GI - Bowel Obstruction: Causes and investigations

Question 1

What is bowel obstruction?

Answer 1

-Mechanical blockage of bowel -blockage of normal passage of intestinal contents

Question 2

-Aetiology - commonest causes

Answer 2

• SBO: adhesions (60%) and herniae
• LBO: colorectal neoplasia (60%), Diverticular disease (20%), volvulus (5%)
• GI malignancy is primary LBO Dx until proved otherwise

Question 3

Presentation of BO 0- 4 cardinal features

Answer 3

• Abdominal pain: colicky, central (but depends on gut region), constant/localised pain (suggests strangulation/ impending perf)
• Distension: especially with lower obstruction
• Vomiting: early in high obstruction vs late/absent in lower obstruction
• Absolute constipation: flatus and faeces

Question 4

Pathophysiology

Answer 4

• Bowel segment becomes occluded
• Gross dilation of proximal limb = increased peristalsis of bowel
• This leads to increased secretion of large vols of electrolyte rich fluid into bowel (3rd spacing)
• *Urgent fluid resus/ and I/O moniting essential
• Closed loop: 2nd obstruction proximally (eg ileocaecal valve competent) = surgical emergency as bowel will continue to distend, stretch bowel wall until ischaemic and perforates

Question 5

What should you say in differential Dx?

Answer 5

• Paralytic ileus
• Toxic megacolon
• Constipation

Question 6

Other causes of BO: non mechanical

Answer 6

Non mechanical = paralytic ileus, which can occur as a result of:

• post op
• peritonitis
• pancreatitis or any localised inflammation
• poisons/drugs: anti AChM (eg TCAs)
• pseudo-obstruction
• Metabolic (low K+/Na/Mg/uraemia)
• Mesenteric ischaemia

Question 7

Other causes of BO- mechanical - intra-luminal

Answer 7

• Impacted matter: faeces, worms
• untussusception
• gallstones

Question 8

Other causes of BO- mechanical - intra-mural

Answer 8

• Benign stricture (IBD, surgery, ischaemic colitis, diverticulitis, radiotherapy)
• neoplasia
• congenital atresia

Question 9

Other causes of BO- mechanical - extra-mural

Answer 9

• Hernia
• Adhesions
• Volvulus
• extrinsic compression (pseudocyst, abscess, haematoma, tumour, congenital bands)

Question 10

Examination: signs and cause

Answer 10

• Raised HR: hypovolaemia and strangulation
• Dehydration, hypovolaemia
• Fever: suggests inflammatory disease or strangulation
• Surgical scars: possible source of strictures
• hernias: check all
• mass: neoplastic or inflammatory
• bowel sounds: increased (mechanical obstruction) vs decreased (ileus)
• PR: empty rectum, rectal mass, hard impacted stool, blood from higher pathology

Question 11

Ix- lab tests

Answer 11

• Bloods: FBC (raised WCC), U&Es (dehydration/electrolyte abnormalities), amylase (raised in strangulation/perforation), ABG (raised lactate in strangulation)
• *Remember to do group and save as may need surgery

Question 12

Ix- imaging and others

Answer 12

• CT: modality of choice in suspected BO
• AXR
• CXR (erect for gas)
• Contrast fluoroscopy: useful in SBO caused by adhesions from previous surgery

Question 13

Ix- imaging: AXR specifics

Answer 13

• SBO: dilated bowel (>3cm), central abdominal location, valvulate conniventes (lines completely crossing bowel) are visible
• LBO: dilated bowel (<6cm or >9cm if at caecum), peripheral location, haustral lines (lines not completely crossing bowel) visible

Question 14

Mx- conservative

Answer 14

• Resus: NBM, IV fluids, catheter and I/O, NGT (decompresses upper GIT, stops vomiting and presents aspiration)
• Adhesions in SB: resolve with conservative Rx (if not ischaemic/strangulated) in 80% of cases - perform water soluble contract study - if it doesn’t reach colon by 6h then unlike to resolve alone and pt needs surgical intervention.
• Pt with SBO/LBO who has not had previous surgery - rarely settles without surgery

Question 15

Mx- Therapy

Answer 15

• Analgesia: may need strong opioid
• ABX: ceftriaxone + metronidazole if strangulation/perforation
• Gastrograffin study: oral or via NGT
• Consider need for parenteral nutrition

Question 16

What signs can indicate resolution of obstruction?

Answer 16

• Reducing pain
• Reducing NGT aspirate volumes
• Passage of flatus
• Resolution of signs on repeat xray

Question 17

Mx- Surgical indications

Answer 17

• Closed loop obstruction (caecum >10cm)
• Obstructing neoplasm
• Strangulation/perforation
• failure of concervative Mx (up to 72h)

Question 18

Mx - Surgical principals

Answer 18

• Aim to treat cause
• typically involves resection of obstructing lesion
• if unresectable, pt may be offered bypass solution
• colon not been cleansed before surgery t/f most surgeons do proximal ostomy post-resection
• endoscopically placed expanding metal stents offer palliation or a bridge to surgery allowing optimisaation

Question 19

Mx - Surgery options

Answer 19

• **Must consent pt for possible resection and possible stoma
• SBO: adhesiolysis
• LBO: Hartmann’s, colectomy (plus primary anastomosis), palliative bypass procedure, caecostomy, transverse loop colostomy or loop ileostomy