1.12 Mesenteric Ischemia

Question 1

Describe the three major vascular trunks arise from the aorta to supply the intestines.

Answer 1

o Celiac axis: supplies oxygenated blood to the foregut which includes portions of the liver, spleen, gallbladder, pancreas, esophagus, and stomach.

o Superior mesenteric artery (SMA): delivers blood to the small intestine (distal duodenum extending to the appendix), in addition to the ascending and proximal transverse colon.

o Inferior mesenteric artery (IMA): distributes blood to the distal portion of transverse colon, the descending colon, and the rectum.

Question 2

Your patient is suffering from mesenteric ischemia. In broad terms, what causes this, how is it categorized?

Answer 2

• Results from decreased blood flow
  
  • Hypoperfusion: shock, vasospasm, or vascular occlusion
• Categorized as either acute or chronic based on how quickly the condition develops

Question 3

Your patient has acute mesenteric ischemia (AMI). Why is mortality rate 40-70%?

What circumstance leads to 70% fatality?

Describe the causes of Occlusive AMI versus Non-Occlusive AMI.

Describe Mesenteric Venous Thrombosis specifically.

Answer 3

• AMI
  
  • 40-70% mortality due to necrosis, perforation, and sepsis
  • 70% fatality if diagnoses > 24h after onset
• Occlusive AMI
  
  • Causes
    
    • 50% caused by SMA embolus (i.e. a fib, endocarditis)
    • 15-25% of cases caused by arterial thrombosis (i.e. CHF, PAD, CAD)
    • Vasospasm in intestinal vessels
    • Mesenteric vessel occlusion due to intestinal torsion from strangulated hernia or volvulus
• Non-Occlusive AMI
  
  • Lead to: bowel ischemia or infarction due to decreased mesenteric blood flow
  • Causes
    
    • Low CO
    • Hotn (MAP < 45)
    • Shock causes non-occlusive vasoconstriction of the splanchnic vasculature (liver, pancreas, spleen, gut circulation)
      
      • Small intestine can compensate for decreases in up to 75% of blood flow, but only for a max of 12h
    • Vasopressors, esp at max doses
  • Mesenteric Venous Thrombosis
    
    • Less common (15-25%)
    • Causes
      
      • Hypercoagulability, abd trauma, intra-abdominal hypertension, vasculitis, pancreatitis, cirrhosis, IBD
      • Intravascular volume loss d/t surgery, intra-abdominal infections, oral contraceptives, smoking

Question 4

Describe your patient’s classic AMI presentation.

How about abd exam?

Answer 4

• AMI Presentation:
  
  • Sudden onset of severe abdominal pain
  • Pain is out of proportion to the patient’s abdominal exam
  • Pain is typically periumbilical area or epigastrium.
• Abdominal exam:
  
  • Diffuse, non-specific tenderness without peritoneal signs such as guarding or rebound tenderness.
  • GI bleeding occurs late in the disease process

Question 5

Your patient with AMI commonly has involvement of which regions of the mesenteric vasculature?

Describe the patho and potential impact

Answer 5

• Location(s) of ischemia:
  
  • Commonly, “watershed” regions are involved.
  • Watershed regions are supplied by the distal ends of two major arteries.
  • The rectum, rectosigmoid junction, splenic flexure, and left colon, which are supplied by both the SMA and IMA.
• During hypovolemia or hypoperfusion, watershed areas are susceptible to ischemia
• The abrupt decrease in blood flow to these portions of the large intestine leads to abdominal pain, which may be located in the left side
• If the entire thickness of the bowel wall is involved, bowel perforation and peritonitis can occur

Question 6

Your patient with chronic mesenteric ischemia is likely to have what risk factors?

What portion of the bowel is usually affected?

What is the patho/progression of the disease?

When do symptoms usually occur, and what are the symptoms?

Answer 6

• Patients with CMI typically have wide-spread atherosclerotic disease, including CAD
  
  • Risk factors include: Smoking, DM, HTN, and HLD
• CMI typically affects the small intestine
• Patho/progression:
  
  • Inflammation occurs over a period of time
  • Collateral circulation develops
  • Symptoms occur when two of the three major arteries are affected
• Symptoms
  
  • Symptoms occur gradually and may include abdominal pain, nausea, vomiting, and may progress to gastrointestinal bleeding
  • Pain after eating (typical onset is between 10-180 minutes after eating), due to the need for increased post-prandial intestinal blood flow
  • Pain can lead to fear of eating (sitophobia) and weight loss.

Question 7

Describe your diagnostic process for mesenteric ischemia.

What should give you a particularly high index of suspicion?

Labs?

Lab findings?

Imaging?

Imaging findings?

Answer 7

• Diagnosis
  
  • Mesenteric ischemia is often a diagnosis of exclusion
  • Early diagnosis and intervention decrease mortality.
  • Have a high index of suspicion of AMI in patients with acute abdominal pain out of proportion to exam findings, especially those over age 60 with a history of vascular disease
    
    • Some may have abdominal bruits
    • Some may have decreased lower extremity hair growth
    • May have weak peripheral pulses
• Lab tests:
  
  • BMP, lactic acid, LFTs, CBC, PT, aPTT, LDH, and stool guiac
  • Leukocytosis, metabolic acidosis, and elevated lactic acid levels are common as AMI progresses
  • These lab values may be normal early in the course of AMI
• Imaging:
  
  • Biphasic CTA (CT angiography) abdomen & pelvis with and without IV contrast is the most common test for definitive diagnosis
    
    • Benefits: Non-invasive and are able to evaluate for multiple causes of abdominal pain and leukocytosis compared to angiography
    • Non-contrasted scan allows for visualization of arterial calcification
    • Arterial and venous phases (biphasic) help determine the presence of arterial and venous thrombosis
    • CTA is 96% sensitive and 94% specific for detecting mesenteric ischemia
    • Oral contrast is not needed to diagnose intestinal ischemia
    • Findings
      
      • CT scans can assess for bowel wall edema or intramural hemorrhage
      • Reperfusion events are associated with bowel wall thickening and mesenteric fat stranding on CT
      • Free fluid within the abdominal cavity is commonly found in patients with non-occlusive AMI
      • Free air is an uncommon finding

Question 8

Describe your initial treatment for acute mesenteric ischemia

Answer 8

• NPO, bowel rest initiated, nasogastric decompression
• Medical therapy includes smoking cessation, control of HTN, and administering statins and aspirin
• Goal is to restore adequate organ perfusion
  
  • Isotonic IV fluids helps prevent worsening ischemia.
  • If possible, avoid using vasoconstrictor agents to increase BP since they may worsen AMI due to decreased mesenteric blood flow.
  • Inotropic therapy may improve hemodynamics by increasing stroke volume (SV) and cardiac output (CO).
  • Broad-spectrum antibiotics (gram negative & anaerobic coverage) are indicated in patients with evidence of AMI due to the risk of necrotic bowel perforation and peritoneal contamination
  • IV analgesia.

Question 9

Describe definitive treatment for mesenteric ischemia

Answer 9

• Medical therapy is commonly used for non-occlusive disease
  
  • Continuously infusing nitroglycerin, or other parenteral vasodilators may augment blood flow
  • Continuous infusions of papaverine are administered into the mesenteric arteries with intra-arterial catheters placed during angiography to improve circulation to the gut
    
    • Papaverine decreases arterial spasms, allowing for improved blood flow
• Patients without perforation or any absolute contraindications
  
  • Administering thrombolytics within eight hours of the onset of abdominal pain may restore blood flow
• Patients with acute occlusion who present with acute abdominal pain, signs of peritoneal irritation, evidence of necrosis, and/or clinical deterioration
  
  • Should have exploratory laparotomy with surgical embolectomy and/or bowel resection may be necessary depending on size of the clot(s) and the extent of the intestinal ischemia
• Post-operatively
  
  • Patients are anticoagulated with either low-molecular weight (LMWH) or unfractionated heparin (UFH)
  • Hypercoagulable patients may require life-long oral anticoagulation
  • Patients with CMI can undergo angioplasty and stenting of the affected artery
  • Signs of stent restenosis are similar to those patients have pre-treatment, including post-prandial pain
  • Post-operatively, patients are at risk for bleeding, infection, deep venous thrombosis (DVT), and protracted ileus
  • Patients who are post-bowel resection for AMI may require long-term parenteral nutrition (PN)
  • Patients who have had significant amounts of bowel resected are at risk for diarrhea and malabsorption of nutrients.