Blood loss causes anemia by two main mechanisms: (1) by the direct loss of red cells; and (2) if the loss of blood is protracted, it will gradually deplete iron stores, eventually resulting in iron deficiency. The latter type of anemia is covered in Chap. 97. Here, we are concerned with the former type, that is, posthemorrhagic anemia, which follows acute blood loss. This can be external (e.g., after trauma or obstetric hemorrhage) or internal (e.g., from bleeding in the gastrointestinal tract, rupture of the spleen, rupture of an ectopic pregnancy, subarachnoid hemorrhage, leaking aneurysm). In any of these cases, after the sudden loss of a large amount of blood, there are three clinical/pathophysiologic stages. (1) At first, the dominant feature is hypovolemia, which poses a threat particularly to organs that normally have a high blood supply, like 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 because the hemoglobin concentration is not affected. On physical exam, tachycardia, tachypnea, decreased pulse pressure, cold skin that appears pale and mottled, and decreased urine output may be noted. (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, for example, 7 g/dL, it means that about half of the entire blood has been lost. (3) Provided bleeding does not continue, the bone marrow response will gradually ameliorate the anemia. In this phase of the process, the reticulocyte count and erythropoietin levels will be elevated. The physiologic increase in marrow red cell production reflected by the increase in reticulocytes is similar to the marrow response to hemolysis.
The diagnosis of acute posthemorrhagic anemia (APHA) is usually straightforward, although sometimes internal bleeding episodes (e.g., after a traumatic injury), even when large, may not be immediately obvious. Look for physical findings that may help localize the bleeding. Grey Turner sign (flank ecchymosis) may reflect retroperitoneal bleeding. Cullen sign (umbilical ecchymosis) may suggest intraperitoneal or retroperitoneal bleeding. Dullness to chest percussion may suggest intrapleural bleeding. Whenever an abrupt fall in hemoglobin has taken place, whatever history is given by the patient, APHA should be suspected. Supplementary history may have to be obtained by asking the appropriate questions, and appropriate investigations (e.g., a sonogram or an endoscopy) may have to be carried out.
TREATMENT Anemia Due to Acute Blood Loss
In patients who are hemodynamically unstable, the usual airway, breathing, and circulation assessments take priority. In the face of bleeding associated with hypotension, pharmacologic support with vasopressors is critical. With respect to anemia treatment, a two-pronged approach is ...