Massive transfusion, historically defined as the replacement by transfusion of 10 units of red cells in 24 hours, is a response to massive and uncontrolled hemorrhage. With more rapid and effective therapy, definitions such as five units over three hours are more effective in identifying patients needing rapid issue of blood products for serious injuries because of uncontrolled hemorrhage. Such transfusion episodes are associated with a number of hemostatic and metabolic complications . Massive transfusion involves the selection of the appropriate amounts and types of blood components to be administered, and requires consideration of a number of issues including volume status, tissue oxygenation, management of bleeding and coagulation abnormalities, as well as changes in ionized calcium, potassium, and acid-base balance.
An overview of the Acute Trauma Life Support approach to massive transfusion with crystalloid fluids and packed red cells is presented here [2,3], as is the “damage control” approach using red cells and plasma in a 1:1 ratio . Other issues related to the use of blood products are discussed separately. (See "Use of blood products in the critically ill" and "Indications and hemoglobin thresholds for red blood cell transfusion in the adult" and "Red blood cell transfusion in adults: Storage, specialized modifications, and infusion parameters" and "Initial evaluation and management of shock in adult trauma".)
The most common situation leading to massive transfusion is trauma. Other situations leading to massive transfusion, such as ruptured abdominal aortic aneurism, liver transplant, and obstetric catastrophes are less frequent. In a review of experience in a major trauma center during the year 2000, 8 percent of all admitted patients were given red cells, 3 percent received more than 10 units of red cells during their admission, and 1.7 percent received 10 units in the first 24 hours . More recently, an NIH-sponsored collaboration of trauma centers studying the cytokine response to massive transfusion and other groups reported that the fraction of all patients receiving red cells who go on to receive 10 units of red cells has decreased by 40 percent as more plasma and platelets are given earlier . Taken together, these data suggest that most injured patients never need massive transfusion and can be treated based on physical assessment and laboratory tests, but approximately 1.7 percent of the most severely injured will require more prompt treatment of coagulopathy, which in turn reduces total blood use in some of them. Appropriate care requires knowing both forms of resuscitation and when to use them. (See "Initial evaluation and management of shock in adult trauma".)
RED CELL AND VOLUME REPLACEMENT
Correction of the deficit in blood volume with crystalloid volume expanders will generally maintain hemodynamic stability, while transfusion of red cells is used to improve and maintain tissue oxygenation [7,8]. Each unit of packed red blood cells (RBCs) contains approximately 200 mL of red cells and, in an adult, will raise the hematocrit by roughly 3 to 4 percentage points unless there is continued bleeding. (See "Indications and hemoglobin thresholds for red blood cell transfusion in the adult".)
At rest, oxygen delivery is normally four times oxygen consumption, indicating the presence of an enormous reserve. Thus, if intravascular volume is maintained during bleeding and cardiovascular status is not impaired, oxygen delivery will theoretically be adequate until the hematocrit (packed cell volume) falls below 10 percent. This is because adequate cardiac output plus increased oxygen extraction can compensate for the decrease in arterial oxygen content. However, increasing cardiac work to increase output requires more oxygen, so the “critical point” where oxygen consumption becomes delivery dependent is higher.