Endoscopic Retrograde Cholangiopancreatography (ERCP) is one of the most technically challenging procedures in gastrointestinal endoscopy. Selective deep cannulation is a critical step for the performance of ERCP. The incidence of difficult cannulation has been reported in many studies, ranging from 10% to 40% in patients with native papilla. Difficult cannulation is an independent risk factor for post-ERCP pancreatitis (PEP).

The definition of difficult cannulation has been proposed by European Society of Gastrointestinal Endoscopy (ESGE) guidelines. Initial cannulation is considered difficult with the presence of one or more of the following: more than 5 min for attempting to cannulate; more than 5 contacts with the papilla; more than 1 unintended pancreatic duct cannulation or opacification. The clear definition of difficult cannulation is important for making decisions during or after ERCP, including determining the appropriate time to transfer to advanced cannulation techniques (e.g. early precut) and whether prophylactic methods should be administrated to reduce the risk of PEP. Although 5-5-1 criteria have been widely used during ERCP practice or in relevant studies, it remains unclear whether the current criteria are suitable for the cannulation procedure with trainee involvement. Because of inexperienced manipulation of the scope and accessories, the involvement of trainees generally increases the overall cannulation time and attempts, which are the two important parameters in the criteria of difficult cannulation. Thus, the investigators hypothesized that the definition of difficult cannulation in trainee-involved cannulation might be different from the traditional 5-5-1 criteria.

Inclusion Criteria:

• patients with native papilla

Exclusion Criteria:

• indications of major or minor pancreatic duct (PD) cannulation; no attempts of cannulation due to inaccessible papilla; cannulation via the papillary fistula; patients with duodenal stenosis or anatomical deformity secondary to prior surgery.

patients with native papilla who underwent ERCP in Xijing Hospital in China