to minimize the effect of this blood loss is to return it to the patient in some form. Generally this can be done via “pump blood” or cell salvage devices. The majority of blood loss during CPB is returned to the pump via drains or the pump sucker (dedicated suction line that returns to the bypass circuit). Blood that is lost post bypass is collected via a dedicated suction line and then stored via a cell salvage device. This stored blood will be washed and filtered and will contain only red cells. The pump blood, on the other hand, is whole blood and will contain factors, platelets, and residual amounts of heparin. Therefore new or persistent bleeding should likely be addressed differently depending on which of these two was used for blood return.
There are multiple cell salvage systems, but the most common use saline to wash the salvaged blood and centrifuge off the supernatant and heparin, creating a hemoconcentrated product for reinfusion. The efficiency of the system is based on the ratio of blood suctioned to red cells salvaged. This ratio is not 1 : 1 due to red cell injury or loss at separate aspects of the system. The first and likely most damage is at the suction tip. There is also clotting and damage through the suction tubing and injury of the red cells during the washing method.
The literature regarding cell salvage in adults is robust and relatively consistent in its benefits in decreasing transfusion needs. The pediatric literature shows similar efficacy, although the number of studies is much less robust. The only study in the pediatric cardiac population included 106 patients weighing less than 20 kg, but investigators stored the cell-salvaged blood for up to 24 hours following its collection, which is not consistent throughout pediatric cardiac institutions, which generally limit reinfusion for 4 to 6 hours following collection. The study demonstrated significantly fewer autologous RBC transfusions, coagulant product transfusions, and donor exposures early in the hospital course, but there was only a trend toward significance by the end of the hospital stay, likely due to heterogeneity in subjects and procedures. This study is discussed further in the postoperative portion of the chapter.
Cell salvage efficiency has been one of the limitations in its use in pediatrics. The older devices often required more than 300 mL of volume to be able to adequately wash and filter the blood for reinfusion. New technology has improved this process significantly, and now there are devices that require between 40 and 60 mL ( Fig. 25.1 ). Further studies are needed to evaluate the efficacy of the superefficient cell salvage devices in the pediatric population.
Mechanisms to Minimize Surgical Blood Loss
Antifibrinolytics.
There are two primary antifibrinolytics currently used in pediatric surgery, tranexamic acid (TXA) and epsilon-aminocaproic acid (EACA). These medications are similar and work primarily by inhibiting plasmin, but TXA is more potent and generally more expensive. Their efficacy in both adult and pediatric cases are similar in many surgical situations. There are two prospective comparison studies in newborns undergoing cardiac surgery that show similar efficacy. Generally both medications are thought to decrease blood loss and potentially decrease transfusion requirements. The choice of which antifibrinolytic to use is based on institutional preference.
There have been a number of pharmacokinetic studies completed in an attempt to determine the optimal dosing parameters for both TXA and EACA. There was single study in neonates undergoing CPB with EACA in which a loading dose of 40 mg/kg, an infusion of 30 mg/kg/h, and a pump prime concentration of 100 mg/L maintained an optimal concentration in the majority of the patients. Dosing for other age-groups is usually a load of 100 mg/kg with an infusion range between 30 and 50 mg/kg/h. A similar study in patients with TXA showed that an optimal dosing strategy was based on the age and weight of the patient. In 2007 approximately 50% of all patients undergoing cardiac surgery in the Society of Thoracic Surgery database received antifibrinolytics. The current percentage is likely significantly higher with more widespread use at pediatric cardiac institutions and the removal of aprotinin from the US market in 2007. Certain institutions are selective with their use of antifibrinolytics, with the Fontan surgery and other single-ventricle repairs being common exceptions.
Surgical Technique.
Surgical technique is the most important component of blood conservation in pediatric cardiac surgery. Excellent surgical hemostasis can make much of intraoperative blood conservation moot. The same can be said of poor surgical hemostasis because surgical bleeding will persist until the cause is found and repaired. A combination of excellent surgical technique and a blood conservation plan is the most optimal for the patient. Significant blood loss often is expected in many pediatric cardiac cases, and some amount of blood use is inevitable. Approximately 90% of all pediatric cardiac surgical patients are transfused with some component of blood products during the entire perioperative period. Therefore the question for the practitioner is often what, when, and how much to transfuse rather than if transfusion should occur.
Blood Utilization
Packed Red Blood Cells.
The purpose of transfusing packed red blood cells (PRBCs) is to attempt to optimize systemic oxygen delivery. Anemia has been found to be a risk factor in some studies for infections, acute kidney injury, and mortality in pediatric patients undergoing cardiac surgery. The same adverse outcomes are present in patients who are transfused more than others. The balance between oxygen delivery via transfusion and minimizing the risks of transfusion is the goal of optimal PRBC utilization.
The oxygen delivery in healthy individuals at rest is thought to be at least twice the amount required. However, patients with congenital cardiac disease have variable physiologies (e.g., mixing lesions, differential pulmonary to systemic blood flow) that can significantly alter expected oxygen requirements. Cyanosis further alters oxygen content, thereby increasing the need for circulating red blood cells as an adaptive response. Multiple studies have attempted to find the optimal transfusion trigger intraoperatively. The most in-depth study looked at psychomotor development scores at nonlinearly increasing hematocrit levels. This study found developmental delays at hematocrit levels less than 24%. The generalizability of this study can be questioned due to the fact that it was completed only in infants, none of whom were patients with single-ventricle physiology or had aortic arch reconstruction. It was also completed on infants who underwent low-flow bypass for a period of time. The study gives a basic framework on which future investigations may be based, though adjustment for cardiac lesion, age, and bypass technique needs to be considered. Though there have been other transfusion threshold studies, only one has been initiated in the operating room. The study was in noncyanotic patients with CHD between 6 weeks and 6 years of age and had a liberal threshold of 10.8 g/dL and a conservative threshold of 8 g/dL for hemoglobin. Outcome differences were shown in LOS and amount of PRBCs transfused benefiting the conservative group.
Fresh Frozen Plasma.
Approximately 50% of pediatric patients undergoing cardiac surgery receive a transfusion of FFP in the operating room. The primary purpose of FFP use is to minimize alterations in the coagulation cascade during CPB. Generally FFP is used in pump priming for infants and neonates despite limited evidence for its use. A single study of only 20 patients showed a decrease in blood product and cryoprecipitate use but not platelets, FFP, or PRBCs. Two other studies, including the largest on this topic (80 patients), showed no clinical benefit of priming with FPP. Once again, the variability in the pediatric cardiac population makes it difficult to accurately generalize any of the studies. There were no patients undergoing reoperations included in the studies, and some did not include higher- complexity operations.
Platelets.
Intraoperative platelet use is variable, with only approximately 30% of all pediatric patients undergoing cardiac surgery receiving them. The percentage is higher for neonates and infants compared with older patients and is associated with longer duration of surgery. Platelet-associated bleeding on bypass is likely multifactorial. Platelet destruction occurs when blood flows through the oxygenator and CPB tubing. The functional abnormalities are widespread, including increased activation, alteration of platelet surface adhesion receptors, and platelet signaling. Indications for platelet transfusion differ across institutions. Many transfuse platelets to all neonates, whereas some transfuse platelets according to CPB duration or specific surgical procedure. The timing of platelet administration is more uniform because they are given after CPB once protamine has been completed. Further platelet administration is often considered if the site of persistent bleeding is thought to be the microvasculature.
Cryoprecipitate.
Although cryoprecipitate initially was used to treat hemophilia A, its use has been expanded to acquired causes of hypofibrinogenemia, including that which occurs with CPB. The likely mechanism of hypofibrinogenemia in CPB is a consumptive process that occurs with a large amount of blood loss and as a result of the effects of blood flowing through the bypass circuit. It is the least likely blood product to be transfused in patients with CHD undergoing cardiac surgery. The potential benefits are the small volume compared to the amount of fibrinogen contained when compared to FFP. There are no studies evaluating its use, but it may be beneficial in infants and neonates who may not tolerate large volumes of FFP or who have isolated hypofibrinogenemia.
Transfusion Algorithms/Coagulation Studies.
The overwhelming evidence of the harm of transfusions has forced pediatric cardiac centers to alter their transfusion practices. Many centers have started to use laboratory data in an attempt to decrease the amount of blood products used. Laboratory data may help identify underlying causes of bleeding and address the appropriate causes. Some studies have shown the efficacy of using laboratory data and demonstrated a decreased use of overall blood products.
A variety of laboratory studies may be considered from basic coagulation studies, such as international normalized ratio, prothrombin time, partial thromboplastin time, platelet count, and fibrinogen, to functional studies ( Fig. 25.2 ) like TEG (TEG; Haemonetics Corporation, Braintree, MA), thromboelastometry (TEM) and rotational thromboelastography (ROTEM) (Pentapharm GmbH, Basel, Switzerland). Please refer to Chapter 24 for additional explanation of these laboratory studies. There are some concerns that the routine use of these studies could potentially increase blood product utilization in attempt to make laboratory study results normal without the abnormality showing any clinical effect. Therefore an important component for some of these algorithms is the presence of “abnormal” bleeding. This is a subjective evaluation by the surgeon and impacts the potential accuracy and generalizability of the algorithms. For these reasons some experts advocate the use of coagulation studies only in high-risk bleeding patients (e.g., redo sternotomies, neonates, and patients undergoing deep hypothermic circulatory arrests).
Factor Concentrates.
Please refer to Chapter 24 for a full discussion of factor depletion and potential mechanisms for bleeding.
The primary factors in coagulation are present in FFP. Factor concentrates give a concentrated dose of specific factors and are primarily used in patients with hemophilia who lack specific coagulation factor(s). There has been an increase both in the number of factor concentrates available in recent years and in their use in pediatric cardiac surgery. There is little high-quality evidence for the use factor concentrates, and much of the literature is limited to case reports or relatively small case series. Factor concentrates have been used predominantly as a rescue therapy for patients with persistent medical bleeding during the perioperative period ( Table 25.1 ). The lack of empiric data along with the expense, and risks, of these products has led many institutions to create strict protocols for their use. Further studies are needed to establish the role of factor concentrates in blood conservation and utilization.
| Drug Name | Accepted Clinical Use | Dosing |
|---|---|---|
| Antithrombin III (Thrombate III) | Hereditary antithrombin deficiency Possible clinical use: low antithrombin III in the setting of ECMO or CPB | Prophylaxis: 25-40 units/kg Treatment: (Desired − Measured AT III level) × wt in kg/1.4 |
| Factor VIIa (NovoSeven) | Hemophilia A/B, factor VII deficiency, Glanzmann thrombasthenia Uncontrolled bleeding despite adequate FFP, cryoprecipitate, platelets Intrabronchial administration for pulmonary hemorrhage | Dosing dependent on diagnosis: For bleeding post cardiac surgery: 60 mcg/kg |
| Factor VIII (Advate) | Hemophilia A | Prophylaxis: 20-40 units kg Treatment: (Desired VIII − Baseline VIII level) × (weight in kg)/2 |
| Factor VIII (Recombinant) | Hemophilia A | Treatment: (Desired FVIII increase [%]) × (weight in kg)/2 |
| Factor IX (BeneFix) | Hemophilia B | Prophylaxis: 25-40 units/kg twice weekly Treatment, children: (Desired IX − Baseline IX level) × (weight in kg) × 1.4 Treatment, adult: (Desired IX − Baseline IX level) × (weight in kg) × 1.2 |
| FEIBA (aPCC antiinhibitor) | Bleeding in the setting of oral anticoagulants Hemophilia A and B with inhibitors | 50-75 units/kg |
| Fibrinogen concentrate (RiaSTAP) | Congenital fibrinogen deficiency | Prophylaxis: 20-30 mg/kg weekly Treatment: 70 mg/kg |
| Prothrombin complex concentrate (Kcentra) | Reversal of vitamin K antagonists (Warfarin) | Dependent on INR: 25-50 units/kg for children |
| von Willebrand factor (Humate-P) | von Willebrand disease | Type I: Loading dose: 50-75 IU Maintenance: 40-60 IU every 6-25 h (target VWF concentration of > 50) Type II/III: Loading dose: 60-80 IU Maintenance dose: 40-60 IU |
Ultrafiltration.
Ultrafiltration is a method of removal of fluid and high-molecular-weight solutes and inflammatory mediators across a semipermeable membrane after or during CPB. There are numerous types of ultrafiltration, but the most common in pediatrics is modified ultrafiltration. This process occurs immediately after bypass and was first described in the early 1990s. Conventional ultrafiltration is still used at some centers, and fluid removal occurs while on CPB. Ultrafiltration has beneficial effects on blood conservation and utilization, including increasing hematocrit, platelets, and coagulation factors and decreasing postoperative transfusions.
Special Considerations
Fresh Whole Blood
The use of fresh whole blood (FWB) in pediatric cardiac surgery is still a topic of debate. The proponents believe that giving blood with all its procoagulant and anticoagulant factors allows for a better balance between clot formation and destruction, which may minimize the amount of blood required during the surgery. There may also be benefits with minimizing the number of donor products in decreasing the overall risk with transfusion and the associated inflammatory response. The contrary view is that whole blood can be difficult to obtain at many centers, and there is a potential waste of products by not partitioning out each component. Most centers that use FWB primarily use it in neonates and infants, who have a higher rate of overall blood utilization. The evidence for FWB use in priming the circuit and for continued resuscitation is not completely clear. The studies have primarily been completed in single centers with differing methods. Three prospective studies have shown a benefit to the use of whole blood. Two of these studies used FWB not only in the prime but also for continued resuscitation. These studies were consistent in showing that FWB decreased postoperative blood loss. The more recent study also showed a decrease in LOS, inotropic scores, and ventilation times with FWB. This blood was also reconstituted from separate components from the same donor. Priming with FWB alone has two conflicting studies; Mou et al. showed no benefit and at worse, possible harm, whereas Valleley et al. demonstrated a benefit in donor exposure and postoperative bleeding. Complicating this further is that the study by Mou et al. compared a reconstituted blood prime (PRBCs and FFP) to whole blood, whereas the study by Valleley et al. had a CPB prime containing only PRBCs. The conflicting data, the difficulty in obtaining FWB, and the potential waste of products have kept it from being consistently used in neonates and infants throughout the United States.
Blood Utilization and Blood Conservation—Postoperative Management
Iatrogenic anemia is common in infants and children following cardiac surgical procedures secondary to hemodilution and hemolysis related to CPB strategies, crystalloid and albumin boluses/infusions postoperatively, and frequent sampling. Ongoing blood loss through mediastinal and chest tubes is commonplace, particularly in the first 48 hours after surgery, and can be significant when compounded by inadequate surgical hemostasis or exacerbated by hypothermia, coagulopathy, hypofibrinogenemia, platelet dysfunction, and thrombocytopenia. Efforts to maintain hemodynamic stability and ensure adequate oxygen delivery include PRBC transfusion for volume expansion and improved oxygen-carrying capacity and plasma products to correct coagulopathy and replace fibrinogen and platelets and control/resolve bleeding.
Complicating postoperative management is the prevalence of decreased myocardial performance and systemic vasodilation/systemic inflammatory response syndrome that occurs following CPB, which may impair the patient’s ability to increase cardiac output and maintain oxygen delivery in response to anemia. Unique factors related to CHD impact blood conservation and utilization. First, morphologic/structural changes (single-ventricle physiology and/or intracardiac or great-vessel-level shunting) may increase the volume and/or pressure load on either the systemic and/or pulmonary ventricle(s) and may limit the patient’s ability to augment cardiac output by increasing ventricular stroke volume (hypertrophy and/or diastolic dysfunction) and overcome increased afterload (systolic dysfunction). Additionally, in cases of single-ventricle physiology and/or intracardiac or great-vessel-level shunting, changes in downstream pulmonary and/or systemic vascular resistance threaten the adequacy of blood flow to the other vascular bed (pulmonary or systemic). For these reasons, patient status post palliation or repair for CHD is uniquely vulnerable to anemia, bleeding, and alterations in hemodynamics, oxygenation, and ventilation. Red cell and coagulant product transfusions are important components of the medical management of these patients (see Table 25.1 ).
It is impossible to control for all the confounding factors that affect anemia, severity of illness, PRBC transfusion, and outcomes, which is why use of prospective randomized controlled trials (RCTs) is paramount ( Fig. 25.3 ). There are now a few RCTs examining transfusion strategies in postoperative pediatric cardiac surgery, but it must be emphasized that the results of such trials should be interpreted with caution because each pediatric patient undergoing cardiac surgery has unique cardiac morphology and physiology that may change over time and may differ depending on the clinical situation, which may also change. For example, even when grouped according to cardiac diagnoses, developmental differences (gestational age, postnatal age, weight), and the presence of additional congenital extracardiac defects and/or chromosomal abnormalities or genetic syndromes, prevent the generalization of transfusion management of these children. Great differences in physiology exist even in those who carry the same cardiac diagnosis. For example, patients with tetralogy of Fallot have varying degrees of right ventricular outflow tract obstruction and may have supravalvar, valvar, or subvalvar pulmonary stenosis, resulting in different degrees of right ventricular hypertrophy and varied atrial level shunting These anatomic differences lead to variation in oxygen saturations, preload dependence, and cardiac function and make generalization of anemia tolerance, even with this specific structural diagnosis, impossible. CPB and surgical techniques vary greatly among surgeons and across institutions. Differences in anesthesia, perfusion, and critical care management strategies also impact anemia tolerance and complicate generalization of transfusion strategies in the literature to the specific patient.
