Colorectal surgery: Small Bowel Obstruction Flashcards
Describe a way of classifying bowel obstructions [3]
Name three suggestions for the each of the above [9]
Extramural: block bowel from outside
- Adhesions (congenital or aquired)
- Hernia
- Volvulus (caecal; sigmoid; small bowel)
- Compression from lymph nodes
Intramural: blockage from within the wall
- Tumours (adenocarcinoma, GISTs, lymphoma, leiomyosarcoma)
- Strictures bowel has narrowed due to: diverticular, ischaemic, IBD, post op,
- Intussusecption (wall of bowel moves into itself & blocks itself, most commonly at terminal ileum and caecum)
Intraluminal: within the wall
- Gall stones
- Bezoar
- Foreign body
- Meconium
Where does most of bowel obstruction occur? [1]
Why is this clinically significant? [1]
Small bowel: 75%; more likely to cause vomiting (& pain - colicky)
Large bowel: 25%: more likely to cause distension and absolute constipation (& pain - colicky)
What is the imaging that is the investigation of choice for bowel obstruction? [1]
State other imaging used [1]
CT: imaging of choice;
XR
What is gastrograffin AXR? [1]
When is its use indicated? [1]
Gastrograffin:
* Water soluble contrast for small bowel adhesive obstruction.
* If gastrograffin has passed into colon then suggests that will resolve (if not then surgery is indicated)
The “big three” causes account for around 90% of cases of bowel obstruction.
What are they? [3]
Where are they found (small or large bowel) [3]
Adhesions: small bowel
Hernias: small bowel
Malignancy: large bowel
Describe the pathophysiology of small bowel obstruction [5]
- Passage of food, fluids and gas, through the intestines becomes blocked
- Obstruction results in a build up of gas and faecal matter proximal to the obstruction
- This causes back-pressure: resulting in vomiting and dilatation of the intestines proximal to the obstruction.
- When there is an obstruction, and fluid cannot reach the colon, it cannot be reabsorbed: as a result, there is fluid loss from the intravascular space into the gastrointestinal tract leading to hypovolaemia & shock
- The higher up the intestine the obstruction, the greater the fluid losses as there is less bowel over which the fluid can be reabsorbed.
How does bowel obstruction lead to bowel ischaemia, infarction, necrosis, and perforation? [3]
- With time, bowel wall oedema forms
- This compresses the intestinal veins and lymphatics, reducing the venous drainage of the bowel
- As this occurs, it compresses intestinal arterioles and capillaries
- This prevents arterial perfusion to the bowel wall.
What is the most common cause of SBO? [1]
Adhesions
What’s a pneumonic for remembering the causes of small bowel obstruction?
“HANG IVs”
Hernias 2%
Adhesions (from previous surgery with formation of intra abdominal adhesions, commonly colorectal and gynaecological surgery)
Neoplasms (malignant, benign, primary or secondary) (5%)
Gallstone ileus
Intussusception
Volvulus
Strictures (eg Crohn’s disease (6%), ischaemia)
State 4 causes of intestinal adhesions that could contribute to the formation of bowel obstruction [4]
Abdominal or pelvic surgery (particularly open surgery)
Peritonitis
Abdominal or pelvic infections (e.g., pelvic inflammatory disease)
Endometriosis
What specifically leads to the colicky pain experienced in SBO? [2]
dilation of the intestine
AND
the continuing intestinal peristalsis
Describe the difference in presentation of more proximal and more distal bowel obstructions [2]
In more proximal bowel obstructions:
- patients tend to present earlier
- abdominal pain and vomiting are the predominant symptoms.
In distal small bowel obstructions:
patients usually present after 2-3 days of abdominal pain.
- The predominant symptoms are abdominal distension and constipation.
Describe bowel sounds of SBO [3]
- Initially high pitched (tinkling)
- Increased frequency
- In delayed presentations, bowel sounds can be reduced due to secondary ileus
Describe presentation of SBO [4]
- Absence of passing flatus (90%) or stool (80%)
- Abdominal pain (90%): Ranges in severity; Often cramping in nature; Intermittent every 3-4 minutes.
- Nausea and vomiting (80%)
- May be bilious
- Abdominal distension (65%)
Describe the relationship between abdominal pain and vomiting in SBO? [1]
- Abdominal pain often precedes vomiting (constant pain may indicate bowel ischaemia)
How can you tell from the AXR if the small bowel is involved? [2]
Valvulae conniventes
Normally more central
