Pathophysiology of perioperative anaemia

Perioperative anaemia is a common clinical entity. It is usually due
to combination of various mechanisms, including: pre-existing
anaemia prior to surgery; anaemia due to impaired erythropoiesis,
including alterations of metabolism of iron and erythropoietin
(EPO); anaemia due to increased destruction of red blood cells
(RBCs); and anaemia due to iatrogenic causes. Postoperatively,
anaemia resembles anaemia of chronic disease and is probably
related to the effects of inflammatory mediators released during
and after surgery on the production and survival of RBCs. Proinflammatory
cytokines, such as tumour necrosis factor, impair
erythropoietin-dependent signalling and iron homeostasis. Iatrogenic
causes, notably excessive phlebotomies, remain a major
cause of perioperative anaemia. With increasing emphasis on
restrictive blood transfusion strategies, understanding these
mechanisms is important for the clinician.