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Randomized clinical trial of fluid and salt restriction compared with a controlled liberal regimen in elective gastrointestinal surgery (Br J Surg 2013; 100: 1739–1746)

On the surface, this trial by Dr Kalyan and colleagues seems to contradict the results of earlier trials suggesting that salt and water restriction was beneficial to surgical outcome. Several factors may explain the ‘negative’ results of this trial. There was a significant difference between the two groups with regard to the amount of water and sodium received. Nevertheless, weight gain in the liberal group on day 2 was 1·3 kg and weight loss in the ‘restricted’ group was 1·4 kg. Hence, the liberal group had a marginally positive and the restricted group a slightly negative balance. The early trials of standard versus restricted regimens tended to overload the standard groups with salt and water, with weight gain in the standard groups being in the range of 3–7 kg. A literature review1 has suggested that, once postoperative weight gain secondary to fluid retention exceeds 2·5 kg, oedema and complications are more likely to develop. A weight gain of less than this is unlikely to result in increased complications. There has now been a paradigm shift in perioperative fluid therapy, and patients undergoing elective abdominal surgery are less likely to be overloaded with salt and water to the extent seen in the early trials. Chloride load must also be considered when interpreting the results. The base crystalloid used in this trial was Hartmann’s solution, which has a lower chloride content than 0·9 per cent saline (111 versus 154 mmol/l) and is less likely to cause hyperchloraemia2. Saline infusions have been associated with greater interstitial fluid overload, impaired renal haemodynamics and greater fluid retention than infusions of balanced crystalloids2. Chloride-avid fluid regimens can result in more complications, especially acute kidney injury requiring renal replacement therapy, than regimens with low chloride loads3. The aim of modern-day fluid therapy is a near-zero fluid balance. Too much or too little fluid (and salt) is likely to be of detriment to the patient4.