Background and Goal of Study: Perioperative hypothermia is a recognized and common side effect of anesthesia, which inhibits normal thermoregulation. Therefore, the guideline recommends that intravenous fluids with volumes > 500 ml should be warmed to 37°C using a fluid warming device. The changes in the temperature of the delivered fluid can be influenced by the device-specific maximum flow rate as well as the outflow tubing length from the warming device. We conducted to compare the fluid warming performances of Mega Acer Kit®, which is designed for warming the fluid via the lumen of the heated circuit, with Ranger™ and ThermoSens® according to flow rates and distances.

Materials and methods: We set Mega Acer Kit® (group M), Ranger™ (group R) and ThermoSens® (group T) according to the manufacturers' instructions and infused fluids, which had been stored in the operating room over the previous 24 hr, using infusion pump at sequent flow rates 440 ml/hr, 650 ml/hr, 860 ml/hr, 1140 ml/hr and fully dropping state. We simultaneously recorded fluid temperatures at the inlet point and two outlet points [76 cm (proximal) and 166 cm (distal) from each device] every 1 min for 10 min after the 10 min of equilibration period between each infusion rate. We repeated each test eight in each device. 

Results and discussion: The temperature at inlet point showed no significant differences among the groups. At a flow of 440 ml/hr, the temperature of proximal outlet point was significantly higher in group M (34.3 ± 1.1°C) compared with group R and T (29.3 ± 0.8°C and 30.4 ± 0.1°C, p < 0.05). However, it was significantly lower than that of group R and T at 1140 ml/hr and fully dropping state (37.8 ± 0.4°C and 36.7 ± 0.1°C, p < 0.05). The temperature of distal outlet point also showed the similar results with more significant decrease (p < 0.05), except at fully dropping state in group R and T (37.2 ± 0.2°C and 36.0 ± 0.1°C).

Conclusion(s): We suggest that for effective warming cold fluid, Mega Acer Kit® is suitable at lower flow rate below 860 ml/hr, whereas ThermoSens® and Ranger™ is suitable at higher flow rates above 1140 ml/hr with less than 76 cm of outflow line. 

References: 
1. Anaesthesia. 2006;61:571-5.
2. Anesthesia and analgesia 2004, 99(3):788-792.
3. J Anesth. 2015 Aug;29(4):499-507.

The experimental comparison on the fluid warming performances of the Ranger™, ThermoSens®, and Mega Acer Kit® according to flow rates and distances