Elsevier

Critical Care Clinics

Volume 20, Issue 2, April 2004, Pages 159-178
Critical Care Clinics

Anemia in the critically ill

https://doi.org/10.1016/j.ccc.2004.01.002Get rights and content

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Erythropoiesis

Erythropoiesis is the development of mature red blood cells (RBCs, erythrocytes). Like all blood cells, RBCs begin as stem cells. The first cell that is recognizable as specifically leading down the RBC pathway is the proerythroblast. As development progresses, the nucleus becomes somewhat smaller, and the cytoplasm becomes more basophilic because of the presence of ribosomes. As the cell begins to produce hemoglobin, the cytoplasm attracts both basic and eosin stains, and is called a

Inflammation and anemia

The normal range of serum erythropoietin concentrations in healthy individuals is 5 to 30 IU/L [10]. Current thinking is that the primary mechanism for the production of erythropoietin is the reduction of oxygen supply to the kidney. A sudden drop in hemoglobin, especially in an otherwise healthy individual, causes an exponential increase in the production of erythropoietin, which can be measured in the circulation within minutes of the initial insult [10], [11], [12]. This normal response of

Iron-deficiency anemia

The most common cause of anemia is iron deficiency. In iron deficiency, there is a decrease in the amount of iron available for metabolic processes. Iron deficiency occurs when more than 10% of RBCs show hypochromasia (a decrease in the hemoglobin in the red cell so that they appear pale in color). Iron is stored most often in the body in the hemoglobin. About 30% of iron also is stored as ferritin and hemosiderin in the bone marrow, spleen, and liver. Patients with iron deficiency have been

Hemolytic anemia

Hemolytic anemia is a disorder in which the RBCs are destroyed (hemolysis) faster than the bone marrow can produce them. There are two types of hemolytic anemia: intrinsic and extrinsic. Intrinsic hemolytic anemia is the destruction of the RBCs because of a defect within the RBCs themselves. Intrinsic hemolytic anemias often are inherited, such as sickle cell anemia and thalassemia. These conditions produce RBCs that do not live as long as normal RBCs. In extrinsic hemolytic anemia, RBCs are

Bleeding-related anemia

Bleeding events in medicine and surgery often cause many patients to become anemic. Patients may become anemic after surgery, in the ICU, and during septic insults. Surgical blood loss is an important determining factor in a patient's postoperative hematocrit and hemoglobin (Hb) concentration. Many patients who do not experience significant blood loss, however, still experience significant reductions in Hb concentrations following surgery. These reductions cannot be explained by intraoperative

Anemia and renal failure

The association of chronic renal failure and anemia has been recognized since the early 19th century. The anemia of renal failure usually is characterized by normochromic and normocytic blood cells. There is usually hypoplasia of the erythroid precursors in the bone marrow. The anemia aggravates as the renal function further declines, and the hematocrit may reach levels as low as 20% or 15%.

Anemia in renal failure can be explained partially by a decreased production of erythroid precursors and

Anemia in cancer patients

Anemia is a common complication of malignancy, occurring in over 50% of patients [46]. Anemia in cancer patients is multi-factorial and may occur as either a direct effect of the cancer, as a result of the cancer treatment, or because of chemical factors produced by the cancer. Recent data have suggested that anemia may be related to poorer outcomes following chemotherapy [47].

The factors contributing to anemia that are caused by the effects of the cancer itself are summarized in Table 1.

Physiological response and tolerance of anemia

Oxygen (O2) is carried in blood in two distinct forms: bound to hemoglobin within the RBC and dissolved in the plasma. The actual oxygen content of arterial blood (CaO2) is determined by the concentration of Hb in the blood, the arterial oxygen saturation of Hb (SaO2), the oxygen binding capacity of Hb, the arterial oxygen partial pressure (PaO2), and the oxygen solubility of plasma. These variables are interrelated and can be expressed in the following equation:CaCo2=(Hb× SaO2× HbO2binding

Transfusion

Evidence indicates that allogeneic blood transfusion allows for the development of immune down-regulation. Allogeneic blood transfusion has been shown to enhance the survival of renal allografts [64] and may increase the recurrence rate of resected malignancies [65] and activate infections associated with CMV [66] and HIV [37].

The mechanism of this immunomodulation remains unclear. Animal and human data suggest that these immune effects are most likely caused by or mediated by transfused

Red blood cell storage

During preservation, allogeneic RBCs undergo functional and structural changes and biochemical alterations collectively referred to as the storage or cold lesion. Numerous authors have shown that RBCs older than 7 days begin to have a decrease in RBC deformability and shape abnormalities, acidosis, and a decrease in blood clotting, and these abnormalities progress up to the end of the storage period [74].

Several retrospective studies support the possible adverse effects of transfusion with

Hemodilution and critical hematocrit

The intentional dilution of blood volume often is referred to as acute normovolemic hemodilution (ANH) anemia. Acute normovolemic hemodilution is a technique in which whole blood is removed from a patient while the circulating blood volume is maintained with acellular fluid. Blood is collected by means of central lines with simultaneous infusion of crystalloid or colloid solutions. Collected blood is reinfused after major blood loss has ceased, or sooner if indicated. Blood units are reinfused

Summary

The anemia of critical illness is a distinct clinical entity with characteristics similar to that of chronic disease anemia. Several solutions to the processes of anemia, such as blunted erythropoietin production and erythropoietin response and abnormalities in iron metabolism have been developed.

The transfusion of RBCs provides immediate correction of low hemoglobin levels, which may be of value in patients with life-threatening anemia. Avoidance of RBC and blood component transfusion,

Acknowledgements

The author would like to thank Robert Frumento, PhD, for his invaluable and astute assistance in preparing this chapter.

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