Evaluation of a blood warmer that utilizes a 40 degrees C heat exchanger

Most commercial blood warmers are unable to warm blood components to greater than 35 degrees C at rapid flow rates (greater than 100 mL/min) because of problems with inefficient heat transfer and resistance to the flow of blood through the instrument's tubing. A new blood warmer, using a closed-flow 40 degrees C counter-current water bath and large-bore tubing, is able to warm cold (10 degrees C) packed red cells to temperatures greater than 35 degrees C even at flow rates of 500 mL per minute. To evaluate the effects on red cells of prolonged exposure to the 40 degrees C heat exchanger, blood from five volunteers stored for 42 days in AS-1 was run through the blood warmer using flow rates equivalent to the transfusion of a unit of blood over 4 hours. Compared with unwarmed blood, these blood units showed no significant changes in plasma hemoglobin, mean corpuscular hemoglobin concentration, potassium, ATP, pH, and osmotic fragility. In vivo survivals of chromium-51-labeled warmed autologous red cells were greater than 75 percent in four volunteers and 49.5 percent in the fifth volunteer, whose abnormally low unwarmed red cell ATP level suggested a storage problem. Thus, this blood warmer, which warms blood efficiently at high flow rates, causes no red cell damage, even with prolonged exposure of old red cells to the 40 degrees C heat exchanger.