Heating capabilities of the Hotline and Autoline at low flow rates.

Background: At low flow rates, fluid warmers using coaxial warming tubes are superior in preventing heat loss. This laboratory investigation was performed in order to compare the heating capabilities of two coaxial fluid warmers.

Methods: The Hotline and the Autoline were investigated by using normal saline at various flow rates (10-99 ml x h(-1)). Final infusion temperatures were measured six times in a row at the end of the tubing by using a rapid-response thermometer. Final temperatures were compared with those of infusions, which passed through disposable i.v. tubing covered and warmed using an 'off label' convective air warming system (WarmTouch). Measurements were performed at two different room temperatures (20 and 24 degrees C). Each group was analyzed with respect to differences between various flow rates as well as differences between the groups at comparable flow rates by using a three-way anova with multiple comparisons according to Tukey's procedure. Significance was defined at P < 0.05.

Results: Both devices heat infusions at low flow rates efficiently above 34 degrees C, with the Hotline being more effective than the Autoline (P < 0.0001). Except for the lowest flow rate (10 ml x h(-1)), the Hotline delivered infusion temperatures between 38 and 39 degrees C, while the Autoline warmed the infusions upto 36 degrees C. While heating capability of the Hotline was improved with elevated room temperatures at low flow rates (10-60 and 80 ml x h(-1)), the Autoline demonstrated lower infusion temperatures throughout elevated room temperature at flow rates between 20 and 90 ml x h(-1). Both devices heated infusions more efficiently compared with 'off label used' convective air warmer (each with P < 0.0001).

Conclusions: Both the Hotline and the Autoline heated infusions sufficiently at low flow rates. However, the heating capability of the Hotline was superior and can further be increased at low flow rates by increasing the room temperature.