Caloric Loss Associated with Apheresis
Authors: Donahue Robert E , Metzger Mark E , Leitman Susan F , Cullis Herb 
Published: October 2019

Abstract
A common complaint attributed to apheresis is chill and hunger. Most likely this is a result of heat loss when blood is externalized from the body. This energy loss has not been quantitated. To determine caloric loss we monitored temperature loss using sterilized Omega hypodermic type K thermocouple probes inserted 20cm from the subject into the draw and return line, the centrifuge chamber, and the body. Inlet, return, centrifuge, and body temperature were recorded at one minute intervals using an Omega RDXL4SD Data Logger. Either a 38oC water bath (sham subject, n=2 per device) or rhesus macaque (weight 5-7 kg) undergoing apheresis served as subject. By definition one calorie (4.2 joules) is the amount of energy required to heat 1mL of water 1oC. By knowing that the heat capacity of blood is 3.6 joules/mL, we can calculate calorie loss per procedure. A total of 15 small volume apheresis procedures were performed with the Fenwal CS3000 on 12 rhesus macaques using a modified single small volume chamber procedure (Donahue et al., BLOOD 87:1644-53, 1996), 7 procedures were performed on 3 rhesus macaques using a Spectra Optia, and 6 procedures were performed on 3 rhesus macaques using a Fenwal Amicus device. Using water, the average temperature difference between inlet and return line dropped logarithmically (R2>0.89) for all three instruments as flow rate was increased (Fig. 1). Similarly the calorie loss/min logarithmically increased (R2>0.89) (Fig. 2) as flow rate increased. For CS3000 rhesus apheresis procedures, the drop in temperature between draw and return lines was 8.7(SD 1.5) oC at a flow rate of approximately 11mL/min, 9.5(0.9) oC for the Optia at a flow rate of 10mL/min, and 10.3(1.2) oC for the Amicus at a flow rate of 11mL/min. This drop was not significantly different between instruments (p=0.10). Procedures did differ in the amount of blood processed. For the CS3000, the blood volume processed per procedure (1013(18) mL) was significantly less (p<0.001) than either the Optia (1425(201) mL) or Amicus (1473(36) mL). In addition, centrifuge chamber temperature differed between the CS3000 (33.1(1.6) oC) and the Optia (28(1.9) oC) or Amicus (26.0(1.0) oC) (p<0.001) as the CS3000 has a chamber heating element. For the CS3000, calorie loss per procedure was 7712(1823) calories, for the Optia 11827(1987) calories, and the Amicus 13199(1354) calories. The significant difference (p<0.001) in caloric loss between the CS3000 and the other instruments was due to the larger blood volume processed using the Optia and Amicus. To prevent calorie loss we developed a method using a 50oC heated water bath in which a segment of the return line (38 cm or more) was placed in the water bath to equilibrate draw and return line temperatures without altering extracorporeal blood volume. On performing this procedure, we successfully matched draw and return line temperatures. This report documents for the first time caloric loss during apheresis procedures. In addition, it introduces a method to limit such a loss. Although adults >50kg may tolerate apheresis-associated caloric loss with only mild to moderate symptoms, pediatric patients, small animals, and debilitated and aging subjects, may not. Here we demonstrate the extent of calorie loss and a means to prevent it.
Figure 1 Figure 1. Figure 2 Figure 2.

Disclosures
No relevant conflicts of interest to declare.