Figure 1

Test apparatus, 4 units of RC surrounded by coolant packs in a polystyrene box. One RC unit placed in a pressure cuff (which was inflated as required, to express the contents of the RC unit) and connected via a 220 mm insulated IV line and 3-way stopcock to the inlet of the blood warmer. A tube was connected from the blood warmer outlet via a 3-way stopcock to a waste bag on top of an electronic balance and the balance output was recorded at approximately 30-second intervals – for determining the outlet flow rate. 10 mL samples were withdrawn from the inlet stopcock when the RC from the unit first began flowing into the blood warmer, and from the outlet stopcock at the point where the unit was estimated to be half full and as the RC unit emptied. As each RC unit emptied, it was removed from the IV line and replaced with a full one (until all RC units in the polystyrene box had been used). K-type thermocouples, connected to a temperature logger, were placed in the blood warmer inlet and outlet ports, in the polystyrene box and in the latent heat storage material inside the blood warmer. Three-way stopcocks were placed immediately upstream from the thermocouple in the blood warmer inlet line and immediately downstream from the thermocouple in the blood warmer outlet line.