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Blood is a living tissue that is composed of a variety of cells suspended in a watery fluid
called plasma. Its function is to circulate through the heart, arteries, veins, and capillaries,
carrying nourishment, vitamins, electrolytes, hormones, antibodies, warmth, and oxygen
to the body’s tissues and transporting wastes and carbon dioxide to excretory organs.
Blood is a chemical, a fluid, and a temperature regulator. The cellular components of the
blood – red blood cells, white blood cells, and platelets – comprise 45% of its total volume.
The remaining 55% is plasma. Approximately 7% to 10% of an adult’s body weight is
blood.
• Whole blood is used exactly as it is received from the donor. It contains the various blood
components: red blood cells, white blood cells, plasma, platelets, clotting factors, and
immunoglobulins. Because the use of whole blood has a greater effect on fluid volume
than any of the components does, it is used only when needed or when individual blood
components are not available. Whole blood is generally transfused only when a patient
loses a large amount of blood.
• Blood-component therapy is based on separating or “fractionating†whole blood into its
cellular and plasma components. Because patients seldom need all the components of
whole blood, it is medically wise to transfuse only the component needed to manage the
specific disorder or disease. Blood-component therapy allows several patients to benefit
from one unit of donated whole blood, a more efficient use of the blood supply.
• Red blood cells, also called erythrocytes, contain hemoglobin, a complex iron-containing
protein that carries oxygen throughout the body and gives blood its red color. Red blood
cells are produced in the bone marrow, live for about 120 days in the circulatory system,
and are eventually broken down by the spleen. Red cells raise hematocrit and hemoglobin
levels without significantly increasing blood volume. They are recovered from whole blood
after donation by removing the plasma portion of the blood. Often referred to as “packed
red blood cells,†this component is transfused to restore or maintain adequate organ
oxygenation. Indications for red blood cell transfusion include anemia due to neoplastic
blood disease, conditions that affect red blood cell production, sickle-cell anemia, blood
loss due to trauma, surgical blood loss, and to offset some of the effects of chemotherapy.
Packed red blood cells are kept refrigerated at a specific temperature and are viable for 42
days but may be frozen for extended storage up to 10 years.
• Plasma, the liquid portion of the blood, is composed of about 92% water and 7% plasma
proteins. Plasma contains albumin, fibrinogen, globulins, and other clotting proteins. In
addition to maintaining blood pressure and providing essential proteins, plasma serves as
the medium for the cellular exchange of vital minerals and electrolytes and for the
elimination of cellular waste products. Fresh frozen plasma is obtained by centrifuging
whole blood and freezing it within hours after donation. Plasma is used to treat bleeding
and coagulation disorders, to replace fluid volume for patients with massive burns and for
those with liver failure, a
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