Small Bowel Obstruction

Small bowel obstruction is mechanical interruption of small intestinal transit. Adhesions are the commonest cause after previous abdominal surgery, followed by hernias, malignancy, Crohn disease, volvulus and less commonly intussusception or gallstone ileus.

The clinically important distinctions are partial versus complete obstruction, simple versus strangulated obstruction, and single transition point versus closed loop obstruction. Strangulation means compromised bowel perfusion and requires urgent surgery.

Fluid sequestration into the obstructed bowel, vomiting and reduced intake produce intravascular depletion, electrolyte disturbance and acute kidney injury. Proximal obstruction causes earlier vomiting and less distension. Distal obstruction produces greater distension and later faeculent vomiting.

• Typical presentation is colicky central abdominal pain, vomiting, abdominal distension and reduced passage of stool or flatus.
• Early obstruction may still allow passage of stool from distal bowel. Absolute constipation therefore usually develops later and should not be required for diagnosis.
• Examination may reveal distension, visible peristalsis, tympany and initially high pitched bowel sounds. Bowel sounds become reduced when obstruction is prolonged, bowel becomes ischaemic or associated ileus develops.
• Continuous rather than colicky pain, focal tenderness, involuntary guarding, fever, persistent tachycardia or haemodynamic deterioration should raise concern for strangulation or perforation.

Always examine the groins and previous operative scars. An incarcerated external hernia can be missed if the assessment stops at the abdomen.

• Check full blood count, renal function, electrolytes and lactate. Hypochloraemic metabolic alkalosis may occur with persistent proximal vomiting. Metabolic acidosis and rising lactate increase concern for hypoperfusion or ischaemia, but a normal lactate does not exclude early strangulation.
• CT abdomen and pelvis with IV contrast: confirms the transition point and cause; closed loop configuration, reduced bowel enhancement or associated free fluid should lower the threshold for urgent surgery. CT is recommended because it provides information on cause, severity and bowel viability that plain radiography cannot reliably provide.

Keep fasting, establish IV access and correct intravascular depletion with balanced crystalloid. Replace potassium, chloride and magnesium according to measured deficits. Monitor urine output in significant dehydration.

Insert a nasogastric tube when there is persistent vomiting, significant gastric distension or high grade obstruction. Routine decompression is less important in a comfortable patient with mild partial obstruction and little vomiting, but aspiration risk must be considered.

A patient without peritonitis, strangulation, ischaemia or another surgically correctable emergency can undergo an initial trial of nonoperative management with:

• Bowel rest
• IV fluid and electrolyte replacement
• Nasogastric decompression when indicated
• Serial abdominal examination
• Repeat physiological and biochemical assessment

Antibiotics are not routinely required for uncomplicated mechanical obstruction.

Operate without delay for generalised peritonitis, suspected strangulation, bowel ischaemia, perforation, a closed loop with threatened bowel, incarcerated hernia that cannot be safely reduced, or progressive clinical deterioration.

For adhesive obstruction without emergency features, a water soluble contrast challenge is useful. Passage of contrast into the colon within about 24 hours strongly predicts resolution. Failure of contrast to reach the colon suggests a high likelihood of failure of conservative treatment.

Most uncomplicated adhesive obstructions that will resolve do so within the first few days. WSES considers approximately 72 hours a reasonable upper limit for a monitored conservative trial when the patient remains clinically stable. Continuing beyond this requires strong justification and repeated reassessment.

At surgery, treat the cause, release the obstruction and assess bowel viability. Adhesiolysis alone is sufficient when bowel is viable. Resect frankly necrotic or perforated bowel. Primary anastomosis is reasonable when perfusion is good and physiology and contamination are acceptable. Severe shock, heavy contamination or questionable bowel viability may favour diversion or staged surgery.

Laparoscopy is appropriate in selected patients, particularly suspected single band obstruction with limited distension. Markedly dilated bowel, complex adhesions and multiple previous laparotomies increase enterotomy risk and may favour an open approach.