Colonoscopy is currently accepted as the gold standard in screening, surveillance and prevention for colorectal cancer (CRC), and therefore, its quality is a major priority.

The quality of colonoscopy is greatly dependent on the quality of the bowel preparation, which can be limited by stool, foam, bubbles and other debris. In fact, colonic bubbles are described in 30 to 40% of colonoscopies, possibly undermining the quality of the exam, impairing the endoscopists view, demanding the further use of water or simethicone and eventually increasing fatigue and costs, while diminishing diagnostic accuracy.

Although previous attempts, to date no endoscopic scale is validated regarding the presence of bubbles and most widely accepted and already validated scales do not include the presence or absence of bubbles in their definition, leading to the use of different home-made scales in randomized trials and impairing any solid meta-analysis conclusion. As so, the goal of this study is to develop and validate a new colonic bubble score (Colon Endoscopic Bubble Scale - CEBuS).

Colonoscopy bowel preparation quality is a major concern since inadequate bowel preparation can reach levels as high as 30% which lead to several guidelines in this area, with the recent recommendation of at least 90% of good bowel preparations for all colonoscopies. In fact colonic mucosal visualization can be limited by residual stool, bubbles, bile and other debris increasing the risk of missing lesions.

Around 30 to 40% of the exams can have bubbles increasing the risk of missing lesions and in the other hand increasing the time of the exam, generating more fatigue in the endoscopist and increasing the costs.

The influence of colon bubbles in bowel preparation and strategies to solve them, for example with the use of simethicone in the bowel preparation, were addresses in recent studies, summarized in a 2018 meta-analysis recommending the use of simethicone in the bowel preparation scheme.

Current recommendations advise the use of validated scales to evaluate bowel preparation quality, but the three major validated scales, Boston, Ottawa and Aronchick, does not address the problem of graduation of colonic bubbles and possible actions to undertake regarding the severity of the bubbles concentration. The advent of multiple randomized trials addressing the use of simethicone in the bowel preparation to reduce or eliminate bubble formation lead to attempts to design scales to graduate the concentration of bubbles in the colon.

To date suggested scales are heterogeneous regarding the graduation (3 to 4 levels), defining criteria for each level with some based on percentage of colonic circumference obscured by bubbles to the amount of bubbles that could lead to miss a polyp of 5 or 10 millimetres.Two recently published studies on the influence of simethicone on bowel preparation tried to validate a colonic bubble scale, based on previous suggested and non-validated scales, although with only fair to moderate inter-observer variability.

Therefore, the main goal of this project is to build and validate a comprehensive scale to graduate bubbles in the colon, assessing the inter- and intra-observer reliability of the scale. As a secondary objective, to determine the clinical attitude more frequent for each grade of the bubbles scale, among experts and residents.

Aims: Build and validate a new colonic bubble score (Colon Endoscopic Bubble Scale - CEBuS).

Inclusion Criteria:

• For the expert group: at least 15 years of regular practice in colonoscopy
• For the trainee group: 5 years or less in the practice of colonoscopy

Exclusion Criteria:

• Non endoscopist and if out of the experience standards required.

Were selected for the study 23 observers - 10 experts and 13 in-training/young specialists endoscopists from six European countries (Portugal, France, Italy, Romania, Poland and Slovakia).