List the potential causes of anaemia in critically ill patients, and outline how you would determine which factors were contributory.
Anaemia in critically ill patients is usually multifactorial. Potential causes can be categorised into decreased production (as a small proportion [approx 1%] of circulating RBCs are destroyed each day), increased destruction, loss of RBCs and haemodilution. Decreased production includes problems with nutrients (eg. iron, folate, B12), disease involving bone marrow (eg. infiltration, myelodysplasia), depressant effects of drugs (eg. chemotherapy) or irradiation, and low levels of stimulatory hormones (eg. EPO in renal failure, thyroid hormones). Increased destruction can occur in haemolytic anaemias: either congenital (eg. thalassaemia major, sickle cell) or acquired (eg. Coomb’s positive auto-immune, TTP-HUS, infection with malaria or clostridiae etc). Increased RBC loss can occur via injuries, bleeds into viscera or organs (eg. GI tract, GU tract, lungs) and iatrogenic (procedures, blood samples for testing). Dilutional anaemia usually occurs in the context of rapid or extensive non-blood fluid resuscitation.
Evaluation of cause includes obvious but essential role of history (trauma, drugs and therapies, nutrition, chronic disease, infection, review of blood tests and procedures etc) and examination (trauma, sites of potential blood loss [including PR], jaundice, hepato-splenomegaly etc.). Simple investigations include morphological assessment of blood (eg. MCV, blood film: red and white cell mophology), reticulocyte count, electrolytes and renal and liver function tests. More specific tests as indicated include assays for folate/B12/ferritin, indicators of haemolysis (eg. haptoglobin, Coomb’s test), Hb electropheresis, cultures for infection (±thick/thin film) etc.
This question is identical to Question 9 from the second paper of 2005.