Bowel obstruction Flashcards
What are the 2 different types of bowel obstruction by cause?
1. Mechanical (e.g. abdominal/pelvic malignancy, volvulus, hernias, strictures)
- Caused by physical barrier
2. Functional (e.g. toxic megacolon, inflammation, electrolyte derangement, or recent surgery)
- Caused by dysfunctional bowel
What is the pathophysiology of mechanical bowel obstruction?
Bowel segment becomes occluded leading to gross dilatation of the proximal limb of bowel and therefore increased peristalsis. This leads to secretion of large volumes of electrolyte-rich fluid into the bowel (“Third-spacing”)
What are the most common causes of small bowel obstruction?
- Adhesions
- Herniae
What are the most common causes of large bowel obstruction?
- Malignancy
- Diverticular disease
- Volvulus
What are the 3 categories causes of obstruction can be divided into, based on their location?
- Intraluminal
* Within the lumen of the bowel - Mural
* Within the bowel wall itself - Extramural
* Originating from outside of the bowel
What are the intraluminal causes of bowel obstruction?
- Gallstone ileus
- Ingested foreign body
- Faecal impaction
What are the mural causes of bowel obstruction?
- Malignancy
- Inflammatory strictures
- Intussusception
- Diverticular strictures
- Meckel’s diverticulum
- Lymphoma
What are the extramural causes of bowel obstruction?
- Hernias
- Adhesions
- Peritoneal metastasis
- Volvulus
What is the difference between open loop and closed loop obstruction?
Open loop = Intestinal flow blocked distally but proximal loop open. This can be decompressed by vomiting or nasogastric intubation.
Closed loop = Intestinal flow blocked both distally and proximally. THIS IS A MEDICAL EMERGENCY as bowel continuously distends until bowel becomes ischemic or perforates
Can be due to volvulus or competent ileocecal valve in large bowel obstruction.
What are the 4 cardinal features of bowel obstruction?
- Colicky/cramping abd pain (due to the bowel peristalsis)
* Pain that has become constant or is worse on movement is a RED FLAG that ischemia may be developing - Vomiting
- Early in proximal/small bowel obstruction
- Late in distal/large bowel obstruction
- Obstipation (Absolute constipation) = Cannot pass gas or stool
- Late in proximal/small bowel obstruction
- Early in distal/large bowel obstruction
- Abd distension
* Acute (Volvulus) or gradual (malignancy)
How does the appearance of vomit typically develop over time?
Initially gastric contents, then bilious, until finally faeculent
Compare the presentations of small bowel obstruction & large bowel obstruction.
What are the signs of bowel ischaemia? & Why are they important to notice?
- Pain worsened by movement
- Focal tenderness
- Pyrexia
Important as early recognition and surgery can prevent the need for bowel resection & reliance on life-long stoma.
How would you examine a patient with suspected bowel obstruction?
- A-E approach (inc. fluid assessment)
- Abdominal exam (inc. examination of hernial orifices)
What signs may you find on examination?
- Evidence of underlying cause:
- Surgical scars
- Cachexia (due to malignancy)
- Hernia
- Abd distension
- Focal tenderness
- Guarding & Rebound tenderness
- IF ischemia is developing
- Tympanic sound on percussion
- “Tinkling” bowel sounds on auscultation
What are your differentials for bowel obstruction?
- Pseudo-obstruction
- Paralytic ileus
- Toxic megacolon
- Constipation
What investigations are useful in a case of suspected bowel obstruction?
- Urgent bloods
- FBC, CRP, U&Es, LFTs, Group & Save
- Important to monitor for electrolyte disturbances & third-space losses
- VBG
- High lactate = SIGN OF ISCHEMIA
- Metabolic derangement secondary to dehydration or excessive vomiting
-
CT Abdo-Pelvis w/ IV contrast (1st line imaging modality)
* Definitive diagnostic investigation - AXR
-
Erect CXR
* To assess for free air under the diaphragm IF clinical features suggest bowel perforation. - Contrast fluoroscopy (Water soluble contrast study)
- Useful in small bowel obstruction caused by adhesion from prev surgery
- Shown to predict quite reliably whether or not obstruction will settle.
Why is CT abdo-pelvis with IV contrast preferred to AXR?
- More sensitive for bowel obstruction
- Can differentiate between mechanical obstruction and pseudo-obstruction
- Can demonstrate the site and cause of obstruction (hence useful for operative planning)
- May demonstrate the presence of metastases if caused by a malignancy
How are small bowel obstruction & large bowel obstruction different on AXR?
Note: An incompetent ileocaecal valve in large bowel obstruction may show concurrent large & small bowel dilatation
- What is management of a patient with confirmed bowel obstruction but NO SIGNS of ischemia/strangulation?
- NBM & insert NG tube to decompress bowel (suck)
- IV fluid resuscitation & electrolyte repletion
- Urinary catheter & fluid balance
- Analgesia PRN w/ anti-emetic if giving oral
* Given by parenteral route where possible
How is adhesional small bowel obstruction managed? & what is the success rate?
Adhesional small bowel obstruction resulting from prev surgery is treated conservatively on the first instance with 80% success rate
What is the prognosis for large bowel obstruction in a patient who has not had prev. surgery (“virgin abdomen”)?
Rarely settles without surgery
If not settled within 24 hours of initiating conservative management, what action should be taken?
Water-soluble contrast study (Constrast fluoroscopy)
- If contrast does not reach colon within 6 hrs then it is unlikely that patient will resolve & patient should be taken to theatre.
What are the indications for surgery?
- Suspicion of ischemic bowel or closed loop bowel obstruction
- Small bowel obstruction in virgin abd
- A cause that requires surgical correction (e.g. strangulated hernia or obstructing tumour)
- Failure to improve w/ conservative measures within 48 hrs
What surgery is typically required?
Depends on underlying cause but most commonly laparotomy
Stoma may be required if resection is required as re-joining bowel is rarely possible.
What are the major complications of bowel obstruction?
- Bowel ischemia
- Bowel perforation leading to faecal peritonitis (High mortality!)
- Dehydration & renal impairment
