Sedative drugs are widely-used during endoscopic procedures. The administration of these drugs contain the potential hazard of breathing and cardiac complications. Moreover it is well-known that the dorsal position is in some ways associated to breathing problems while patients are asleep. We assume this also to be true related to short anesthesia during colonoscopy. Patient positioning may therefore have a positive effect on the safety during colonoscopy by reducing the absolute time that sedated patients spend in a supine position. We compiled a randomized trial which compares the appearance of breathing and cardiovascular complications by performing colonoscopy either in a dorsal or in a left lateral position.