The infant is laid on his or her back, usually under a radiant warmer. The umbilical vein is catheterized with a fluid-filled catheter. The catheter is connected to an exchange transfusion set, incorporating lines to and from a waste container and a pack of donor blood. These are connected by means of a four-way stopcock, to which is also attached the syringe used to remove and replenish the infant's blood. The exchange transfusion now goes ahead in cycles, each of a few minutes duration. Slowly the infant's blood is withdrawn, and the fresh, pre-warmed blood or plasma is injected. After the exchange transfusion, an umbilical catheter may be left in place in case the procedure needs to be repeated within a few hours.