Dry or wet - which is the best for your patient?

Perioperative fluid therapy is the subject of much controversy, and the existing evidence seems contradictory. The aim of this paper is to present the (missing) evidence supporting the current standard fluid therapy, as well as the original trials examining the effects of fluid therapy on outcome of surgery. To emphasise the fluid loss that actually occurs during surgery, the literature examining the evaporation from the abdominal wound, the fluid accumulations in the traumatised tissues, as well as the postulated changes in functional extracellular volume (i.e. the 'loss to third space') is briefly presented and critically analysed. An attempt is made to evaluate all the trials examining the influence of fluid volume on outcome of surgery. The trials of goal-directed fluid therapy can be divided into two categories: the trials that examine the effect of zero fluid balance and the goal of normal bodyweight (the original restricted fluid trials), and the trials examining the effect of giving fluid to a target physiological value measured with either a pulmonary artery catheter or with an ultrasound Doppler device placed in the oesophagus. In addition to the goal-directed trials, the trials examining the effect of fixed volume fluid therapy will be presented. These 'fixed volume trials' concern mostly patients undergoing minor surgical procedures in an outpatient surgical setting. The following conclusions are reached: current fluid therapy is not at all evidence based. The fluid losses that actually occur during surgery are highly overestimated. The perspiration from the surgical wound as well as the fluid accumulated in traumatised tissue is very small in elective surgery. The 'loss to third space' is based on flawed methodology and most probably does not exist. The results of the goal-directed trials examining the effect of fluid therapy guided by a catheter in the pulmonary artery have not been unanimous, and the most exhaustive of these trials including 1 999 patients failed to show any benefit. The trials giving fluid to a maximal stroke volume guided by a Doppler in the oesophagus have several weaknesses, making the results of the trials very difficult to interpret, yet the method seems promising. The trials focusing on zero fluid balance with the goal of normal body weight have shown that fluid overload with crystalloids causes harm, and avoidance of this fluid overload convincingly improves the outcome. This approach is confirmed by the trials giving a fixed volume of fluid during outpatient surgery, showing improved postoperative recovery by replacing the deficit caused by fasting. Patients undergoing major surgery should not be treated with a fixed fluid volume.