Cell saver physics – a review

Abstract

Cell salvage, cell saver, cell processor or autologous blood transfusion is the process of collecting a patient’s blood from the surgical field, washing, filtering and transfusing it back to the same patient. There are six basic steps involved in cell salvage. Step one involves the collection of shed blood into a reservoir with an anticoagulant-saline mixture. Step two is the filtration of debris and clots. In step three, the red blood cells (RBCs) are separated from the nonerythrocyte components. This process may be likened to clothes in the washing machine. Washing with saline removes contaminants in step four and the RBCs are resuspended in saline and transferred to the reinfusion bag. Waste products are transferred into the waste bag in step five. In step six, the resuspended, washed RBCs are collected in a bag at room temperature which can be reinfused. The functioning of the cell saver is based on Newton’s First and Second Laws of Motion, where centripetal forces are generated to separate the blood components depending on their density. The denser RBCs are driven to the outer wall of the centrifuge bowl with the plasma collecting on the inside. A typical yield will retrieve 50–95.8% RBCs with a final haematocrit of 50–70%. Cell savers are used in procedures with a large volume of anticipated blood loss, high risk of bleeding, low preoperative haemoglobin, in patients with rare blood groups or multiple antibodies and in some Jehovah’s Witness patients.