A laboratory evaluation of the heat generating capacity of prewarmed fluid compared with two commercial in-line fluid warming devices

Abstract

The NICE guideline for the management of inadvertent peri-operative hypothermia (IPH) in adults recommends warming all intra-operative fluids. It has been estimated that if in-line fluid warmers are used to implement these guidelines, the cost of the consumables required may be up to £9.45 per patient. A less expensive alternative would be the use of fluid that has been prewarmed in a heating cabinet. We compared the heat delivery of fluid administered from a prewarmed bag, taken from an operating room heating cabinet, against that delivered through two standard in-line warming devices. By investigating the effect of different flow rates of the prewarmed fluid, we explored the effect of heat loss on the efficacy of administration of such fluid. Finally, we investigated the effect of insulation on the rate of cooling of the prewarmed bags. Methods The simulated bench study compared the temperature at the distal (patient) end of a fluid giving set. The following types of fluid administration were studied: 1 Fluid previously warmed in a heating cabinet set at 43 °C. 2 Fluid given via an Astotherm (Stihler Electronic, Stuttgart, Germany) in-line fluid warmer. 3 Fluid given via a Ranger (Arizant, Wakefield, UK) in-line fluid warmer. 4 Fluid previously warmed in a heating cabinet set at 43 °C and insulated. A 120-cm Baxter (Baxter Healthcare, Newbury, UK) fluid giving set was attached to a one-litre bag of 0.9% saline set at a height of 1 m. In-line warming devices had a further 120-cm extension distal to the warming element. Temperature was recorded from the bag and distal end of the giving set. Fluid was administered over 30 min (flow rate 30-35 ml.min-1). ANOVA compared the area under the curve for the temperature versus time plots for the devices tested. Results Table 1 shows that fluid was warmed most efficiently by the Ranger, however we found that the total heat capacity of fluid delivered from prewarmed bags was similar to that delivered via the Astotherm.(p < 0.05). Simple insulation markedly decreased the heat loss from the prewarmed fluid bags (p < 0.05) and improved the performance (Table 1). Discussion The NICE practice guidelines recognised that the use of fluid warmers 'in a large number of surgical patients would have significant implications for the use of NHS resources'. This study demonstrates that the delivery of warmed fluid can potentially be realised at minimal additional cost. The development of thermal insulation will further improve the performance of prewarmed fluids. Future work will determine if this effect is demonstrable under clinical conditions.