Anaemia and transfusion triggers in critically ill patients - What we have learnt thus far.

Anaemia is a common finding in critically ill patients, the cause of which is multi-factorial including: sepsis, haemolysis (and disseminated intravascular coagulation), iatrogenic blood loss secondary to laboratory sampling, post-operative anaemia, bone marrow suppression/failure, decreased production of erythropoietin, anaemia secondary to drugs/toxins, overt or occult blood loss, functional iron deficiency, poor nutrition and haemodilution. Anaemia is associated with deleterious outcomes including increased risk of cardiac-related morbidity and mortality and decrease in oxygen-carrying capacity in the face of increased metabolic demands. There is a growing body of evidence, which demonstrates that packed red blood cell transfusions are associated with poorer outcomes. Clinicians therefore need to weigh the potential benefit of treating anaemia against the desire to avoid unnecessary transfusions. We explored current literature regarding transfusion triggers and morbidity and mortality associated with packed red blood cell transfusions transfusion, concentrating on studies that have been conducted in critical care patients. In addition, we reflected on trials which considered the viability of iron transfusion and erythropoietin in critically unwell patients.