Acute blood loss

History The answers to questions with high discriminating value can quickly narrow the range of potential causes of diarrhea and help determine whether treatment is needed. Important elements of the narrative history are detailed in Fig. 122-1. Physical Examination The examination of patients for signs of dehydration provides essential information about the severity of the diarrheal illness and the need for rapid therapy. Mild dehydration is indicated by thirst, dry mouth, decreased axillary sweat, decreased urine output, and slight weight loss.

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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).

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Pyrimidine 5'-Nucleotidase (P5N) Deficiency P5N is a key enzyme in the catabolism of nucleotides arising from the degradation of nucleic acids that takes place in the final stages of red cell maturation. How exactly its deficiency causes HA is not well understood, but a highly distinctive feature of this condition is a morphologic abnormality of the red cells known as basophilic stippling. The condition is rare, but it probably ranks third in frequency among red cell enzyme defects (after G6PD deficiency and PK deficiency).

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Autoimmune Hemolytic Anemia (AIHA) Except for countries where malaria is endemic, AIHA is the most common form of acquired hemolytic anemia. In fact, not quite appropriately, the two phrases are sometimes used synonymously. Pathophysiology AIHA is caused by an autoantibody directed against a red cell antigen, i.e., a molecule present on the surface of red cells. The autoantibody binds to the red cells. Once a red cell is coated by antibody, it will be destroyed by one or more mechanisms.

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Severe acute AIHA can be a medical emergency. The immediate treatment almost invariably includes transfusion of red cells. This may pose a special problem because if the antibody involved is "unspecific," all the blood units crossmatched will be incompatible. In these cases it is often correct, paradoxically, to transfuse incompatible blood, the rationale being that the transfused red cells will be destroyed no less but no more than the patient's own red cells, and in the meantime the patient stays alive.

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PNH has about the same frequency in men and women, and it is encountered in all populations throughout the world, but it is a rare disease: its prevalence is 1–5 per million (it may be somewhat less rare in Southeast Asia and in the Far East). There is no evidence of inherited susceptibility. PNH has never been reported as a congenital disease, but it can present in small children or in people in their seventies, although most patients are young adults. Clinical Features The patient may seek medical attention because one morning she or he has passed "blood instead of urine."...

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Bone Marrow Failure—Relationship between PNH and AA It is not unusual that patients with firmly established PNH have a previous history of well-documented AA. On the other hand, sometimes a patient with PNH becomes less hemolytic and more pancytopenic and ultimately has the clinical picture of AA. Since AA is probably an organ-specific autoimmune disease in which T cells cause damage to hematopoietic stem cells, the same may be true of PNH, with the specific proviso that the damage spares PNH stem cells. Skewing of the T cell repertoire in patients with PNH supports this notion.

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Table 101-5 Drugs that Carry Risk of Clinical Hemolysis in Persons with G6PD Deficiency Definite Risk Risk Possible Risk Doubtful Antimalarials Primaquine uine Chloroq Quinine Dapsone/chlorp roguanil Sulphonamides/s ulphones ole Sulphametoxaz zine Sulfasala ole Sulfisoxaz Others idine Sulfadim ne Sulfadiazi Dapsone Antibacterial/anti biotics Cotrimoxazole xacin Ciproflo Chloramp henicol Nalidixic acid cin Norfloxa pAminosalicylic acid Nitrofurantoin Niridazole Antipyretic/analg esics Acetanilide Acetylsa Acetylsali licylic acid high cylic acid 3 g/d) Phena...

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Figure 101-6 Peripheral blood smear from a 5-year-old G6PD-deficient boy with acute favism. A very small minority of subjects with G6PD deficiency have CNSHA of variable severity. The patient is always a male, usually with a history of NNJ, who may present with anemia or unexplained jaundice, or because of gallstones later in life. The spleen may be enlarged. The severity of anemia ranges from borderline to transfusion-dependent. The anemia is usually normo-macrocytic, with reticulocytosis. Bilirubin and LDH are increased.

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Abnormalities of the Glycolytic Pathway (Fig. 101-1) Since red cells, in the course of their differentiation, have sacrificed not only their nucleus and their ribosomes but also their mitochondria, they rely exclusively on the anaerobic portion of the glycolytic pathway for producing energy in the form of ATP. Most of the ATP is required by the red cell for cation transport against a concentration gradient across the membrane. If this fails, due to a defect of any of the enzymes of the glycolytic pathway, the result will be hemolytic disease.

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Clinical Presentation and Diagnosis The spectrum of clinical severity of HS is broad. Severe cases may present in infancy with severe anemia, whereas mild cases may present in young adults or even later in life. In women, HS is sometimes first diagnosed when anemia is investigated during pregnancy. The main clinical findings are jaundice, an enlarged spleen, and often gallstones; frequently it is the finding of gallstones in a young person that triggers diagnostic investigations.

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Pyruvate Kinase Deficiency: Treatment Management of PK deficiency is mainly supportive. In view of the marked increase in red cell turnover, oral folic acid supplements should be given constantly. Blood transfusion should be used as necessary, and iron chelation may have to be added if the blood transfusion requirement is high enough to cause iron overload. In these patients, who have more severe disease, splenectomy may be beneficial.

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Epidemiology G6PD deficiency is widely distributed in tropical and subtropical parts of the world (Africa, Southern Europe, the Middle East, Southeast Asia, and Oceania) (Fig. 101-5) and wherever people from those areas have migrated; a conservative estimate is that at least 400 million people have a G6PD-deficiency gene. In several of these areas, the frequency of a G6PD-deficiency gene may be as high as 20% or more.

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Table 101-2 General Features of Hemolytic Disorders General examination Jaundice, pallor Other findings physical Spleen may be enlarged; bossing of skull in severe congenital cases Hemoglobin From normal to severely reduced MCV, MCH Usually increased Reticulocytes Increased Bilirubin Increased (mostly unconjugated) LDH Increased (up to 10X normal with intravascular hemolysis) Haptoglobin Reduced to absent Note: MCV, mean corpuscular volume; MCH, mean corpuscular hemoglobin; LDH, lactate dehydrogenase.

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Figure 101-1 RBC metabolism. The Embden-Meyerhof pathway (glycolysis) generates ATP for energy and membrane maintenance. The generation of NADPH maintains hemoglobin in a reduced state. The hexose monophosphate shunt generates NADPH that is used to reduce glutathione, which protects the red cell against oxidant stress. Regulation of 2,3-bisphosphoglycerate levels is a critical determinant of oxygen affinity of hemoglobin.

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Hemolytic Anemias Due to Abnormalities of the MembraneCytoskeleton Complex The detailed architecture of the red cell membrane is complex, but its basic design is relatively simple (Fig. 101-2). The lipid bilayer, which incorporates phospholipids and cholesterol, is spanned by a number of proteins that have their hydrophobic transmembrane domains embedded in the membrane. Most of these proteins have hydrophilic domains extending toward both the outside and the inside of the cell.

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Peripheral blood smear from patients with membrane-cytoskeleton abnormalities. A. Hereditary spherocytosis. B. Hereditary elliptocytosis, heterozygote. C. Elliptocytosis, with both alleles of the α-spectrin gene mutated. [From L Luzzatto, in J Gribben and D Pravan (eds): Molecular Hematology, 2d edition. Oxford, Blackwell, 2005; with permission.] Table 101-3 Inherited Diseases of the Red Cell MembraneCytoskeleton Gene Chromoso mal Location Protei n Produced s) Disease( with s Comment Certain Mutations (Inheritance) SPTA1 1q22-q23 αSpectrin HS (recessive) Rare.

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Harrison's Internal Medicine Chapter 101. Hemolytic Anemias and Anemia Due to Acute Blood Loss Definitions A finite life span is a distinct characteristic of red cells. Hence, a logical, time-honored classification of anemias comprises three groups: decreased production of red cells, increased destruction of red cells, and acute blood loss. Red cell destruction and acute loss, both associated with increased reticulocyte production, are covered in this chapter. Red cell production defects are discussed in Chaps. 98, 99, and 100.

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Posterior Ischemic Optic Neuropathy This is an infrequent cause of acute visual loss, induced by the combination of severe anemia and hypotension. Cases have been reported after major blood loss during surgery, exsanguinating trauma, gastrointestinal bleeding, and renal dialysis. The fundus usually appears normal, although optic disc swelling develops if the process extends far enough anteriorly. Vision can be salvaged in some patients by prompt blood transfusion and reversal of hypotension. Optic Neuritis This is a common inflammatory disease of the optic nerve.

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