Small Bowel Obstruction

DEFINITION
SBO.

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INCIDENCE
Common surgical emergency.
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AETIOLOGY

Congential
Adhesion bands, imperforate anus, meconium in mucoviscoidosis.

Acquired
Herniae (second most common)
- ventral, inguinal, femoral, internal.
Intussusception.
- more common in kids. 
- generally a lead point in adults, e.g malignancy
- operation generally reqd.
Volvulus.
Inflammatory strictures
Neoplasms internal or external to bowel wall.
Foreign bodies.
Gallstone ileus.
Ischaemia.
Superior mesenteric artery syndrome.
Adhesions (most common).
- most usually within 1 year of initial laparotomy.
- 2/3 in initial postop period
Radiation enteritis.
Trauma
- haematomas; can be very slow to resolve, but be patient.

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BIOLOGICAL BEHAVIOUR

Pathophysiology
Fluid and gas rapidly accumulate proximal to the obstruction site.
Peristaltic activity declines after a few hours.
Stasis and bacteria make fluid feculent.
Fluid is rapidly lost into the bowel.
Presentation depends on site and elapsed time and severity

Natural History
1/4 will need surgery in index admission
Patients undergoing initial operative management will get fewer recurrences.

Complications
Ischaemic.
Then perforate.
If there is closed loop obstruction, urgent laparotomy - high risk of perforation.
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MANIFESTATIONS

Symptoms
 The more proximal the obstruction, the earlier they present.
2-3 day symptom complex for distal obstructions.

Local
'Colic'
Can't get comfortable,
Cramping.
Relaxes when spasm subsides - disappears altogether for a time.
- typically lasts 1-2mins, with several minutes between.
Nausea and vomiting
- food to start, later green/brown.
- time to vomiting relates to site of obstruction.
- if feculent, confirms the diagnosis.
Not passing flatus or faeces unless partial.
Abdominal distension.

Complications
Onset of bowel ischaemia heralded by constant severe pain, fever, tachycardia, tenderness and guarding.
- only partly relieved by analgesia, becoming systemically unwell.

Other
Features of supervening pathology, eg herniae pain (presents early).

Metabolic Derangement
Gauge degree of dehydration and electrolyte derangement.

Signs

Observe
Search for scars, herniae, masses.

Palpate
Rebound tenderness.
Rising pulse rate.
(Both esp if strangulated).

Percuss
Resonant abdomen.

Auscultation
Tinkling, active, high pitched.
Later absent, indicating secondary ileus.

Is there ischaemia?
Experienced clinicians are wrong 50% of the time and all features and tests are soft
Be particularly concerned in any patient with escalating need for narcotics

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INVESTIGATIONS

Imaging
AXR
1. Is there an obstruction?
Supine film is usually enough.
- erect adds little of extra value, though fluid levels helpful.
- dilation = >4cm
- colonic gas may indicate partial or early obstruction
- if both small and large bowel distended, ?LBO with incompetent iliocaecal valve / ?pseudo-obstruction.

2. Where?
String of pearls / stepladder distribution of air-fluid levels on AXR
Look for air in biliary tree - ?gallstone ileus.

3. Strangulated?
Suggested clinically.
- oedematous small bowel loops can suggest ischaemia, difficult to diagnose.

CT
Shows obstruction and elucidates the cause.
Oral and IV contrast if possible.
- can give fluids and NAC 400mg qid for IV if reqd.
High sensitivity for closed loops, strangulation and perforation
- lower for ischaemia.
--> signs include wall thickening, free fluid or pneumatosis

US
In pregnancy, perhaps.

Other
Contrast studies dangerous.
Small bowel studies
- non-op management, no signs of obstruction but failing to resolve (gastrograffin).
Enteroclysis

Biochemistry
In protracted cases
- hypokalaemia, hypochloraemia and metabolic alkalosis develop.
- concomitant paradoxic aciduria
FBC may show WCC elevated if impending bowel ischaemia.
Lactate.
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MANAGEMENT

Decision Making
Judgment to operate depends on several factors
- aetiology, presentation, prior surgical history, partial vs complete, timing etc.
Differentiate dysmotility and ileus
Patients with recurrent or partial obstructions likely to resolve and deserve trial of non-op management
- be patient and avoid entering a hostile abdomen, even requiring TPN if necessary.
Complete or high-grade = more likely to need surgery.
Generally 1-5 days depending on 1st or recurrent presentations etc.
- operate on complete obstructions after 24h if first presentation
- wait even longer that 5d if multiple operations, TPN if reqd.

Management

1. Drip and suck.
NG tube
- decompress if vomiting.
- converts to an open obstruction
- unabated intraluminal distension leads to mucosal ischaemia = bad.
IV Fluids
- huge amounts lost into bowel (osmotic effect), and vomited out.
--> large volume resuscitation of several litres volume likely to be required.
Analgesia

2. Monitor vital signs, urine output

3. Gastrograffin Challenge.
100ml in NG tube then clamped.
Plain XR after 4-6h
- does not reduce need for surgery
- but does shorten hospital stay (resolves pts managed non-operatively faster).
- will force obstruction to declare itself
- often given at admission, then repeat XR in morning shows status of gut, can help inform operative decision making.

4. Operate to find cause and relieve obstruction
- required in ~20%; higher in 1st presenters.
- immediate if herniae or impending ischaemia / peritonism, otherwise often delayed a short period for resuscitation.
- ie act urgently if severe uncontrolled pain, peritonism, raised WCC: significant risk of ischaemia.
- if there is no previous intra-abdo surgery, there is less likelihood of obstruction conservatively settling.

Previous malignancy
Known recurrent / major disease - non-op therapy preferred.
- but if persists, 2/3 will have an easily fixable lesion
- 1/3 will have carcinomatosis: very difficult to ascertain with imaging.
Disease more likely if obstruction develops soon after primary operation.

Early post-op obstruction
Usually settle conservatively
Timing of re-operation critical
Beware that adhesions are vascular, cohesive and thickened in the 10-30d postoperative window.

Operative Principles

1. Enter abdomen through virginal midline area if possible
- access peritoneal space with care.

2. May not even have a defined point of obstruction
- careful adhesiolysis often therapeutic.

3. Relieve and treat as per cause

4. Completely evaluate bowel viability
- if uncertain, be patient, wet, warm, packs, have a coffee break for 10minutes then reevaluate
- described using Doppler and fluorescein to test viability
But probably easier to resect (if limited) or relook (if extensive)

5. Decompress?
- absolutely minimally to enable closure of abdomen.

Laparoscopic?
Relatively contraindicated in massive distension, multiple laparotomies or peritonitis.
Atraumatic graspers, and proceed.

Adhesion prevention
Many have been studied, including fibrinolytics, steroids, NSAIDS
- none have worked.
Bioresorbable membranes hold the most promise
- e.g seprafilm
- thin transparent films
Effective in preventing adhesions to intra-abdominal surfaces
Cochrane review: decrease adhesion severity but no effect on rate of SBO or need for re-operation.
- main point of use is probably easier re-entry ... weak.


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References
Hill, J.  Surgical Emergencies.
Cameron 10th