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large bowel obstruction

Written by Aw Pei Ying Amanda Aw

Last Reviewed: September 2019

Review Due: September 2020

 

DEFINITION1

‘a partial or complete mechanical interruption to the flow of large bowel contents’

 

AETIOLOGY1,2

Can be classified in terms of intraluminal, intramural or extraluminal causes. The most common causes for large bowel obstruction are marked with an ‘*’

Intraluminal 

  • Constipation

  • Foreign bodies

 

Intramural

  • Malignancy* (90% of large bowel obstructions) 

  • Diverticular strictures*

  • Crohn’s disease (strictures) 

  • Other benign strictures (radiation-induced, ischaemic, anastomotic) 

 

Extraluminal 

  • Adhesions 

  • Sigmoid volvulus*

  • Caecal volvulus*

  • Pelvic abscess

  • Gynaecological neoplasms

  • Endometriosis

SIGNS AND SYMPTOMS1-4

The four cardinal symptoms of intestinal obstruction are pain, distention, vomiting and absolute constipation (i.e. the inability to pass solid or gas via the rectum). Other signs and symptoms largely depend on whether it is a complete or incomplete obstruction, the patency of the ileocaecal valve and the presence of complications (strangulation or perforation).

 

Symptoms 

  • Pain 

    • Typically referred to hypogastrium (from hindgut origin) 

    • Colicky – initially due to increased peristalsis to overcome obstruction

    • Constant & diffuse – with further distention and reduced peristalsis

    • If severe, suspect strangulation or perforation

  • Distention (late feature)

  • Vomiting (late feature or if the ileocaecal valve is incompetent)

  • Absolute constipation

    • “absolute” = no faeces or flatus, “relative” = flatus passed only 

    • NB: bowel contents distal to the obstruction may still be passed initially, thus confusing the clinical picture 

 

Signs

  • Empty rectum (PR is mandatory) 

  • Tympanic abdomen 

  • Bowel sounds (hyperactive initially but may be absent in advanced obstruction)

  • Palpable abdominal mass or hernial orifices

Red Flags

These features suggest a complicated obstruction (perforation or strangulation) that require urgent senior review and surgery:

  • Shock 

  • Severe localised tenderness/peritonism (impending perforation)

  • Severe tenderness & rigidity (peritonitis secondary to perforation)

 

PATHOPHYSIOLOGY1,2,4

Mechanical obstruction results in the dilatation of the proximal large bowel, leading to an increase in intraluminal pressure. Initially, this causes reduced mesenteric venous outflow and mucosal oedema, causing the transudative loss of fluids and electrolytes into the proximal bowel lumen. This causes severe dehydration and electrolyte imbalances. The bowel wall progressively becomes ischaemic as arterial blood supply becomes compromised with further oedema and mucosal ulceration, predisposing to bacterial translocation and septic complications. The ischaemic bowel wall is also prone to perforation that results in faecal peritonitis.

 

Sigmoid or caecal volvulus occurs due to the rotation of the colonic segment on its mesentery. Following a complete 360-degree twist, closed loop obstruction occurs.

 

Closed loop obstruction also occurs in the presence of a distal obstruction with a patent ileo-caecal valve (ie. competent valve). This further increases the intraluminal pressure and causes caecal perforation (due to the Law of Laplace where the maximal tangential pressure occurs where the maximum radius is – the caecum having the largest diameter). Occasionally, the ileo-caecal valve is incompetent and this allows automatic decompression of colonic contents into the ileum which causes vomiting. An NG tube for decompression will be useful when the ileo-caecal valve is incompetent, but serves no therapeutic purpose when it is competent.

 

Investigations

laboratory1

FBC

Can show raised WBC in perforation or anaemia in possible malignancy 

U&E

Monitor for dehydration and electrolyte imbalances and assess baseline renal function

LFTs

Amylase 

Group & Save (if planning for emergency surgery)

imaging1

Abdominal X-Ray

  • Features to look for a plain abdominal radiograph include:

    • Dilated large bowel loops in the periphery with haustrations (see 3-6-9 Rule box)

    • “Coffee-Bean Sign” showing a sigmoid or caecal volvulus 

    • Distal colon or rectum empty of gas 

    • Free gas (if perforated) 

Erect CXR

  • May show sub-diaphragmatic free gas in the case of bowel perforation 

CT Abdomen/Pelvis with IV Contrast

  • Useful in identifying the location and cause of obstruction +/- free gas 

  • May be useful for staging in colonic adenocarcinoma

N.B: A contrast enema is contraindicated in suspected perforation or peritonitis

3-6-9 rule

 

Normal bowel diameter on abdominal x-ray is:

  • <3cm for small bowel

  • <6cm for large bowel

  • <9cm for caecum

Above this, the bowel should be considered dilated, possibly secondary to an obstruction.

treatment

supportive1-4

  • IV access and IV fluids (due to fluid and electrolyte loss)

  • Urinary catheter (monitor fluid balance) 

  • IV analgesia 

  • Keep NBM 

  • NG tube ‘drip and suck’ (though of no therapeutic value in providing bowel rest during closed-loop obstruction)

  • Supplemental oxygen

  • IV antibiotics (due to risk of bacterial translocation) 

  • Liaise with stoma nurse to mark stoma site pre-op (most LBOs often require emergency surgery)

N.B: Laxatives should not be prescribed in acute obstruction, due to risk of perforation.

emergency surgery1,2

Indications for emergency surgery include strangulation and perforation. In comparison to a small bowel obstruction, the threshold for surgery is lower in a large bowel obstruction.

Resectable 

  • Right-Sided 

    • Right hemicolectomy with stoma or primary anastomosis 

  • Left-Sided 

    • Left hemicolectomy with stoma (Hartmann’s) or with mucous fistula or primary anastomosis (with on-table colonic lavage) 

 

Non-Resectable 

  • Right-Sided

    • Diverting proximal stoma 

    • Ileo-transverse bypass

  • Left-Sided

    • Diverting transverse loop colostomy 

  • Endoscopic Stenting 

    • Palliative procedure or bridge to surgery in acute obstruction

volvulus1

Sigmoid Volvulus 

  • Endoscopic detorsion and decompression (flexible sigmoidoscopy + insertion of flatus tube)

Caecal Volvulus 

  • Operable 

    • Resection +/- ileostomy (non-viable colon)

    • Caecopexy +/- caecostomy and appendicostomy (viable colon) 

  • Inoperable 

    • Colonoscopic or percutaneous decompression

 

differentials1-4

The main differential diagnosis in patients presenting with features of a large bowel obstruction is Acute Colonic Pseudo-Obstruction, which is characterised by large bowel distension in the absence of a mechanical obstruction.

It cannot be distinguished from a true obstruction on a plain radiograph and requires a rectal contrast enema or CT with rectal contrast.

 
 

EPIDEMIOLOGY1-4

Bowel obstruction represents 5% of emergency admissions in the UK, with colorectal cancer accounting for the majority of cases. Large bowel obstructions are less common than small bowel obstructions.

 

REFERENCES

  1. Malietzis G, Jenkins JT. Large bowel obstruction. BMJ Best Practice.

  2. Bailey & Love’s Short Practice of Surgery. 27th Edition.

  3. Oxford Handbook of Clinical Medicine. 9th Edition (2017). 

  4. Feltbower S. Bowel obstruction. RCEM Learning.