Abstract: We included 14 trials (n = 565), 13 (n = 525) of which compared intravenous administration of amino acids to a control (usually saline solution or Ringer's lactate). The remaining trial (n = 40) compared intravenous administration of fructose versus a control. We noted much variation in these trials, which used different types of surgery, variable durations of surgery, and different types of participants. Most trials were at high or unclear risk of bias owing to inappropriate or unclear randomization methods, and to unclear participant and assessor blinding. This may have influenced results, but it is unclear how results might have been influenced. No trials reported any of our prespecified primary outcomes, which were risk of hypothermia and major cardiovascular events. Therefore, we decided to analyse data related to core body temperature instead as a primary outcome. It was not possible to conduct meta-analysis of data related to amino acid infusion for the 60-minute and 120-minute time points, as we observed significant statistical heterogeneity in the results. Some trials showed that higher temperatures were associated with amino acids, but not all trials reported statistically significant results, and some trials reported the opposite result, where the amino acid group had a lower core temperature than the control group. It was possible to conduct meta-analysis for six studies (n = 249) that provided data relating to the end of surgery. Amino acids led to a statistically significant increase in core temperature in comparison to those receiving control (MD = 0.46°C 95% CI 0.33 to 0.59; I2 0.0%; random-effects; moderate quality evidence). Three trials (n = 155) reported shivering as an outcome. Meta-analysis did not show a clear effect, and so it is uncertain whether amino acids reduce the risk of shivering (RR 0.36, 95% CI 0.13 to 1.00; I2 = 93%; random-effects model; very low-quality evidence). Intravenous amino acids may keep participants up to a half-degree C warmer than the control. This difference was statistically significant at the end of surgery, but not at other time points. However, the clinical importance of this finding remains unclear. It is also unclear whether amino acids have any effect on the risk of shivering and if intravenous nutrients confer any other benefits or harms, as high-quality data about these outcomes are lacking.

Plain-language summary: We looked for evidence up to November 2015. We included 14 randomized studies (involving 565 participants). Thirteen studies compared people who received normal care with additional intravenous amino acids against people who received normal care but no amino acids (the control group). One study compared people who received fructose with those in a control group. Studies involved adults undergoing planned or emergency surgery. We did not include studies in which participants were deliberately kept cold during surgery, were receiving skin grafts or were under local anaesthetic. We can be certain that at the end of surgery, people receiving intravenous nutrients are up to a half-degree warmer than people receiving control (based on evidence from six studies involving 249 participants). However, there was more uncertainty about the effects of intravenous nutrients at other time points, with some studies suggesting that intravenous nutrients keep participants warmer and other studies reporting that participants were colder than those receiving the control. We are uncertain if keeping people up to half a degree warmer is important to those involved in caring for people who are having surgery. We are also uncertain if giving intravenous nutrients reduces the risk of people shivering (based on evidence from three studies involving 155 participants). Most of the evidence was moderate to low in quality. The methods used to assign participants to treatment groups was often inadequate or unclear, and we were uncertain if the people assessing outcomes were aware of which treatment group participants were in. This may have biased the results, but we are unsure what effect it may have had on results overall.