Thermal energy balance during in vitro continuous veno-venous hemofiltration

Hypothermia has been recognized as a potential side effect of continuous hemofiltration, but the thermal energy loss within the extracorporeal circuit has not yet been quantified. The authors measured temperature decrease and thermal energy balance in vitro at different points within the extracorporeal circuit of the Acu-men (Fresenius Medical Care, Bad Homburg, Germany), a new device for continuous hemofiltration. The device employs a disposable cartridge with a pneumatic blood pump as the driving force for the blood. Furthermore, a volumetric balancing chamber is used to balance filtrate with replacement fluid. At a blood flow of 120 ml/min, a filtrate volume of 1.4 L/hr, and a replacement fluid temperature of 20 degrees C, temperature decreased from the beginning to the end of the extracorporeal circuit from 37.0 degrees C to 32.4 degrees C. This corresponds to a calculated in vitro thermal energy loss of 3,300 kJ/d. The in vivo thermal energy loss might be significantly less because of baroreceptor induced peripheral vasoconstriction, with reduced heat loss through the skin. The blood tubing contributed 26%, the hemofilter 31%, and the produced filtrate 43% to the negative thermal energy balance. Heat transmission within the volumetric balancing system of the Acu-men reduced the heat loss by 15%. Heating of replacement fluid to 30 degrees C, 37 degrees C, or 42 degrees C reduced the thermal energy loss by 22%, 48%, and 72%, respectively.