Abstract: We included in this review 24 studies with a total of 1250 participants. The trials included various numbers and types of participants. Investigators used a range of methods to warm fluids to temperatures between 37°C and 41°C. We found that evidence was of moderate quality because descriptions of trial design were often unclear, resulting in high or unclear risk of bias due to inappropriate or unclear randomization and blinding procedures. These factors may have influenced results in some way. Our protocol specified the risk of hypothermia as the primary outcome; as no trials reported this, we decided to include data related to mean core temperature. The only secondary outcome reported in the trials that provided useable data was shivering. Evidence was unclear regarding the effects of fluid warming on bleeding. No data were reported on our other specified outcomes of cardiovascular complications, infection, pressure ulcers, bleeding, mortality, length of stay, unplanned intensive care admission and adverse events. Researchers found that warmed intravenous fluids kept the core temperature of study participants about half a degree warmer than that of participants given room temperature intravenous fluids at 30, 60, 90 and 120 minutes, and at the end of surgery. Warmed intravenous fluids also further reduced the risk of shivering compared with room temperature intravenous fluids Investigators reported no statistically significant differences in core body temperature or shivering between individuals given warmed and room temperature irrigation fluids. Warm intravenous fluids appear to keep patients warmer during surgery than room temperature fluids. It is unclear whether the actual differences in temperature are clinically meaningful, or if other benefits or harms are associated with the use of warmed fluids. It is also unclear if using fluid warming in addition to other warming methods confers any benefit, as a ceiling effect is likely when multiple methods of warming are used.

Plain-language summary: We searched medical databases up until February 2014 to find studies comparing warmed fluids with unwarmed fluids and other methods of warming the patient. We found 24 relevant trials with 1250 adult patients undergoing all types of surgery. We did not include studies for which it was intended that the patient would become cold (such as to facilitate heart bypass surgery). We had intended to collect data on which patients became hypothermic (when their body temperature dropped to below 36 degrees Celsius), but no trials reported this, so we collected data on patient temperatures at various time points throughout surgery. We found evidence of moderate quality showing that if patients had the fluids they were given into their veins warmed up, they were about half a degree Celsius warmer and shivered less than those who received unwarmed fluids; however, we were unable to show a significant difference in patients who received warmed fluids to wash out parts of their bodies. We have demonstrated that warming fluids does keep adult patients warmer; however it is unclear whether this alone can make a difference in the severe complications that becoming cold may cause.