Chapter 6 Bowel obstruction
Bowel obstruction is most common in surgery practice. It often leads to different complications and death of patients. Physician has to diagnose a case, to define the policy of treatment, to choose the optimum method of treatment in patients with bowel obstruction.
A small-bowel obstruction (SBO)
It is caused by a variety of pathologic processes. The most common cause of SBO is postsurgical adhesions. Postoperative adhesions can be the cause of acute obstruction within 4 weeks of surgery or of chronic obstruction decades later. The incidence of SBO parallels the increasing number of laparotomies performed in developing countries. Other aetiologies of SBO include malignant tumor (20%), hernia (10%), inflammatory bowel disease (5%), volvulus (3%).
SBOs can be partial or complete, simple (i.e., nonstrangulated) or strangulated. If not diagnosed and properly treated, vascular compromise leads to bowel ischaemia and further morbidity and mortality. Because as many as 40% of patients have strangulated obstructions, differentiating the characteristics and aetiologies of obstruction is critical to proper patient treatment.
SBO accounts for 20% of all acute surgical admissions. Mortality and morbidity are dependent on the early recognition and correct diagnosis of obstruction. If untreated, strangulated obstructions cause death in 100% of patients. If surgery is performed within 36 hours, the mortality decreases to 8%. The mortality rate is 25% if the surgery is postponed beyond 36 hours in these patients.
Obstruction of the small bowel leads to proximal dilatation of the intestine due to accumulation of gastro-intestinal secretions and swallowed air. This bowel dilatation stimulates cell secretory activity resulting in more fluid accumulation. This leads to increased peristalsis both above and below the obstruction with frequent loose stools and flatus early in its course.
Vomiting occurs if the level of obstruction is proximal. Increasing small-bowel distention leads to increased intraluminal pressures. This can cause compression of mucosal lymphatics leading to wall lymphoedema. With even higher intraluminal hydrostatic pressures, increased hydrostatic pressure in the capillary beds results in massive third spacing of fluid, electrolytes, and proteins into the intestinal lumen. The fluid loss and dehydration that ensue may be severe and contribute to increased morbidity and mortality. Strangulated SBOs are most commonly associated with adhesions and occur when a loop of distended bowel twists on its mesenteric pedicle. The arterial occlusion leads to bowel ischaemia and necrosis. If left untreated, this progresses to perforation, peritonitis, and death. Bacteria in the gut proliferate proximal to the obstruction. Microvascular changes in the bowel wall allow translocation to the mesenteric lymph nodes. This is associated with an increase in incidence of bacteremia due to Escherichia coli, but the clinical significance is unclear.
Abdominal pain (characteristic with most patients). Pain, often described as crampy and intermittent, is more prevalent in simple obstruction. Often, the presentation may provide clues to the approximate location and nature of the obstruction. Usually pain that occurs for a shorter duration of time and is colicky and accompanied by bilious vomiting may be more proximal. Pain lasting as many as several days, which are progressive in nature and with abdominal distention, may be typical of a more distal obstruction. Changes in the character of the pain may indicate the development of a more serious complication (i.e., constant pain of strangulated or ischaemic bowel).
Vomiting. This is associated more with proximal obstructions.
Diarrhoea (an early finding).
Constipation (a late finding) as evidenced by the absence of flatus or bowel movements.
Previous abdominal or pelvic surgery and/or previous radiation therapy (may be part of patient’s medical history).
History of malignancy (particularly ovarian and colonic).
Abdominal distention. Duodenal or proximal small bowel has less distention when obstructed than the distal bowel has when obstructed.
Hyperactive bowel sounds occur early as GI contents attempt to overcome the obstruction. Hypoactive bowel sounds occur late.
Exclude incarcerated hernias of groin, femoral triangle, and obturator foramina. Proper genitourinary and pelvic examinations are essential.
Look for the following during rectal examination. Gross or occult blood, which suggests late strangulation or malignancy.
Check for symptoms commonly believed to be more diagnostic of intestinal ischaemia, including the following:
tachycardia (>100 beats/min);
No reliable way exists to differentiate simple from early strangulated obstruction on physical examination. Serial abdominal examinations are important and may detect changes early.
Serum chemistries, liver panels. Results are usually normal or mildly elevated.
Creatinine. Elevations may indicate dehydration.
CBC: WBC may be elevated with a left shift in simple or strangulated obstructions. Increased hematocrit speaks to volume state (i.e., dehydration).
Lactate dehydrogenase tests
Radiography. Order plain radiographs first for patients in whom SBO is suspected. At least 2 views, supine or flat and upright, are required. Too findings were more predictive of a higher grade or complete SBO: presence of air-fluid differential height in the same small-bowel loop and presence of a mean level width greater than 25 mm. When these findings are present, the obstruction is most likely high grade or complete. When both are absent, a low (partial)-grade SBO is likely or nonexistent. Absent or minimal colonic gas indicates SBO (fig.19).
Small bowel loops contain transverse folds known as valvulae conniventes or plica circularis. These folds are well seen in this patient with small bowel obstruction. Usually the colon is decompressed and hardly visible (fig. 20).
This is valuable in detecting presence of obstruction and in differentiating partial from complete blockages. This study is useful when plain radiographic findings are normal in the presence of clinical signs of SBO or if plain radiographic findings are nonspecific. It distinguishes adhesions from metastases, tumor recurrence, and radiation damage. Enteroclysis offers a high negative predictive value and can be performed with 2 types of contrast. Barium is the classic contrast agent used in this study. It is safe and useful when diagnosis obstructions provided no evidence of bowel ischaemia or perforation exists. Barium has been associated with peritonitis and should be avoided if perforation is suspected.
CT scanning is useful in making an early diagnosis of strangulated obstruction and in delineating the myriad other causes of acute abdominal pain, particularly when clinical and radiographic findings are inconclusive. It also has proved useful in distinguishing the aetiologies of SBO, i.e., extrinsic causes such as adhesions and hernia from intrinsic causes such as neoplasms or Crohn’s disease. It also differentiates the above from intraluminal causes such as bezoars. CT scanning is about 90% sensitive and specific in SBO diagnosis. CT scanning is the study of choice if the patient has fever, tachycardia, localized abdominal pain, and/or leukocytosis. It is capable of revealing abscess, inflammatory process, extraluminal pathology resulting in obstruction, and mesenteric ischaemia. CT scanning enables the clinician to distinguish between ileus and mechanical small bowel in postoperative patients. Obstruction is present if the small-bowel loop is greater than 2.5 cm in diameter dilated proximal to a distinct transition zone of collapsed bowel less than 1 cm in diameter (fig. 21).
A smooth beak indicates simple obstruction without vascular compromise; a serrated beak may indicate strangulation. Bowel wall thickening indicates early strangulation. CT scanning is useful in identifying abscesses, hernias and tumors.
Ultrasonography is less costly and less invasive than CT scanning. It may reliably exclude SBO in as many as 89% of patients. Specificity is reportedly 100%.
Ultrasonography signs of SBO:
dilatation of small bowel lumen;
“pendulous” movements of bowel content.
A strangulated obstruction is a surgical emergency. In patients with a complete SBO, the risk of strangulation is high and early surgical intervention is warranted. Patients with simple complete obstructions in whom nonoperative trials fail also need surgical treatment but experience no apparent disadvantage to delayed surgery.
Adhesions. Decreasing intraoperative trauma to the peritoneal surfaces can prevent adhesion formation.
Malignant tumor. Obstruction by tumor is usually caused by metastasis. Initial treatment should be nonoperative; surgical resection is recommended when feasible.
Inflammatory bowel disease. To reduce the inflammatory process, treatment generally is nonoperative in combination with high-dose steroids. Consider parenteral treatment for prolonged periods of bowel rest. Undertake surgical treatment, bowel resection, and/or stricturoplasty if nonoperative treatment fails.
Intra-abdominal abscess. CT-guided drainage is usually sufficient to relieve obstruction.
Radiation enteritis. If obstruction follows radiation therapy acutely, nonoperative treatment accompanied by steroids is usually sufficient. If obstruction is a chronic sequel of radiation therapy, surgical treatment is indicated.
Acute postoperative obstruction. This is difficult to diagnose because symptoms often are attributed to incisional pain and postoperative ileus. Treatment should be nonoperative. If nonoperative treatment fails, surgical treatment is indicated.
With proper diagnosis and treatment of the obstruction, prognosis is good. Complete obstructions treated successfully nonoperatively have higher incidence of recurrence than those treated surgically.
A large-bowel obstruction (LBO)
LBO may be caused by neoplasms or anatomic abnormalities such as volvulus, incarcerated hernia, stricture or constipation.
LBO from an anatomic abnormality leads to colonic distention, abdominal pain, anorexia, and, late in the course, feculent vomiting. Persistent vomiting may result in dehydration and electrolyte disturbances.
LBO is a surgical entity. The morbidity and mortality often are related to the surgical procedure used to relieve the colonic obstruction and, in the long term, to the underlying disease that caused the obstruction.
Colonic obstruction is most common in elderly individuals because the incidence of neoplasms and other causative diseases is higher in this population.
Hirschsprung’s disease resembles colonic obstruction in the pediatric population.
History focuses initially on the failure to pass stools or gas. One should attempt to distinguish complete bowel obstruction from partial obstruction, which is associated with passage of some gas or stools, and from ileus. Further historical questioning may be directed at the patient’s current and past history in an attempt to determine the most likely cause.
Complete obstruction is characterized by the failure to pass either stools or flatus and 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 stools, 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, by peritoneal signs, or by the presence of pronounced fever and leukocytosis.
History of chronic weight loss and passage of maelanotic bloody stool suggests neoplastic obstruction.
Conversely, a history of recurrent left lower quadrant abdominal pain over several years is more consistent with diverticulitis, a diverticular stricture, or similar problems.
A history of aortic surgery suggests the possibility of an ischaemic stricture.
Abdominal examination. Perform the examination in standard manner, i.e., inspection, auscultation, percussion, and palpation. LBO may be characterized by diminished or, in later stages, absent bowel sounds. The abdomen is distended and may be tender. The presence of true involuntary guarding or peritoneal signs should raise the specter of another intra-abdominal process, such as an abscess. The practice of seeking rebound tenderness is misleading and potentially cruel. Many patients without peritoneal signs complain vigorously after an aggressive rebound maneuver. Seeking tenderness and pain by having the patient cough or by shaking the bed probably is more useful.
Examination of inguinal and femoral regions. This should be an integral part of the examination. Incarcerated hernias represent a frequently missed cause of bowel obstruction. In particular, colonic obstruction often is caused by a left-sided inguinal hernia with the sigmoid colon incarcerated in the hernia.
Digital rectal examination. Perform this to verify the patency of the anus in a neonate. The examination focuses on identifying rectal pathology that may caus the obstruction and determining the contents of the rectal vault. Hard stools suggest impaction. Soft stools suggest obstipation. An empty vault suggests obstruction proximal to the level that the examining finger can reach. Faecal occult blood testing should be performed, and a positive result may suggest the possibility of a more proximal neoplasm.
Studies are directed at evaluating the dehydration and electrolyte imbalance that may occur as a consequence of LBO and at ruling out ileus as a diagnosis. Suggestion of an abnormal anion gap also should prompt an arterial blood gas measurement and/or a serum lactate level measurement. A decreased haematocrit level, particularly with evidence of chronic iron-deficiency anemia, may suggest chronic lower gastrointestinal bleeding, particularly due to colon cancer. A stool test also should be performed, for similar reasons. Although bowel obstruction, or even constipation, may mildly elevate the WBC count, substantial leukocytosis should prompt reconsideration of the diagnosis. Ileus, secondary to an intra-abdominal or extra-abdominal infection or another process, is a possibility.
Flat and upright abdominal roentgenography demonstrates dilation of the large bowel and air fluid levels. Сolonic air suggests 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. This finding can be misleading, particularly if the patient has undergone rectal examinations or enemas. The characteristic bird’s beak of volvulus may be seen.
If differentiation between obstipation and obstruction is required, imaging with contrast is indicated (fig. 22). If localization is required for surgical intervention, imaging with contrast is indicated. Water-soluble gastrografin has important advantages over barium as a contrast agent and generally should be employed first. It usually does not cause chemical peritonitisk, if the patient has colonic perforation.
CT scanning is not used initially in patients with large bowel obstruction unless a diagnosis has been made. CT scan, particularly with rectal contrast, may demonstrate a mass or evidence of metastatic disease.
Other tests. Fiber-optic endoscopy may be useful in evaluating left-sided colonic obstruction, including the anatomic location and pathology of the lesion. Because the cecum is not reached in such cases, the endoscopist must be alert to the possibility of incorrectly identifying anatomic landmarks and the location of the obstruction. Although flexible endoscopy is relatively comfortable for the patient and provides a better view than rigid sigmoidoscopy, the latter also may be used, depending on the availability of resources and training of personnel. Right-sided colonic obstruction is more difficult to evaluate without first administering an oral bowel preparation, which is contraindicated in the setting of bowel obstruction.
Endoscopic reduction of volvulus. This procedure is indicated for sigmoid volvulus when peritoneal signs are absent, which would imply dead bowel or perforation. It also is indicated when evidence of mucosal ischaemia is not present upon endoscopy. An experienced person should perform the procedure. A rigid sigmoidoscope may be used if a flexible instrument is not available. The endoscopist must have sufficient experience with this technique. Reduction of a volvulus does not imply cure.
The sigmoid usually revolvulizes if definitive treatment is not carried out. These patients generally are admitted, subjected to mechanical bowel preparation, and managed surgically by sigmoid resection, unless contraindications are present.
Barium enema for reduction of intussusception. This is useful and often successful in children in whom a pathological leading point for the intussusception is unlikely. It should be performed by an experienced radiologist because the risk of perforation is significant. In adults, typically a pathologic leading point for the intussusception is present. Success is far less likely, and patients still require surgery to deal with their pathology.
Cleansing enemas. Perform these if obstipation is suspected rather than true large bowel obstruction. Also perform them to prepare the distal colon for endoscopic evaluation.
Endoscopic dilation and stenting of colonic obstruction This procedure is indicated for colonic near total obstruction through which some small amount of lumen remains. The procedure may be palliative in a high-risk patient with an unresectable malignancy, accepting a risk of reobstruction of the stent, or preparatory to surgical resection. In cases in which the stent is deployed prior to surgery, it permits relief of the acute obstruction, resuscitation of the patient, and mechanical bowel preparation prior to a one-stage colonic resection and reanastomosis, thus avoiding temporary or permanent colostomy. The procedure should be performed only by an endoscopist experienced in such procedures. Surgical consultation and backup should be available, as the risk of perforation is increased during attempts at such procedures, with a potentially catastrophic result.
It involves resuscitation, correction of fluid and electrolyte imbalance, and nasogastric decompression to temporarily treat the obstruction and prevent vomiting and aspiration.
Surgical care is directed at relieving the obstruction. In most patients, the obstructing lesion is resected. Because the colon has not been cleansed, anastomosis often is 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 comorbidity and surgical risk or in the presence of an unresectable tumor, a diverting proximal colostomy or ileostomy may be performed without resection.
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 employed in patients with rectal obstruction that cannot be managed without a combined abdominoperineal approach.
Cecostomy should not be performed because the diversion is inadequate.
In younger patients some surgeons would consider primary anastomosis, rather than ileostomy, in the right colon, assuming no intraoperative hypotension, blood loss, or other complications are present.
If resection and proximal colostomy or ileostomy is performed, a mucous fistula generally is extracted from the distal end, unless the obstruction is rectosigmoid, in which case the distal end may be oversewn or stapled and left to drain transanally.
If the cause of the obstruction can be relieved nonsurgically, through procedures such as decompressign a volvulus, or if the obstruction is only partial, deferring surgery temporarily and supporting the patient while the large bowel is cleansed so that primary anastomosis may be performed more safely is preferable.
Further оutpatient сare
Care after discharge focuses on surgical convalescence and, if relevant, the need to care for the disease that caused the obstruction. An obstructing colon cancer may require postoperative chemotherapy, depending on the stage of the disease. The patient who is chronically obstipated may need stool softeners.
If the patient has received a colostomy or ileostomy, a decision regarding whether it is temporary or permanent may have been made at the time of discharge, depending on the patient’s diagnosis, comorbidity, and postoperative convalescence.
Most patients who retain a rectum are, at least in principle, candidates for reanastomosis at a subsequent stage. Generally, it is performed 2–3 months after the initial operation.
Careful counseling and assessment are required before proceeding with the second procedure. Counseling is directed at the risks of the second procedure because the patient must understand that this surgery is elective and that a colostomy or ileostomy is compatible with a reasonable lifestyle.
Often, local colostomy support groups and meeting with other patients with colostomies are helpful at this time. Patients who had stool incontinence before their first operation, those with substantial surgical risks, and patients with decreased mental status who are cared for in nursing homes may potentially be better off without a reanastomosis.
In addition, the remaining colon, both proximally and distally, must be evaluated radiographically or endoscopically to rule out synchronous colonic lesions such as neoplasms because the presence of the LBO prevented this from being performed before the first procedure.
Prior to surgical decompression, the patient’s overall medical condition and presence of any comorbidities that define surgical risk determine the prognosis. After surgical decompression, prognosis is determined by the underlying disease.
After abdominal surgery, a normal physiological ileus occurs. This type of ileus spontaneously resolves within 2–3 days after sigmoid motility returns to normal. However, the terms postoperative adynamic ileus or paralytic ileus are defined as ileus of the gut persisting for more than 3 days following surgery. Ileus occurs from hypomotility of the gastrointestinal tract in the absence of a mechanical bowel obstruction. This suggests that the muscle of the bowel wall is transiently impaired and fails to transport intestinal content. This lack of coordinated propulsive action leads to the accumulation of both gas and fluids within the bowel. Although ileus has numerous causes, the postoperative state is the most common scenario for ileus development. Frequently, ileus occurs after intraperitoneal operations, but it may also occur after retroperitoneal and extra-abdominal surgery. The longest duration of ileus is noted to occur after colonic surgery.
Causes of adynamic ileus:
Most cases of ileus occur after intra-abdominal operations.
Drugs (e.g., opioids, antacids, coumarin, amitriptyline, chlorpromazine).
Metabolic (e.g., low potassium, magnesium, or sodium levels; anemia, hyposmolality).
Trauma (e.g., fractured ribs, fractured spine).
Biliary and renal colic.
Head injury and neurosurgical procedures.
Intra-abdominal inflammation and peritonitis.
According to some hypotheses, postoperative ileus is mediated via activation of inhibitory spinal reflex arcs. Anatomically, 3 distinct reflexes are involved: ultrashort reflexes confined to the bowel wall, short reflexes involving prevertebral ganglia and long reflexes involving the spinal cord. The long reflexes are the most significant. Spinal anaesthesia, abdominal sympathectomy, and nerve-cutting techniques have been demonstrated to either prevent or attenuate the development of ileus.
The surgical stress response leads to systemic generation of endocrine and inflammatory mediators that also promote the development of ileus. Rat models have shown that laparotomy, eventration, and bowel compression lead to increased numbers of macrophages, monocytes, dendritic cells, T cells, natural killer cells, and mast cells, as demonstrated by immunohistochemistry. Calcitonin gene-related peptide, nitric oxide, vasoactive intestinal peptide, and substance P function as inhibitory neurotransmitters in the bowel nervous system.
Nitric oxide and vasoactive intestinal peptide inhibitors and substance P receptor antagonists have been demonstrated to improve gastrointestinal function.
Patients with ileus typically present with vague, mild abdominal pain and bloating. They may report nausea, vomiting, and poor appetite. Abdominal cramping is usually not present. Patients may or may not continue to pass flatus and stool.
Patients may have distended and tympanic abdomens, depending on the degree of abdominal and bowel distension. The abdomen may be tender.
A distinguishing feature is absent or hypoactive bowel sounds unlike the high-pitched sound of obstruction. The silent abdomen of ileus reveals no discernible peristalsis or succussion splash.
Laboratory studies and blood work should focus on evaluations for infectious, electrolytic, and metabolic derangements.
On plain abdominal radiographs, ileus appears as copious gas dilatation of both small intestine and colon.
Most cases of postoperative ileus resolve with watchful waiting and supportive treatment. Patients should receive intravenous hydration. For patients with vomiting and distension, use of a nasogastric tube provides symptomatic relief.
Underlying sepsis and electrolyte abnormalities, particularly hypokalemia, hyponatremia, and hypomagnesemia, may worsen ileus. These contributing conditions are easily diagnosed and corrected.
Discontinue medications that produce ileus (e.g., opiates). The use of postoperative narcotics can be diminished by supplementation with NSAID. NSAIDS may improve ileus by improving local inflammation and by decreasing the amount of narcotics used.
The presence of ileus does not preclude enteral feeding. Postpyloric tube feeding into the small bowel can be performed.
Use of prokinetic agents has had moderate success, a serotonin agonist, has reportedly been successful in treating ileus.