A case of impaired consciousness due to water intoxication during underwater endoscopic submucosal dissection for colorectal cancer.

An 85-year-old woman complained of a large amount of sudden bloody stool. A blood test revealed anemia, and colonoscopy showed an elevated tumor (> 50 mm in size) in the ascending colon, with biopsy findings suggested the likelihood of adenocarcinoma. Based on these observations, bleeding from the tumor was determined to be the cause of anemia. As she declined surgery, underwater endoscopic submucosal dissection (ESD) was performed, during which saline solution was supplied from the tip of the knife and electrolyte-free water was supplied from the endoscopic sub-fed port. After treatment initiation, her level of consciousness gradually declined, and convulsive seizures appeared. A blood test revealed marked hyponatremia, with a serum sodium level of 109 mEq/L. Ultimately, it was determined that the patient developed water intoxication with underwater ESD, due to the absorption of electrolyte-free water into the bloodstream. ESD was promptly terminated, serum sodium compensation by intravenous infusion was started, and the patient's impaired consciousness improved. This case suggests that water intoxication during underwater ESD represents a potentially life-threatening complication, particularly for large tumors during prolonged procedures in elderly patients.