Author(s): Jeffrey R Lewis 1 , Lawrence B Cohen [*] 2
bowel preparation; colonoscopy; colon polyps; colorectal cancer; endoscopic complications; sedation
Colonoscopy quality has improved during the past decade due to advances in image technology, bowel preparation and sedation techniques. Nonetheless, opportunities for further improvement in outcome measures of colonoscopy remain. For example, studies from diverse settings have shown that colonoscopy is less effective in preventing proximal compared with distal cancers. Improved detection of proximal adenomas and serrated lesions would likely help to bridge this difference in outcome between proximal and distal cancers. This article presents a state-of-the-art review of bowel preparation, premedication and sedation and describes recent studies and how these findings may one day further enhance our practice of colonoscopy.
The ideal bowel preparation for colonoscopy safely clears the colon of fecal material, exposing the mucosa and rendering it amenable to thorough inspection. Substantial evidence exists that better colon preparation is associated with increased detection of colon polyps. Recently, several articles have reviewed the subject of bowel preparation for colonoscopy and compared the efficacy, safety and tolerability of the available formulations. Additionally, a multisociety consensus document on this subject was released by the American Society of Gastrointestinal Endoscopy (ASGE) and American College of Gastroenterology  . This section focuses on current research regarding dietary considerations, new preparation formulations, the timing of preparation administration and predictors that help to identify patients who are most likely to have an inadequate bowel preparation.
For decades, dietary restriction of fiber and other solid food was assumed to be necessary to achieve high-quality colon cleansing. This belief, premised upon anecdotal experience, was evaluated by Wu et al ., who assessed the quality of bowel cleansing in 800 Taiwanese patients following a 4-l polyethylene glycol (4-l PEG) preparation  . Patient compliance with dietary restriction and the quality of bowel cleansing were assessed, the latter using the Ottawa Bowel Preparation Scale (Ottawa), which is a validated instrument for assessing bowel preparation (Table 1)  . They found an inverse relationship between dietary fiber intake and the bowel cleanliness score (r = -0.475; p < 0.001), indicating that a low-fiber diet makes for a better bowel preparation. Questions remain about diet and bowel preparation, such as whether the quality of bowel cleansing with a low-residue diet is comparable to that achieved with a liquid diet. The authors are certain that there will be more work in this field during the next few years.
The holy grail of colonoscopy is a bowel preparation that is both effective and well tolerated by patients. A recent meta-analysis by Belsey et al. suggested that sodium phosphate and PEG 3350-based preparations are equally effective, and both were superior to magnesium sulfate and stimulant laxative-based regimens  . Unfortunately, safety concerns related to the development of phosphate nephropathy have limited the role of sodium phosphate as a bowel cleansing agent for colonoscopy.
A variety of PEG-based bowel preparations are now used in the USA, including 2- and 4-l formulations. The commercially...