Changes of Serum Electrolytes During Bowel Prep With PEG 3350 + Ascorbic Acid - a Prospective Study

Hypothesis: Patients who undergo bowel preparation with PEG 3350 + ascorbic acid may have significant changes of serum electrolytes. A new PEG solution (Moviprep = PEG 3350 + ascorbic acid) for colonoscopy reduces the amount of cathartic solution to 2 liters, but requires drinking of additional liquid for optimal results. Ingestion of a high volume of free water bears a risk for severe changes of serum electrolytes, particularly for sodium and potassium. In this trial, patients undergo regular bowel preparation for standard colonoscopy with Moviprep (2 liters Moviprep split-dose plus ≥2 liters of free liquid until sufficient cleansing is achieved). Blood samples for serum sodium, potassium, chloride, magnesium, phosphate, calcium and serum osmolarity are taken before the beginning of the prep procedure and right before colonoscopy. The interval between both blood samples that will be compared is roughly 24 hours. Additionally, the volume of prep solution and additional liquid is recorded. The quality of bowel preparation is visually rated during colonoscopy with a validated score. Pre- and postpreparation serum parameters will be compared. Primary outcome measure is the proportion of patients who have a serum sodium beyond the reference values after the completion of bowel preparation. Secondary outcome parameters are the proportion of patients with other serum electrolytes or serum osmolarity beyond the reference. Moreover, changes of serum electrolytes and osmolarity will be correlated with the amount of prep solution and liquid.