Colonoscopic examination of the large bowel (inserting a flexible endoscope with a camera at its tip through the anus and up into the rectum and colon) is sometimes required during a colorectal resection (abdominal operation to remove a segment or piece of colon or rectum) in order to find a small cancer, polyp, bleeding site, or simply to inspect the bowel after the two ends have been rejoined together. In order to get a good look at the large intestine with a colonoscope it is necessary to pump some gas into the colon via the scope in order to distend and inflate it. The gas that is almost universally used is room air. Since it is very hard, if not impossible, to fully suction out the gas from the colon once the exam is finished, the colon is usually quite bloated or distended after the colonoscopy. This dilatation can persist for hours or days since air is not well absorbed through the bowel wall into the body. A distended colon can cause some problems during both traditional open (big incision) surgery and laparoscopicassisted (minimally invasive) surgery. During a big incision operation, colonic distension and swelling can make it hard to close the incision at the end of the operation and can make breathing more difficult.

In contrast, during a laparoscopic procedure, the colorectal dilatation can greatly decrease the amount of working and maneuvering room that is available to the surgeon to the point where the laparoscopic approach may have to be abandoned in favor of the big incision method. Thus, colon distension following sigmoidoscopy done with air during an abdominal operation can cause problems for the patient and the surgeon.

An alternative gas that can be pumped into the colon during colonoscopy is carbon dioxide (CO2). Unlike air, CO2 is very rapidly reabsorbed into the body from the colon, about 250 times faster than air. There is now a machine available which makes it possible to easily and safely use CO2 gas to distend the colon during colonoscopy. The investigators believe that the use of CO2 during intraoperative colonoscopy or sigmoidoscopy (exam of only the last 2 to 2 ½ feet of the colon) will not cause long lasting bloating or distension of the colon as opposed to air. Patients undergoing either open (big incision) or laparoscopic (multiple small incisions) rectal or sigmoid colon resection usually need to have intraoperative sigmoidoscopy at the end of the operation to inspect the inside of the colon and rectum and to check for an air leak in the vicinity of the rejoining point (anastomosis). In this study one half of the patients will, by the flip of a coin, get CO2 during their sigmoidoscopy while the remaining half will have air used to inflated the colon during their examination. After the sigmoidoscopic exam is completed the scope will be removed, without suctioning, and the colon diameter near the rectum measured by the surgeons looking and working in the abdomen. The size of the colon will again be measured every 5 minutes for the next 20 minutes while the surgeons prepare to close the abdomen and end the surgery. At the end of the 20 minute period, if the colon remains distended, the scope will be reinserted and the excess gas suctioned out. The surgeons carrying out this study believe that the colons of those patients getting CO2 gas for the sigmoidiscopy will more rapidly shrink in size towards their original diameter than the patients who get air pumped into the colon.