The most effective transfusion practice in critically ill ICU patients is unknown. Currently the data is unclear as to whether a liberal or restrictive transfusion policy is of most benefit to patients in the short and longer term. The aim of this study is to test the hypothesis that liberal use of RBCs (Hb transfusion trigger ≤90g/L; target Hb range 91-110 g/L) to correct anaemia improves clinical outcomes compared with a restrictive transfusion trigger (Hb transfusion trigger ≤70 g/L; target Hb range 71-90 g/L) in anaemic critically ill patients requiring prolonged ICU stay (≥4 days).