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Gastroenterology > Intestinal obstruction > Flashcards

Intestinal obstruction Flashcards

1
Q

Explain mechanical v paralytic obstruction.

A

Mechanical: site at which forward passage is prevented but above which bowel is normal.
Paralytic: whole bowel inactive.

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2
Q

Describe open v closed loop obstructions.

A

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).

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3
Q

Describe the pathophysiology of bowel obstruction.

A
  • 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.
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4
Q

What are the clinical features of bowel obstruction?

A

Vomiting, distension, obstipation, pain.

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5
Q

What are the characteristics of pain associated with bowel obstruction?

A

Often first symptoms.

Central, colicky, comes in waves.

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6
Q

Pain of strangulated touching inner abdominal wall?

A

Contacts parietal peritoneum therefore well-localised, severe pain.

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7
Q

Describe vomiting of intestinal obstruction.

A

Higher obstruction, earlier more profuse vomiting.
Food/faeculent.
Less common distal to ileocaecal valve (i.e. large bowel obstruction).

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8
Q

Describe constipation of bowel obstruction.

A 
Absolute constipation (faces and flatus).
Early in large, later in small bowel obstructions.
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9
Q

Which obstruction level produces greatest distension in small bowel?

A

The lower the obstruction, the greater the distension

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10
Q

Important abdo examination (inspection/palaption) features of bowel obstruction?

A
  • 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.
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11
Q

Characteristics of auscultation in SBO?

A

Increased frequency of segmental sounds: high pitched and tinkling.

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12
Q

Imaging in suspected BO? What questions to be answered?

A

Supine AXR

1) Is this an obstruction?
2) SBO or LBO?
3) What level of obstruction?
4) Specific cause apparent?

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13
Q

How does BO appear on AXR?

A

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.

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14
Q

What is indicated by raised WCC/metabolic acidosis in suspected BO?

A

Active inflammatory cause or strangulation

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15
Q

What are the indications for non-operative management of BO?

A
  • 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)
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16
Q

What does conservative BO Mx involve?

A

-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.

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17
Q

What are the operative indications in BO Mx?

A
  • 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
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18
Q

How are the mechanical causes of bowel obstruction classified?

A

Intraluminal, mural and extramural.

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19
Q

What are the intraluminal causes of bowel obstruction?

A
  • Gallstone ileus
  • Food bolus
  • Meconium ileus
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20
Q

What is a gallstone ileus?

A

Sizeable stone in gallbladder erodes into adjacent duodenum. Carried distally until it impacts (usually in narrow ileum). Rare in 1st world.

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21
Q

Clinical features of gallstone ileum?

A

Hx may reveal repeated bouts of previous partial obstruction.
Exam: considerable distension (length of SB involved).

22
Q

Ix in gallstone ileus?

A

Radiology often Dx: features of intestinal obstruction + air in biliary tree (often).

23
Q

Rx gallstone ileus?

A

Enterotomy slightly proximal to impaction. Examine bowel for additional stones.

24
Q

Common causes of food bolus BO?

A
  • poor chewing of food (e.g. edentulous pt)
  • previous gastric resection with pylorus destruction
  • high consumption of indigestible fibre
25
Q

Clinical features of food bolus obstruction?

A

Similar to gallstone ileus (low SBO with considerable distension).

26
Q

Rx food bolus BO?

A

Usually operative.

Bolus can often be milked distally into LB. Rarely necessary to open the bowel.

27
Q

What are the mural causes of mechanical bowel obstruction?

A
  • Neonatal obstructions and intussusception
  • Inflammatory
  • Neoplastic
28
Q

What are the inflammatory causes of bowel obstruction?

A

Crohn’s disease, TB, diverticulitis.

May cause inflammatory/fibrous strictures, adherence of a loop of bowel to inflammatory area.

29
Q

How does diverticulosis cause LBO?

A

Adhesions between the inflamed colon and the small bowel OR inflammatory mass in the colon which leads to LBO.

30
Q

What mechanism protects the bowel from adhesion development? How fails?

A

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.

31
Q

What are the extramural causes of BO?

A

Adhesions, external hernia, internal hernia, volvulus.

32
Q

What is an internal hernia?

A

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).

33
Q

What are the clinical features of internal hernia causing obstruction?

A

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.

34
Q

What is a volvulus?

A

Twist of a bowel around its mesenteric axis. Both obstruction and ischaemia of loop may occur.

35
Q

Describe the aetiology of a volvulus.

A

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.

36
Q

What are the clinical features of SB volvulus?

A

As per acute SBO + localised pain if strangulated.

If considerable length of SB involved: circulatory disturbance (shock).

37
Q

Clinical fx of LB sigmoid volvulus?

A

As per LBO +:

  • pt elderly
  • acute presentation
  • +/- signs of circulatory insufficiency (due to infarction)
  • grossly distended, drum-like abdo
  • supine AXR: Omega sign
38
Q

Management of caecal LB volvulus?

A

Closed loop obstruction ==> generally operative mx (esp if signs of peritoneal irritation).
Resection of ileum and right colon. Reconstruction via ileo-transverse anastomosis.

39
Q

Management of sigmoid LB volvulus?

A

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.

40
Q

What is ileus?

A

Intestinal obstruction due to failure of motility (cf mechanical obstruction). Usually affects SB.

41
Q

What is the classification of aetiology of paralytic (dysdynamic) ileus?

A

Either dysfunction of sympathetic outflow or peripheral inhibition of peristalsis. Either post op (due to bowel handling) or secondary causes.

42
Q

What are the mechanisms of sympathetic outflow dysfunction causing ileus?

A
  • 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)
43
Q

What are the biochemical causes of ileus?

A

Interferes with normal contractility of SM.

Hypoxia, hypokalemia, uraemia, DM.

44
Q

What are the pharmacological causes of ileus?

A

Neurological/muscular inhibition:

  • antimuscarinics
  • ganglion blockers
  • antidiarrhoeal agents
45
Q

What are the clinical features of ileus?

A

As per intestinal obstruction but w/o pain or bowel sounds.

  • absence of colic
  • abdominal silence on auscultation
  • SB and LB distension on XR
46
Q

How should ileus be managed?

A
  • identify cause: eliminate or wait out
  • NGT
  • maintain water and electrolyte balance (if >5/7 ==> parenteral feeding).
47
Q

What is Ogilvie’s syndrome?

A

Ileus due to widespread retroperitoneal infiltration by malignant disease.

48
Q

What is pseudo obstruction?

A

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.

49
Q

What are the clinical features of pseudo-obstruction?

A
  • As per LBO minus increased bowel sounds
  • Caecum and transverse colon dilate
  • XR does not show cut off (as for mech LBO)
50
Q

How can pseudo-obstruction be distinguished from mechanical LBO?

A
  • DRE may be diagnostic: gush of faecal fluid and flatus on withdrawal of finger.
  • Water soluble contrast enema, CTA or colonoscopy

Gastroenterology (54 decks)

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