In this double-blind, randomised and controlled study 150 Patients referred to colonoscopy were assigned to either CO2 or air insufflation. We recorded basic characteristics of colonoscopy and the amount of drugs used for sedation. Patients and investigators filled out questionnaires to record pain, abdominal bloating and flatulence.

Between April 2012 and August 2014 150 patients referred to the University Hospital of Leipzig for colonoscopy were randomly assigned to either CO2 or air insufflation.

All examinations were performed by one of four experienced endoscopists. The patients usually received sedation. For sedation midazolam and propofol was used. At the beginning of the examination the patients usually received between 3-5 mg of midazolam and 20-40 mg propofol. During endoscopy propofol was titrated by administration of 20 mg at the time according to and pain reaction of the patient and required depth of sedation.

All patients had nasal insufflation of oxygen with 2 litres per minute. All sedated patients were monitored for pulse, blood pressure and blood oxygen saturation.

For bowel cleansing a solution of Macrogol 3350 (Moviprep®, Norgine) was administered orally according to the manufacturer.

All colonoscopies were performed using Fujifilm Endoscopes (EC 590 Series). For examinations with use of carbon dioxide the Fujifilm CO2 Insufflator GW-1 was used with appropriate water bottle and endoscope valve. The air pump of the light source Fujifilm System 4400 was deactivated according to the manufacturer.

Inclusion Criteria:

• older than 18 years
• informed consent

Exclusion Criteria:

• former colonic resections
• severe heart or lung disease (NYHA III or IV)
• Pregnancy
• Patients with planned gastroscopy within 24 hours