Patients undergoing bowel prep for colonoscopy had significantly greater decreases in potassium after prep with sodium phosphate, compared with those whose prep involved polyethylene glycol, based on data from a meta-analysis of more than 2,000 patients.
Electrolyte disturbances, though rare, represent a serious adverse event associated with bowel preparation, and the prevalence remains unclear, Atsushi Sakuraba, MD, of the University of Chicago said in an interview. Dr. Sakuraba, who was not involved in the study, said he was surprised by some of the study findings. “The incidence and degree of hypokalemia associated with sodium phosphate bowel preparation was greater than what I would have thought.”
Authors of the current analysis, led by Ankie Reumkens, MD, of Maastricht (the Netherlands) University Medical Center, noted in Digestive Endoscopy that the severity of adverse events is not directly related to the degree of electrolyte disturbance. “Electrolyte disturbances may vary from asymptomatic via mild and moderate symptoms (i.e., muscle weakness, constipation, nausea, and vomiting), to severe symptoms (i.e., paralysis, seizures, cardiac arrhythmias, coma, and death).” Although current guidelines do not include recommendations for electrolyte measurement, the European Society of Gastrointestinal Endoscopy recommends against routine use of sodium phosphate (NaP) despite a low level of evidence. Although polyethylene glycol (PEG) is the preferred choice for older patients and in patients with renal impairment, heart failure, and inflammatory bowel disease, the investigators noted that NaP and picosulfate with magnesium titrate (SPMC) have been associated with higher patient tolerance and compliance.
Bowel preparation solutions are available in high-volume versions that include high-volume PEG, while low-volume options include low-volume PEG, NaP, and SPMC; despite the variety of choices, bowel preparations of any type may cause electrolyte disturbances, and their extent, magnitude, and risk factors have not been well studied.
In their systemic review and meta-analysis, the researchers examined the pooled prevalence of electrolyte disturbances; the primary endpoint was the pooled prevalence of hypokalemia, hyponatremia, hyperphosphatemia, and hypocalcemia after bowel preparation, and the changes in mean potassium values. The review was based on 13 studies published between Jan. 1, 1995, and July 1, 2021, with a total of 2,386 patients.
Overall, hypokalemia occurred in 17.2 % of patients who underwent NaP for bowel preparation versus 4.8% of those who underwent PEG. Hyponatremia occurred in 0.9% of NaP patients versus3.3% of PEG patients; hyperphosphatemia occurred in 37.3% and 0.65% of NaP and PEG patients, respectively; and hypocalcemia occurred in 15.6% and 8.1% of NaP and PEG patients, respectively.
Pharmacokinetics may explain the increased disturbances in electrolyte balance with NaP, the researchers noted.
“PEG is iso-osmotic with plasma, causing no net absorption or excretion of water or ions,” they said, but “NaP is highly osmotic and therefore results in fluid shifts from the systemic compartment to the gastrointestinal tract.”
The study findings were limited by several factors including the potential underreporting of the prevalence of electrolyte disturbances, the exclusion of patients with renal insufficiency, heart failure, and bowel problems, and the incomplete data on bowel cleansing scores and adverse events, the researchers noted. More data on the prevalences of electrolyte disturbances after low-volume bowel preparations are needed to inform evidence-based recommendations, especially in light of the increased numbers of colonoscopies and increasing numbers of older patients and patients with comorbidities.