Intestinal Obstruction - Small Bowel Obstruction vs Large Bowel Obstruction

intestinal or bowel obstruction is a condition that comes from either a mechanical blockage of the bowels or a functional issue where the bowels no longer propel digested contents properly through the gastrointestinal tract mechanical bowel obstruction can be divided into small bowel or large bowel obstructions and generally each have different causes which are mostly divided into extramural meaning outside the wall of the bowel mural meaning within the wall of the bowel and intraluminal meaning inside the bowel lumen small bowel obstruction is more common than large bowel obstruction with around 80 percent being small bowel the most common cause for small bowel obstruction are post-surgical adhesions they are bands of scar tissue that form as a result of the surgery and can cause the affected tissue to stick together which in the case of the intestines can make them kink or twist leading to an obstruction around sixty six percent of people will have post operations with ten to twenty five percent of these patients going on to develop an obstruction adhesions can also occur in some instances without surgery hernias are another common cause in particular inguinal hernias neoplasm can also cause small bowel obstruction but this is typically due to external compression rather than a cancer of the small bowel itself mural causes include inflammatory strictures such as in crohn's disease and we may also see interception which is where part of the bowel passes into a contiguous piece like a telescope another is meccal's diverticulum and these two are more common in children intraluminal causes include a gallstone ileus where a larger gallstone may pass into the intestine via a fistula between the gallbladder and the intestine ingested foreign bodies may also cause an intraluminal small bowel obstruction large bowel obstructions make up around 20 of mechanical obstructions extramural causes include diverticular disease involving strictures usually at the sigmoid colon and also volvulus which is a twisting of the bowel again in this instance it's most commonly seen at the sigmoid colon however the most common cause overall for a large bowel obstruction is colorectal adenocarcinoma which is responsible for around 60 percent of cases an intraluminal cause could be fecal impaction patients with intestinal obstruction will typically manifest an abdominal pain which in small bowel obstruction is usually a cramping or colicky pain in the center of the abdomen due to peristalsis that may be working against the obstruction while in large bowel obstructions the spasms typically last longer or is continuous and is felt lower in the abdomen this pain is often accompanied with abdominal distension vomiting is also likely with proximal obstructions suffering from vomiting earlier than more distal obstructions also obstructions that are in the small bowel are more likely to vomit bilious material or even undigested food contents while in large bowel obstructions vomiting may be fecular constipation may also be seen but in this case it is the opposite in that it happens sooner in distal obstructions while it is a late finding in proximal obstructions as a result of the obstruction the patient may have electrolyte imbalances and dehydration due to the vomiting as well as therefore a risk for aspiration pneumonia in terms of the diagnosis the physical exam will typically show tenderness on palpation but signs such as guarding or rebound tenderness may suggest the perforation or ischemia of the bowel bowel sounds are characteristically tinkly sounding like bubbles rising blood tests are done as the full blood count may show a microcytic anemia which would be consistent with a colorectal cancer while leukocytosis may suggest ischemia or perforation especially if combined with a raised lactate as mentioned we may also see electrolyte imbalances with hypokalemia being frequent and a high creatinine may indicate an acute kidney injury which is a common complication due to the vomiting and dehydration the preferred imaging modality is a ct scan of the abdomen and pelvis with contrast especially as it can help in pre-operative planning another imaging modality is an abdominal x-ray where you may see dilated gas-filled loops or air fluid levels which can indicate obstruction in some instances it's possible to determine if a small or large bowel obstruction is present based on the bands on the bowels these are known as the horse straw of the large bowel which do not go all the way across the bowel while the valvulate convents in the small bowel do however this may vary with position and exposure therefore it is not perfectly reliable there is also a rule of sizes where the small bowel is normally smaller than three centimeters the large bowel less than six centimeters unless they're at the cecum which is less than nine centimeters some patients may require surgery while others can be managed conservatively conservative management is selected when there is no suspicion of ischemia or perforation and the management will include iv fluids as well as monitoring the urine output usually using a catheter the urine output should be above 0.5 milliliters per kilogram per hour and the patient will likely be made nail by mouth and a nasogastric tube placed in order to decompress the bowel as the ng tube can drain the gi contents however in obstructions where no previous surgery has taken place and therefore is unlikely to have adhesions surgery is more likely to be required the type of surgery is dependent on the cause therefore may involve a reparation of a hernia or a section of a tumor there may also be a resection of the blocked region with a rejoining of the newly formed two ends this is termed an anastomosis this is particularly true in patients with colorectal cancer who may undergo a hemicolectomy where half of the colon is removed in some instances a stoma may be needed which is an opening of the bowels onto the skin stenting is another possibility which is seen often in palliative cases in order to reduce symptoms however this is also sometimes done as a bridge to surgery