Hypermagnesemia caused by fecal-mass obstruction in stenotic rectal cancer following preoperative administration of magnesium citrate.

Background: Hypermagnesemia is a rare complication, leading to fatal cardiovascular and respiratory conditions. We present severe hypermagnesemia developed in a patient with a rectal stenosis after pretreatment with oral magnesium citrate for rectosigmoid surgery.

Case presentation: A 78-year-old woman demonstrated consciousness disturbance, muscle weakness, and respiratory depression requiring tracheal intubation after preparation with oral magnesium for rectosigmoid surgery. Endoscopic examination showed a rectal obstruction due to fecal impaction. General condition improved after emergency Hartmann's surgery. Blood test revealed a remarkable increase of serum magnesium level to 17.5 mg/dL when the general condition deteriorated, which would have been responsible for her symptoms. She was discharged from the ICU after extubation on the third postoperative day with a normal magnesium level.

Conclusions: Pretreatment with large doses of oral magnesium-containing bowel cleanser may cause severe hypermagnesemia in patients with colorectal stenosis.