1.2 Hematology for the Otolaryngologist
Key Features
Head and neck surgery patients may require screening for, and correction of, hematologic disorders.
An overview of blood components, disorders, and transfusion complications is provided in this chapter.
Blood Loss Management
Estimated Blood Volume (EBV)
95–100 mL/kg for premature infant
85–90 mL/kg for full-term infant
80 mL/kg for infants up to 12 months
70–75 mL/kg for adult males
65–70 mL/kg for adult females
Allowable blood loss = [EBV × (Hct – target Hct)]/Hct
Replace every 1 mL blood loss with 3 mL crystalloid, 1 mL colloid, or 1 mL packed red blood cells (PRBCs).
PBRC Transfusion Guidelines
One unit PRBCs increases Hct ~ 3% and hemoglobin (Hb) ~ 1 g/dL in adults.
10 mL/kg PRBCs increases Hct ~ 10%
Compatibility Testing
Type specific: ABO-Rh typing only; 99.80% compatible.
Type and screen: ABO-Rh and screen; 99.94% compatible.
Type and crossmatch: ABO-Rh screen, and crossmatch; 99.95% compatible. Crossmatching confirms ABO-Rh typing, detects antibodies to the other blood group systems, and detects antibodies in low blood titers.
Screening donor blood: Hematocrit is determined; if normal, the blood is typed, screened for antibodies, and tested for hepatitis B, hepatitis C, syphilis, human immunodeficiency virus-1 (HIV-1), HIV-2, and human T cell lymphotropic viruses 1 and 2.
Blood Component Therapy
The archaic perioperative axiom of transfusing patients to maintain Hb of 10 and a hematocrit of 30 has fallen by the wayside. Although these are indeed safe guidelines for patients with coronary artery disease, transfusions are currently guided by hemodynamics, intraoperative blood loss, and laboratory values such as the arterial blood gas. Blood replacement in a complex surgical patient is part of goal-directed fluid therapy guided by the clinical response seen in continuously monitored flow parameters (see Chapter 2.3).
Whole blood: 40% hematocrit; used primarily in hemorrhagic shock.
PRBCs: Each unit has a volume of 250 to 300 mL with a hematocrit of 70 to 85%.
Platelets: A normal platelet count is 150,000 to 400,000/mm3. Thrombocytopenia is defined as <150,000/mm3. Intraoperative bleeding increases with counts between 40,000 and 70,000/mm3, and spontaneous bleeding can occur with counts <20,000/mm3. During most surgeries, platelet transfusions are probably not needed unless the count is less than 50,000/mm3. One unit of platelets will increase platelet count 5000 to 10,000/mm3. The usual dose is 1 unit of platelets per 10 kg body weight. Platelets are stored at room temperature; ABO compatibility is not necessary.
Fresh frozen plasma (FFP): Acute reversal of warfarin requires 5 to 8 mL/kg of FFP. ABO compatibility is mandatory. A 250 mL bag contains all coagulation factors except platelets. 10 to 15 mL/kg will increase plasma coagulation factors to 30% of normal. Fibrinogen levels will increase by 1 mg/mL of plasma transfused.
Cryoprecipitate: Indications include hypofibrinogenemia, von Willebrand′s disease, and hemophilia A. ABO compatibility is not necessary. Each 10 to 20 mL/bag contains 100 units of factor VIII-C, 100 units of von Willebrand factor (vWF), 60 units of factor XIII, and 250 mg of fibrinogen.
Massive Transfusions
A massive transfusion is defined as the replacement of a patient′s total blood volume in less than 24 hours. It also applies to the acute administration of more than half the patient′s estimated blood volume per hour.
Universal Donor Blood
Group O, Rh-negative blood should be reserved for patients close to exsanguination. If time permits, crossmatched or uncrossmatched type-specific blood should be administered. Group O, Rh-negative blood should not be given as whole blood. The serum contains high anti-A and anti-B titers, which may cause hemolysis of recipient blood.
If more than 4 units of group O, Rh-negative whole blood is administered, type-specific blood should not be given subsequently because the potentially high anti-A and anti-B titers could cause hemolysis of the donor blood.
Patients administered up to 10 units of group O, Rh-negative PRBCs may be switched to type-specific blood, since there is an insignificant risk of hemolysis from the small volume of plasma administration with PRBCs.
Complications of Transfusions
Immune Reactions (Hemolytic versus Nonhemolytic)
Hemolytic Reactions
• Acute Hemolytic Reaction. An acute hemolytic reaction occurs when ABO-incompatible blood is transfused, resulting in acute intravascular hemolysis; the severity of a reaction often depends on how much incompatible blood has been given. Symptoms include fever, chills, chest pain, anxiety, back pain, and dyspnea; in anesthetized patients, the reaction may present with fever, tachycardia, hypotension, hemoglobinuria, and diffuse oozing in the surgical field. Free Hb in plasma or urine is evidence of a hemolytic reaction. Risk of a fatal hemolytic transfusion reaction: 1:600,000 units.
• Delayed Hemolytic Reaction. Typically, this reaction is delayed 2 to 21 days after the transfusion. The symptoms are generally mild and may include malaise, jaundice, and fever; treatment is supportive. A delayed hemolytic reaction is caused by incompatibility of minor antigens (i.e., Kidd, Duffy, Kelly, etc.), causing hemolysis.
Nonhemolytic Reactions
• Febrile Reaction. A febrile reaction is the most common nonhemolytic reaction (0.5–1.0% of RBC transfusions and up to 30% of platelet transfusions). The reaction is the result of the action of recipient antibodies against donor antigens present on leukocytes and platelets; treatment includes stopping or slowing the infusion and antipyretics.
• Urticarial Reaction. An urticarial reaction occurs in 1% of transfusions; it is thought to be due to sensitization of the patient to transfused plasma proteins. It is characterized by erythema, hives, and itching without fever. Treat with antihistamine drugs.
• Anaphylactic Reaction. Anaphylactic reactions are rare (1:500,000). Patients with IgA deficiency may be at an increased risk because of the transfused IgA reaction with anti-IgA antibodies.
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