Red Blood Cell Transfusion

Signs & Symptoms of Acute Blood Loss

  The loss of 500 mL of blood within 5 minutes is well tolerated by the average adult blood donor.  Therefore, it is usually not necessary to transfuse patients with a single unit of RBCs since the recipient probably needs the blood no more than the donor. Patients who have suddenly lost more than 20 to 30% of their blood volume are more critical and develop symptoms in spite of compensatory mechanisms such as peripheral vasoconstriction and fluid shift from the extravascular to the intravascular space. Hemodilution begins almost immediately after the onset of hemorrhage and continues up to 72 h after cessation of bleeding. Although this influx of fluid does not improve oxygen carrying capacity, it does help to maintain blood volume and stabilize circulation. In this situation, transfusion of a single unit of RBCs along with crystalloid solutions is justifiable since the patient has lost the equivalent of three units of blood.  Adult patients in hemorrhagic shock have usually lost 35 to 40% of their blood volume, or approximately 2 liters.   Blood volume should be immediately replaced with crystalloid solutions such as lactated Ringer's solution or normal saline. The early administration of fluids allows sufficient time for ABO typing of the recipient, which takes only a few minutes. In this way, ABO type specific blood can be given instead of empirically giving O negative blood, which often is in short supply.   Numerous publications have debated the risks and benefits of using hemoglobin levels between 6 and 10 g/dL as a transfusion trigger for patients with acute blood loss. Generally, isovolemic patients with a hemoglobin <7 g/dL may require transfusion, while most patients with a hemoglobin >9 g/dL will not.   The Transfusion Requirements in Critical Care Trial (TRICC) was a multi-center prospective randomized controlled clinical trial conducted in Canada in 1999, which compared the clinical outcomes in intensive care patients randomized to a restrictive versus a liberal transfusion strategy (NEJM 1999; 340: 409-17). Patients in the restrictive cohort were transfused when their hemoglobin concentration fell below 7 g/dL and their hemoglobin was maintained between 7–9 g/dL, while patients in the liberal transfusion group were transfused when their hemoglobin concentration fell below 10 g/dL and their hemoglobin was maintained between 10–12 g/dL.  

TRICC Trial Outcomes

   The TRICC trial demonstrated that a more restrictive transfusion strategy was safe in the ICU patient population and that the liberal use of transfusions increased the risk of death. Multiple other studies have subsequently demonstrated that allogeneic transfusions cause immunomodulation leading to increased ICU and hospital length of stay as well as nosocomial infections and mortality.   Transfusion medicine has evolved over the last few years. Because allogeneic transfusions are a potential risk for patients, physicians should attempt to limit transfusions by aggressively preventing anemia in hospitalized patients. The decision to transfuse RBCs should be based on the entire clinical picture and not solely on the hemoglobin level.   Reversible causes of chronic anemia such as vitamin B12, folate, and iron deficiency should be ruled out prior to transfusion. Erythropoietin sensitive anemia such as anemia of chronic renal insufficiency and the anemia associated with zidovudine (AZT) treatment of HIV patients should also be ruled out. Red cell transfusions may be required to alleviate the symptoms of anemia or to reduce morbidity associated with a patient’s underlying disease. Symptoms in normovolemic patients that may indicate the need for transfusion include dyspnea, syncope, transient ischemic attacks, postural hypotension, tachycardia, tachypnea, and angina.   Chronic anemia patients undergo compensatory changes that acclimate them to lower hemoglobin levels. A point of fundamental importance is that blood volume is decreased only slightly in patients with chronic anemia due to compensatory increases in plasma volume. Thus, transfusion of chronically anemic patients may cause hypervolemia which has the potential for precipitating cardiac decompensation, particularly in elderly patients or in patients with known heart failure.   Physicians must not be overly aggressive in the transfusion of patients with severe anemia. Transfusion will improve functional status in symptomatic patients up to a hemoglobin level of 10 g/dL. Transfusions beyond this level provide no further improvement in functional status in most patients. This is especially true for patients with impaired cardiac output because their inability to compensate for increased blood viscosity can actually decrease tissue oxygenation. The major exception is patients with severe chronic obstructive pulmonary disease (COPD) who may still be symptomatic at hemoglobin levels of 10 g/dL and require a hemoglobin level between 10 and 12g/dL to alleviate symptoms. Patients taking medications, such as beta-blockers, may not be able to mount an adequate sympathetic response to blood loss. Transfusion to a hemoglobin level of 10 g/dL may be necessary to relieve symptoms.   Transfusion in the Setting of Angina Angina may be indicative of an impending myocardial infarction. Indications for transfusion of patients with myocardial infarction are unclear. Transfusion may improve myocardial oxygen delivery, but may also increase myocardial oxygen consumption secondary to increased blood volume and blood viscosity. The decision to transfuse should be based on critical patient evaluation and internal hemodynamic pressure monitoring. Hemoglobin of 8 g/dL is usually tolerable in surgical patients without risk factors for ischemia, while hemoglobin of 10 g/dL may be better for patients with increased risk. Perioperative myocardial infarction is more likely when the hemoglobin is <9 g/dL, especially if the patient has tachycardia.   Perioperative Transfusion Red cell transfusion has often been used empirically prior to general anesthesia when the hemoglobin is less than 9 or 10 g/dL. There are no data that strongly support this practice. Rather than use a formula approach, proper preoperative assessment should correlate the adequacy of the hemoglobin level with the cause and duration of the anemia, the patient's cardiac and pulmonary status and the type and probable duration of the surgery. The key to tolerance of anemia is the maintenance of normovolemia and compensatory mechanisms that increase cardiac output and improve oxygen transport. Each patient should be evaluated based upon the anticipated ability of his/ her cardiovascular system to compensate.   Hemodynamic instability may also occur during acute blood loss, usually after loss of 15% or more of blood volume. Accordingly, red cell transfusion is indicated if acute blood loss causes the blood pressure to drop by 20% or to a level of <100 mm Hg, or if the pulse increases to >100/min. The transfusion of colloid and/or crystalloid solutions is also necessary in bleeding patients to maintain adequate blood volume. As long as normovolemia is maintained with colloid and/or crystalloid solutions and the patient's hemoglobin level is adequate, it is not necessary to replace all losses of red cells. Fresh frozen plasma should not be used for volume replacement since this incurs the unnecessary risk of infectious disease transmission.   Postoperative hemoglobin in the range of 8-9 g/dL appears to be safe for patients free of cardiovascular disease, and justification should be provided if blood is transfused other than to replace losses at this level. On the other hand, compensation for acute anemia requires increased cardiovascular performance. Moderate hemodilution (below a hemoglobin of 8-10 g/dL) does affect cardiac workload, and its risks should be weighed carefully in patients with extensive cardiovascular disease.   Each unit increases an adult's (70kg) hemoglobin 1g/dL and hematocrit 3%.   Follow up measurement of the recipient's hemoglobin and/or hematocrit can be performed between 15 minutes and 24 hours post-transfusion. The optimal time interval for assessment is 15 minutes. Hemoglobin levels obtained at 24 hours post-transfusion are 10% higher than values obtained after 15 minutes.