Pseudo-obstruction

Clinical and radiological appearance of mechanical colonic obstruction in the absence of a discrete obstructing lesion.

• AKA 'Ogilvie's syndrome' named in 1948

Epidemiology

• Typically seen in hospitalised patients with some sort of acute illness and at least one of the below associations

Associations

• Post-surgical: occurs post-surgically in abdominal/orthopaedic procedures, average onset 4/7 post-op
• Neurologic disease:
  • Parkinson's disease
  • Alzheimer disease
  • Stroke
  • Spinal cord injury
• Cardiac
  • CCF
  • MI
• Pulmonary
  • COPD
• Trauma
  • Major trauma
  • Shock
  • Burns
  • Retroperitoneal haematoma
• Metabolic
  • Diabetes
  • Renal failure
  • Electrolyte disturbances
  • Hyperparathyroidism
  • Uraemia
• Infectious
  • CMV
  • VZV
• Obstetric
  • LUCS (especially right colon)
  • Normal and instrumental delivery
• Miscellaneous
  • SLE
  • Scleroderma
• Drugs
  • Opiates
  • Chemotherapy
  • Anti-Parkinson drugs
  • Anticholinergics
    • TCAs including amitriptyline have strong anticholinergic properties
  • Antipsychotics
  • Clonidine

Pathophysiology

• Hypothesised to involve dysregulation of the colonic autonomic innervation
• Possible relative excess of sympathetic over parasympathetic activity, disrupted colonic reflex arcs, chronic disease, and medications

Presentation

• Distension, pain, nausea, vomiting
• Obstipation is common, but some patients will have diarrhoea due to hypersecretion of water
• Exam:
  • Tympanic abdomen
  • Bowel sounds usually present
• Systemic toxicity or peritoneal signs should raise concern for impending ischaemia or perforation
  • Leucocytosis
  • Fever
  • Caecum >12cm
  • Tenderness/peritonism

Diagnosis

• Differential:
  • Acute mechanical obstruction
  • Chronic intestinal pseudo-obstruction
  • Toxic megacolon
  • Pseudomembranous colitis
  • Adult Hirschsprung disease
• CT typically demonstrates dilated proximal colon with sparing of distal colon, however sometimes extends to rectum
  • Contrast enemas not recommended according to some sources- risk of precipitating complications
  • However some surgeons do ask for them
• AXR useful in monitoring

Management

• Principles
  • Need to resolve colonic dilatation to prevent perforation (risk increases markedly >12cm)
  • Deploy gradually escalating interventions contingent upon the degree of distension
• Treat underlying causes aggressively

Initial supportive care (successful in 70-90%)

• • Bowel rest + IVF
    • NBM or with trophic enteral feeds is standard
  • Electrolytes - aim potassium >4 and magnesium >1
  • Review medications - minimise opiates, anti-diarrhoeals, anticholinergics, antipsychotics, CCBs
  • NGT does not have clear data to support efficacy
  • No oral aperients
  • Mobilise/SOOB/regular repositioning
    • Can alternate between knee-chest, supine, prone, lateral decubitus
  • Serial x-rays (daily)
    • Main parameter is caecal diameter
    • 7% risk of perforation with diameter 12-14cm; 23% risk with diameter >14cm; 0 risk with diameter <12cm
  • Some surgeons give prokinetics. Note there are multiple RCTs showing no change to colonic motility after metoclopramide/erythromycin, and cisapride is dangerous.
  • Fleet enemas are very commonly given as BD (I can't find evidence for or against it, apart from textbooks saying to be careful with enemas, but supported by Schein)
  • If thinking about neostigmine in next few days, stop the beta blockers early (if possible)

Neostigmine

• • Useful if patients fail to improve after 24-48 hours, or have caecum >12cm (both groups are higher risk for perforation)
  • Potent acetylcholinesterase inhibitor that enhances colonic motor activity
  • Efficacy 60-100%
  • 2mg stat IV (give less if renal impairment), injected over 3-5 minutes, normally 30 mins to effect
  • Can trial second dose after 24 hours
  • Seems to work especially well in post-op patients who develop pseudo-obstruction
  • Contraindications
    • Recent cardiac event
    • HR <60 or BP < 90
    • Acidosis
    • Pregnancy
    • Beta blocker therapy
    • Peritonitis/mechanical obstruction
    • Caution patients with asthma/COPD, cardiac issues, CKD/AKI
  • Adverse effects:
    • Bradyarrhythmias 5-10% - therefore needs continuous cardiac monitoring and atropine available
    • Bronchoconstriction, hypotension, agitation, abdo cramps, diaphoresis
    • Can sometimes give glycopyrrolate 0.4mg to attenuate these effects
  • Success rates 60-94%, with 31% having a recurrence requiring more neostigmine

Pyridostigmine

• • Acetylcholinesterase inhibitor that can be given PO and does not require a monitored environment
  • Note, this is a slightly off-label use, although it seems to be becoming more common, and is supported by UTD
  • ECG prior to exclude arrhythmia
  • Avoid if HR<60
  • Onset 16 minutes, duration 6 hours
  • Can cause mild anticholinergic side effects, although these were only seen 4.3% of patients in a 2023 ANZJS systematic review
  • Dose 60-540mg daily in chronic pseudo-obstruction
  • I think 60mg BD is a reasonable starting dose for acute pseudo-obstruction

Endoscopic decompression

• • Perforation 2-3% - needs to be an experienced endoscopist
  • Don't need to prep
  • Minimise insufflation
  • If can't reach caecum, hepatic flexure is usually sufficient
  • Decompression alone is effective in 50%, which can be increased by placement of a rectal tube
  • Rectal tube placed on low intermittent suction and flushed every 6 hours, and remove after 72 hours if not manually dislodged with return of peristalsis
    • Especially useful for patients with unmodifiable contributing factors which are going to persist
  • If subtle signs of ischaemia are found in the bowel, but the patient is generally not unwell, may be ok to decompress and watch, without adverse sequelae

Percutaneous caecostomy

• • Useful in patients with very high perioperative risk, and failing other treatment
  • Placed endoscopically or radiologically

Surgery

• • Indicated with failed supportive care, neostigmine, and endoscopic decompression; or peritonitis
  • Mortality 30-60%
  • Operation determined according to the condition of the colon and the patient
    • If perforated - laparotomy with subtotal/total colectomy, with either primary anastomosis or stoma, but probably should have stoma
    • Percutaneous 'blowhole' caecostomy can be considered (supported by Schein if other measures fail)
    • Loop transverse colostomy may be a good choice to retain colon function but allow decompression too

Chronic intestinal pseudo-obstruction (CIPO)

• May need to be on liquid diet long-term (perhaps due to co-existing gastroparesis)
• UTD suggests prucalopride 2-4mg daily as first choice, followed by pyridostigmine