Prospective randomized double blind phase IV trial studying the efficacy and safety of the
tonicity of two different perioperative maintenance solutions: an isotonic solution
containing NaCl 0.9 in glucose 5% with an added 40 mmol/L of potassium or a commercially
available premixed solution (Glucion 5%) containing a.o. 54 mmol/L of sodium and 26 mmol/L of
potassium. Both solutions are administered at 27 mL/kg of ideal body weight, as recommended
by current guidelines (NICE 174) and both solutions are widely used in daily clinical
practice. The primary hypothesis is that isotonic maintenance solutions lead to more fluid
retention than hypotonic fluids. Metabolism of both solutions is assessed by sequential
analysis of urine and serum and clinical parameters.