Transfusion of blood products is a common occurrence during surgery. Anesthesia technicians may be called upon to retrieve blood products, help check them in, and help administer them. Transfusion of incompatible blood products to a patient can cause serious patient injury, and anesthesia technicians should be familiar with basic transfusion medicine. This chapter provides an introduction to the different types of blood products, what makes them compatible or incompatible with a patient, how they should be administered, and the potential complications or adverse reactions from the transfusion of blood products.

The different blood types (blood groups) and their relationship to the immune system is the basis of transfusion science. Blood types are inherited and represent contributions from both parents. A total of 30 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT). A blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). Antigens, which may be proteins, carbohydrates, glycoproteins, or glycolipids, are present on the cellular membrane of RBCs and are also secreted to plasma and body fluids. Antigens determine the blood group type. In 1900, Karl Landsteiner discovered the ABO blood groups for which he received the 1930 Nobel Prize in Medicine and Physiology. The ABO antigen system is the most important determinant of blood type grouping in transfusion medicine. The two major RBC antigens are known as A and B. The blood groups are A, B, AB, and O, where O is when the RBCs lack both A and B antigens. People with AB blood type have RBCs that have both antigens. People with RBCs that only have the A or B antigen are blood type A and B, respectively.

ABO compatibility remains the major safety consideration of blood product transfusions (Table 23.1). Compatibility means that the recipient does not recognize the blood transfusion as foreign. Immune systems of virtually all individuals produce antibodies directed against antigens they do not have (anti-B antibodies in type A individuals, anti-A antibodies in type B individuals, and anti-A and anti-B antibodies in type O individuals). The process whereby foreign antigens from blood groups cause production of antibodies directed against them in the recipient is called alloimmunization. This concept is extremely important to the understanding of transfusion medicine. If a patient receives blood (recipient) that has antigens that are foreign to the recipient, the recipient can mount a massive immune reaction (allergic reaction) against the foreign blood. These reactions are particularly severe if the recipient has preformed antibodies (a primed immune system) against the foreign antigen. This type of reaction is akin to an anaphylactic reaction except that the foreign antigen is the transfused blood. Humans form antibodies to A or B antigens in the first years of life if they do not have them on their own RBCs. This is thought to be from exposure to environmental antigens (food, bacteria, virus, etc.). Thus, humans are usually “primed” against ABO-incompatible blood. A reaction to ABO-incompatible blood is called an acute hemolytic transfusion reaction and is fatal in about 10% of cases. The recipient may not only manifest symptoms of an anaphylactic reaction (low blood pressure, fever, bronchospasm) from the immune mediators released but also suffer because his or her immune system attacks the foreign blood cells, causing them to hemolyze (rupture) and release free hemoglobin into the
bloodstream. Free hemoglobin is a large protein and is very toxic to the kidney. It is not surprising that many of the first recipients of blood transfusions, before there was an understanding of blood group antigens, died from a severe transfusion reaction. Other types of transfusion reactions will be discussed below. The primary cause of transfusing ABO-incompatible units (incorrect blood type) is clerical errors in patient identification or errors in sample labeling.

The second most important blood group system is the Rhesus (Rh) system. Rh positivity is indicated by the presence of D antigen in the membrane of the RBC; D antigen is absent in Rh (D)-negative individuals. About 15% of people are Rh (D)-negative. Unlike anti-A or anti-B antibodies, Rh (D)-negative individuals do not produce anti-Rh (D) antibodies until they are exposed to Rh (D)-positive blood. When an Rh (D)-negative individual is exposed to Rh (D)-positive cells, sensitization occurs and the immune system can produce anti-D alloantibody. Any subsequent exposure to Rh (D)-positive blood can result in a severe adverse reaction. Sensitization can occur by transfusion or during pregnancy. If an Rh (D)-negative mother is pregnant with an Rh (D)-positive baby (the baby inherited the Rh (D) antigen from the father), the mother will become sensitized to the Rh (D) antigen. This happens because there can be some mixing of the baby’s blood with the mother’s blood at delivery. Once a mother is sensitized to the Rh (D) antigen, she can form antibodies that can attack the blood of a subsequent fetus if the fetus is Rh (D)-positive. Even in emergencies, Rh (D)-positive blood should not be given to Rh (D)-negative patients to avoid sensitization. Typically, type-O Rh (D)-negative blood (O neg) is stored by hospitals for emergency transfusion because of its near-universal safety for patients with untyped blood due to its lack of AB or Rh (D) antigens.

Several other blood group systems exist in addition to the ABO and Rh (D) systems: Lewis, I system, P system, MNSsU system, Kell Protein, and the Duffy and Kidd antigens. These antigens can be present on RBCs and result in incompatibility, but these are not necessarily tested for in every patient because they are either extremely rare, extremely common, or compatibility can be ensured by providing warmed blood (above 30°C).

Patients who have received multiple transfusions over the course of their life are at higher risk of developing antibodies, and it may be more difficult to find a compatible unit. Procuring a compatible unit can take extra time and may result in a surgical delay.

Before any RBC unit is given to a patient, it undergoes several different tests to ensure that it is compatible with the recipient. The tests are separate from the testing done for diseases such as hepatitis and human immunodeficiency virus (HIV). Screening of potential donors and rigorous testing of donated units have largely eliminated the risk of units containing HIV, hepatitis, and other infections. The first test, known as the type and screen, is done on donated blood before releasing the unit. This test determines the blood type—A, B, AB, O, and Rh (D)-positive/negative. This testing is also done on the patients to determine their blood type as well as screen for the presence of antibodies to A or B and antibodies against other antigens known to cause hemolytic reactions. The test is performed by mixing the sample blood (the patient’s blood or the donated blood) with a solution containing antibodies against the antigen being screened. For example, if one wants to determine if a patient has A antigen on his or her RBCs

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