الفهرس 
Anemia in Critical IllnessOnly 14 pages are availabe for public view
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Abstract
Anemia is a hemoglobin concentration in blood that is below the expected value. Anemia is prevalent in the critically ill patients and is associated with adverse outcome. Anemia impairs the body ability to oxygenate the vital organs, as 98% of O2 are bound to hemoglobin. Moreover, also for effective oxygen transport to tissues, red cells need to transit capillaries and release oxygen from hemoglobin but changes in red cell metabolism and cell deformability which occur during critical illness hinder this mechanism.
The key to the provision of safe and sufficient blood for transfusion is unpaid volunteers. The minimum mandatory infection screen on all donations is for hepatitis B and C, human immunodeficiency virus, human T-lymphotropic virus and syphilis, and extra tests are performed as required. Modern transfusion practice is based on the use of blood components rather than whole blood donations. Whole blood donations of 405–495 ml (mean 470 ml) are collected into 63 ml of citrate phosphate dextrose (CPD) anticoagulant. All blood donations are filtered to remove white blood cells (pre-storage leucodepletion) to leave <5×106 leucocytes in the pack.
The goal of packed red blood cell transfusion in the critically ill patient is to increase oxygen delivery to and, hence consumption by tissues. A transfusion threshold of 7 g/dl or below, with a target Hb range of 7–9 g/dl, should be the default for all critically ill patients, unless specific co-morbidities or acute illness-related factors modify clinical decision-making. Transfusion trigger should not exceed 9 g/dl in most critically ill patients.
Anemia is well tolerated by critically ill patients with hemoglobin values between 7–9 g/dl and does not adversely affect outcome in comparison with maintaining a value more than 10 g/dl. Restrictive transfusion policy with these lower ranges of hemoglobin levels was associated with lower rates of new organ failures and acute respiratory distress syndrome. Cardiac surgery, elderly patients undergoing ‘high-risk’ hip surgery and gastrointestinal hemorrhage have shown no advantages with a liberal transfusion policy. A higher transfusion trigger may be beneficial in patients with ischemic stroke, traumatic brain injury with cerebral ischemia, acute coronary syndrome (ACS) or in the early stages of severe sepsis.
Lowering hemoglobin transfusion threshold and adherence to restrictive transfusion policy decreases the risks of blood transfusion to greatly lower levels. The most clinically important adverse effects of transfusion in medical patients are infectious or immunological phenomena.
Strategies are made to decrease blood transfusion such as restrictive transfusion strategy, noninvasive hemoglobin monitoring, pharmacological measures and the use of blood alternatives.
Noninvasive hemoglobin measurement with Pulse CO-Oximetry avoids repeated blood sampling and; therefore, eliminates blood loss. It also has the additional advantage of providing continuous measurements so blood transfusion is only done when indicated and may be a feasible alternative to invasive hemoglobin monitoring.
Pharmacological measures to reduce transfusion include the use of tranexamic acid which should be included in major traumatic hemorrhage protocols and may be safely used in most surgical blood conservation programs. Recombinant activated factor vII was used in prophylactic or therapeutic trials in patients without hemophilia and no evidence of reduced mortality was found but; at the most, a modest reduction in blood loss or transfusion rates was achieved. Desmopressin may reduce bleeding in uremic patients with platelet dysfunction due to kidney failure.
Alternatives to transfusion include erythropoiesis stimulating agents (which are used in treatment of anemia and reduction of transfusion in adult patients receiving chemotherapy). Artificial oxygen carriers or hemoglobin substitutes such as perfluorocarbons can transport both oxygen and carbon dioxide. They are tried but their utility in critically ill patients is doubtful.