Introduction: Colonoscopy and bowel preparation cause a number of serum electrolytes changes.
Aims: To determine the prevalence of these changes in patients who underwent colonoscopy and to identify risk factors for these effects.
Patients and methods: Forty five patients undergoing colonoscopy were assessed prospectively. They have been previously randomized to receive either sodium phosphate (NaP) or polyethylene glycol (PEG) as preparation. Serum levels of sodium and potassium were analyzed before colonoscopy, immediately after the end of colonoscopy, and 1 hour thereafter. Serum calcium and phosphorus levels were measured just before colonoscopy.
Results: Twenty five patients (55.5%) received PEG and 17 (37.7%) NaP. Three patients (6.6%) did not follow the recommended bowel preparation instructions and were excluded from the study. Five patients (11%) developed hyponatremia, of whom, in 4 cases (8.8%), it occurred after the procedure. Thirteen patients (28.8%) developed hypokalemia, of whom it occurred after the end of the procedure in seven (15.5%). There was a non-significant trend to decreased serum potassium levels 1 hour after colonoscopy in patients prepared with NaP (63.6 vs 36.4%). The multivariate analysis showed that low potassium levels were independently associated with age and NaP preparation. Hypocalcemia was observed in 2 patients (4%) and hypophosphatemia in 8 (18%). Hyperphosphatemia was found in 8 cases (18%). Non-significant increases in phosphorus levels were observed in the NaP group.
Conclusions: Temporal sequences of the development of serum electrolyte disturbances suggest that colonoscopy itself might play a role in the pathogenesis of these changes. Preparation for colonoscopy with NaP and the age of patients are risk factors for the development of hypokalemia.