THERMAL-ENERGY BALANCE DURING IN-VITRO CONTINUOUS VENOVENOUS HEMOFILTRATION

Hypothermia has been recognized as a potential side effect of continuo us hemofiltration, but the thermal energy loss within the extracorpore al circuit has not yet been quantified. The authors measured temperatu re decrease and thermal energy balance in vitro at different points wi thin the extracorporeal circuit of the Acu-men (Fresenius Medical Care , Bad Homburg, Germany), a new device for continuous hemofiltration. T he device employs a disposable cartridge with a pneumatic blood pump a s the driving force for the blood. Furthermore, a volumetric balancing chamber is used to balance filtrate with replacement fluid. At a bloo d 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 beg inning 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 ene rgy loss of 3,300 kJ/d. The in vivo thermal energy loss might be signi ficantly less because of baroreceptor induced peripheral vasoconstrict ion, with reduced heat loss through the skin. The blood tubing contrib uted 26%, the hemofilter 31%, and the produced filtrate 43% to the neg ative 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 re duced the thermal energy loss by 22%, 48%, and 72%, respectively.