Bioelectrical Response to Preoperative Hydration in Colorectal Surgery

The prospective component is protocol-assigned, non-randomized, open-label, and single-group. Dosing weight is the lower of actual body weight measured at T0 and ideal body weight calculated from sex and height using the Robinson equations. An eGFR of at least 60 mL/min/1.73 m² is an eligibility criterion and is not used to calculate fluid volume.

From infusion start through T60, food, drink, and other intravenous fluids are withheld unless clinically required. Routine walking to the toilet and standing scale is permitted. Only T0 and T60 research BIA measurements are performed. Clinical care takes priority over the protocol, and symptoms or clinician concern require stopping the infusion and performing a medical assessment.

Short-term outcomes are assessed through 90 postoperative days. Long-term outcomes include overall survival and, in participants with malignant disease, recurrence-free survival for up to five years.

The complete ambispective research program also includes 240 consecutive eligible patients operated on immediately before implementation of the prospective protocol. Their data are obtained retrospectively from existing University Hospital of Split records without contact or additional procedures, under the approved waiver of consent. This historical comparison is not a prospectively assigned ClinicalTrials.gov arm and is not included in the anticipated enrollment of 120.

Inclusion criteria

• Age 18 years or older
• Scheduled for elective colon or rectal resection at University Hospital of Split
• Written informed consent before research-specific procedures
• Able to stand safely and complete both BIA measurements
• Preoperative eGFR at least 60 mL/min/1.73 m²
• Clinically eligible for the protocol fluid volume

Exclusion criteria

• Emergency surgery
• eGFR below 60 mL/min/1.73 m² or oliguria
• Heart failure or clinically significant cardiac disease making fluid loading inappropriate
• Edema, pulmonary congestion, or clinically significant ascites
• Active implantable electrical device
• Limb amputation, inability to undergo standardized standing BIA, or unsafe standing
• Clinically significant electrolyte abnormality
• Pregnancy
• Contraindication to Ionolyte or any clinician safety concern
• Inability to provide valid informed consent