Bowel Obstruction 

• Bowel obstruction occurs when the normal flow of intraluminal contents is interrupted. 
• Obstruction can be mechanical or functional and may occur in the small or large bowel. T
• small bowel is involved in about 80 of case%s of mechanical intestinal obstruction. 
• Ischemia, which complicates up to 42 percent of bowel obstructions, significantly increases mortality associated with bowel obstruction.
• Mechanical bowel obstruction may be classified as
  • partial (incomplete) or complete (see Table 1)
  • simple or complicated (see Table 2)
  • A complete bowel obstruction may progress to complicated bowel obstruction when intestinal ischaemia, necrosis, and/or perforation develop.

Partial vs Complete bowel obstruction

Partial Bowel Obstruction	Complete Bowel Obstruction
Partial passage of flatus or stool	Failure to pass flatus or stool
Not usually associated with peritonitis	Generally associated with peritonitis

Simple vs Complicated bowel obstruction

Simple Bowel Obstruction	Complicated Bowel Obstruction
Absence of peritonitis	Associated with perionitis
Generally reflects early or partial obstruction	Obstruction has progressed to intestinal ischaemia/ gangrene and/or perforation

Small bowel obstruction

• Acute, mechanical small bowel obstruction is a common surgical emergency. Without resolution it is fatal, progressing to intestinal necrosis, perforation, sepsis, and multisystem organ failure.
• Symptoms to consider:
  • Abdominal pain, bloating, nausea, vomiting, inability to pass flatus or stool
• Signs to consider:
  • Abdominal distension, abdominal tenderness, peritonitis, hyperactive and high pitched bowel sounds, presence of hernias
• Common risk factors in adults:
  • Previous abdominal or pelvic surgery (with the formation of intra-abdominal adhesions).
  • Abdominal wall or groin hernia, such as inguinal hernia with incarceration
  • Intestinal inflammation, such as diverticulitis or Crohn’s disease
  • Intestinal malignancy (prior hx or risk factors for neoplasm)
  • Rare causes include radiation enteritis, foreign body ingestion, intra-abdominal abscess (e.g. perforated appendicitis/diverticulitis), gallstone ileus, intestinal bezoar, intussusception and volvulus.
• Imaging
  • Plain films:
    • Initial imaging should include upright CXR and erect/supine AXR films (or lateral decubitus film if the patient cannot sit upright) – these have a sensitivity of 70-83% and specificity of 67-83% for small bowel obstruction. 
    • Plain film findings that suggest small bowel obstruction:
      • Dilated loops of small bowel proximal to the obstruction > 3 cm
      • Predominantly central dilated loops
      • Three instances of dilatation > 2.5 – 3 cm
      • Valvulae conniventes are visible
      • Gas-fluid levels
        • suspicious if >2.5 cm in width and in same loop of bowel but at different heights (> 2 cm difference in height).
      • However, obstruction (which may be high-grade mechanical obstruction) may also present with the following features:
        • Gasless abdomen:
          • gas within the small bowel is a function of vomiting, NG tube placement and level of obstruction
        • String-of-beads sign:
          • small pockets of gas within a fluid-filled small bowel

• CT abdomen:
  • provides more information than plain films. May be useful to identify the specific site (i.e. transition point) and severity of the obstruction (partial vs complete). 
  • It will also give information about the aetiology, by identifying hernias, masses or inflammatory changes, and potential complications, such as ischaemia or perforation.

• Management
  • Consideration of other life-threatening diagnoses with similar symptoms (Perforated viscus, Pancreatitis, AAA)
  • Emergency surgery is indicated in:
    • Perforation or impending perforation
    • Strangulated small bowel obstruction
    • Patients considered for emergency surgery should be receive preoperative antibiotic prophylaxis and made NBM in preparation for surgery in addition to supportive case detailed below.
• All patients should receive supportive care:
  • NBM until surgical review
  • IV fluids
  • Monitoring of urine output
  • Analgesia
  • Anti-emetics
    • can be a useful for emesis and/or nausea in cases where surgery is contraindicated (ondansetron 4mg IV q8H prn)
  • Consider NG tube for gastric decompression (vomiting or severe symptoms of gastric distension)
    • The need for gastrointestinal decompression varies from patient to patient and remains a matter of clinical judgment. 
    • It is suggested with significant distension, nausea, and/or vomiting. 
    • Such patients likely have complete or high-grade obstruction; decompression of the distended stomach improves patient comfort and also minimizes the passage of swallowed air, which can worsen distension.
    • For patients with recurrent SBO who have undergone multiple prior operations, and in whom another operation is felt to be particularly risky, nasogastric decompression is a component of conservative management to avoid further surgery.
  • Patients who do not require emergency surgery are initially treated conservatively for 48-72 hours. Failure to respond to conservative treatment would lead to consideration for surgery.
  • Gastrografin
    • may be diagnostic and therapeutic in SBO due to surgical adhesions. 
    • The appearance of water-soluble contrast in the colon on an abdominal X ray within 24 hours of its administration predicts resolution of an adhesive small bowel obstruction. 
    • While gastrografin does not reduce the need for surgery it does reduce hospital stay in those patients who do not require surgery.

Large bowel obstruction

• Acute colonic distension can occur due to the following causes:
  • Mechanical obstruction
  • Toxic megacolon
    • complication of inflammatory bowel disease/Clostridium difficile infection
  • Acute colonic pseudo-obstruction (Ogilvie’s syndrome)
• Symptoms:
  • Abdominal pain (normally colicky), bloating, change in bowel habit, tenesmus, rectal bleeding, recent weight loss, nausea and vomiting
• Signs:
  • Abdominal distension, tympanic abdomen, abdominal tenderness, abdominal rigidity, palpable rectal mass or empty rectum
• Risk factors:
  • Malignancy (colorectal cancers and other neoplasms e.g. pancreatic ca, ovarian ca, lymphoma)
  • Prior abdominal surgery, especially prior colorectal resection and stricture formation
  • Volvulus – common in institutionalised elderly patients (5%)
  • Rare causes include hernia, foreign body, benign neoplasm, gynaecological neoplasm, pelvic abscess, or endometriosis
• Consideration of other life-threatening diagnoses with similar symptoms
  • Perforated viscus, Pancreatitis, AAA
  • Strictures (i.e. diverticular, inflammatory, ischaemic, radiation-induced, or anastomotic)
• Imaging
  • plain films that may demonstrate large bowel obstruction include:
    • Colonic distension: gaseous secondary to gas-producing organisms in faeces
    • Collapsed distal colon: very few or no air-fluid levels are found in the large bowel because water is reabsorbed
    • Small bowel dilatation, which depends on duration of obstruction, incompetence of the ileocaecal valve
    • No air in the rectum has little or no air
    • In advanced cases one may see the stigmata of an ischaemic colon, namely:
    • Intramural gas (pneumatosis coli)
    • Portal venous gas
    • Free intra-abdominal gas (pneumoperitoneum)
    •  

• CT abdomen:
  • more sensitive and specific for colorectal obstruction than plain films (>90% each). Will also distinguish between true obstruction and pseudo-obstruction, as well as determine the cause of obstruction and complications.
• Management
  • Supportive care
  • NBM
  • IV fluids
  • Monitor urine output
  • Analgesia
  • NG tube usually unnecessary, may be used if there is severe distension and vomiting
  • If there is evidence of perforation or impending perforation, emergency surgery is indicated. In
  •  the absence of perforation, definitive treatment depends on cause. 
  • Treatment in most cases of mechanical large bowel obstruction is surgery, with the exception of:
    • Sigmoid volvulus, where first line treatment is flexible or rigid sigmoidoscopy and insertion of a rectal tube.
  • Benign strictures, which should be treated based on the severity of symptoms, the underlying disease process, and the patient’s general condition.

Toxic megacolon

• Toxic megacolon is a complication of
  • inflammatory bowel disease (IBD) 
  • infectious colitis
• characterized by
  • colonic dilatation
  • systemic toxicity.
  • The diagnosis of toxic megacolon should be considered in all patients presenting with abdominal distension and acute or chronic diarrhoea. 
  • The diagnosis is clinical, based upon the finding of an enlarged dilated colon accompanied by severe systemic toxicity. The initial evaluation should be aimed at establishing the diagnosis and at determining the underlying cause.
• Radiographic criteria:
  • Dilated colon (>6cm, sometimes up to 15cm), commonly in the right or transverse colon but sometimes involving the descending colon
  • Multiple air-fluid levels in the colon with disturbance of the colonic haustrae
  • Deep mucosal ulcerations may appear as air-filled crevices between large pseudopolypoid projections extending into the colonic lumen
• PLUS at least three of the following:
  • Fever >38ºC
  • Heart rate >120 beats/min
  • Neutrophilic leukocytosis >10,500/microL
  • Anaemia
• PLUS at least one of the following:
  • Dehydration
  • Altered sensorium
  • Electrolyte disturbances
  • Hypotension

Pseudo-obstruction

• Paralytic ileus and colonic pseudo-obstruction (Ogilvie’s syndrome) cause functional obstruction, because of uncoordinated or attenuated intestinal muscle contractions.
• Functional bowel obstruction is characterized by signs and symptoms of a mechanical obstruction of the small or large bowel in the absence of an anatomic lesion that obstructs the flow of intestinal contents.
• Paralytic ileus occurs
  • after some degree after almost all open abdominal operations. 
  • Peritonitis
  • Trauma
  • intestinal ischemia
  • medications (eg, opiates, anticholinergics)
• Symptoms
  • are similar to that of mechanical obstruction
  • BUT on imaging there is air in the colon and rectum
  • CT abdomen
    • no demonstrable mechanical obstruction. 
• Treatment
  • dependent on the cause
  • Prolonged post-operative ileus often responds to conservative treatment
    • bowel rest
    • correction of electrolyte disorders
    • reduction of opioid medications
    • cessation of the precipitating drug.
• Acute colonic pseudo-obstruction, or Ogilvie’s syndrome
  • is a variant of ileus
  • characterized by massive colonic dilatation