The Use of Blood Products in Critically Ill Patients

Abstract

SUMMARY B lood is a life saving liquid organ. Whole blood is a mixture of cellular elements, colloids and crystalloids. As different blood components have different relative density, sediment rate and size they can be separated when centrifugal force is applied. Blood components include cellular components and non-cellular components. Cellular blood components include whole blood, packed red cells, platelet concentrate and granulocyte. Non-cellular blood components include plasma as fresh frozen plasma, liquid plasma and frozen plasma, cryoprecipitate and cryodepleted plasma. Plasma, a viscous fluid, accounts for about 55% of blood; the formed elements make up about 45% of the total volume of blood. An average woman has about 5 liters of blood; an average man has approximately 6 liters of blood in the body. Blood accounts for about 8% of total body weight. Blood is circulated around the body within the cardiovascular system, transporting O2, necessary metabolic substrates and hormones to the cells, while removing CO2 and waste products. Plasma, the liquid phase of blood, has many functions, involving colloid osmotic effects, transport, signaling, and immunity and clotting. The cellular elements of blood are responsible for gas transport, immunity and some aspects of hemostasis. Whole blood can provide improved O2 carrying capacity, volume expansion, and replacement of clotting factors and was previously recommended for rapid massive blood loss. Packed RBCs are ordinarily the component of choice with which to increase Hb. Indications depend on the patient. O2 -carrying capacity may be adequate with Hb levels as low as 7 g/L in healthy patients, but transfusion may be indicated with higher Hb levels in patients with decreased cardiopulmonary reserve or ongoing bleeding. When only volume expansion is required, other fluids can be used concurrently or separately. Fresh frozen plasma is an unconcentrated source of all clotting factors without platelets. Indications include correction of bleeding secondary to factor deficiencies for which specific factor replacements are unavailable, multifactor deficiency states (eg, massive transfusion, disseminated intravascular coagulation [DIC], liver failure), and urgent warfarin reversal, although prothrombin complex concentrate is the first choice if available. FFP should not be used simply for volume expansion.