Intestinal obstruction Flashcards
Explain mechanical v paralytic obstruction.
Mechanical: site at which forward passage is prevented but above which bowel is normal.
Paralytic: whole bowel inactive.
Describe open v closed loop obstructions.
Open loop: bowel content can escape proximally.
Closed loop: segment of gut obstructed at both ends (large bowel always potentially closed loop due to ileocaecal valve).
Describe the pathophysiology of bowel obstruction.
- Proximal to obstruction contractions increase in frequency and magnitude
- Bowel diameter increases, contractions fail.
- Intestinal wall becomes oedematous; decreased reabsorption –> extracellular volume depletion
- If strangulation: bowel becomes ischaemic –> SIRS –> lactic acidosis. 4-6h dies: rupture –> bacterial peritonitis.
What are the clinical features of bowel obstruction?
Vomiting, distension, obstipation, pain.
What are the characteristics of pain associated with bowel obstruction?
Often first symptoms.
Central, colicky, comes in waves.
Pain of strangulated touching inner abdominal wall?
Contacts parietal peritoneum therefore well-localised, severe pain.
Describe vomiting of intestinal obstruction.
Higher obstruction, earlier more profuse vomiting.
Food/faeculent.
Less common distal to ileocaecal valve (i.e. large bowel obstruction).
Describe constipation of bowel obstruction.
Absolute constipation (faces and flatus). Early in large, later in small bowel obstructions.
Which obstruction level produces greatest distension in small bowel?
The lower the obstruction, the greater the distension
Important abdo examination (inspection/palaption) features of bowel obstruction?
- Distension: relates to level of obstruction
- Scar: ? source = adhesions
- Mass on palpation: ? source obstruction
- Irreducible mass at hernial orifice - strangulated hernia
- Tenderness and guarding: highly suggestive of strangulation in acute presentations.
Characteristics of auscultation in SBO?
Increased frequency of segmental sounds: high pitched and tinkling.
Imaging in suspected BO? What questions to be answered?
Supine AXR
1) Is this an obstruction?
2) SBO or LBO?
3) What level of obstruction?
4) Specific cause apparent?
How does BO appear on AXR?
Distended gas and fluid filled loops. In erect posture there will be fluid levels.
Adjacent loops may be separated by variable distance: indicates oedema.
Gas pattern outlines walls of LB; may localise cause of obstruction.
What is indicated by raised WCC/metabolic acidosis in suspected BO?
Active inflammatory cause or strangulation
What are the indications for non-operative management of BO?
- Evidence there is no threat to bowel viability (strangulation, perforation) as suggested by signs of hypovolaemia, SIRS, peritoneal irritation.
- Incomplete obstruction with features which suggest non-progression e.g. Crohn’s disease
- Complete SBO (e.g. adhesions)
What does conservative BO Mx involve?
-Proximal decompression with NGT
-Water and electrolyte replacement
-4-6h reevaluation clinical state (pain, distension, CV r/v, bowel sounds)
-Repeat XR/biochem Ix as required
Up to 5 days conservative Mx.
What are the operative indications in BO Mx?
- strangulation (inc irreducible hernia)
- complete LBO with tenderness in RIF (indicates closed loop obstruction with imminent caecal perforation)
- failure of conservative mx
- a cause (e.g. Ca) requiring surgical removal
How are the mechanical causes of bowel obstruction classified?
Intraluminal, mural and extramural.
What are the intraluminal causes of bowel obstruction?
- Gallstone ileus
- Food bolus
- Meconium ileus
What is a gallstone ileus?
Sizeable stone in gallbladder erodes into adjacent duodenum. Carried distally until it impacts (usually in narrow ileum). Rare in 1st world.
Clinical features of gallstone ileum?
Hx may reveal repeated bouts of previous partial obstruction.
Exam: considerable distension (length of SB involved).
Ix in gallstone ileus?
Radiology often Dx: features of intestinal obstruction + air in biliary tree (often).
Rx gallstone ileus?
Enterotomy slightly proximal to impaction. Examine bowel for additional stones.
Common causes of food bolus BO?
- poor chewing of food (e.g. edentulous pt)
- previous gastric resection with pylorus destruction
- high consumption of indigestible fibre
Clinical features of food bolus obstruction?
Similar to gallstone ileus (low SBO with considerable distension).
Rx food bolus BO?
Usually operative.
Bolus can often be milked distally into LB. Rarely necessary to open the bowel.
What are the mural causes of mechanical bowel obstruction?
- Neonatal obstructions and intussusception
- Inflammatory
- Neoplastic
What are the inflammatory causes of bowel obstruction?
Crohn’s disease, TB, diverticulitis.
May cause inflammatory/fibrous strictures, adherence of a loop of bowel to inflammatory area.
How does diverticulosis cause LBO?
Adhesions between the inflamed colon and the small bowel OR inflammatory mass in the colon which leads to LBO.
What mechanism protects the bowel from adhesion development? How fails?
Peritoneal mesothelial cells have potent fibrinolytic activity based on conversion of plasminogen to plasmin. Generally breaks down fibrin before it becomes fibrous tissue.
Peritoneal inflammation may lead to b/d of fibrinolysis –> normal healing –> fibrous tissue deposition.
What are the extramural causes of BO?
Adhesions, external hernia, internal hernia, volvulus.
What is an internal hernia?
Takes place into recess of a peritoneal fold formed either during development (e.g. around duodenojejunal jxn at ligament of Treitz) or post-op (e.g. lateral to colostomy/ileostomy).
Common post lap gastric bypass for obesity (SB may herniate between jejunal and transverse colon mesenteries = Peterson’s space).
What are the clinical features of internal hernia causing obstruction?
Intestinal obstruction w/o cause.
Bowel may be strangulated but as not touching parietal peritoneum will be without signs of peritoneal irritation. Early op imp in pts with obstruction w/o discernible cause.
What is a volvulus?
Twist of a bowel around its mesenteric axis. Both obstruction and ischaemia of loop may occur.
Describe the aetiology of a volvulus.
SB: less common. apex of loop involved tethered by adhesion to abdo wall or adjacent viscera. Rotation may occur around this; if >180 ==> strangulation.
LB: two main sites
i) caecum: when persistent mesentery (uncommon).
ii) sigmoid colon (existing mesentery more extensive than normal). Generally elderly.
What are the clinical features of SB volvulus?
As per acute SBO + localised pain if strangulated.
If considerable length of SB involved: circulatory disturbance (shock).
Clinical fx of LB sigmoid volvulus?
As per LBO +:
- pt elderly
- acute presentation
- +/- signs of circulatory insufficiency (due to infarction)
- grossly distended, drum-like abdo
- supine AXR: Omega sign
Management of caecal LB volvulus?
Closed loop obstruction ==> generally operative mx (esp if signs of peritoneal irritation).
Resection of ileum and right colon. Reconstruction via ileo-transverse anastomosis.
Management of sigmoid LB volvulus?
Non-op Mx 1st choice.
Introduce sigmoidoscope/colonoscope –> pass along wide bore flatus tube –> carefully untwist LB.
Elective excision of sigmoid to prevent recurrence.
Always op if: peritoneal irritation suggesting strangulation, failure of primary Mx.
What is ileus?
Intestinal obstruction due to failure of motility (cf mechanical obstruction). Usually affects SB.
What is the classification of aetiology of paralytic (dysdynamic) ileus?
Either dysfunction of sympathetic outflow or peripheral inhibition of peristalsis. Either post op (due to bowel handling) or secondary causes.
What are the mechanisms of sympathetic outflow dysfunction causing ileus?
- Reflex inhibition: e.g. temporary post op ileus, spinal injury, acute disorders e.g. renal colic
- Pelvic and retroperitoneal bleeding or effusion e.g. trauma, anticoagulation, acute pancreatitis
- Malignant infiltration e.g. Ogilvie’s syndrome (ileus ass w/ malignant disease in retroperitoneum)
What are the biochemical causes of ileus?
Interferes with normal contractility of SM.
Hypoxia, hypokalemia, uraemia, DM.
What are the pharmacological causes of ileus?
Neurological/muscular inhibition:
- antimuscarinics
- ganglion blockers
- antidiarrhoeal agents
What are the clinical features of ileus?
As per intestinal obstruction but w/o pain or bowel sounds.
- absence of colic
- abdominal silence on auscultation
- SB and LB distension on XR
How should ileus be managed?
- identify cause: eliminate or wait out
- NGT
- maintain water and electrolyte balance (if >5/7 ==> parenteral feeding).
What is Ogilvie’s syndrome?
Ileus due to widespread retroperitoneal infiltration by malignant disease.
What is pseudo obstruction?
Dysdynamic ileus affecting the LB.
Common in elderly and those confined to bed due to comorbidity (e.g. hip fracture).
Resp disease with hypoxia common accompaniment.
What are the clinical features of pseudo-obstruction?
- As per LBO minus increased bowel sounds
- Caecum and transverse colon dilate
- XR does not show cut off (as for mech LBO)
How can pseudo-obstruction be distinguished from mechanical LBO?
- DRE may be diagnostic: gush of faecal fluid and flatus on withdrawal of finger.
- Water soluble contrast enema, CTA or colonoscopy
