This study evaluated the warming capabilities of Hotline and S-line under the conditions of two different flow rates and three starting fluid temperatures, as well as before and after the use of an extension line. At the faster fluid administration rate, Hotline was superior to S-line for warming with regard to both TProx and TDistal by approximately 10 °C and 20 °C in the room-temperature and cold saline groups, respectively. However, at 100 ml/hr, there was no statistical difference between the TDistal obtained with Hotline and S-line. The fluid lost a significant amount of heat as it traveled an additional 90 cm at 100 ml/hr. Thus, Hotline would be more effective in preventing hypothermia during rapid fluid administration. Furthermore, at 100 ml/hr, the delivery of warmed fluids would be more effective without the extension line in both Hotline and S-line.
TProx in S-line was significantly higher at 100 ml/hr than at 250 ml/hr when using cold or room-temperature fluid, which suggests that a certain amount of time was required to sufficiently warm the fluid. In contrast, TProx in Hotline was warmed to approximately 40 °C at both rates (100 and 250 ml/hr) using either cold or room-temperature fluids. The difference in heating capacity between these devices was likely due to the differences in their respective heating mechanisms, i.e., a coaxial circulating water bath (Hotline) versus a dry heating profile (S-line). The dry-heating system is expected to incur greater heat losses on account of the exposed portion of the extension line in ambient temperature. Thus, the Hotline coaxial warming system is apparently more effective than S-line in preventing hypothermia during rapid fluid administration.
In this study, three different temperature groups were used to investigate the influence of the initial fluid temperature on TProx. At 100 ml/hr, the TProx values in both Hotline and S-line were less affected by changing the initial fluid temperature than at 250 ml/hr. However, changing the initial fluid temperature notably affected TProx at 250 ml/hr in S-line: 28.2 °C (27.6–28.4), 18.2 °C (17.6–19.5), and 44.8 °C (44.7–45.4) in room-temperature, cold, and warm saline groups respectively. The corresponding TDistal values were 27.8 °C (27.0–27.9), 19.1 °C (18.5–20.0), and 43.9 °C (43.5–44.2), respectively. Adjusting the initial temperature affected TProx in S-line, and pre-warming the fluid helped increased the fluid temperature. Careful calibration of the initial fluid temperature should maximize the delivery of an appropriately warmed fluid in S-line. At the same time, precautionary measures should be taken against the preparation of fluid that is too hot.
It is clinically important to determine whether warmed fluids can be delivered to the patient without heat loss as they pass through a non-insulated extension line. Interestingly, in this study, a statistically significant change in fluid temperature was observed after the extension line in every experimental condition regardless of the fluid warmer type, initial fluid temperature, or flow rate. The change in fluid temperature was more pronounced at the low flow rate than at the high one. The fluid lost a significant amount of heat as it traveled an additional 90 cm at a rate of 100 ml/hr. This finding warrants the utilization of additional measures for hypothermia prevention when using an extension at the low flow rate, especially when administering fluids to patients with a high risk of developing hypothermia such as neonatal and older patients . Furthermore, it is essential to minimize heat loss as the fluid travels down the extension line, which can be achieved by an extension line innovation or by applying supplemental measures against hypothermia.
Several limitations of this study should be noted. In an actual clinical setting, the fluid administration rate, initial fluid temperature, and extension line length may differ from the conditions used in this study. For example, during rapid fluid resuscitation, the infusion rate can be as high as 60 to 80 mL/kg per hour . Also, in this study, the fluid temperature in the warm temperature group was greater than 45 °C, which can be problematic because the proteins in red blood cells can degenerate at a temperature higher than 45 °C . Moreover, precautionary measures should be taken against preparing fluids that are excessively hot for clinical practice. Finally, extension lines longer than 90 cm can be employed in certain clinical scenarios. Longer extension lines could affect the fluid temperature more markedly than the line length employed in this study.