Interestingly, anemia and the need to restore adequate oxygen delivery (DO 2 ) are the most common indications for transfusion, rather than acute bleeding [3, [5] [6] [7] [8] [9] [10] . Anemia in the critically ill patient is a multifactorial phenomenon that has been compared to the so-called "anemia of chronic illness" [11] . Apart from evident causes of anemia, such as primary blood losses (e.g., trauma, surgery, gastrointestinal bleeding), multiple other etiologies contribute to its pathophysiology and often coexist in the same patient [11] . These include blood losses related to minor procedures or phlebotomy, and hemodilution secondary to fluid resuscitation. Some studies have suggested that blood sampling may average as much as 40 ml/day [3, 4] , but the amount of blood required may decrease with technological developments in analytic methods. Other mechanisms for anemia include an inflammatory response with blunted erythropoietin (EPO) production, abnormalities in iron metabolism, and altered proliferation and differentiation of medullar erythroid precursors [11] . As a consequence, RBC deformability is decreased [12] , whereas RBC adherence to the endothelium is increased, especially in septic patients, potentially leading to microcirculatory impairment and tissue hypoxia [13] .