Page 1925 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 111 Principles of Red Blood Cell Transfusion 1705

Randomized clinical trials have evaluated the effects of differ- benefit. The other study showed a lower risk of apnea and major brain
ent transfusion thresholds in distinct clinical settings; however the injury for the liberal transfusion arm of the study. Therefore, the
thresholds used in the studies differ widely. Many of the studies safest transfusion trigger in the preterm infant still remains unclear,
found no difference in outcome. Most studies were not powered and further studies are indicated. Most institutions assess the clini-
to adequately evaluate clinically important outcomes. Few studies cal situation and consider the postnatal age and whether a neonate
included more than 100 patients. The Transfusion Requirements in has oxygen requirements when determining the need for a RBC
Critical Care trial included 838 intensive care unit (ICU) patients transfusion.
who were randomized to a restrictive transfusion strategy (transfused The dose of a RBC transfusion in a neonate can vary by institution
at Hb 7 g/dL) or liberal strategy (transfused at 10 g/dL). The 30-day between 5 and 20 mL/kg. Few studies have assessed the optimal dose
mortality was slightly lower in the restrictive group (18.7% versus in this patient population and further studies are needed. Paul et al
23.3%), but not significantly lower. The FOCUS trial, a 2600 compared 10 and 20 mL/kg and found that the larger volume did
patient, multicenter randomized trial designed to determine whether not cause impaired pulmonary function. Wong et al demonstrated
patients with cardiovascular disease or risk factors undergoing surgical extra transfusion episodes could be avoided with 20 mL/kg versus
repair of the hip benefit from a lower (<8 g/dL) or liberal transfusion 15 mL/kg, without any additional risk to the patient. Many transfu-
trigger (transfused at 10 g/dL), has recently been completed. The sion services now routinely use RBCs stored in additive solutions for
results showed that liberal transfusion did not reduce mortality or low volume RBC transfusion and thus prefer a dose of 20 mL/kg to
in-hospital morbidity in this patient cohort. Other studies have now account for the lower hematocrit of an additive unit.
been published in the ICU, in sepsis, and in upper gastrointestinal Finally, several trials of erythropoietin therapy in premature
(GI) bleeding that support the use of conservative transfusion infants have been undertaken. The administration of relatively
triggers. On the other hand, there is a need for studies of transfu- high-dose erythropoietin has been shown to raise Hb levels and
sion triggers in patients with cardiac ischemia or in neurosurgery reticulocyte counts in healthy premature infants, but the effect
where clinicians have been reluctant to adopt conservative red cell in sicker neonates is unclear. Although transfusion exposure was
triggers. decreased, the significance of this observation is diminished, given the
promise of new strategies for limiting transfusions and donor expo-
sure. The high cost and the increased risk of retinopathy associated
Red Blood Cell Transfusion in Neonates with erythropoietin treatment does not justify its use in this patient
population.
In neonates it is convenient to consider periodic, small-volume In the case of massive transfusion, the situation differs. There have
transfusion separately from massive transfusion situations. The trigger been marked increases in massive transfusion in recent years in full-
for transfusion and the optimal type of component are very different term as well as premature infants. Hemolytic disease of the newborn
in these two settings. The potential adverse effects may be quite remains a prominent indication for exchange transfusion; however,
distinct. the recent use of intravenous immune globulin to decrease red cell
Low-volume RBC transfusion is rarely indicated in full-term antibody levels in newborns has decreased the necessity of this pro-
infants unless acute blood loss has occurred at birth or an intrauterine cedure. The two triggers for exchange are (a) rapidly rising levels of
situation has led to prenatal anemia. In contrast, premature infants unconjugated bilirubin that may lead to kernicterus and permanent
are frequent recipients of transfusions. In the intensive care setting, central nervous system damage and (b) congestive heart failure sec-
the premature infant is subjected to frequent blood sampling, and ondary to severe anemia. Whole blood exchange transfusion is
iatrogenic anemia may necessitate transfusion. Anemia of prematurity especially beneficial in cases of hemolytic disease of the newborn
is also a well-recognized entity; premature infants have a slightly lower because it clears the bilirubin, the offending antibody, and the
Hb value at birth. In addition, the postnatal decline in Hb occurs antibody-coated red cells before lysis, while providing a source of red
earlier and is more pronounced in premature infants. The mechanism cells lacking the offending antigen. A two-blood-volume exchange is
for anemia of prematurity appears to involve a relatively lower output commonly performed by using a fresh unit of blood concentrated to
of erythropoietin in response to a given degree of anemia. This a final hematocrit level of approximately 50%. In cases of hyperbili-
phenomenon is attributed in part to the fact that the liver, rather than rubinemia resulting from other causes (e.g., that associated with liver
the kidney, is the major site of erythropoietin production in these immaturity in premature infants), phototherapy is the treatment of
infants. Although some practitioners have considered this degree of choice because its effects are usually more sustained, and exchange
anemia to be physiologic, the benign nature of this condition remains transfusion is used only for cases of marked elevations. Extracorporeal
controversial. membrane oxygenation and open-heart surgery are two other situa-
Another debate among neonatologists concerns the triggers for tions that the neonate may be exposed to large volumes of allogeneic
RBC transfusion, as in what clinical signs and symptoms are valid RBCs. The extracorporeal membrane oxygenation circuit requires a
reflections of poor tissue oxygenation. Congestive heart failure and prime with RBCs, as do many of the types of extracorporeal circuits
severe pulmonary disease are generally accepted indications for used for cardiopulmonary bypass.
transfusion, but recurrent apnea, tachypnea, tachycardia, and failure Although accumulating evidence supports the safety of using RBC
to thrive are also used as transfusion triggers. In recent times, the rate units of any age and with any preservative solution for low-volume
of transfusion and the donor exposure rate of premature infants have transfusions in neonates, the same transfusion policies may not apply
consistently declined. These changes, however, reflect improvements to massive transfusion. Newborn physiology is unique in several
in patient care (e.g., microtesting methods resulting in less iatrogenic ways that may have implications for massive transfusion therapy.
blood loss; the use of surfactant resulting in decreased respiratory The newborn does not handle metabolites in a mature fashion.
distress and the use of a single unit to supply one infant over a longer Renal immaturity may lead to problems in clearing potassium or
period) rather than being attributable to changes in the transfusion acid from stored RBCs, and the immature liver may not catabolize
trigger. The prolonged use of single units has become possible with citrate efficiently. These problems are accentuated and protracted
the advent of the sterile docking technology that preserves the full in the premature infant. To address the concern about potassium
shelf-life of the unit of RBCs, as well as with the accumulating load, fresh (<7 days old) or washed RBCs are often used, although
evidence that fresh blood is not necessary for low-volume transfusions the necessity of this practice is actively debated. Fresh blood may
in neonates because supernatant potassium and decreased pH are also be preferred because of its higher 2,3-DPG levels and better
not of concern in this setting. Two recent studies have provided red cell integrity. The citrate problem is probably best handled by
additional information about the relative risks and benefits of using using slow infusion rates, because the use of bicarbonate or calcium
restrictive rather than more liberal criteria for very low birth weight replacement to counteract the acid load or calcium-chelating effects
infants. One study showed that a liberal transfusion practice resulted of citrate is controversial. Finally, the use of RBCs stored in the newer
in more infants receiving transfusion but conferred little evidence of preservative solutions (CPDA-1, Adsol, Nutricel, Optisol) is avoided