An experimental comparison of two methods for warming intravenous crystalloid solutions.

Abstract

We agree with Perl et al. that the release of aluminium from fluid warming devices is a cause for concern 1. Here, we report an experiment that indicates that such devices may be unnecessary in many cases. We measured the temperature of an infusion of compound sodium lactate (CSL) (Baxter Healthcare Ltd, Northampton, UK) using various warming strategies and flow rates. With all components at room temperature, we ran a 1-l bag of CSL through a giving set and 100 cm extension (BD Connecta, Becton Dickinson, Helsingborg, Sweden), and used an infusion pump (COLLEAGUE, Baxter International Inc, Deerfield, IL, USA) to set flow rates. We measured temperatures at the ‘patient’ end of the extension using a thermistor (Level 1, Smiths Medical, Minneapolis, MN, USA, accuracy ± 0.2 °C). We passed the extension tubing under a warm air device blanket (Bair Hugger, 3M, Maplewood, MN, USA), and inserted a fluid warmer (Ranger, 3M) between the giving set and the extension when needed. We investigated four conditions: fluid warmer unconnected + warm air device turned off (control); fluid warmer set to 41 °C + warm air device turned off (fluid warming); fluid warmer removed + warm air device set to 38 °C with high airflow (air warming); and fluid warmer set to 41 °C + warm air device set to 38 °C with high airflow (combined). We investigated five flow rates for each condition, and recorded temperatures every minute until we obtained three consecutive readings within 0.2 °C of each other. There was no change in temperature in the control experiment. With fluid warming, the temperature was lower at low flow rates, indicating that heat was rapidly lost to the environment downstream of the warmer. With air warming, temperature was greater at low flow rates, indicating that heat was gained from the warmed air. The combined condition resembled air warming at low flow rates, and fluid warming at high flow rates, mitigating the deficiencies of each individual system (Fig. 1). The National Institute for Health and Care Excellence (NICE) recommends that intravenous fluids are warmed when more than 500 ml are infused, and that patients are actively warmed when their anaesthetic duration exceeds 30 min 2. At low infusion rates (up to 250 ml.h−1), our experiment indicates that fluid is warmed effectively simply by passing the giving set extension under a warm air device. We believe that low flow rates are appropriate in many elective anaesthetics in relatively volume-replete patients. Therefore, when warm air devices are used, fluid warmers can often be omitted without negative effects. This has financial and environmental benefits, and potential implications for patient safety 1.