Colorectal - Ischemic Colitis

Question 1

What are the risk factors for ischemic colitis?

Answer 1

1. Embolic / Thrombotic Hx
2. Hypotensive Episodes
3. Medication
   4, Surgery
4. Hypercoagulability
5. Cardiac Hx
6. Others - Vasculitis, Mechanical Obstruction (tumours, adhesions, hernia, volvulus)

Question 2

What is the arterial supply and watershed areas of the colon?

Answer 2

Arterial supply (Colon & Rectum)
- SMA (L1): Ileocolic, right colic and middle colic arteries

• IMA (L3): Left colic, sigmoid, superior rectal arteries
• Internal Iliac Artery (L4): Middle and inferior rectal arteries
• Marginal Artery of Drummond: a continuous arterial arcade,
  running along the distal mesentery near the inner border of the colonic
  wall
• Arc of Riolan (meandering mesenteric artery): connects the middle colic branch of SMA with the left colic branch of the IMA at the root of the mesentery. (can be absent as an anatomical variant)

Watershed areas
- Right Colon – vulnerable in systemic low flow states (i.e. hypotension from haemorrhage / sepsis, heart failure), also vulnerable to embolic occlusion (2 reasons: ileocolic is a terminal branch of SMA, straight take-off from SMA (making it susceptible to embolic occlusion)
- Splenic Flexure – receives blood supply from SMA & IMA
- Rectosigmoid Junction – vulnerable in presence of IMA stenosis with age from atherosclerosis, post-surgery (i.e. IMA ligation)

Question 3

What can be expected on history?

Answer 3

• Symptoms are dependent on severity of the ischemia + medical history is critical in diagnosis of ischemic colitis
• Sudden onset of abdominal pain (crampy), not well localized
• Mild hematochezia, starting within 24hr of abdominal pain
• Low-grade fever
• Nausea and vomiting

Question 4

What is the progression like?

Answer 4

3 progressive clinical stages have been described:
- Hyperactive phase – severe abdominal pain with passage of bloody, loose stools (blood loss is mild)
- Paralytic phase – pain becomes more continuous and diffuse, abdomen more tender and distended without bowel sounds
- Shock phase – massive fluid, protein and electrolytes start to leak through the damaged gangrenous mucosa. Severe
dehydration with shock and metabolic acidosis may develop

Question 5

What might be found on PE?

Answer 5

Clinical Examination
- Vital signs: any hypotension, tachycardia (any AF)
- Abdomen: tenderness over affected colon, any signs of peritonism
- DRE: blood in stools

Question 6

How to differentiate between small bowel or colonic ischemia?

Answer 6

Question 7

Investigations

Answer 7

Biochemical
- FBC: leukocytosis >15 in 75%, high Hb/ Hct (due to plasma loss/ hemoconcentration),
- U/E/Cr: assess hydration status, renal function
- ABG: Metabolic acidosis (persistent) – 50%
- Lactate
- PT/PTT: hypercoagulable states (if present, can add Protein C/S, AT III)
- Raised amylase / LDH
- Markers for ischemia – lactate, LDH, amylase level, leucocytes, ALP

Imaging
- AXR (supine)
▪ Colonic Dilatation
▪ Thumb-printing (i.e. from submucosal haemorrhage and oedema in the colon) – most common finding, non-specific
▪ Mural thickening
▪ Intramural air/ air in portal venous system (ischemia)
▪ Free air

• CTAP (with contrast) – can localize site of colitis
  ▪ Segmental pericolonic fat stranding
  ▪ Thickened bowel wall
  ▪ Assess for etiology & complications (i.e. transmural ischemia, perfration)
• Occlusion as the underlying etiology: SMA thrombosis or superior mesenteric vein / portal vein thrombosis,
• Transmural Ischemia: intestinal pneumatosis, portal venous gas, lack of bowel wall enhancement
• Perforation: free air
• Endoscopy (gold-standard, i.e. colonoscopy / sigmoidoscopy)
  ▪ Mild ischemic colitis
• Pale appearing mucosa
• Mucosal edema
• Mucosal erythema
• Petechial haemorrhage
• Single longitudinal ulcer (i.e. single-stripe sign)
  ▪ Severe ischemic colitis
• Dusky mucosa
• Submucosal haemorrhage
• Hemorrhagic ulceration
• Segmental distribution with abrupt change to normal mucosal in unaffected region
• Histology – inflammatory cell infiltration, mucosal oedema, sloughing, altered crypt morphology, haemorrhage within the lamina propria

Question 8

Management?

Answer 8

Non-surgical Management (80%)
- NBM (bowel rest)
- IV analgesia (i.e. IV paracetamol + IV tramadol)
- Aggressive fluid hydration (aim to optimize perfusion to ischemic colon)
- ± NGT decompression – if having nausea / vomiting, dilated bowel loops
- Empirical broad-spectrum antibiotics – colonic ischemia → intestinal epithelial barrier failure → bacterial translocation → septic complications (i.e. IV ceftriaxone & flagyl)
- serial abdominal examination
- ± limit vasopressor use, optimize cardiac output
- ± endoscopy (to evaluate for worsening ischemia)
Surgical Management (20%)
- Indications (acute): peritonitis, pneumoperitoneum, massive haemorrhage, transmural necrosis (i.e. pneumatosis / portal venous gas
- Indications (chronic): intractable symptoms >2wks, recurrent sepsis, chronic colitis, ischemic stricture, malnutrition from protein losing colopathy

• Surgical Intervention
  ▪ Midline incision, evaluation of small / large intestine for signs of ischemia
  ▪ ± segmental colonic resection with well-perfused resection margin +/- end ileostomy / colostomy
  ▪ ± temporary abdominal closure with planned second relook laparotomy in 24 hours (if extensive / patchy involvement)
  ▪ ± subtotal colectomy & end ileostomy (i.e. if entire colon ischemic)