Preoperative laboratory screening for coagulation deficiencies is controversial. Routine screening is not warranted in patients who do not have historical evidence of a bleeding problem (233). Patients who are seriously ill or who will be undergoing extensive surgical procedures should undergo testing preoperatively to determine prothrombin time, partial thromboplastin time, fibrinogen level, and platelet count.
Abnormally high or low white blood cell counts are not an absolute contraindication to surgery; they should be considered relative to the need for surgery. Evaluation of an elevated or decreased white blood cell count should be undertaken before elective surgery. Patients with absolute granulocyte counts lower than 1,000/mm3 are at increased risk of severe infection and perioperative morbidity and mortality and should undergo surgery only for life-threatening indications (234).
Packed red blood cells, which may be stored for several weeks, are used for most postoperative transfusions. Most clotting factors are stable for long periods. The exceptions are factors V and VIII, which decrease to 15% and 50% of normal, respectively. Most hematologic problems observed in the postoperative period are related to perioperative bleeding and blood component replacement. Although the primary cause of the bleeding is usually lack of surgical hemostasis, other factors, including deranged coagulation, may compound the problem. Such coagulopathy can result from massive transfusion (less than one blood volume) and is thought to be caused by dilution of platelets and labile coagulation factors by platelet-and factor-poor packed red blood cells (PRBCs), fibrinolysis, and disseminated intravascular coagulation.
Areviewin Transfusion questioned the traditional practice of limiting blood component replacement in massive transfusion. Summarizing 14 articles and encompassing nearly 4,600 patients, the conclusions note a decrease in all-cause mortality with more liberal transfusion of platelets and fresh frozen plasma (FFP) (235).
A task force for the American Society of Anesthesiologists recommended critical values for replacement in patients with massive transfusion and microvascular bleeding (193): 1.
Platelet transfusion usually is indicated for counts less than 50,000/mm3 (with intermediate platelet counts, i.e., 50,000/mm3 to 100,000/mm3, the transfusion of platelet concentrates should be based on the risk of more significant bleeding).
2.
Fresh frozen plasma therapy is indicated if the prothrombin or activated partial thromboplastin time values exceed 1.5 times the normal value.
3.
Cryoprecipitate transfusion is indicated if fibrinogen concentrations decrease to less than 80 to 100 mg/dL.
Cryoprecipitate transfusions are recommended for prophylaxis in nonbleeding perioperative patients with fibrinogen deficiencies or von Willebrand disease refractory to desmopressin acetate and bleeding patients with von Willebrand disease (232).
Donor blood is stored in the presence of citrate, which chelates calcium to prevent clotting, increasing the theoretical risk of hypocalcemia following massive transfusion. Citrate is metabolized at a rate equivalent to 20 U of blood transfused per hour; thus, routine supplementation of calcium is unnecessary. Close monitoring of calcium levels is required in patients with hypothermia, liver disease, or hyperventilation because citrate metabolism may be slowed. Hepatic metabolism of citrate to bicarbonate can result in metabolic alkalosis following transfusion, resulting in subsequent hypokalemia, despite the high level of extracellular potassium in stored blood.