Compared with performing each procedure individually, performing two combined procedures such as colonoscopy consecutive Esophagogastroduodenoscopy (EGD) cause more bowel gases, abdominal distension and post-procedure pain because of longer procedure time related to more bowel insufflated gas than one procedure. To the best of the investigators knowledge, there has been no randomized controlled trial of CO2 versus air for insufflations during combined two procedures, colonoscopy with consecutive EGD. And there are a few well randomized trials concerned CO2 insufflation in patients receiving sedation during colonoscopy.

The aim of the present study was to evaluate the efficacy of CO2 in reducing post-procedural abdominal pain and distension during colonoscopy consecutive EGD and to confirm the safety of CO2 insufflation when it is used during procedure in sedated outpatients.

Inclusion Criteria:

• outpatients between the ages of 18 and 70 years who are scheduled for colonoscopy with consecutive EGD

Exclusion Criteria:

• age < 18 or > 70 years
• pregnancy
• breast feeding
• chronic obstructive lung disease (COPD)
• known CO2 retention and refusal to participate in the study