bowel obstruction

• The most common causes of mechanical bowel obstruction are:

  • Adhesions - most common cause of small bowel obstruction
  • Hernias
  • Tumours - most common cause of large bowel obstruction

  Causes of mechanical obstruction can be divided extrinsic (outside of the bowel wall), mural (affecting the layers of the bowel wall) or intraluminal (within the bowel lumen).
• Other causes of bowel obstruction:

  • Volvulus - large bowel
  • Diverticular disease
  • Strictures - e.g. secondary to Crohn's disease
  • Intussusception - in young children
• A small bowel obstruction on an x-ray will have a stacked coin appearance - valvulae conniventes

  Air fluid level under the diaphragm on an erect x-ray
• Typical symptoms of bowel obstruction include:

  • colicky, cramp-like abdominal pain
  • Abdominal distention
  • Generalised abdominal pain
  • Nausea and vomiting - usually green bilious vomiting
  • Absolute constipation and lack of flatulence
  • Tinkling bowel sounds in early obstruction or absent bowel sounds in late obstruction
• The large bowel can be distinguished on an x-ray by the presence of haustra which stretch part way across the diameter of the bowel loops
• important areas to cover in the history include:

  • Features suggestive of malignancy: anaemia, altered bowel habit, rectal bleeding, weight loss
  • History of previous abdominal surgery, inflammatory bowel disease, diverticulitis or appendicitis
• Adhesions are pieces of scar tissue that bind the abdominal contents together. They can cause kinking or squeezing of the bowel, leading to obstruction. Adhesions typically cause obstruction in the small bowel, rather than the large bowel. 

  The main causes of intestinal adhesions are: 

  • Abdominal or pelvic surgery (particularly open surgery)
  • Peritonitis 
  • Abdominal or pelvic infections (e.g., pelvic inflammatory disease)
  • Endometriosis
• Closed-loop obstruction describes a situation where there are two points of obstruction along the bowel; meaning that there is a middle section sandwiched between two points of obstruction.

  A competent ileocaecal valce does not allow any movement back into the ileum from the caecum - causing a closed loop obstruction. The closed-loop section will continue to expant and leaf to ischaemia and perforation
• A volvulus is defined as a twist of a segment of the bowel around its mesenteric attachment. The sigmoid colon and caecum are the most common areas volvulus occurs
• Intussusception is a paediatric surgical emergency that occurs when a section of the bowel telescopes into its neighbouring distal section, causing bowel obstruction. The most common site is the ileocaecal valve 
• Intussusception most frequently occurs in children aged four to eighteen months and is slightly more common in boys
• The typical triad of symptoms of intussusception:

  • Intermittent, severe abdominal pain
  • Vomiting
  • Redcurrant jelly stool
• Intraluminal causes of bowel obstruction:

  • Foreign bodies
  • Gallstone ileus
  • Faecal impaction
• • Abdominal X-ray: may demonstrate signs of bowel obstruction, including dilated bowel loops with air-fluid levels 
  • CT abdomen & pelvis with IV contrast: the standard of care to confirm the diagnosis and assess the anatomical site, severity, underlying aetiology and complications
• The initial measures for managing bowel obstruction are colloquially referred to as ‘drip and suck’:

  • Drip: intravenous fluids
  • Suck: nil-by-mouth and nasogastric tube insertion
• • Management with surgery indicated in the case of complications, closed-loop obstruction or failed conservative management
• 3/6/9 rule:

  • Small bowel > 3cm
  • Large bowel > 6cm
  • Caecum > 9cm
  • Suggests obstruction
• Sigmoid volvulus:

  • Longstanding chronic constipation
  • Hugh sigmoid loop comes twisted on its mesenteric pedicle - creates closed loop obstruction
  • Venous infarction - can lead to perforation and peritonitis
  • Abdominal distension, absolute constipation
  • Erect AXR - coffee bean sign
  • Flexible sigmoidoscopy - inset flatus tube
  • Last resort - sigmoid colectomy
• Causes:

  • Extrinsic: adhesions (SBO), hernias (SBO) and volvulus (LBO)
  • Mural: tumours (most common cause of LBO), inflammatory strictures (IBD, diverticulitis), intussusception and radiation
  • Intraluminal: foreign bodies, gallstone ileus and faecal impaction
• Functional/pseudo-obstruction:

  • Thought to be related to impairment of the autonomic nervous system e.g. in patients with infection, metabolic disturbances, neurological disorders
  • Medications: opiates and anti-depressants
  • Treatment: correct electrolyte abnormalities, discontinue anti-kinetic drugs e.g. metoclopramide and treat underlying cause
• Signs on exam:

  • Abdominal distension
  • Generalised abdominal tenderness
  • High-pitched or tinkling bowel sounds (early obstruction)
  • Absent bowel sounds (late obstruction)
  • Evidence of underlying cause e.g. scars from previous surgery, obvious hernia
• Adhesions:

  • Scar tissue that bind the abdominal contents together - kinking or squeezing of the bowel
  • Typically causes SBO
  • Abdominal or pelvic surgery
  • Peritonitis
  • Abdominal or pelvic infections e.g. PID
  • Endometriosis
• Initial supportive care:

  • Usually for adhesional SBO (absence of ischaemia or perforation)
  • Drip and suck
  • NBM - bowel rest to reduce peristalsis
  • IVI - maintain hydration and correct any electrolyte disturbance
  • NG tube with free drainage - decompress bowel, relieve distension and vomiting, reduces risk of aspiration
  • Catheterisation
  • Analgesia
  • Antibiotics if perforation
• Once the bowel segment has become occluded, gross dilatation of the bowel occurs. There becomes an increased peristalsis of the bowel, which in turn leads to secretion of large volumes of electrolyte-rich fluid into the bowel (often termed ‘third spacing’). Urgent fluid resuscitation and a careful fluid balance is required.
• Definitive management:

  • Adhesions: water soluble contrast study
  • Sigmoid volvulus: flatus tube insertion via sigmoidoscopy
  • Tumour: endoscopic stenting or surgical resection
  • Stricture: dilation or placement of stent
• Indication for emergency laparotomy:

  • Complicated bowel obstruction - perforation or ischaemia
  • Closed loop obstruction
  • Strangulated hernia
  • Obstructing tumour if not amenable to stenting
  • Failure of non-operative treatment
• Complications:

  • Ischaemia
  • Perforation - leading to faecal peritonitis
  • Severe fluid depletion - AKI and other end-organ injury
• Sigmoid volvulus risk factors:

  • Those with chronic constipation as this slows GI tract transit and patient develop a redundant sigmoid colon (longer than normal) which is more likely to twist on itself
  • Old age
  • Reduced mobility
  • Institutionalised people
  • Neurological conditions e.g. Parkinson's
• Management of caecum volvulus is with right hemicolectomy
• Management of sigmoid volvulus:

  • Supportive: fluids, NG tube
  • Conservative - try to decompress with sigmoidoscope, if successful there will be a rush of air and liquid faeces so pass a flatus tube and leave for 24 hours
  • Surgical management with Hartmann's procedure if can't decompress, any evidence of ischaemia or perforation, or if recurrent episodes