Pseudo-Obstruction

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DEFINITION

Function dilatation of the large intestine in the absence of a mechanical obstruction.

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EPIDEMIOLOGY

Risk Factors

Often the elderly
M>F
Many hospitalized already.
- e.g. trauma (~20%),
- obstetric / pelvic procedures (20%)
- sepsis (10%), cardiac (10%), neuro (10%).
Rarely develops spontaneously.
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AETIOLOGY

See below
Orginally described by Ogilvie on the basis of tumour invasion of the retroperitoneal sympathetic nerve bed at the coeliac plexus

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BIOLOGICAL BEHAVIOUR

Pathophysiology

Imbalance of autonomic input to the colon.
Probably sympathetic over-activity and/or parasympathetic suppression
Yields an adynamic functionally-obstruction distal colon and a relaxed proximal colon.

Complications

Can be so intense that R colon distends and becomes ischaemic and perforates;
As per La-Place's law.
Extreme distension can result in abdominal compartment syndrome.
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MANIFESTATIONS

Distention, tympany, anorexia
Possibly nausea and vomiting, constipation / diarrhoea
Can be tenderl
Bowel sounds variable and unhelpful.
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INVESTIGATIONS

AXR
CT very helpful
Constrast enema very helpful and can be therapeutic

Elevated WCC supports ischaemia
Electrolyte derangement common and should be corrected.

Rule out infectious / inflammatory causes
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MANAGEMENT

Conservative

Serial observation
Fasting
Electrolyte correction
Cessation of narcotics and anticholinergics
Nasogastric rarely helps
Rectal tube overall not been proven helpful

Medical

Consider if lack of progress

Neostigmine 2 mg IV
Reversible anticholinesterase inhibitor.
- interferes with breakdown of acetylcholine; indirectly stimulates nicotinic and muscarinic receptors
--> parasympathomimetic; relaxes the offending colon segment
Often works within a few minutes.
- side effects include bradycardia, bronchospasm, salivation, nausea, cramps.
--> monitoring (+30 min after) and close surveillance.
--> atropine (1 mg) dose should be at hand in case of bradycardia
Works in the majority but 40% need a second dose
Contraindicated if:
-  perf suspected, HR<60, BP <90 or heart block without pacer, bronchospasm, pregnancy, significant renal failure 

Gastrograffin
Enema may be therapeutic with hyperosmolar contrast medium promoting peristalsis.

Colonoscopy

Consider if neostigmine ineffective

Careful colonoscopy to decompress a grossly distended caecum
Successful in >50% but repeat scopes may be reqd.
Limit insufflation; perf rate ~2%

PEG
Daily dose may promote resolution - one small trial.

Operative

Indications:
- suspected perf
- caecal diameter >12cm

If caecum perforates

--> R hemicolectomy; NOTE functional obstruction is in the L colon... no primary anastomosis.
--> Fashion an end-ileostomy, bring out distal end through same hole, forming a double-barrell stoma.
If med Rx fails, producing abdominal compartment syndrome (very unusual).

If failure of medical management

No signs of recovery in 5-6 days, consider laparotomy.
Operation depends on stability and operative findings.
Most commonly colostomy or ileostomy with our without mucous fistula.
Must consider total abdominal colectomy if disease extent severe.

If physiologically frail:

--> caecostomy
- percutaneous or guided by CT / endoscopy / laparoscopy.
- messy and has a high incidence of problems like leak around it and abdo wall cellulitis
- use a soft, large-bore tube and surround its site with double purse-string sutures
- carefully attach it to the abdominal wall.
--> tend to obstruct and need regular flushing.
- an alternative is a formal 'matured' caecostomy
--> exteriorize a portion of caecum and suture it to surrounding skin.
--> can be performed in local anaesthesia in medically ill patients.

Prognosis
80% resolve
Mortality very high with perforation; ~50%
Mortality rates overall of >10% are not uncommon in context of these patients.

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REFERENCES
Cameron 10th
Shein 3rd

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