Small bowel obstruction
Mechanical small bowel obstruction is one of the most common surgical emergencies. A traditional adage, ‘let the sun never set or rise’ on a bowel obstruction, indicating the need for immediate operative intervention, does not apply to all patients. However, it does highlight the importance of careful evaluation of patients with small bowel obstruction. Aggressive nonoperative and operative management has reduced mortality from 50% to 5% over the past 50 years.
The causes of small bowel obstruction vary widely with geographic region and patient's age group. The most common cause inWestern society is post-surgical adhesions, followed by external hernias (Causes of small bowel obstruction). The pathogenesis of adhesions is not well understood and, until recently, there was no clinically useful medication or manoeuvre that prevents formation of adhesions. Recently there has been interest in various bioresorbable membranes or gel (Seprafilm™ or Spraygel™) placed between the viscera and abdominal wall at the end of surgery which may help prevent adhesions.
Small bowel obstruction leads to rapid accumulation of fluid and gas in the bowel proximal to the site of obstruction. In typical cases, there is initial active peristalsis proximal to the obstruction.Within a few hours, the peristaltic activity declines. Oedema and increasing distension supervene. Stasis and bacterial overgrowth make the fluid faeculent. Appearance of faeculent fluid with a foul odour in the vomitus or from a nasogastric tube confirms the diagnosis of obstruction.
Classic presentations of small bowel obstruction include:
- crampy abdominal pain
- nausea and vomiting
- abdominal distension
Patients with a proximal small bowel obstruction are likely to present early (within a day) with pain and vomiting; abdominal distension and constipation are less likely. Patients with a distal obstruction frequently have a more prolonged symptom complex with a 2–3-day history of crampy abdominal pain prior to vomiting; distension and constipation are predominant features. The bowel sounds are initially hyperactive and high-pitched. In delayed presentation, the bowel sounds may be reduced, indicating onset of secondary ileus.
The symptom complex also varies with the underlying aetiology. Small bowel obstruction due to hernia tends to present early and more acutely with a tense and irreducible external hernia, that associated with a neoplasm is more indolent and that due to adhesions intermediate in presentation.
Recognition of strangulated obstruction with bowel ischaemia and impending perforation is important. Clinical features of bowel ischaemia include constant and severe abdominal pain associated with tenderness and guarding, tachycardia, fever and leucocytosis.
Supine and erect abdominal radiographs
Specific radiographic findings suggestive of small bowel obstruction include a dilated small bowel with air-fluid levels, often in a stepladder distribution on the erect film (Plain X-ray of the abdomen showing a mechanical small bowel obstruction with multiple loops of distended small bowel with ‘step-ladder’ air-fluid pattern in the erect film.). Presence of colonic gas may indicate an incomplete obstruction or the presence of an adynamic ileus rather than a complete mechanical obstruction. Presence of foreign bodies causing obstruction, such as gallstones, should be noted. Plain radiographs are not always diagnostic. In a proximal obstruction, there may be few radiographic abnormalities.
The use of barium is unpopular because of the risk of inspissation of barium proximal to the point of obstruction and the potential for peritioneal contamination if bowel perforation is present.
Agastrografin small bowel follow-through study will establish the extent (complete vs. incomplete) and degree of small bowel obstruction (Gastrografin small bowel follow-through showing an obstruction in the mid-small bowel.). Gastrografin is hyperosmolar and may stimulate peristaltic activity of the small bowel. Caution is exercised in the dehydrated patient because gastrografin may exacerbate dehydration by sequestration of third-space fluid in the intestinal lumen. The intestinal mucosa is not well defined by the water-soluble gastrografin study. A good alternative, providing better anatomic detail, is a mixture of half barium and half water-soluble contrast.
There is no specific laboratory test that is diagnostic of intestinal obstruction. However, with a more protracted history, a hypokalaemic, hypochloraemic metabolic alkalosis may develop. Full blood examination may show leucocytosis if there is impending bowel ischaemia, and anaemia may indicate a malignant cause. Deranged liver function tests with hypoalbuminaemia may be associated with poor nutrition or sepsis.
Fluid and electrolyte replacement
Careful assessment of fluid and electrolyte status is important. A patient whose obstruction has been present for many hours, when there has been vomiting and sequestration of large amounts of fluid in the intestinal third-space, may require intravenous administration of several litres of isotonic saline to replace the deficit.
Pulse, blood pressure and tissue turgor are monitored as indices of fluid status. Urine output is also monitored. A urine output of at least 0.5 mL/kg per hour is a useful index of adequate fluid replacement. In critical cases, insertion of a urinary Foley catheter is useful. Central venous or pulmonary artery pressure monitoring is considered in older patients with a history of cardiac disease.
Decompression of the upper gastrointestinal tract is initiated early in the management to avoid vomiting, and to reduce gastric and small bowel distension.
Analgesia is prescribed with caution so as not to mask signs of peritoneal irritation, which may indicate impending bowel ischaemia.
Most patients with small bowel obstruction undergo an initial phase of resuscitation and decompression. Any signs of intestinal strangulation with vascular compromise should prompt immediate surgical intervention. Non-operative management is continued in patients with a partial small bowel obstruction and without signs of intestinal strangulation. Repeated evaluation of the abdomen and the general status of the patient is important. If there has been no significant improvement after 48 hours, operative intervention is generally indicated.
In adhesive obstruction, surgery is indicated where there are concerns of intestinal ischaemia or the patient fails to improve after a short period of non-operative management. Constant, rather than intermittent, pain suggests bowel ischaemia. Bowel obstruction due to hernia in the inguinal or femoral area requires prompt surgery, as the bowel entrapped within the hernia can develop irreversible ischaemia and gangrene.
Pre-operative preparations include adequate fluid and electrolyte replacement, prophylaxis with broadspectrum antibiotics covering aerobes and anaerobes, anti-thrombotic prophylaxis with compressive stockings and subcutaneous heparin.
Avoidance of aspiration pneumonitis is ensured with adequate nasogastric decompression and a rapidsequence induction of anaesthesia with cricoid pressure until the endotracheal tube has been inserted.
Surgery is sometimes easy when a single adhesive band or an external hernia is the cause of obstruction, and surgery may be complex where there are dense adhesions. Closed-loop obstruction, with occlusion at both ends of the loop of bowel, may arise from torsion or complex adhesions of the small bowel, and obstructed external hernia. The intraluminal pressure rapidly rises and the risk of perforation is accelerated. The object at surgery is to find the junction of the dilated and collapsed bowel. The viability of a segment of intestine is determined by observation. In doubtful cases, a warm pack is placed over the bowel in question and the bowel re-examined several minutes later. If the bowel is not viable, a simple resection and primary anastomosis is performed. Sometimes, as with carcinomatosis or extensive pelvic adhesions, a side-to-side bypass is the better choice.
Obstruction due to external hernia is usually dealt with through the herniorrhaphy incision. The entrapped bowel is examined prior to returning it to the general peritoneal cavity. The hernia is then repaired. Local signs of inflammation at the hernia site may indicate strangulation of the entrapped bowel or omentum.
Recurrent small bowel obstruction
After the initial operation of adhesiolysis for obstruction, the recurrence rate of further adhesive obstruction is about 20%. Repeated bouts of adhesive small bowel obstruction can be incapacitating: moreover, repeated operative intervention can be met with increasing technical difficulties and further episodes of adhesive obstruction. The first episode of adhesive small bowel obstruction is usually managed by prompt surgical intervention because of the risk of strangulation. When obstruction recurs, a non-operative management with nasogastric decompression and maintenance of fluid and electrolyte balance is generally preferred, provided that there is no evidence of bowel compromise. Increasing pain, fever, leucocytosis, high nasogastric output, lack of bowel function, abdominal distension and increasing bowel dilatation on plain abdominal X-ray are indicators for swift surgical intervention.
At surgery, gentle handling of the bowel and precision in dissection is important. A long intestinal tube introduced through a gastrostomy may help to splint the small bowel. Such a tube is left in place for at least 3 weeks but its efficacy has not been fully established.
Early post-operative small bowel obstruction
Mechanical small bowel obstruction presenting early in the post-operative period following abdominal surgery presents a diagnostic and therapeutic dilemma. The diagnosis may be obscured by paralytic ileus and the clinical features may be confused with the ‘normal’ convalescence following a laparotomy. With any prolongation of ileus beyond 5 days, mechanical obstruction should be suspected. Post-operative adhesions are most extensive about 10–21 days after a laparotomy. A gradual process of resolution then occurs. Apart from adhesions, other causes of mechanical small bowel obstruction include internal hernias, peritoneal defects and intra-abdominal abscesses.
Strangulation of the bowel in post-operative obstruction is uncommon. Careful repeated observation is important. Nasogastric decompression and replacement of fluid and electrolytes are essential. Parenteral nutritional support is often indicated if the obstructive episode lasts longer than 7 days. Plain radiograph of the abdomen is helpful in diagnosis. The presence of gas throughout the small and large bowel suggests a paralytic ileus. In cases where the diagnosis is uncertain, the use of dilute barium or gastrografin follow-through study will determine the severity of the obstruction and may lead to relief of the obstruction.
Timing of surgical intervention is difficult. Most patients will settle with non-operative management. The presence of complete obstruction, intra-abdominal sepsis or an excessively prolonged obstructive course are common indications for exploratory operation. In many situations, localised sepsis may be drained percutaneously under computed tomographic or ultrasonic guidance.
Metastatic malignant tumours
A history of neoplasm should not necessarily imply that carcinomatosis is the cause of small bowel obstruction. Some of these patients can have a benign cause of obstruction, such as an adhesive band. Management of patients with documented recurrent malignancy must be individualised. Peritoneal seedlings may lead to multiple narrowed segments. Strangulation is rare as the bowel loops are relatively fixed. Retroperitoneal and mesenteric deposits may contribute to the impaired motility.
A minimal-residue diet may reduce obstructive symptoms and acute episodes usually settle with nasogastric decompression. In patients with a relatively good prognosis, operative intervention with resection or bypass may achieve effective palliation.
Treatment of small bowel obstruction secondary to Crohn's disease is usually non-operative initially. Treatment with steroids and metronidazole reduces oedema and inflammation. If obstruction persists, surgery is necessary. A phlegmonous segment is resected and a fibrotic stricture is treated with strictureplasty.
Gallstones may ulcerate through the gall bladder into the duodenum and pass down the small bowel. For a gallstone to cause mechanical small bowel obstruction, it is usually larger than 2.5 cm. The common site of impaction is about 60 cm from the ileocaecal valve because this is the narrowest part of the small bowel. Patients are often elderly, presenting with a subacute small bowel obstruction. Plain radiograph of the abdomen reveals a small bowel obstruction with a gallstone in the right lower quadrant and gas in the biliary tree. At surgery, the obstructing gallstone is crushed and emptied into the large bowel. Alternatively, an enterotomy is made and the gallstone removed from the small bowel. The gall bladder is left alone so as not to disturb the cholecyst-duodenal fistula.
Chen SC, Lin FY, Lee PH, et al. Water-soluble contrast study predicts the need for early surgery in adhesive small bowel obstruction. Br J Surg. 1998;85:1692–1695.
Ellis H, Moran BJ, Thompson JN, et al. Adhesion-related hospital readmission after abdominal and pelvic surgery: a retrospective cohort study. Lancet. 1999;353:1476–1478.
Fevang BT, Fevang J, Lie SA, Soreide O, Svanes K, Viste A. Long-term prognosis after operation for adhesive small bowel obstruction. Ann Surg. 2004 Aug;240(2):193–201.Tjandra JJ, Ng K.Asprayable hydrogel adhesion barrier facilitates closure of defunctioning loop ileostomy: a randomized trial. Dis Colon Rectum. 2004;47.