Determine the influence of the papilla's morphology on the various outcomes of endoscopic retrograde cholangiopancreatography (ERCP), namely on the success of biliary cannulation, on complications, and on the need to use rescue cannulation techniques;

1. Background

   ERCP is an advanced procedure which is widely used in the diagnosis and treatment of a variety of benign and malignant pancreatobiliary disorders1,2,3,4,5.

   Selective cannulation of the common bile duct (CBD) is the most important and challenging step in a biliary endoscopic retrograde cholangiopancreatography6,7. However, in the first ERCP, even in experienced hands, biliary cannulation may fail in up to 15 % - 35 % of cases when using standard methods alone8.

   Since the first description of the "Vater's papilla" by Abraham Vater in 17209, the variability in papillary morphology has been widely recognized10. The use of high quality digital images has led to a clear need and desire to create an endoscopic classification based on the papilla's morphology. During the last decade, several authors have proposed different classifications in order to predict the success of cannulation, complications and the need for more advanced cannulation techniques11,12,13,14,15. However, all the proposed classifications, with the exception of one, fail because they have not been submitted to a validation process. The only validated one is the proposed by Haraldsson13, which still has the drawback of not incorporating some of the papillary morphologies.

   Given the need, our research group created a new classification (entitled "Viana Classification") that not only incorporates more morphologies but was also validated in due course.

   Hence, the next step is to explore the potential implications of papillary morphology on the success of biliary cannulation, complications resulting from ERCP and the need to use rescue techniques (fistulotomy and double-guidewire cannulation) in the event of failure of the standard cannulation.

2. Financial resources

   All participants included in this study will perform ERCP, laboratory tests and other complementary diagnostic tests after a duly justified medical prescription (the exact same exams that the patient would do if there wasn't this study). Therefore, there are no additional costs or consumption of hospital resources.

3. Ethical considerations

   In this study, participants will be included after informed consent. Anonymity and confidentiality will be safeguarded by assigning an individual numeric code. It will also be explained the possibility of withdrawing from the study at any time, with the guarantee of the total elimination of data. All researchers involved in the study will adhere to the Rules of Ethical Conduct and Best Practices in order to comply with the precepts of the Declaration of Helsinki, the Convention on Human Rights and Biomedicine, the guidelines of the Council for International Organizations of Medical Sciences and the Guide to Good Clinical Practice.

4. Statistical analysis

   Qualitative variables will be summarized using absolute and relative frequencies, and quantitative variables will be summarized using the mean and standard deviation or the median and interquartile range, depending on their distribution profiles. The normality of the quantitative variables will be assessed using the histogram distribution.

   Relations between categorical variables will be assessed using a chi-square test and Fisher´s exact test. Differences between two or more groups of independent non-normally distributed quantitative variables will be evaluated using a Kruskal-Wallis test.

   To explain the risk of pancreatitis, a binomial logistic regression model with multiple predictors will be performed.

   The null hypothesis will be rejected when the test statistics p-values are less than <0.05. Statistical analysis, sample size calculation and graphics will be performed using Stata software (StataCorp. 2015. Stata Statistical Software: Release 14. College Station, StataCorp LP)

5. Expected results

The results from this study will contribute to a better understanding of the influence of papillary morphology on cannulation difficulty. In the event of demonstrating that some morphologies imply greater difficulty in cannulation, strategies may be created, such as the use of ab initio rescue techniques, in order to improve the results of ERCP, namely the cannulation rate.

We will conduct a prospective observational study.

Inclusion Criteria:

• ERCP with indication for biliary access
• Naïve papilla

Exclusion Criteria:

• Patients unable to understand the informed consent
• Patients with surgically altered anatomy
• Patients with tumors of the papilla
• Previous sphincterotomy
• Spontaneous papillary fistula
• Papilla not visualized

All individuals referred for CPRE in the Digestive Endoscopy Unit of the Santa Luzia Hospital, Unidade Local de Saúde do Alto Minho, will be invited to participate in the study, in the period between June 1, 2020 to June 1, 2022.