Fluid TherapyIsotonic SolutionsColloidsRehydration SolutionsHyponatremiaPlasma SubstitutesHypovolemiaIntraoperative CarePerioperative CareColorectal SurgeryWater-Electrolyte BalanceBlood Volume DeterminationGoalsGenetic VariationHydroxyethyl Starch DerivativesPostoperative CareSodium ChloridePostoperative ComplicationsHemodynamicsProspective StudiesTreatment Outcome