MODEL RELEASED. Blood transfusion patients. Blood bags (not seen, off top) are providing blood to be added to the patients' bloodstreams through the blood-filled tubing attached to their arms. Elevating the blood bags above the patients allows gravity to be used to provide the pressure to add the blood. Blood transfusions are carried out to replace blood in people with blood disorders, or those who have lost blood through trauma or surgery. The blood group and type needs to be matched to that of the patient. Common blood disorders that can require regular transfusions include thalassaemia, anaemia and haemophilia.