In cases of severe abdominal pain, severe abdominal distension, large amount of ascites, recent abdominal surgery or cervical spine surgery, intra-abdominal catheter insertion, severe obesity, it is difficult to position in prone or left lateral, therefore, ERCP may be performed in the supine position. In supine position for ERCP, there has been documented increased risk of cardiopulmonary adverse event and decreased success rate of selective bile duct cannulation.