Small & large bowel obstruction

Question 1

What is bowel obstruction?

Answer 1

A mechanical blockage of the bowel, whereby a structural pathology physically blocks the passage of intestinal contents.

15% of acute abdomen cases are found to have a bowel obstruction.

Question 2

What happens when the bowel is obstructed?

Answer 2

Bowel segment occlusion results in dilatation of the proximal bowel, resulting in an increased peristalsis of the bowel.

This leads to secretion of electrolyte-rich fluid into the bowel (often termed ‘third spacing’).

Urgent fluid resuscitation and careful fluid balance is required.

Question 3

What is a closed loop obstruction?

Answer 3

A second obstruction proximally (i.e. volvulus) = closed-loop obstruction (2 obstruction points).

This is a surgical emergency as the bowel will continue to distend, stretching the bowel wall until it becomes ischaemic or perforates.

Question 4

What is the most common cause of small bowel obstruction?

Answer 4

Adhesions and hernias

Question 5

What is the most common cause of large bowel obstruction?

Answer 5

Malignancy (colon cancer), diverticular disease, and volvulus (sigmoid), constipation,

Question 6

What are the intra-luminal causes of bowel obstruction?

Answer 6

Gallstone ileus, ingested foreign body, faecal impaction

Question 7

What are the mural causes of bowel obstruction?

Answer 7

Cancer, inflammatory strictures, intussusception, diverticular strictures, Meckel’s diverticulum, lymphoma

Question 8

What are the extra-mural causes of bowel obstruction?

Answer 8

Hernias, adhesions, peritoneal metastasis, volvulus

Question 9

What are the cardinal features of bowel obstruction?

Answer 9

Abdominal pain – colicky or cramping in nature (2nd to the bowel peristalsis, occurs early and decreases in long-standing obstruction)

Vomiting – early in proximal small bowel obstructions (bilious vomit - dark green bile) and late in distal large bowel obstructions (faecal vomit)

Nausea & anorexia

Abdominal distension – increases as obstruction progresses with tinkling bowel sounds

Absolute constipation – occurring early in distal obstruction and late in proximal obstruction

Question 10

What signs are visible on examination?

Answer 10

Evidence of underlying cause (e.g. surgical scars, cachexia from malignancy, or obvious hernia) or abdominal distension.

Assess the patient’s fluid status, as third-spacing can occur in bowel obstruction.

Palpate for focal tenderness* (guarding and rebound tenderness on palpation).

Bowel obstruction = abdominal tenderness => shouldn’t have features of guarding or rebound tenderness, unless ischaemic

Percussion: tympanic sound
Auscultation: ‘tinkling’ bowel sounds
(Both signs characteristic of bowel obstruction)

Question 11

What are the differential diagnosis for bowel obstruction?

Answer 11

Pseudo-obstruction, paralytic ileus, toxic megacolon, and constipation

Question 12

Which laboratory investigations are carried out for bowel obstruction?

Answer 12

Routine urgent bloods: FBC, CRP, U&Es, LFTs, and a Group and Save (G&S) ; important to monitor for electrolyte changes and third-space losses.

A venous blood gas for signs of ischaemia (high lactate) + for any metabolic derangement (2nd to dehydration or excessive vomiting).

Question 13

Which is the preferred imaging investigations of choice for bowel obstruction?

Answer 13

CT scan w/ IV contrast of the abdomen and pelvis

Question 14

Why is a CT scan better than AXR for bowel obstruction?

Answer 14

CT imaging is more useful than AXRs:

(1) more sensitive for bowel obstruction;
(2) differentiates between mechanical obstruction & pseudo-obstruction;
(3) demonstrates the site & cause of obstruction (useful for operative planning);
(4) demonstrates the presence of metastases if caused by a malignancy (useful in operative planning).

Question 15

AXR is still sometimes used for initial investigation for bowel obstruction. Which AXR findings are seen in small bowel obstruction?

Answer 15

Small bowel obstruction:

Dilated bowel (>3cm)

Central abdominal location

Valvulae conniventes visible (lines completely crossing the bowel)

Question 16

AXR is still sometimes used for initial investigation for bowel obstruction. Which AXR findings are seen in large bowel obstruction?

Answer 16

Large bowel obstruction:

Dilated bowel (>6cm, or >9cm if at the caecum)

Peripheral location

Haustral lines visible (lines not completely crossing the bowel, ‘indents that go Halfway are Haustra’)

An incompetent ileocaecal valve in a large bowel obstruction may show concurrent large and small bowel dilatation on AXR.

An erect chest x-ray may be requested to assess for free air under the diaphragm if bowel perforation suspected.

Question 17

What is the definitive management of bowel obstruction?

Answer 17

Depends on the aetiology and complications of bowel ischaemia, perforation, and/or peritonism.

These patients are intravascularly fluid deplete => need urgent fluid resuscitation and careful fluid balance + catheter.

Closed loop bowel obstruction or bowel ischaemia (strangulation) = urgent surgery - (pain worsened by movement, focal tenderness and pyrexia)

Large bowel obstruction = surgery

Question 18

Small bowel & ileum obstruction is usually managed conservatively initially.

What is the conservative management of bowel obstruction?

Answer 18

No ischaemia or strangulation, initial management is essentially conservative aka ‘drip and suck’ management:

1. Nil-by-mouth with a nasogastric tube to decompress the bowel (‘suck’) start IV fluids and correct electrolyte disturbances (‘drip’)
2. Urinary catheter and fluid balance
3. Analgesia (opiates) with suitable anti-emetics
4. Blood: Amylase, FBC, U&E
5. Adhesional small bowel obstruction from previous surgery is treated conservatively (unless there is evidence of strangulation / ischaemia)
6. Water soluble contrast study if bowel obstruction doesn’t resolve within 24 hours of conservative management.
   If contrast does not reach the colon by 6 hours then it’s very unlikely it will resolve => patient should be taken to theatre.
7. Large or small bowel obstruction in a patient who has not had previous surgery rarely settles without surgery.

Question 19

Under which circumstances is surgical management for bowel obstruction required?

Answer 19

Surgical intervention is indicated in patients with:

1. Suspicion of intestinal ischaemia or closed loop bowel obstruction
2. A cause that requires surgical correction (such as a strangulated hernia or obstructing tumour)
3. If patients fail to improve with conservative measures (typically after ≥48 hours)
4. Surgery depends on the underlying cause but typically = laparotomy.
5. If bowel is resected, re-joining of obstructed bowel is often not possible and a stoma may be necessary.

Question 20

What are the complications of bowel obstruction?

Answer 20

Bowel ischaemia

Bowel perforation leading to faecal peritonitis (high mortality)

Dehydration and renal impairment

Question 21

What is a red flag symptom for ischaemia of bowel obstruction?

Answer 21

Colicky pain in a suspected case of bowel obstruction that becomes constant in nature or worse on movement should be a “red flag” that ischaemia may be developing

Question 22

What is a paralytic ileus obstruction?

What causes it?

Answer 22

Iléus obstruction = decreased bowel motility/absence of normal peristaltic contractions
Bowel sounds absent and pain is less severe.

Causes: abdo surgery, pancreatitis, peritonitis, spinal injury, hypokalaemia, hyponatraemia, uraemia, perineal sepsis and drugs

Question 23

What is pseudo-obstruction?

What are its predisposing factors?

Answer 23

Resembles mechanical GI obstruction but with no obstruction lesion.

Predisposing factors: puerperium, pelvic surgery, trauma, cardiorespiratory and neuro disorders

Question 24

What is sigmoid volvulus?

Who does it affect?

Answer 24

Bowel twists on its mesentery = severe, rapid strangulated obstruction.

Common in the elderly, constipated and co-morbid patients.

Question 25

How is sigmoid volvulus treated?

If left untreated, which complications can occur?

Answer 25

Managed by inserting flatus tube or sigmoidoscopy or sigmoid colectomy.

If not treated successfully, can lead to perforation or fatal peritonitis.

Question 26

How do you differentiate between a small or large bowel obstruction?

Answer 26

Small bowel obstruction: vomiting occurs early, bilious vomiting, less distention, colicky/ cramping pain high in abdomen

Large bowel obstruction: pain is more constant, vomiting occurs late, faecal vomiting.

Imagining (AXR or CT) to confirm

Question 27

What happens in strangulated bowels and how do these patients present?

Answer 27

Blood supply is compromised.

Sharper, more constant localised pain ; peritonism ; fever + increased WCC (+signs of mesenteric ischaemia)