الفهرس 
BLOOD PHYSIOLOGYOnly 14 pages are availabe for public view
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Abstract
B
lood accounts for 7% of the human body weight. The average adult has a blood volume of roughly 5 liters, composed of plasma and several kinds of cells (occasionally called corpuscles). These formed elements of the blood are erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets). By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.
Blood performs many important functions within the body, most important of which is the supplementation of oxygen to tissues. The hemoglobin, an iron-containing protein, facilitates transportation of oxygen by reversibly binding to this respiratory gas and greatly increasing its solubility hi blood. In contrast, carbon dioxide is almost entirely transported extracellularly dissolved in plasma as bicarbonate ion. Thus the most important adverse effect of anemia is decreased tissue oxygen delivery, owing to the associated decrease in arterial content of oxygen (CaO2).
Blood transfusion is the process of transferring blood or blood-based products from one person into the circulatory system of another. Blood transfusions can be life-saving in some situations, such as massive blood loss due to trauma, or can be used to replace blood lost during surgery. Blood transfusions may also be used to treat a severe Anemia or thrombocytopenia caused by a blood disease. People suffering from hemophilia or sickle-cell disease may require frequent blood transfusions. Early transfusions used whole blood, but modern medical practice commonly uses only components of the blood. Over 300 years passed between the description of blood circulation and implementation of routine transfusion medicine.
The risks of blood transfusion should always be considered in perspective to the benefits of having red cells, platelets and plasma available to support complex surgical procedures and to correct critical cytopenias and coagulopathies. Blood donation is a gift and should not be wasted.
Blood availability has become a safety issue. Mounting concern for blood safety has excluded an increasing number of potential volunteer donors; just as the need for blood grows.
The transfusion trigger is used to describe a set of conditions under which transfusion is considered to be indicated and for which no further justification is required. It is not a secret to say that the decision to transfuse is always debatable, and setting a universal target transfusion trigger for all patients bypassing different individual variations is a common mistake. Moreover, this decision must be individualized, and each patient should represent a lone call.
The physiological transfusion triggers can be based on signs and symptoms of unpaired global oxygenation (lactate, SvO2 & ScvO2) or even better, regional tissue oxygenation (ECG; ST-segment, DSST & P300 latency).
The continuous delivery of a sufficiency of oxygen is critical to sustaining function and survival of every tissue and organ of the body. Accordingly, the development of a blood substitute that is instantly available for administration, usable without matching to each recipient, storable for long periods without refrigeration, provides superior oxygen delivery, free of the risk of infection and with a wide margin of safety, will find utility for a broad range of clinical applications in conditions and situations where fresh, grouped, typed and cross-matched blood is unavailable or is unable to provide adequate oxygen delivery.
Blood centers and transfusion services will continue to perform research and provide education so that all transfusion risks are appropriately recognized and managed, until ultimately they are reduced to a negligible concern for transfusing anesthetists and their patients.