Large Bowel Obstruction

Large Bowel Obstruction


Hello, Dr. Jennifer Hanna, and this is Large Bowel Obstructions. The learning objectives are to understand the etiology and pathophysiology of large bowel obstruction, understand the clinical presentation of LBO, the work-up involved in the diagnosis of LBO, the conservative and surgical treatment options for LBO, and the prognosis of and complications associated with LBO. This is the outline of the talk. Large bowel obstruction is an emergency condition that requires early identification and intervention. It can result from either mechanical interruption of the flow of intestinal contents or by the dilation of the colon in the absence of any anatomic lesion called a pseudo-obstruction. The challenges in managing this condition are distinguishing colonic obstruction from ileus, ruling out nonsurgical causes, and determining the best surgical management. Distinguishing between a true mechanical obstruction and a pseudo-obstruction is important as well, as the treatment differs. Approximately 60% of mechanical large bowel obstructions are caused by malignancies, 20% are caused by diverticular disease, and 5% are the result of colonic volvulus. The most common causes of adult large bowel obstruction are as follows. Neoplasms leading to obstruction, which tend to have a gradual onset and result from tumor growth narrowing the colonic lumen. Strictures can be from an ischemic or diverticular cause. Diverticulitis, in particular, is associated with muscular hypertrophy of the colonic wall. Repetitive episodes of inflammation cause the colonic wall to become fibrotic and thickened, leading to luminal narrowing. Volvuli leading to large bowel obstruction can be either colonic, sigmoid, or cecal. A colonic volvulus results from a colon twist on its mesentery, which impairs the venous drainage and arterial inflow. Symptoms of this condition are usually abrupt. A sigmoid volvulus typically occurs in older, debilitated individuals with a history of chronic constipation, or those living in an institutionalized setting. Other causes include intussusception, which is primarily a pediatric disease, incarcerated hernia, impaction or obstipation, and gallstone ileus. Acute colonic pseudo-obstruction has many etiologies. This disorder is typically seen in elderly patients who are hospitalized with a severe illness. In a retrospective review of more than 1,400 cases of acute colonic pseudo-obstruction, the most common predisposing conditions were operative and nonoperative trauma, infections, and cardiac disease. Mechanical obstruction of the large bowel causes bowel dilatation above the obstruction, which in turn causes mucosal edema and impaired venous and arterial blood flow to the bowel. Bowel edema and ischemia increase the mucosal permeability of the bowel, which can lead to bacterial translocation, systemic toxicity, dehydration, and electrolyte abnormalities. Bowel ischemia can lead to perforation and fecal soilage of the peritoneal cavity. The pathophysiology of acute colonic pseudo-obstruction, or Ogilvie Syndrome, is not clear, but it is thought to result from an autonomic imbalance, which results from decreased parasympathetic tone or excessive sympathetic output. This condition usually occurs in the setting of a wide range of medical or surgical illnesses. If untreated, colonic ischemia or perforation can occur. It is characterized by a loss of peristalsis and results in the accumulation of gas and fluid in the colon. The right colon and cecum are most commonly involved. The risk of perforation for acute colonic pseudo-obstruction ranges from 3% to 15%. The mortality rate is 15% with early care. Mortality increases to 36% if colonic ischemia or perforation develops. Obtain the patient’s history bowel movements, flatus, obstipation, changes in the caliber of stools, or passage of melanotic stools, which may suggest carcinoma and symptoms. Major complaints in patients with large bowel obstruction include abdominal distention, nausea, vomiting, and crampy abdominal pain. An abrupt onset of symptoms makes an acute obstructive event, such as a cecal or sigmoid volvulus, a more likely diagnosis. A history of chronic constipation, long-term cathartic use, and straining at stools implies diverticulitis or carcinoma. Complete obstruction is characterized by the failure to pass either stool or flatus in the presence of an empty rectal vault upon rectal examination unless the obstruction is in the rectum. Partial obstruction in which the patient appears obstipated, but continues to pass some gas or stool, is a less urgent condition. Distinguishing colonic ileus from organic obstruction is important. Ileus may be suggested by abdominal pain as a dominant feature of the clinical presentation, but may also be suggested by peritoneal signs, or the presence of pronounced fever and leukocytosis. Right-sided colonic lesions can grow quite large before obstruction occurs because of the large capacity of the right colon and soft stool consistency. Sigmoid colon and rectal tumors caused colonic obstruction much earlier in their development because the colon is narrower, and the stool is harder in that area. Although a complete physical examination is necessary, key elements of the physical examination should focus on thorough examination of the abdomen, groin, and rectum. Abdominal distention may be significant in patients with a large bowel obstruction. The bowel sounds may be normal early on, but usually become quiet, and the abdomen is hyperresonant to percussion. Palpation of the abdomen reveals tenderness. Fever, severe tenderness, and abdominal rigidity are ominous signs that suggest peritonitis secondary to perforation, with the cecum being the area most likely to perforate. The presence of true involuntary guarding or peritoneal signs should raise the specter of another intra-abdominal process, such as an abscess. An abdominal mass or fullness may be palpated if a tumor is present in the cecum. Evaluation of the inguinal and femoral regions should be an integral part of the examination in a patient with suspected large bowel obstruction. Incarcerated hernias present a frequently missed cause of bowel obstruction. In particular, a colonic obstruction is often caused by a left-sided inguinal hernia with the sigmoid colon incarcerated in the hernia. Perform a digital rectal examination to verify the patency of the anus and a neonate. Hard stools suggest impaction, soft stools suggests obstication. An empty vault suggests obstruction proximal to the level that the examining finger can reach. Fecal occult blood testing should be performed. A positive result may suggest the possibility of a more proximal neoplasm, though this may also be seen with sigmoid diverticulitis. Laboratory studies are directed at evaluating the dehydration and electrolyte imbalance that may occur as a consequence of large bowel obstruction, and at ruling out ileus as a diagnosis. Routine complete blood cell count, serum chemistries, and urine specific gravity should be evaluated. A decreased hematocrit level, particularly with evidence of chronic iron-deficiency anemia, may suggest chronic lower GI bleeding, particularly due to colon cancer. A stool gualac test also should be performed for similar reasons. Although bowel obstruction, or even constipation, may mildly elevate the white blood cell count, substantial leukocytosis should prompt a reconsideration of the diagnosis. Ileus secondary to intra-abdominal or extra-abdominal infection, or another process, is a possibility. The suggestion of an abnormal anion gap should prompt an arterial blood gas measurement and/or a serum lactate level measurement. Obtain a prothrombin time, PTT, as well as a type and cross match in cases of significant bleeding, presumed coagulopathy secondary to sepsis, or prior to surgical intervention. Obtain an upright chest radiograph to determine whether free air is present, as is demonstrated in the chest radiograph shown with air under the diaphragm. This would suggest perforation of a hollow viscous and ileus rather than organic obstruction. However, the absence of free air does not exclude perforation, as this finding may be absent in half of all perforations. Flat and upright abdominal radiographs may demonstrate dilation of the small and/or large bowel, air fluid levels, sigmoid or cecal volvulus, or intramural air, which can be an ominous sign that suggests colonic ischemia. Tracing air around the colon into the left gutter and down into the rectum, or demonstrating an abrupt cut-off in colonic air, suggest the anatomic location of the obstruction. A dilated colon without air in the rectum is more consistent with obstruction. The presence of air in the rectum is consistent with obstipation, ileus, or partial obstruction. However, this finding can be misleading, particularly if the patient has undergone rectal examinations or enemas. Contrast studies include an enema with water-soluble, or barium contrast, or computer tomography with IV, PO, and/or rectal contrast. These modalities can be used if the diagnosis of a large bowel obstruction is suspected but not proven. Differentiation between obstipation and obstruction is required, and if localization is required for surgical intervention. Contrast studies that reveal a column of contrast ending in a bird’s beak are suggestive of colonic volvulus, as demonstrated in the radiograph here of a cecal volvulus. Water-soluble gastrografin should be used first over barium as a contrast agent because it usually does not cause chemical peritonitis if the patient has colonic perforation. It also has an osmotic laxative effect that may actually wash out an obstipated colon. If large bowel perforation is ruled out using a gas for gastrografin study, but a more detailed and atomic definition is required, a barium enema may be performed. CT scanning is generally not used initially in patients with large bowel obstruction unless the diagnosis is still in question. It can be useful to help rule out intra-abdominal abscess or other causes of ileus. It may also be useful in ruling out synchronous lesions, which might motivate a more extended resection. Initial therapy in patients with suspected large bowel obstruction include, volume resuscitation, appropriate preoperative antibiotics, gastric decompression, and timely surgical consultation. Antibiotic coverage must include gram-negative aerobic and gram-negative anaerobic organisms. Patients with complete large bowel obstruction should receive nothing by mouth. Patients with a partial obstruction may tolerate minimal clear liquids, oral medications, and a gradual bowel preparation. Medications that slow colonic motility, including narcotics and anticholinergics, should be stopped if possible. Oral laxatives are contraindicated if large bowel obstruction is suspected. If any evidence suggests a simple constipation, patient should be managed with transrectal enemas. For this subset of patients in whom the obstruction is not only malignant, but also reflects substantially disseminated or even inoperable disease, consideration of completely nonoperative palliative therapy within the context of a palliative care or hospice approach may be appropriate. For acute colonic pseudo-obstruction, if no perforation is present, pseudo-obstruction is treated with conservative management for the first 24 hours. This includes bowel rest, hydration, and management of underlying disorders. Pharmacological treatment of acute colonic pseudo-obstruction with neostigmine or colonoscopic decompression may be effective in cases that do not resolve a conservative management. Surgical intervention for acute colonic pseudo-obstruction is associated with a high mortality and morbidity, so it is reserved for refractory cases or cases complicated by perforation. Endoscopic dilation and stenting of colonic obstruction for palliation is indicated for colonic near total obstruction, for which some small amount of lumen remains in a high-risk patient with an unresectable malignancy, accepting a risk of reobstruction of the stent. In cases in which the stent is deployed before surgery, this procedure permits relief of the acute obstruction, resuscitation of the patient, and mechanical bowel preparation before a 1-stage colonic resection and re-anastomosis, thus avoiding temporary or permanent colostomy. Surgical consultation and backup should be available, as the risk of perforation has increased during attempts at such procedures. Endoscopic reduction is indicated for sigmoid volvulus when peritonial signs are absent, which would imply dead bowel or perforation. Endoscopic reduction is not indicated for the less common cecal or transverse colonic volvulus. Reduction of a volvulus does not imply cure. The sigmoid usually revolvulizes if definitive treatment with sigma resection is not carried out. Barium enema for reduction of intussusception useful and often successful in children in whom a pathologic lead point for the intussusception is unlikely. In adults, typically a pathologic lead point for the intussusception is present. Success is far less likely, and patients still require surgery to deal with their pathology. Surgical intervention is directed at relieving the obstruction. A diverting transverse loop colostomy may be the least invasive procedure for a very ill patient with a left colonic obstruction. It permits relief of the obstruction and further resuscitation without compromising chances for a subsequent resection. A sigmoid colostomy without resection may be used in patients with a rectal obstruction that cannot be managed without a combined abdomino-peroneal resection. For an obstruction in the right colon, ileostomy should be performed. However, in younger patients without substantial co-morbidity, some surgeons would consider primary anastomosis, assuming no intraoperative hypertension, significant blood loss, or other complications are present. If the cause of the obstruction can be relieved nonsurgically through procedures such as decompressing a volvulus, or if the obstruction is only partial, deferring surgery temporarily in supporting the patient while the large bowel is cleansed so that a primary anastomosis may be performed more safely, is preferable if slow, pre-operative mechanical bowel preparation is indicated for patients who have incomplete obstruction, provided the patient can tolerate it. In most patients, the obstructive lesion is resected. Because the colon has not been cleansed, anastomosis this is often risky. After resection, most surgeons perform a proximal colostomy if the obstruction is on the left side, or ileostomy if it is on the right side. In patients with substantial co-morbidities, and that are a high risk surgical candidate, or in the presence of an unresectable tumor, a diverting proximal colostomy or ileostomy may be performed without resection. Surgical treatment of left colon carcinomas include resection and diversion without primary anastomosis, or a section with primary anastomosis and intraoperative lavage. Right colonic obstructions are treated with a right colectomy in a primary anastomosis between the ileum and the transverse colon, or resection and diversion without a primary anastomosis, as in the case with left colon carcinomas. Patients with persistent obstruction secondary to diverticular disease, despite appropriate medical management, are treated surgically. Surgical resection follows the same principles as the treatment of carcinomas. Elective colonic resection is offered to patients with recurrent disease. Sigmoidoscopy with volvulus reduction is the initial procedure of choice for sigmoid volvuli. If it cannot be reduced initially by these means, the second choice is sigmoid colectomy. Even if reduction is successful, an elective sigmoidectomy should be performed because of the high incidence of recurrence. The primary treatment of cecal volvuli is also surgical. A cecopexy often needs to be performed to prevent recurrence. Second choice is colonoscopy due to the high risk of colon perforation. Adult colonic intussusception is treated with primary colon resection without prior reduction.

One thought on “Large Bowel Obstruction

Leave a Reply

Your email address will not be published. Required fields are marked *