Đang chuẩn bị liên kết để tải về tài liệu:
Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss (Part 18)

Anemia Due to Acute Blood Loss Blood loss causes anemia by two main mechanisms: first, by the direct loss of red cells; second, because if the loss of blood is protracted, it will gradually deplete the iron stores, eventually resulting in iron deficiency. Iron-deficiency anemia is discussed in Chap. 98. Here we are concerned with post-hemorrhagic anemia, which follows acute blood loss. This can be external (as after trauma or due to postpartum hemorrhage) or internal (e.g., from bleeding in the gastrointestinal tract, rupture of the spleen, rupture of an ectopic pregnancy). In any of these cases—i.e., after the sudden. | Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss Part 18 Anemia Due to Acute Blood Loss Blood loss causes anemia by two main mechanisms first by the direct loss of red cells second because if the loss of blood is protracted it will gradually deplete the iron stores eventually resulting in iron deficiency. Iron-deficiency anemia is discussed in Chap. 98. Here we are concerned with post-hemorrhagic anemia which follows acute blood loss. This can be external as after trauma or due to postpartum hemorrhage or internal e.g. from bleeding in the gastrointestinal tract rupture of the spleen rupture of an ectopic pregnancy . In any of these cases i.e. after the sudden loss of a large amount of blood three clinical pathophysiologic stages are noted. 1. At first the dominant feature is hypovolemia which poses a threat particularly to organs that normally have a high blood supply such as the brain and the kidneys therefore loss of consciousness and acute renal failure are major threats. It is important to note that at this stage an ordinary blood count will not show anemia as the hemoglobin concentration is not affected. 2. Next as an emergency response baroreceptors and stretch receptors will cause release of vasopressin and other peptides and the body will shift fluid from the extravascular to the intravascular compartment producing hemodilution. Thus the hypovolemia gradually converts to anemia. The degree of anemia will reflect the amount of blood lost. If after 3 days the hemoglobin is say 7 g dL it means that about half of the entire blood volume had been lost. 3. Provided bleeding does not continue the bone marrow response will gradually ameliorate the anemia if erythropoietin production the erythroid progenitors and iron supply are normal. Within about 2-3 days after acute hemorrhage reticulocytes will increase in the blood and reach a maximum 7-10 days after the hemorrhage has been controlled. Reticulocyte counts of 20 may be achieved. The diagnosis