Warmed fluids for preventing hypothermia during operations

During surgical operations, patients may become cold as the result of a combination of factors including the action of anaesthetic drugs, the presence of uncovered skin and the administration of cold fluids into the veins or to parts of the body where surgery is taking place to wash them. Becoming cold during surgery can be unpleasant and can cause excessive shivering after the operation. It can also cause heart problems and bleeding problems and can contribute to problems with pressure sores and wound healing and longer hospital stay. This review seeks to find out whether warming the fluids given into veins or used to wash parts of the body may prevent patients from becoming cold.

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.

Authors' conclusions: 

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.

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Background: 

Inadvertent perioperative hypothermia (a drop in core temperature to below 36°C) occurs because of interference with normal temperature regulation by anaesthetic drugs, exposure of skin for prolonged periods and receipt of large volumes of intravenous and irrigation fluids. If the temperature of these fluids is below core body temperature, they can cause significant heat loss. Warming intravenous and irrigation fluids to core body temperature or above might prevent some of this heat loss and subsequent hypothermia.

Objectives: 

To estimate the effectiveness of preoperative or intraoperative warming, or both, of intravenous and irrigation fluids in preventing perioperative hypothermia and its complications during surgery in adults.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2014, Issue 2), MEDLINE Ovid SP (1956 to 4 February 2014), EMBASE Ovid SP (1982 to 4 February 2014), the Institute for Scientific Information (ISI) Web of Science (1950 to 4 February 2014), Cumulative Index to Nursing and Allied Health Literature (CINAHL) EBSCOhost (1980 to 4 February 2014) and reference lists of identified articles. We also searched the Current Controlled Trials website and ClinicalTrials.gov.

Selection criteria: 

We included randomized controlled trials or quasi-randomized controlled trials comparing fluid warming methods versus standard care or versus other warming methods used to maintain normothermia.

Data collection and analysis: 

Two review authors independently extracted data from eligible trials and settled disputes with a third review author. We contacted study authors to ask for additional details when needed. We collected data on adverse events only if they were reported in the trials.

Main results: 

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.

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