Water-assisted colonoscopy, or 'underwater colonoscopy', uses water rather than gas to inflate the bowel during colonoscopy. It is a new but safe and well-proven technique that benefits patients by making a colonoscopy more comfortable, reducing the amount of sedation drugs required, and increasing the chances of all the polyps that might be present in your bowel being identified and removed. If you'd like to hear a Radio New Zealand article on this technique, click here. If you'd like to understand the science behind it, please read on.
Colonoscopy has traditionally been performed by inflating the bowel with air or carbon dioxide to allow views of the interior. Much as with a balloon, distending the bowel with gas causes it to lengthen and stretches the wall, and this causes discomfort or pain (see video), and potential difficulty in passing the colonoscope all the way around the colon. In addition, stretching out the bowel wall thins it like with a balloon, and this makes removal of flat polyps more difficult and hazardous.
Water-assisted colonoscopy uses water to open up the bowel instead of gas, so the colonoscope ‘submarines’ around the colon. Water does not stretch the bowel beyond its natural resting state so water filling itself almost never causes pain. With water filling, the bowel wall is not thinned out by stretching, and polyps project obviously inwards, so polyp identification and removal is easier and safer (see video below). Water also magnifies views by one-third over air alone, so fine details of the bowel wall and any polyps are more easily seen.
The technique of water-assisted colonoscopy was first described in medical literature in 2007, and there are now several studies demonstrating that such procedures require less pain relief and sedation, improve the completion rate in difficult procedures, and increase the numbers of polyps found at colonoscopy compared to those performed using gas (see reference list below). My own data (see right) shows that conversion from air to routine water insufflation of the colon increased polyp detection rate by 60%. The right hand video below demonstrates how water may improve polyp detection.
See the article from Radio New Zealand News, "New water treatment eases colonoscopies".