Physiology_of_Transfusion_Therapy-1

Physiology_of_Transfusion_Therapy-1 - Physiology of...

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Physiology of Transfusion Therapy Vithal V. Vernenkar, D.O. Dept. of Surgery St. Barnabas Hospital
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Indications for Transfusion Enhance oxygen carrying capacity of blood by expanding red call mass. Replace clotting factors, either lost, consumed, or not produced.
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Enhancement of Oxygen Carrying Capacity Majority of arterial blood oxygen binds with hemoglobin reversibly. Release of O2 to tissues depend on many factors, the oxygen saturation being the most important. The saturation of hemoglobin molecules with O2 determines the binding affinity.
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Enhancement of Oxygen Carrying Capacity As saturation increases, affinity decreases, release of O2 to tissues is then enhanced. The partial pressure of O2 required to saturate 50% of the Hb molecules is called P-50. P-50 value is increased with fever, acidosis, increased 2,3 DPG, thus O2 is released to tissues with greater ease under these circumstances. However with hypothermia, alkalosis, and decreased 2,3 DPG affinity is increased, release decreased.
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O2 Carrying Capacity Tissue oxygenation also depends on tissue oxygen demands. Under normal circumstances, there is a physiologic reserve between O2 delivery (1000cc/min) and consumption (250cc/min). Despite this large reserve, clinical circumstances, such as massive MOSF, can have consumption outstripping delivery.
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O2 Carrying Capacity Hb normally ranges between 12-18g/dL depending on race, age, sex, medical condition. Old tradition of keeping Hb at 10 is not valid. A Hb of 7-8 has been demonstrated to be adequate except in patients with CAD, COPD. It is clear that the rate and magnitude of blood loss, state of tissue perfusion, pre-existing cardiopulmonary disease all affect the ability of the patient to tolerate lower concentrations of Hb.
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O2 Carrying Capacity Decreased levels of 2,3 DPG increase O2- Hb binding affinity. 2,3 DPG levels may decrease by 30% in blood stored for greater than 2 weeks, by 60-70% in 3 weeks. When transfused, this old blood has a significantly diminished ability to release O2 to tissues.
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The second most common indication for transfusion is repletion of hemostatic agents. It is not safe to simply correct abnormal lab
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Physiology_of_Transfusion_Therapy-1 - Physiology of...

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