Question 7

College answer

a)

Plain films: - Identical to mechanical obstruction: dilated bowel loops: may have fluid levels CT demonstrates dilated large bowel without a clear transition point or obstructing lesion.

b)

Trauma, especially fractures 

Recent surgery, especially involving spinal anaesthesia 

Burns 

Diabetes Mellitus

Uraemia

Severe medical illness, such as pneumonia, myocardial infarction, or heart failure 

Neurologic conditions 

Chemotherapy (e.g., all-trans retinoic acid, methotrexate, vincristine) 

Retroperitoneal pathology, such as malignancy or haemorrhage 

Electrolyte disturbance 

Medication (e.g., narcotics, phenothiazine’s, calcium channel blockers, alpha-2-adrenergic agonists, epidural analgesics)  

c)

Initial management of acute colonic pseudo-obstruction consists of conservative therapy in patients without significant abdominal pain or signs of peritonitis and those who have one or more potential factors that are reversible.  

Treat underlying disease, stop aggravating drugs, avoid laxatives, and keep NPO. NG tube – encourage mobility. Consider opiate reversal agents e.g. GI naloxone or SC Naltrexone

If fail or progress consider neostigmine:  In patients with caecal diameter >12 cm (varies) or failure of 24 to 48 hours of conservative therapy. Up to 2 mg slow IV and repeat if needed. Lower doses may also be effective. Studies have shown high response rate with low rate of recurrence. Side effects include abdominal pain, hypersalivation, vomiting and bradycardia. Perforation may occur if there is unrecognised mechanical obstruction.

Colonoscopy decompression: Those patients who fail or who have contraindications to neostigmine. Technically difficult and perforation is a risk. No randomised trials.

Surgery: In the absence of a colonic perforation, cecostomy tube or a segmental or subtotal resection with primary anastomosis can be performed. In the patients with a colonic perforation, a total colectomy, ileostomy, and Hartmann procedure are performed to retain the option of future ileorectal anastomosis

Examiners Comments:

Management plan poorly structured in many cases. Overall reasonably well answered.

Discussion

a)

Radiological features of colonic pseudo-obstruction:

• Plain radiography: findings identical to mechanical obstruction, i.e. dilated bowel loops
• CT findings: gaseous dilatation of the colon with no stricture, mass or clear transition point. A "smooth transition" may be seen, which is a slight discrepancy in diameter between the proximal and distal bowel loops - less than 50% (Choi et al, 2008).

b)

The list of risk factors for colonic-pseudo-obstruction specifically is derived from Saunders et al (2005) and Wells et al (2017):

• Surgical: Cardiac surgery, solid organ transplantation, major orthopaedic surgery, spine surgery
• Cardiorespiratory    Shock, myocardial infarction, congestive heart failure, chronic obstructive pulmonary disease
• Neurological    Dementia, Parkinson’s disease, Alzheimer’s disease, stroke, spinal cord injury
• Metabolic    Electrolyte imbalance, diabetes, renal failure, hepatic failure
• Medications    Opiates, anti-Parkinson agents, anticholinergics, antipsychotics, cytotoxic chemotherapy, clonidine
• Obstetric/gynaecological    Caesarean section, normal vaginal delivery, instrumental delivery, preeclampsia, normal pregnancy, pelvic surgery
• Infectious    Varicella-zoster virus, herpes virus, cytomegalovirus
• Miscellaneous    Major burns/trauma, severe sepsis, idiopathic

For ileus and constipation in general, you would expect the following risk factors:

Modifiable ICU-related risk factors

• Delayed enteral nutrition (delayed for longer than 24 hrs) - although early enteral nutrition has also been blamed, and in fact in ICU patients nasogastric nutritional formula is at least as likely to cause constipation as diarrhoea ( Montejo et al, 1999).
• Reduced mobility
• Deep sedation
• Heavy opiate use
• Anticholinergic drug side effects
• Calcium channel blockers
• The use of paralysing infusions
• Electrolyte disturbance, eg.hypokalemia hypercalcemia and hypomagnesemia
• Dehydration, inadequate fluid resuscitation (or excess diuresis)
• Hypotension (SBP under 90mmHg - Gacouin et al, 2010)
• Hypoxia (P/F ratio under 150 - also Gacouin et al)

Non-modifiable disease risk factors

• Abdominal surgery
• Severe illness
• Paralysis (eg. spinal cord injury) 
• Prior alcohol or cannabis use
• Nicotine withdrawal

c)

Most of this comes from Saunders et al (2005). Options for management of colonic pseudo-obstruction can be divided into categories:

Supportive

• Nil by mouth
• Correct electrolytes
• Ensure the patient is well-hydrated
• Nasogastric tube on free drrainage or low wall suction
• Rectal tube to gravity drainage
• Limit anti-motility medications, such as opiates and anticholinergic agents
• Mobilise the patient and sit them out ouf bed

Pharmacological (pro-motility) management

• Oral or nasogastric naloxone
• Methylnaltrexone
• Enema
• Erythromycin
• Neostigmine

Interventional (decompressive) management

• Sigmoidoscopy
• Colonoscopy 
• Surgical decompression
• Caecostomy 
• Colectomy, ileostomy, and Hartmann procedure