Morgan and Mikhail's Clinical Anesthesiology Chapter 51

Metadata

• Author: John Butterworth
• Full Title: Morgan and Mikhail's Clinical Anesthesiology Chapter 51
• Category: #books

Highlights

• Serial hematocrits or ../../../Knowledge/Medicine/Haemoglobin concentrations reflect the ratio of RBC to plasma, not necessarily blood loss, and rapid fluid shifts and intravenous replacement affect such measurements (Page 2)
• The transfusion point can be determined preoperatively from the hematocrit blood volume (Table 51–5). Patients with a normal and by estimating hematocrit should generally be transfused only after losses greater than 10% to 20% of their blood volume. The timing of transfusion initiation is based on the patient’s surgical procedure, comorbid conditions, and rate of blood loss. The amount of blood loss necessary for the hematocrit to fall to 30% can be calculated as follows:

TABLE 51–5 Average blood volumes.

1. Estimate blood volume from Table 51–5.
2. Estimate the red blood cell volume (RBCV) at the preoperative hematocrit (RBCVpreop). volume is maintained.
3. Estimate RBCV at a hematocrit of 30% (RBCV30%), assuming normal blood
4. Calculate the RBCV lost when the hematocrit is 30%; RBCVlost = RBCVpreop – RBCV30%.
5. Allowable blood loss = RBCVlost × 3. (Page 4)

Example: An 85-kg woman has a preoperative hematocrit of 35%. How much blood loss will decrease her hematocrit to 30%?

Estimated blood volume = 65ml/kg x 85kg = 5525ml
RBCV35% = 5525 x 35% = 1934ml
RBCV30% = 5525 x 30% = 1658ml
Red cell loss at 30% = 1934 - 1658 = 276ml
allowable blood loss = 3 x 276ml = 828ml

Therefore, transfusion should be considered only when this patient’s blood loss exceeds 800 mL. Increasingly, transfusions are not recommended until the hematocrit decreases to 24% or lower (hemoglobin <8.0 g/dL), but it is necessary to take into account the potential for further blood loss, rate of blood loss, and comorbid conditions (eg, cardiac disease). Clinical guidelines for transfusion commonly used include the following:

1. transfusing 1 unit of ../../../Knowledge/Medicine/Red Blood Cell will increase ../../../Knowledge/Medicine/Haemoglobin 1 g/dL and the hematocrit 2% to 3% in adults; and
2. a 10-mL/kg transfusion of red blood cells will increase hemoglobin concentration by 3 g/dL and the hematocrit by 10%.

Almost all individuals not having A or B antigen “naturally” produce antibodies, mainly immunoglobulin (Ig) M, against those missing antigens within the first year of life. (Page 6)

• In contrast to the ABO groups, Rh-negative patients usually develop antibodies against the D antigen only after an Rh-positive transfusion or with pregnancy, in the situation of an Rh-negative mother delivering an Rh-positive baby. (Page 7)
• The probability of developing anti-D antibodies after a single exposure to the Rh antigen is 50% to 70%.

A crossmatch mimics the transfusion: Donor red cells are mixed with recipient serum.

Crossmatching serves three functions:

1. it confirms ABO and Rh typing,
2. it detects antibodies to the other blood group systems, and
3. it detects antibodies in low titers or those that do not agglutinate easily.

Type & Crossmatch versus Type & Screen

In the situation of negative antibody screen without crossmatch, the incidence of serious hemolytic reaction with ABO- and Rh-compatible transfusion is less than 1:10,000. Crossmatching, however, assures optimal safety and detects the presence of less common antibodies not usually tested for in a screen. Because of the expense and time involved (45 min), crossmatches are often now performed before the need to transfuse only when the patient’s antibody screen is positive, when the probability of transfusion is high, or when the patient is considered at risk for alloimmunization.

EMERGENCY TRANSFUSIONS

When a patient is exsanguinating, the urgent need to transfuse may arise prior to completion of a crossmatch, screen, or even blood typing. If the patient’s blood type is known, an abbreviated crossmatch, requiring less than 5 min, will confirm ABO compatibility. If the recipient’s blood type and Rh status are not known with certainty and transfusion must be started before determination, type O Rh-negative (universal donor) red cells may be used. Red blood cells, fresh frozen plasma, and platelets are often transfused in a balanced ratio (1:1:1) in massive transfusion protocols and in trauma damage control resuscitation

• A preservative–anticoagulant solution is added. The most commonly used solution is CPDA-1, which contains citrate as an anticoagulant (by binding calcium), phosphate as a buffer, dextrose as a red cell energy source, and adenosine as a precursor for adenosine triphosphate (ATP) synthesis. CPDA-1-preserved blood can be stored for 35 days, after which the viability of the red cells rapidly decreases. Alternatively, use of either AS-1 (Adsol) or AS-3 (Nutrice) extends the shelf-life to 6 weeks. (Page 9)
• Nearly all units collected are separated into their component parts (ie, red cells, platelets, and plasma), and whole blood units are rarely available for transfusion in civilian practice. When centrifuged, 1 unit of whole blood yields approximately 250 mL of packed ../../../Knowledge/Medicine/Red Blood Cell (PRBCs) with a hematocrit of 70%; following the addition of saline preservative, the volume of a unit of PRBCs often reaches 350 mL. Red cells are normally stored at 1°C to 6°C but may be frozen in a hypertonic glycerol solution for up to 10 years. The latter technique is usually reserved for storage of blood with rare phenotypes. (Page 9)
• The supernatant is centrifuged to yield platelets and plasma. The unit of ../../../Knowledge/Medicine/platelet obtained generally contains 50 to 70 mL of plasma and can be stored at 20°C to 24°C for 5 days. The remaining plasma supernatant is further processed and frozen to yield ../../../Knowledge/Medicine/Fresh Frozen Plasma; rapid freezing helps prevent inactivation of the labile coagulation factors V and VIII. Slow thawing of ../../../Knowledge/Medicine/Fresh Frozen Plasma yields a gelatinous precipitate (../../../Knowledge/Medicine/cryoprecipitate) that contains high concentrations of factor VIII and ../../../Knowledge/Medicine/Fibrinogen. Once separated, ../../../Knowledge/Medicine/cryoprecipitate can be refrozen for storage. One unit of blood yields about 200 mL of plasma, which is frozen for storage; once thawed, it must be transfused within 24 h. Most platelets are now obtained from donors by apheresis, and a single platelet apheresis unit is equivalent to the amount of platelets derived from 6 to 8 units of whole blood. (Page 9)
• The use of leukocyte-reduced (leukoreduction) blood products has been rapidly adopted by many countries, including the United States, in order to decrease the risk of transfusion-related febrile reactions, infections, and immunosuppression. (Page 9)
• Prior to transfusion, each unit should be carefully checked against the blood bank slip and the recipient’s identity bracelet. The transfusion tubing should contain a 170-μm filter to trap any clots or debris. Blood for intraoperative ../../../Knowledge/Medicine/transfusion should be warmed to 37°C during infusion, particularly when more than 2 to 3 units will be transfused; failure to do so can result in profound hypothermia. The additive effects of hypothermia and the typically low levels of 2,3-diphosphoglycerate (2,3-DPG) in stored blood can cause a marked leftward shift of the hemoglobin–oxygen dissociation curve (see Chapter 23) and, at least theoretically, promote tissue hypoxia. (Page 10)
• ../../../Knowledge/Medicine/Fresh Frozen Plasma (FFP) contains all plasma proteins, including most clotting factors. Transfusions of FFP are indicated in the treatment of isolated factor deficiencies, the reversal of warfarin therapy, and the correction of coagulopathy associated with liver disease. Each unit of FFP generally increases the level of each clotting factor by 2% to 3% in adults. The initial therapeutic dose is usually 10 to 15 mL/kg. The goal is to achieve 30% of the normal coagulation factor concentration. (Page 10)
• Patients with antithrombin III deficiency or thrombotic thrombocytopenic purpura also benefit from FFP transfusions. (Page 10)
• Prophylactic platelet transfusions are also indicated in patients with platelet counts below 10,000 to 20,000 × 109/L because of an increased risk of spontaneous hemorrhage.
• Administration of a single unit of platelets may be expected to increase the ../../../Knowledge/Medicine/platelet count by 5000 to 10,000 × 109/L, and with administration of a platelet apheresis unit, by 30,000 to 60,000 × 109/L. (Page 11)
• Transfused platelets generally survive only ==1 to 7 days ==following transfusion. (Page 11)

Acute Hemolytic Reactions

Acute intravascular hemolysis is usually due to ABO blood incompatibility, and the reported frequency is approximately 1:38,000 transfusions. The most common cause is misidentification of a patient, blood specimen, or transfusion unit, a risk that is not abolished with autologous blood transfusion. These reactions are often severe, and may occur after infusion of as little as 10 to 15 mL of ABO-incompatible blood. The risk of a fatal hemolytic reaction is about 1 in 100,000 transfusions. In awake patients, symptoms include chills, fever, nausea, and chest and flank pain. acute hemolytic reaction may be manifested by a rise in temperature, unexplained tachycardia, hypotension, hemoglobinuria, diffuse oozing in In anesthetized patients, an (Page 12)

the surgical field, or a combination of these findings. Disseminated intravascular coagulation, shock, and kidney acute failure can develop rapidly. The severity of a reaction often depends upon the volume of incompatible blood that has been administered.

Management of hemolytic reactions can be summarized as follows:

1. If a hemolytic reaction is suspected, the transfusion should be stopped immediately and the blood bank should be notified.
2. The unit should be rechecked against the blood slip and the patient’s identity bracelet.
3. Blood should be drawn to identify hemoglobin in plasma, to repeat compatibility testing, and to obtain coagulation studies and a platelet count.
4. A urinary bladder catheter should be inserted, and the urine should be checked for hemoglobin.
5. Forced diuresis should be initiated with mannitol and intravenous fluids, and with a loop diuretic if necessary.

• TACO has replaced TRALI as the leading transfusion-related risk for trauma patients. (Page 15)
• To avoid the possibility of significant bacterial contamination, blood products should be administered over a period shorter than 4 h (Page 17)

AUTOLOGOUS TRANSFUSION

• Collection is usually started 4 to 5 weeks prior to the procedure. The patient is usually allowed to donate a unit as long as the hematocrit is at least 34% or hemoglobin at least 11 g/dL. A minimum of 72 h is required between donations to ensure plasma volume has returned to normal. With iron supplementation and erythropoietin therapy, at least 3 or 4 units can usually be collected prior to operation. (Page 19)

Morgan and Mikhail's Clinical Anesthesiology Chapter 51

Metadata

• Author: John Butterworth
• Full Title: Morgan and Mikhail's Clinical Anesthesiology Chapter 51
• Category: #books

Highlights

• Serial hematocrits or hemoglobin concentrations reflect the ratio of RBCs to plasma, not necessarily blood loss, and rapid fluid shifts and intravenous replacement affect such measurements (Page 2)
• The transfusion point can be determined preoperatively from the hematocrit blood volume (Table 51–5). Patients with a normal and by estimating hematocrit should generally be transfused only after losses greater than 10% to 20% of their blood volume. The timing of transfusion initiation is based on the patient’s surgical procedure, comorbid conditions, and rate of blood loss. The amount of blood loss necessary for the hematocrit to fall to 30% can be calculated as follows: TABLE 51–5 Average blood volumes. 1. Estimate blood volume from Table 51–5. 2. Estimate the red blood cell volume (RBCV) at the preoperative hematocrit (RBCVpreop). volume is maintained. 3. Estimate RBCV at a hematocrit of 30% (RBCV30%), assuming normal blood 4. Calculate the RBCV lost when the hematocrit is 30%; RBCVlost = RBCVpreop – RBCV30%. 5. Allowable blood loss = RBCVlost × 3. (Page 4)
• Example: An 85-kg woman has a preoperative hematocrit of 35%. How much blood loss will decrease her hematocrit to 30%? Therefore, transfusion should be considered only when this patient’s blood loss exceeds 800 mL. Increasingly, transfusions are not recommended until the hematocrit decreases to 24% or lower (hemoglobin <8.0 g/dL), but it is necessary to take into account the potential for further blood loss, rate of blood loss, and comorbid conditions (eg, cardiac disease). Clinical guidelines for transfusion commonly used include the following: (1) transfusing 1 unit of red blood cells will increase hemoglobin 1 g/dL and the hematocrit 2% to 3% in adults; and (2) a 10-mL/kg transfusion of red blood cells will increase hemoglobin concentration by 3 g/dL and the hematocrit by 10%. (Page 5)
• Almost all individuals not having A or B antigen “naturally” produce antibodies, mainly immunoglobulin (Ig) M, against those missing antigens within the first year of life. (Page 6)
• In contrast to the ABO groups, Rh-negative patients usually develop antibodies against the D antigen only after an Rh-positive transfusion or with pregnancy, in the situation of an Rh-negative mother delivering an Rh-positive baby. (Page 7)
• The probability of developing anti-D antibodies after a single exposure to the Rh antigen is 50% to 70%. (Page 7)
• A crossmatch mimics the transfusion: Donor red cells are mixed with recipient serum. Crossmatching serves three functions: (1) it confirms ABO and Rh typing, (2) it detects antibodies to the other blood group systems, and (3) it detects antibodies in low titers or those that do not agglutinate easily. (Page 8)
• Type & Crossmatch versus Type & Screen In the situation of negative antibody screen without crossmatch, the incidence of serious hemolytic reaction with ABO- and Rh-compatible transfusion is less than 1:10,000. Crossmatching, however, assures optimal safety and detects the presence of less common antibodies not usually tested for in a screen. Because of the expense and time involved (45 min), crossmatches are often now performed before the need to transfuse only when the patient’s antibody screen is positive, when the probability of transfusion is high, or when the patient is considered at risk for alloimmunization. (Page 8)
• EMERGENCY TRANSFUSIONS When a patient is exsanguinating, the urgent need to transfuse may arise prior to completion of a crossmatch, screen, or even blood typing. If the patient’s blood type is known, an abbreviated crossmatch, requiring less than 5 min, will confirm ABO compatibility. If the recipient’s blood type and Rh status are not known with certainty and transfusion must be started before determination, type O Rh-negative (universal donor) red cells may be used. Red blood cells, fresh frozen plasma, and platelets are often transfused in a balanced ratio (1:1:1) in massive transfusion protocols and in trauma damage control resuscitation (Page 8)
• A preservative–anticoagulant solution is added. The most commonly used solution is CPDA-1, which contains citrate as an anticoagulant (by binding calcium), phosphate as a buffer, dextrose as a red cell energy source, and adenosine as a precursor for adenosine triphosphate (ATP) synthesis. CPDA-1-preserved blood can be stored for 35 days, after which the viability of the red cells rapidly decreases. Alternatively, use of either AS-1 (Adsol) or AS-3 (Nutrice) extends the shelf-life to 6 weeks. (Page 9)
• Nearly all units collected are separated into their component parts (ie, red cells, platelets, and plasma), and whole blood units are rarely available for transfusion in civilian practice. When centrifuged, 1 unit of whole blood yields approximately 250 mL of packed red blood cells (PRBCs) with a hematocrit of 70%; following the addition of saline preservative, the volume of a unit of PRBCs often reaches 350 mL. Red cells are normally stored at 1°C to 6°C but may be frozen in a hypertonic glycerol solution for up to 10 years. The latter technique is usually reserved for storage of blood with rare phenotypes. (Page 9)
• The supernatant is centrifuged to yield platelets and plasma. The unit of platelets obtained generally contains 50 to 70 mL of plasma and can be stored at 20°C to 24°C for 5 days. The remaining plasma supernatant is further processed and frozen to yield fresh frozen plasma; rapid freezing helps prevent inactivation of the labile coagulation factors V and VIII. Slow thawing of fresh frozen plasma yields a gelatinous precipitate (cryoprecipitate) that contains high concentrations of factor VIII and fibrinogen. Once separated, cryoprecipitate can be refrozen for storage. One unit of blood yields about 200 mL of plasma, which is frozen for storage; once thawed, it must be transfused within 24 h. Most platelets are now obtained from donors by apheresis, and a single platelet apheresis unit is equivalent to the amount of platelets derived from 6 to 8 units of whole blood. (Page 9)
• The use of leukocyte-reduced (leukoreduction) blood products has been rapidly adopted by many countries, including the United States, in order to decrease the risk of transfusion-related febrile reactions, infections, and immunosuppression. (Page 9)
• Prior to transfusion, each unit should be carefully checked against the blood bank slip and the recipient’s identity bracelet. The transfusion tubing should contain a 170-μm filter to trap any clots or debris. Blood for intraoperative transfusion should be warmed to 37°C during infusion, particularly when more than 2 to 3 units will be transfused; failure to do so can result in profound hypothermia. The additive effects of hypothermia and the typically low levels of 2,3-diphosphoglycerate (2,3-DPG) in stored blood can cause a marked leftward shift of the hemoglobin–oxygen dissociation curve (see Chapter 23) and, at least theoretically, promote tissue hypoxia. (Page 10)
• Fresh frozen plasma (FFP) contains all plasma proteins, including most clotting factors. Transfusions of FFP are indicated in the treatment of isolated factor deficiencies, the reversal of warfarin therapy, and the correction of coagulopathy associated with liver disease. Each unit of FFP generally increases the level of each clotting factor by 2% to 3% in adults. The initial therapeutic dose is usually 10 to 15 mL/kg. The goal is to achieve 30% of the normal coagulation factor concentration. (Page 10)
• Patients with antithrombin III deficiency or thrombotic thrombocytopenic purpura also benefit from FFP transfusions. (Page 10)
• Prophylactic platelet transfusions are also indicated in patients with platelet counts below 10,000 to (Page 10)
• 20,000 × 109/L because of an increased risk of spontaneous hemorrhage. (Page 11)
• Administration of a single unit of platelets may be expected to increase the platelet count by 5000 to 10,000 × 109/L, and with administration of a platelet apheresis unit, by 30,000 to 60,000 × 109/L. (Page 11)
• Transfused platelets generally survive only 1 to 7 days following transfusion. (Page 11)
• Acute Hemolytic Reactions Acute intravascular hemolysis is usually due to ABO blood incompatibility, and the reported frequency is approximately 1:38,000 transfusions. The most common cause is misidentification of a patient, blood specimen, or transfusion unit, a risk that is not abolished with autologous blood transfusion. These reactions are often severe, and may occur after infusion of as little as 10 to 15 mL of ABO-incompatible blood. The risk of a fatal hemolytic reaction is about 1 in 100,000 transfusions. In awake patients, symptoms include chills, fever, nausea, and chest and flank pain. acute hemolytic reaction may be manifested by a rise in temperature, unexplained tachycardia, hypotension, hemoglobinuria, diffuse oozing in In anesthetized patients, an (Page 12)
• the surgical field, or a combination of these findings. Disseminated intravascular coagulation, shock, and kidney acute failure can develop rapidly. The severity of a reaction often depends upon the volume of incompatible blood that has been administered. Management of hemolytic reactions can be summarized as follows: 1. If a hemolytic reaction is suspected, the transfusion should be stopped immediately and the blood bank should be notified. 2. The unit should be rechecked against the blood slip and the patient’s identity bracelet. 3. Blood should be drawn to identify hemoglobin in plasma, to repeat compatibility testing, and to obtain coagulation studies and a platelet count. 4. A urinary bladder catheter should be inserted, and the urine should be checked for hemoglobin. 5. Forced diuresis should be initiated with mannitol and intravenous fluids, and with a loop diuretic if necessary. (Page 13)
• TACO has replaced TRALI as the leading transfusion-related risk for trauma patients. (Page 15)
• To avoid the possibility of significant bacterial contamination, blood products should be administered over a period shorter than 4 h (Page 17)
• AUTOLOGOUS TRANSFUSION (Page 19)
• Collection is usually started 4 to 5 weeks prior to the procedure. The patient is usually allowed to donate a unit as long as the hematocrit is at least 34% or hemoglobin at least 11 g/dL. A minimum of 72 h is required between donations to ensure plasma volume has returned to normal. With iron supplementation and erythropoietin therapy, at least 3 or 4 units can usually be collected prior to operation. (Page 19)