Whatever its site and cause, small bowel obstruction leads to rapid accumulation of fluid and gas in the lumen proximal to the site of obstruction. This event is the result both of swallowed air and of intestinal fluid excretion. Peristalsis causes distension in the distal obstructed segment first, with gradual proximal accumulation of air and intestinal fluid. With so-called high obstruction, in areas such as the proximal jejunum, vomiting may supervene early, relieving the distension. When obstruction is distal, vomiting may not occur until late in the course of the disease.

In typical cases of acute obstruction there is initial active peristaltic activity proximal to the site. Most patients complain of crampy pain. Within a few hours this activity declines, and oedema and increasing distension mark the end of peristaltic activity; there may be no cramps or only occasional cramps. Persistent, steady pain usually indicates ischaemia or perforation. A change in the characteristics of small bowel contents is also characteristic of the later stages of obstruction. Bacterial overgrowth and stagnation make the fluid feculent, with an increase in opacity and a foul odour. Appearance of fluid of this type in the vomitus or from a nasogastric tube confirms the diagnosis of obstruction.

Obtaining a detailed history and performing a thorough examination will provide a diagnosis of underlying cause in more than three-quarters of cases. It is especially important to identify abdominal wall hernias, which frequently strangulate when surgery is delayed.

Laboratory tests are of little value beyond helping to rule out other causes of abdominal pain. The exception to this rule is the plain radiograph of the abdomen, which is especially helpful in confirming the clinical impression of obstruction, and can also, when interpreted by an experienced clinician, add additional useful information as to completeness, site, and aetiology of obstruction. Upright films may show air in the biliary or portal system and beneath the diaphragm; these are important observations with respect to timing of surgery.

A list of the causes of intestinal obstruction is long, even if those normally only encountered during infancy and childhood are excluded. (Table 1) 312. In geographic areas where life expectancy is long and surgical care readily available, at least half of the cases are the result of adhesions, usually postoperative. Hernias, whether of the abdominal wall or internal organs, are the second leading cause. Other important general causes are primary and metastatic tumours, local inflammatory processes such as appendicitis or diverticulitis of the colon, and various strictures, such as those seen in Crohn's disease. The causes and their relative incidence vary widely with geographic region.

The mechanism of the obstruction is more important than the specific aetiology, since this factor bears on the likelihood of bowel compromise. There are four general mechanisms: most dangerous are, first, volvulus with torsion and, second, incarceration in a confined space. Although volvulus can be the result of a failure of fixation of all or the distal part of the small bowel it is more commonly the result of twisting around a fixed point, as from an adhesion or tumour nodule. This event can rapidly lead to vascular compromise and infarction.

Incarceration in a fixed space is usually due to an abdominal wall hernia. Intra-abdominal defects and traps, congenital or acquired, are also sites of potential incarceration. Once entrapped, impaired venous return and torsion may rapidly lead to infarction of the segment.

Obturation of a segment of bowel, usually narrowed by a pathological process such as fibrosis or tumour growth, is the third mechanism. Such obstruction may be intermittent because of the repeated gradual passage of a bolus of intestinal contents through the stricture. A large bezoar or gallstone may obstruct a normal segment of bowel, usually the distal ileum, by this mechanism. Vascular compromise is unlikely in obturation obstruction.

The last mechanism is intussusception. In adults, it is almost always due to an intramural or mucosal lesion. It does not usually lead to ischaemia and infarction.

As a rule, mechanical small bowel obstruction is an urgent indication for surgical intervention. This practice reflects the risks of strangulation and perforation, the fact that persistence of obstruction will eventually require an operation in many cases, and the likelihood of recurrence even with spontaneous resolution.

Preoperative assessment of fluid status with rapid replacement of deficits is important. A patient whose obstruction has been identified many hours from its onset, when there has been vomiting or sequestration of large amounts of fluid in the lumen, intestinal wall and peritoneal cavity, may require administration of several litres of fluid. In these cases, restoration of an adequate urine output serves as a useful general index of adequate replacement. In older patients, especially those with a history of cardiac disease, central venous or pulmonary artery pressure monitoring may be needed. Concurrent, sometimes exacerbated, medical problems such as diabetes mellitus and cardiac impairment must be considered and managed separately.

Nasogastric suction relieves distension from air swallowing and reduces fluid passage into the small bowel; it should be instituted early in management. The use of long intestinal tubes has less justification. They do not pass readily, do not empty the stomach, and delay more definitive management. Generally, they have no useful role in the management of acute obstruction. Although exceptions may be cited, an efficiently functioning nasogastric tube is clearly preferable in most cases.

Though sometimes easy, operative intervention may be complex. The procedure requires the management of the segment of intestine at the site of obstruction, the distended proximal bowel and the underlying cause of obstruction.

If the patient has had a previous surgical incision which, with enlargement, will afford a portal for complete abdominal exploration, it should be used. This approach allows repair of all associated hernias and easy access to the most frequent site of obstruction by adhesions, which is the incision itself. It is usually wise to enter the abdomen through an extension into normal tissues to avoid injury to adherent loops.

In patients with late obstruction and in the elderly, the distended segments should be handled with care as they may easily be torn. The object is to find the junction of dilated and collapsed bowel. Though it may be preferable to follow collapsed loops proximally, this is not usually possible.

Decompression of dilated loops may be desirable to facilitate an anastomosis or closure of the abdominal wound. Closed methods of accomplishing this goal include the milking of contents back into the stomach with aspiration through a nasogastric tube. This method is usually possible without excessive trauma to the bowel only in young children. Alternatively, a long tube may be advanced from the stomach by digital manipulation into the distended loops. Finally, a sump suction device may be passed directly into the distended loops through an enterotomy controlled with a ‘purse string’ suture. Even with careful attention to prevention of local soilage, direct aspiration of enteric contents is associated with an increase in postoperative wound sepsis. Unless clearly needed, the best policy often is to omit decompression altogether.

When indicated, a simple resection of small bowel and direct anastomosis, even when the proximal bowel is distended, is safe enough. Sometimes, as with carcinomatosis or extensive pelvic adhesions, a side-to-side bypass is the better choice. Parenteral administration of antibiotics, begun preoperatively, decreases the incidence of septic complications when resection or bypass is performed.

The determination of the viability of a segment of intestine is a common problem. Generally, the opinion of an experienced surgeon after 10 to 20 min of observation suffices. To prevent early perforation or late strictures, a resection is the best choice when doubt exists. Although fluorescein injections with illumination of the surface with a Wood's lamp and detection of surface flow by Doppler devices provide scientific approaches to the diagnosis, they are neither necessary nor commonly available at the moment they are needed.

When obstruction is due to adhesions the question of whether all or only the offending adhesions should be released is unresolved. Generally, adhesions can be expected to recur when there has been any trauma to serosal surfaces. Thus, as a rule it is probably wise to divide only those adhesions involving the bowel at the site of obstruction and those that prevent restoration of the proximal and distal segments to their normal place of residence in the abdominal cavity.

Reduction of abdominal wall hernias before operation is desirable when easily accomplished. An exception is a hernia in the inguinal or femoral area; prompt operation is required. The surgeon may prefer to be able to examine the incarcerated segment of bowel through the herniorrhaphy incision before it is dropped back in. Another exception is the presence of local signs of inflammation that may indicate strangulation or perforation.

Any laparotomy should be performed with operative measures that minimize adhesion formation, decreasing the incidence of small bowel obstruction. All reasonable steps to minimize serosal trauma should be utilized, including gentle handling and packing of intestine and avoiding the unnecessary introduction of foreign material into the peritoneal cavity. Sutures and ties involving the serosa cause small areas of tissue ischaemia and necrosis which can cause adhesions. Serosal defects should not be repaired if the underlying muscularis and submucosa are intact.

The second preventive measure, of course, is the repair of abdominal wall hernias. Any inguinal hernia that is symptomatic or is the site of occasional temporary bowel incarceration should be repaired, as should all incisional hernias.

Mechanical small bowel obstruction can complicate the postoperative course after any operative entry into the peritoneal cavity. The diagnosis is obscured by ileus and the symptoms and signs that are a usual accompaniments of a laparotomy incision.

Normally, paralysis of peristaltic function resolves within 72 h after a laparotomy involving handling of the intestine. There is then an absence of distension, and the patient reports a return of appetite along with expulsion of flatus and faeces. In cases of obstruction, normal peristaltic function may never return, or may do so only to be interrupted by an episode of obstruction. The superimposition of the signs and symptoms of obstruction on those of convalescence after laparotomy makes the diagnosis elusive.

Most cases are the result of adhesions and involve the ileum. Although the extent of adherence of peritoneal surfaces to each other is variable, the time course usually is not. By 72 h after laparotomy, extensive soft adhesions will have formed. These seem most extensive at about 10 days to 2 weeks, by which time they become dense and vascular. A gradual process of resolution then occurs; this may go on for many years, accounting for appearance of obstruction at remote times. This process of adhesion formation in some cases is abnormally vigorous and may then reflect peritoneal reaction to foreign material introduced during the operation. Sterile peritonitis can be an important contributor to a course of delayed resumption of intestinal function without actual mechanical obstruction. Obstruction by adhesions in the early period is usually the result of kinking and tensions on adherent loops of intestine rather than of obturation. The presence of a stoma or intestinal tube may contribute to these mechanical problems by offering a fixed cicatricial point. Other causes of obstruction include internal hernias and peritoneal defects after partial dehiscence of the deep layer of a wound or the peritoneal floor. An abscess involving adjacent segments of intestine can cause obstruction or can lead to localized ileus.

The clinical problem is to distinguish between cases of mechanical obstruction and those that reflect ileus prolonged by a sterile peritonitis or other factors, such as chronic narcotic use. Fortunately, except when there is a peritoneal defect, strangulation of an obstruction is rare in a postoperative patient. Careful repeated observation of the patient is paramount. Radiography offers the next best help: plain films show gas throughout the small and large bowel in most cases of ileus. In difficult cases, the use of barium will sometimes provide important information (Figs. 1, 2) 954,955.

Careful replacement of fluid and electrolytes is needed, and nutritional support may facilitate overall recovery. It is generally believed that nasogastric decompression is essential and that decompression through a long tube may be helpful; passage of such tubes is most likely to succeed in those patients with mechanical obstruction. The usefulness of long tubes in the overall management of patients is estimated to be high by some surgeons, but many do not find them useful.

The timing of surgical intervention is difficult. Although it is important to relieve mechanical obstruction promptly, operations on patients with profound ileus and in those with extensive nonobstructing adhesions are fruitless and delay recovery. No simple rule can be offered. Generally, complete obstruction, evidence of sepsis, and an unacceptably prolonged course dictate an exploratory operation. An unacceptably long course is the least useful indication.

The risk of strangulation and the likelihood of early recurrence usually dictate prompt operation at the first episode of obstruction. An operation for obstruction due to adhesions carries a higher likelihood of recurrence than a laparotomy for other indications. This is of the order of 20 per cent. When obstruction recurs, the possibility of a cause other than adhesions is lower, and there is perhaps more justification for a non-operative management, in the form of decompression with a nasogastric tube and careful parenteral replacement of lost fluids and electrolytes.

During any period of observation, there will be continued concern about the possibility of bowel compromise. The nature of pain is the best indicator of this complication. Plain and contrast studies are helpful in ruling out complete obstruction, which also serves as an indication for surgical relief. If the obstruction resolves, there is generally no reason for a laparotomy in the patient with recurrent obstruction due to adhesions.

There is no good way to prevent the recurrence of adhesions. Some authorities have suggested that plication of the wall or mesentery of the small bowel to form a ladderlike configuration may be helpful: there is no good evidence for the efficacy of these measures, and few surgeons use them. An in-lying long enteric tube may also produce a configuration of loops less prone to obstruction from adhesions. Such tubes should be left in place for at least 2 weeks, but their efficacy has not been clearly established.

Injuries to the small intestine may follow radiation to any part of the abdominal cavity: many result from therapy for pelvic tumours. Although these injuries may lead to perforation with abscess formation of fistulae, the most common complication is intestinal obstruction.

During the actual course of radiation treatment, damage to the mucosa may lead to ulceration and oedema. Delayed damage to small blood vessels causes more serious complications such as progressive arteritis and eventual thrombosis. Infarction and perforation may ensue, but the more frequent result is the induction of dense adhesions containing collateral vessels, and the occurrence of fibrous strictures. Serosal surfaces of injured intestinal segments acquire a characteristic thickened, scarred, hypervascular appearance.

The cause of acute complete obstruction can only be established at the time of operation. Segments of intestine with a grossly abnormal appearance may not heal; when used for anastomosis, there is a high incidence of failure. A segment with a nearly normal appearance and satisfactory bleeding on transection can be used confidently. Microscopic examination adds little to the surgeon's impression in selecting bowel for anastomosis. Resection is the preferred management. If dissection of radiation-damaged loops of bowel out of the pelvis offers an unacceptable risk, a bypass may be selected. It is better to transect the bowel above the obstruction for an end-to-side anastomosis than to perform a side-to-side bypass in continuity.

A trial of non-surgical management is reasonable when a prior history or contrast study has established the diagnosis of radiation enteritis and obstruction is not complete. Some episodes due to obturation or oedema will resolve and may not recur. Parenteral nutrition may aid the process of resolution.

Peritoneal seeding sometimes leads to multiple narrowed segments and consequent obturation obstruction; this may occur in the absence of other terminal manifestations of the tumour. Strangulation is rare, since the loops are relatively fixed. Retroperitoneal or mesenteric deposits may contribute to the impaired motility.

Patients tend to have intermittent episodes of obturation obstruction. A minimal residue diet may reduce symptoms and acute obstruction usually clears on nasogastric suction. In patients with a relatively good prognosis, there may be a role for surgical intervention for bypass or even resection of obstructed sites. Careful evaluation with contrast studies allows selection of the smallest feasible procedure, to be performed through a limited field. Wide exploration of the abdomen is likely to be both unnecessary and counterproductive.

Obstruction of the distal duodenum due to its compression between the artery and posterior structures, either the aorta or vertebral bodies, has been termed the superior mesenteric artery syndrome. Findings on plain film and contrast studies are dilatation of the stomach and duodenum with a termination by obstruction with a linear configuration at the level of the artery.

The syndrome may follow weight loss, immobilization in bed, and various operative procedures, but it also may occur spontaneously. It is seldom seen in obese patients. There appears to be a component of impaired motility in some patients and abnormalities of fixation of the ligament of Treitz have also been cited. The onset is often insidious with the gradual appearance of nausea and vomiting.

Though conservative measures should first be tried, the majority of patients eventually require surgical relief. Simple gastrojejunostomy does not relieve symptoms. Various measures can be used to adjust the position and fixation of the duodenum and proximal jejunum. Duodenojejunostomy performed through the mesocolon in a side-to-side fashion is most likely to succeed. The jejunum just beyond the ligament of Treitz should been employed in the anastomosis.

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