Colonoscopy in critically ill patients. What conditions call for it? Indications for colonoscopy in the intensive care unit include acute lower intestinal bleeding, sigmoid volvulus, pseudo-obstruction of the colon, and suspicion of pseudomembranous colitis. Although the incidence of cardiorespiratory complications may be higher in these critically ill patients, the procedure can be done safely with proper attention to detail. Because of colonic dilatation, endoscopy can often be done without bowel preparation. 