During this preparation, the patient drinks a large volume of polyethylene glycol solution (approximately 1 gallon) over the course of a few hours. The patient generally passes solid stool, then liquid stool, and finally clear liquid. The clear liquid indicates all stool has been “flushed” from the colon, and the colon is ready for the colonoscopy procedure. Failure of the patient to pass clear liquid during the preparation phase indicates the colon has not been adequately prepared and is a relative contraindication to colonoscopy. It is likely the colon proximal to the obstruction has to distend to accommodate this large volume of fluid, adding to the risk of perforation. The likelihood of perforation is relative to how quickly the bowel distends and the health or otherwise of the colon wall. The colon is quite thin-walled, typically in the 3-5mm range. If the colon distends rapidly, it can perforate in one or more areas due to increased intraluminal pressure. The likelihood of perforation increases if the blood supply of the colon wall is already compromised (by ischemia (poor blood supply)) and especially if pressure within the colon increases due to air insufflation caused by colonoscopy. Given the risk of perforation in a patient with a probable large bowel obstruction, standard high volume preparation would be contraindicated.
High volume bowel preparation for probable bowel obstruction medical expert witness specialties include gastroenterology, general surgery, critical care medicine, and colon-rectal surgery.