EFFICACY OF DIFFERENT INFUSION AND BLOOD- WARMING METHODS - AN EXPERIMENTAL-MODEL

Heat loses during surgery occur mainly to the environment and due to i nfusions and irrigations. Infusions given at room temperature account for a great deal of the total heat deficit during major operations, e. g., the infusion of 53 ml/kg 20 degrees C fluid leads to a loss of 1 d egrees C in mean body temperature. Hence, heating i.v. fluids will add to the effect of other measures aimed at reducing heat loss to the en vironment. We investigated the efficacy of different warming methods f or i.v. fluids in an experimental model by measuring the temperature a t the end of the delivery line. Methods. The following in-line warmers were studied: Hotline HL-90 and System H-250/heat exchanger D-50 (Lev el 1 Technologies, Marshfield, USA), Astotherm IFT 260 (Stihler Elektr onic GmbH, Stuttgart, Germany), RSLB 30 H Gamida (Productions Hospital ieres Francaises, Eaubonne, France), Fair Hugger 241/Modell 500 Protot ype (Augustine Medical, Eden Prairie, USA). They were compared with pr ewarming infusions (39 degrees C) only using the Clinitherm S (Labor T echnik Barkey GmbH, Bielefeld, Germany) and prewarming with ''active i nsulation'' of the delivery line using the Autotherm/Autoline system ( Labor Technik Barkey GmbH, Bielefeld, Germany). We investigated the in fluence of four variables on the efficacy of warming: (1) flow rate (5 0-15,000 ml/h); (2) ambient temperature (20 degrees C and 25 degrees C ); (3) infusion bag temperature (6 degrees C, 20 degrees C, and 39 deg rees C); and (4) length of infusion system downstream from the heat ex changer. Fluid temperatures were measured using thermistors of 1 mm di ameter (Modell YSI 520, Yellow Springs Instruments Co., Yellow Springs , USA) incorporated into 3-way stopcocks. Temperatures were recorded u sing Hellige temperature monitors (Hellige GmbH, Freiburg im Breisgau, Germany) and the signals were collected at 10 Hz through an AD conver ter and averaged over 1 min. Flows were calculated by timed collection into calibrated cylinders; 10 to 12 different flow rates were taken t o define one temperature/flow plot. Effective warming was defined as a temperature >33 degrees C at the end of the infusion line. Results. A t high flow rates (>2,500 ml/h) using 20 degrees C fluids at 20 degree s C ambient temperature, the H-250/D-50 system gave the highest temper atures throughout the range and showed effective warming from 1,300 ml /h on over the entire range tested (35 degrees C at 17,000 ml/h) compa red to the RSLB 30 H Gamida system (3,000-18,000 ml/h) (Fig. 2). This difference in performance was almost abolished with fluids at 6 degree s C (Fig. 4). Similar efficacy could be reached by using prewarmed inf usions that gave effective warming at >2,000 ml/h and reached 39 degre es C at 13,000 ml/h. Prewarmed infusions could be used effectively dow n to >80 ml/h applying ''active insulation'' (Autotherm/Autoline) to t he whole infusion system. The Hotline HL-90 (50-4,700 ml/h) appeared t o be the most effective in-line warmer in the low (<250 ml/h) and midd le (250-2,500 ml/h) flow range, followed by the Astotherm IFT 260 (400 -4,000 ml/h), but only if used with a length of 40 cm down-stream from the heat exchanger (Fig. 1). Increasing this distance to 145 cm marke dly reduced its efficacy below the range of 2,000 mi/min (1,200-3,000 ml/h) (Fig. 5). The Bair Hugger 241 Prototype showed a narrow effectiv e range (700-1,300 ml/h) that could be extended beyond 1,300 ml/h by t he use of prewarmed infusions (Figs. 1 and 3). The performance for 6 d egrees C solutions and ambient temperatures of 25 degrees C are given in Fig. 3 and Table 1. Conclusions. The importance of infusion warming increases with the amount of fluid given. In general, the infusion ba g temperature only influenced the efficacy of in-line warmers within t he high-flow range, challenging the performance of the hear exchanger. The length of uninsulated i.v. line downstream from the heat exchange r influenced the efficacy within the low- and middle-flow range, as di d the room temperature. Prewarmed solutions can be infused very effect ively within the high-flow range. This efficiency can be preserved dow n to the low-flow range by using ''active insulation'' of the infusion system. In-line warming is essential for emergency and rapid massive transfusions.