Bowel obstruction

Introduction

• Small bowel has circumferential plicae circulares and located medially
• Large bowel is peripherally located with haustra
• Haustra are less numerous and spread further apart than plicae circulares

Common causes

• Duodenum
  • Stenosis
  • Foreign body (bezoars)
  • Stricture
  • Superior mesenteric artery syndrome
• Small bowel
  • Adhesions
  • Hernia
  • Intussusception
  • Lymphoma
  • Stricture
• Colon
  • Carcinoma
  • Faecal impaction
  • Ulcerative colitis
  • Volvulus
  • Diverticulitis (Stricture, abscess)
  • Intussusception
  • Pseudo-obstruction

Ileus vs. mechanical

Small bowel obstruction

• Most commonly due to adhesions
• Can arise weeks after surgery but usually months/years
• Second most common is groin hernia
  • Elderly females particularly susceptible to femoral or obturator hernias, which may present with femoral or medial thigh pain
  • Mesenteric hernia can also arise (esp. marathon runners)
• Bariatric surgery can lead to Roux-en-Y hernias
• Primary small bowel adenocarcinomas, polyps, lymphoma
• Hamartomatous polyps (Peutz-Jeghers) 
  • Seen in 10-30yo and cause obstruction in 40% of patients
• Gallstone ileus – SBO with air in biliary tree as has eroded through ducts
• Bezoars mostly vegetable matter or pulp from persimmons
  • Most at risk if previous pyloroplasty
• Capsule retention 1-20% with subsequent obstructive symptoms

Large bowel obstruction

• Neoplasms the most common cause (followed by diverticulitis and sigmoid volvulus)
• Almost never due to hernia or adhesions
• Diverticulitis can lead to mesenteric oedema and obstruction
• Stricture from chronic inflammation of any cause
• Sigmoid volvulus is next most common
  • Elderly, bedridden, psych patients on anticholinergics
  • Coffee bean on AXR
• Caecal volvulus less common but can be seen in gravid patients

pathophysiology

• Obstruction causes build-up of fluids and gas with raised intraluminal pressures even without ongoing oral intake
• Mortality approaches 70% if bowel obstruction proceeds through to raised intraluminal pressures to the point of ischaemia
• This can occur more rapidly in closed-loop obstruction with no proximal escape e.g. incarcerated hernia and complete colon obstruction with closed ileo-caecal valve or previous Nissen fundoplication

Clinical features

• Pain generally cramping and intermittent
• Pain tends to be less intense and more constant in paralytic ileus
• Proximal obstruction often causes bilious vomiting vs. feculent with distal obstruction
• Partial bowel obstruction may still allow flatus and passing motions
• Signs of peritonism suggest gangrenous or perforated bowel
• Absence of stool or air in rectum supports diagnosis of obstruction but presence does not eliminate a more proximal obstruction
• PR may yield mass, stricture, faecal impaction, blood
• Vaginal pessary may cause extrinsic colonic obstruction

Labs

• WCC >20 suggestive of perforation, gangrenous bowel, intra-abdominal abscess or peritonitis
• WCC >40 suggests mesenteric vascular occlusion
• Lactic acidosis and signs of dehydration/AKI

imaging

• Screening AXR can help identify obstruction, severe constipation or free air
• Plain X-rays can identify small or large bowel obstruction
• If clinical suspicion for obstruction is strong, CT with oral and IV contrast can delineate partial/complete obstruction, distinguish partial SBO from paralytic ileus, differentiate strangulated vs. simple SBO and identify a lead point + complications
• AXR
  • Toxic megacolon in IBD diameter >6cm
  • Sensitivity 50% for acute bowel obstruction
  • >5 air-fluid levels is pathological

AXR interpretation

• Name, age, date performed
• Projection, posture, exposure
• Gases
  • Small (2.5-3.5cm) and large bowel (3-5cm) patterns
  • Look for dilation, air-fluid levels, intramural gas, intraperitoneal gas (Rigler’s sign – double wall sign) and extra-peritoneal gas
• Masses
  • Solid organs, retroperitoneal shadow of psoas muscles, transverse process fractures, aortic contour
• Bones
• Stones
  • Renal, ureteric, bladder stones – trace ureter (80% radio-opaque)
  • RUQ/transpyloric plane at L1 for gallstones (20% radio-opaque)

Treatment

• Surgical consult for true obstruction
• NG if vomiting or severe distension
• Vigorous IV fluid replacement
• Closed-loop obstruction, bowel necrosis or caecal volvulus are surgical emergencies
• Pre-operative triple Ab’s
• Stop any medication that slows bowel motility
• Conservative supportive therapy if paralytic ileus suspected

Pseudo-obstruction

• Ogilvie syndrome
• Low colonic obstruction is most common
• Large amounts of gas in large intestine
• Dilated colon with well-defined septa and haustral markings, minimal fluid and no air-fluid levels
• Risk factors
  • Advanced age, TCA’s and other anticholinergics
• Colonoscopy can identify bowel lesions and provide therapeutic decompression
• Surgery may be harmful
• Neostigmine infusion has been shown to be beneficial if do not respond to conservative therapy

Last Updated on October 28, 2020 by Andrew Crofton