Sanne de Bruin

9 General Introduction and scope of the thesis Background In the critically ill blood transfusion is regarded as a common used lifesaving therapeutic intervention. Oxygen delivery is dependent on several factors e.g. haemoglobin levels, cardiac output and arterial oxygen content to transport oxygen to the target organs. In the setting of compromised cardiac output or lower arterial oxygen content which is very common among anaemic critically ill patients, it is thought that increasing hae- moglobin levels may compensate for this. However, in the past decades it has become clear that transfusion, with either RBCs, platelets or plasma, is associated with different adverse effects, including transfusion transmissible infections, allergic reactions, transfusion related acute lung injury (TRALI) and transfusion associated cardiac overload (TACO) 1–3 . Insight in the mechanisms of onset of these complications has led to the design of preventive strategies to reduce the chance of adverse effects after blood transfusion including leukodepletion, solvent/ detergent treatment of plasma, the use of male only plasma products or pooled plasma products and the use of novel additive solutions. Critically ill patients are a population of extra interest within the transfusion research field. These patients can have, due to their underlying disease, a high need for blood components but are also more prone for developing blood transfusion related morbid- ity and mortality 4 . Therefore, the decision whether to transfuse a critically ill patient or not can be very complicated balancing the benefits and risks. While not transfusing anaemic patient with RBCs is associated with risk of dying 5,6 , multiple large randomized controlled trials (RCTs) showed that applying a restrictive RBC transfusion strategy is equally safe or in some studies resulted in a higher survival than a liberal transfusion strategy 7–13 . Therefore, transfusion of RBCs should only be considered when the benefits of transfusions outweigh the potential adverse effects. To summarize, blood transfusion is in concept a good therapy in specific settings but there seems to be room to improve efficiency and safety of blood components or the use of blood components. One of the potential improvements could be the use of other transfusion triggers or in the storage conditions of the different blood components. In this introduction several blood components, including RBCs, platelets and plasma are discussed together with their applications in critically ill patients and storage conditions. 1