Historical Background
Blood transfusion, often a life-saving strategy, historically dates back to the Egyptian and Roman era. Egyptians took a blood bath as a recuperative measure, while the Romans drank the blood of fallen gladiators to cure epilepsy. Deviating from such ancient rituals, Jean-Baptiste Denis performed the first animal-to-human transfusion in 1667, where he administered the blood of a lamb to a 15-year-old boy. Unfortunately, the practice of animal-to-human transfusion led to increased mortality, which put a halt on the transfusion practice for the next 150 years. The first well-documented transfusion with human blood happened on September 26, 1818, followed by multiple reports on transfusion in obstetric hemorrhages. Lack of knowledge of blood groups and screening tests resulted in transfusion-related infectious as well as noninfectious complications in the 19th century.
The discovery of blood groups by Karl Landsteiner in 1900 and advanced techniques equipped with highly sensitive and rapid tests to screen the blood products has made the blood transfusion practice safe in the modern era.
The practice of blood transfusion has been evolving for the last many decades, dominated by the administration of whole blood and fresh frozen plasma (FFP) to the administration of component therapy through the 1970s and 1980s. Since 2010 onward, the practice has shifted from simply correcting anemia and coagulopathy to patient-centered, multipronged approach in relation to evidence-based transfusion medicine, which is termed as patient blood management (PBM).
Although a life-saving strategy, blood transfusion is not without complications. Therefore, a thorough knowledge of blood components and transfusion-related complications is imperative to ensure patient safety and improved outcomes.
Blood Components
The constituents of blood include red blood cells, white blood cells, platelets, and a variety of proteins including coagulation factors. The whole blood after collection from the donor can be fragmented into its components (PRBC, platelets, cryoprecipitate, and fresh frozen plasma).
The individual components after separation are stored in the blood bank at an appropriate temperature in storage devices like freezers, refrigerators, and platelet incubators. These products are released as and when they are requested as per the need of patients and discarded after expiry if not used. The description of individual components is as follows:
Packed red blood cells (PRBCs): Contain the same amount of hemoglobin as the whole blood, but due to plasma removal, the hematocrit of PRBC is approximately 60%. It is stored at 1 to 6°C in the blood bank to decrease the metabolic activity of red blood cells. Crystalloids and colloids facilitate the transfusion of PRBC. The calcium content (e.g., calcium in Ringer lactate may precipitate clotting) and the tonicity (hypotonic and hypertonic fluids can cause swelling and shrinkage of red blood cells, respectively) are important in choosing the appropriate fluid. The recommended solutions compatible with PRBC are 5% dextrose with 0.45/0.9% saline, 0.9 saline, and Normosol-R with
pH 7.4.
PRBC is stored in specific anticoagulant/preservative solutions to increase shelf life. The commonly used preservative solutions are as follows:
Citrate-phosphate-dextrose (CPD): 21 days.
Citrate-phosphate-dextrose-adenine (CPDA): 35 days.
Additives (AS1, AS3, AS5): 42 days.
AS7: 56 days (approved by FDA in 2015; commercially not available).
The additive solutions do prolong the storage duration of PRBC, but as the duration of storage increases, they add to biochemical changes, which are collectively known as red cell storage lesions. During storage, red blood cells metabolize glucose to lactate, hydrogen ions accumulate, and pH decreases. Failure of Na+K+ ATPase pump at 1 to 6°C leads to the gain of intracellular sodium and transfer of potassium from cells to plasma. With time, there is a progressive decrease in ATP, nitric oxide, and 2,3-diphosphoglycerate (2,3-DPG) levels in addition to increased RBC fragility.
Although hemoglobin level has traditionally been used as a trigger to transfuse PRBC, many other factors, such as cardiovascular status, age, anticipated additional blood loss, arterial oxygenation, mixed venous oxygenation, intravascular blood volume, and cardiac output, should be considered to decide upon the need for further transfusion.
ABO compatibility is a must, and one unit of PRBC transfusion raises Hb by 1 g/dL (hematocrit by 3%). The current recommendations regarding PRBC transfusion are as follows:
In healthy adults and most children, the threshold for red cell transfusion is 7 g/dL.
A restrictive transfusion strategy (hemoglobin level of 7–9 g/dL) is not acceptable for preterm infants or children with cyanotic heart disease, severe hypoxemia, active blood loss, or hemodynamic instability.
Red blood cells contain multiple antigens on their surface, which can interact with antibodies present in the serum of recipients, leading to serious hemolytic reactions. Therefore, it is mandatory to do compatibility testing before attempting transfusion, except for the situations where there is no time to compatibility tests (emergent need for blood products in case of trauma, obstetric hemorrhage). The most important and common antigen groups are ABO-Rh. Table 5.1 shows major blood groups and the compatible donors and recipients.
Platelets: Platelet concentrates are obtained either as pooled from four to six donors (known as random donor platelet) or by apheresis from a single donor (known as single donor platelet). Platelets are stored at 20 to 24°C to improve posttransfusion in vivo recovery (as cold exposure inactivates platelets). Platelets are highly sensitive to changes in pH. Constant and gentle agitation promotes gas exchange between platelets and containers, which helps in maintaining the pH. At room temperature, platelet concentrates can be used up to 7 days. Storage at room temperature makes platelet concentrates susceptible to bacterial contamination; hence, they are implicated in septic complications after transfusion. Whenever possible, ABO-compatible platelets should be transfused, but it is not necessary. One unit of apheresis platelets should increase the platelet count in adults by 30,000 to 40,000, while that of random donor platelet increases platelet count by 5,000 to 10,000. The various indications of platelet transfusions are tabulated in Table 5.2.
Fresh frozen plasma (FFP): It is the most frequently used plasma product. It is generally frozen within 8 or 24 hours of donation. It contains all plasma proteins, mainly factors V and VIII. Shelf life is for 12 months when stored at < −18°C. Thawed plasma is stored at 1 to 6°C up to 5 days. The indications for FFP transfusions are:
International normalized ratio (INR)
> 1.6.
Reversal of effect of warfarin in an emergency situation.
Disseminated intravascular coagulopathy (DIC).
Each unit of FFP increases the level of each clotting factor by 2 to 3%. The initial volume of transfusion is 10 to 15 mL/kg. ABO compatibility for FFP transfusion is not mandatory but highly desirable.
Cryoprecipitate: It is derived from thawed plasma at 1 to 6°C. It contains factor VIII, Von Willebrand factor, factor XIII, fibrinogen, and fibronectin. It can be stored for up to 12 months at < −18°C. When the product is requested for use, it should be thawed at 30 to 36°C. As per current recommendations by the American Academy of Blood Bank (AABB), one bag of cryoprecipitate must contain at least 150 mg of fibrinogen and 80 U of factor VIII. One bag of cryoprecipitate raises fibrinogen levels by 5 to 10 mg/dL. The indications for cryoprecipitate infusion are:
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