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Hématologie

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Anemia in intensive care units: physiopathology and therapeutics Volume 15, issue 2, mars-avril 2009

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Authors
Inserm U773, équipe 4, CRB3, Département d’anesthésie-réanimation, Hôpital Bichat-Claude-Bernard, Université Paris-Diderot, Paris, Inserm U773, équipe 4, CRB3, Université Paris-Diderot, Paris, Département d’anesthésie-réanimation, Hôpital Bichat-Claude-Bernard, Paris

Anemia is very frequent among patients hospitalized in Intensive Care Units (ICU) and the recent restrictive use of blood transfusions has led to an increase in the number of patients, up to 80 to 90% of them, that are anemic at discharge. This can have a negative impact on survival or recovery. Anemia of ICU patients is multifactorial, resulting form an inflammatory condition on the one hand and on the other hand from multiple blood samplings/losses. These blood losses have been evaluated to 128 mL/D corresponding to a net lost of 64 mg/D elemental iron. Several mechanisms contribute to the anemia of chronic diseases, including reduced proliferation of erythroid precursors, a blunted erythropoietin production by the kidney, macrophage activation leading to increased erythrophagocytosis and reduced half-life of red blood cells, and finally perturbations of iron homeostasis. Indeed, IL-6 has been shown to strongly up-regulate hepcidin expression thereby reducing recycling of heme iron by macrophages and inducing a drop in serum iron levels. Most of these mechanisms have been demonstrated in ICU patients, with the exception of increased hepcidin production which has not been documented in this setting. Furthermore, repeated blood losses are likely to induce true iron deficiency whereas inflammation leads to iron-restricted erythropoiesis by iron sequestration in macrophages. Stimulation of erythropoiesis represses hepcidin synthesis even in the presence of elevated IL-6 levels and recent data obtained on a mouse model of ICU anemia have shown that stimulation of erythropoiesis by erythropoietin injections or by phlebotomies repress hepcidin expression, even in the presence of elevated IL-6 expression. These results should be an incentive to develop clinical studies to evaluate the benefit of treating ICU anemia with erythropoietin injections, together or not with iron supplementation, aiming at correcting the anemia in the long term rather than reducing blood transfusions, and at improving recovery of the patients.