Acute Mesenteric Ischemia (AMI)

Victor Roman Steele, MD
The Operative Review of Surgery. 2023; 1:253-261.

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Table of Contents

Definitions
Etiology
Presentation and Diagnosis
Treatment
Surgical Technique

References

Definitions

Definitions

  • Intestinal Ischemia: Inadequate Blood Supply to Meet Demands of Intestines
    • Mesenteric Ischemia: Ischemia of the Small Intestine (Often Used Interchangeably with Intestinal Ischemia)
    • Colonic Ischemia: Ischemia of the Large Intestine
  • Splanchnic/Visceral Ischemia: A Broader Term to Describe Ischemia of the Intestine and Other Solid Organs (Liver, Kidney, Spleen)

Classification/Timing

  • Acute Mesenteric Ischemia (AMI) – Rapid Onset Over Hours-Days
    • Most Common Cause: Arterial Embolism
  • Chronic Mesenteric Ischemia (CMI) – Slow Onset Over Weeks-Months

Causes

  • Arterial Pathology:
    • Arterial Embolism
    • Arterial Thrombosis
  • Mesenteric Venous Thrombosis (MVT)
  • Non-Occlusive Mesenteric Ischemia (NOMI)
  • Other General Causes of Intestinal Ischemia:
    • Incarcerated/Strangulated Hernia
    • Internal Hernia
    • Adhesions
    • Bowel Volvulus
    • Extreme Bowel Distention
    • Vasculitis

Bowel Ischemia 1,2

  • Visceral Perfusion Fails to Meet Metabolic Demand
    • Inadequate Collateral Circulation, Smaller Caliber Vessels, and Longer Duration of Ischemia Increase the Risk of Damage
    • Bowel Autoregulation Can Enhance Oxygen Extraction and Perfusion by Vasodilation
    • Small Intestine Can Compensate for a 75% Reduction in Mesenteric Blood Flow for up to 12 Hours 3
  • Bowel Damage is Caused by Both Ischemic Hypoxia and Reperfusion Injury
  • Ischemia Can Progress to Frank Bowel Necrosis and Perforation
  • Bowel Mucosa is Affected First Due to Higher Metabolic Demand
  • Ischemia Causes the Release of Toxic Byproducts and Oxygen Free Radicals
    • Can Incite a Multisystem Organ Failure

Mortality

  • Historically Associated with Exceptionally High Mortality Rates (70-90%) 4,5
  • In-Hospital Mortality Still High But Significantly Decreased (17-21%) 6,7

Necrotic Bowel from Mesenteric Ischemia 8

Etiology

Arterial Embolism

  • Most Common Cause of Acute Mesenteric Ischemia (40-50%) 9,10
  • Embolic Source:
    • Heart (Left Atrium, Ventricle, or Valves) – Most Common
    • Aortic Plaques
  • Risk Factors: 9,11
    • Atrial Fibrillation
    • Recent Myocardial Infarction
    • Prosthetic Valves
    • Ventricular Aneurysm
    • Rheumatic Heart Disease
  • SMA is at High Risk for Embolism Due to Acute Angle Off Aorta (30-60 Degrees) 12,13
    • Decreased Angle of Takeoff Compared to Other Mesenteric Vessels
  • Most Common Site: SMA Just Distal to the Middle Colic Artery
    • SMA Begins to Narrow After the Middle Colic Takeoff
    • Ischemia Spares the Proximal Jejunum and Transverse Colon
  • 20% are Associated with Concurrent Emboli to Other Structures (Spleen, Kidney, etc.) indicating a Proximal Embolic Source 14

Arterial Thrombosis

  • Second Most Common Cause of Acute Mesenteric Ischemia (20-30%) 9,10
  • Often Have History of Chronic Mesenteric Ischemia with “Food Fear” and Weight Loss
  • Most Common Site: SMA Origin
    • Ischemia Involves the Entire Distribution
  • Symptomatic SMA Thrombosis Most Often Has a Concurrent Celiac Occlusion – Due to Collaterals that Would Otherwise Compensate 15
  • Higher Mortality Than Arterial Embolism

Mesenteric Venous Thrombosis (MVT)

  • Least Common Cause of Acute Mesenteric Ischemia (5-10%) 9,10
  • Often Associated with Virchow’s Triad (Vessel Injury, Blood Flow Stasis, and Hypercoagulability)
  • Classification:
    • Primary: Idiopathic
    • Secondary: From Underlying Process (80-90% – Most Common) 10
  • 50% Have a Prior History of Thrombosis 16
  • Often Vague and Less Dramatic Presentation Over 1-2 Weeks with Bloating, Distention, and Nausea

Non-Occlusive Mesenteric Ischemia (NOMI)

  • Third Most Common Cause of Acute Mesenteric Ischemia (20%) 9,10
  • Ischemia Without an Associated Thromboembolic Occlusion
  • Risk Factors:
    • Decreased Perfusion from Low Cardiac Output (Most Common Cause)
    • Hypovolemia
    • Shock States
    • Systemic Vasopressors
    • Prior Myocardial Infarction
    • Abdominal Compartment Syndrome
    • Aortic Regurgitation
    • Hepatic or Renal Failure/Hemodialysis
    • Cocaine-Induced Vasoconstriction
  • Most Vulnerable Sites: Watershed Areas
  • Often More Insidious Onset than Arterial Disease
  • Highest Mortality Rate – Often Associated with Multiple Organ Failure, Heart Failure, and Sepsis

Mesenteric Ischemia with Embolism on CTA 17

Mesenteric Ischemia from SMA Stenosis on CTA 18

Mesenteric Venous Thrombosis on CTA: SMV Thrombus (Blue Arrows), Intact SMA (Red Arrows), Edematous Jejunum (White Arrows) 19

NOMI with Ischemia at Griffith’s Point 20

Presentation and Diagnosis

Presentation 21,22

  • Abdominal Pain (95% – Most Common Symptom)
    • Sudden and Severe
    • “Pain Out of Proportion” – Patient Reports Significant Abdominal Pain That Does Not Correlate to Physical Exam Findings with Only Mild Abdominal Tenderness
  • Nausea and Vomiting (35-44%)
  • Diarrhea (35%)
  • Blood per Rectum (16%)
    • Classically Sudden and Forceful Bloody Diarrhea
  • Abdominal Distention
  • Fever
  • *Clinical Scenarios and History Can Help to Differentiate the Etiology

Diagnosis

  • CTA is the Preferred Diagnostic Imaging and Should Be Performed as Soon as Possible 10
  • Poor Diagnostic Studies:
    • Mesenteric Duplex US – Obscured by Bowel Gas in the Acute Setting and More Operator Dependent
    • Plain Film X-Ray
    • Laboratory Studies – May See Elevated Leukocytosis (90%) and Lactate (88%) but Not Specific 23

Treatment

Initial Managements 10,24,25

  • Aggressive Fluid Resuscitation
  • Aggressive Electrolyte Correction
  • Nasogastric Decompression
  • IV Heparin Infusion
    • Not Necessary for NOMI
  • Broad-Spectrum Antibiotics (High Risk for Bacterial Translocation and Sepsis with Early Loss of the Mucosal Barrier)
  • Indications for Emergent Exploratory Laparotomy: 25
    • Hemodynamically Unstable
    • Overt Peritonitis
    • Perforation

Definitive Treatment

  • Arterial Embolus: Open SMA Embolectomy
    • May Consider Endovascular Intervention in Stable and Nonperitoneal Patients
  • Arterial Thrombosis: Open SMA Bypass
    • May Consider Endovascular Intervention in Stable and Nonperitoneal Patients
  • Mesenteric Venous Thrombosis (MVT): IV Heparin Infusion
    • Rescue Options if Continues to Decompensate Despite Anticoagulation: 10
      • Percutaneous Transhepatic Thrombolysis
      • TIPS with Aspiration or Thrombolysis
      • Arterial Approaches via the SMA
    • Will Also Require Prolonged Anticoagulation at Discharge (6 Months vs Lifelong)
  • Non-Occlusive Mesenteric Ischemia (NOMI): Improve Circulatory Support and Catheter-Directed Intra-Arterial Vasodilators to SMA
    • The Focus of Treatment Should be to Correct the Underlying Cause When Possible 10
    • Vasodilators: Prostaglandin E1 (PGE1), Nitroglycerine, or Papaverine 26,27

Endovascular Treatment

  • Generally Avoided in Acute Mesenteric Ischemia if There is Concern for Bowel Ischemia Requiring an Open Surgical Evaluation 28
  • May Be Preferred if There Are No Signs of Bowel Necrosis and the Expertise is Available with No Contraindications – Evolving 28
    • Decreased Morbidity and Mortality Over Open Surgery for Arterial Occlusive AMI 29
  • Interventions:
    • SMA Embolism:
      • Embolectomy/Percutaneous Aspiration
      • Thrombolysis
    • SMA Thrombosis:
      • Thrombectomy
      • Thrombolysis
      • Percutaneous Transluminal Angioplasty (PTA)
      • Stenting

Surgical Technique

Exploratory Laparotomy

  • Bowel Resection:
    • Resect Areas of Gross Necrosis Before Embolectomy or Revascularization – Risk for Infection After Revascularization
    • Reevaluate Areas of Partial Ischemia After Embolectomy or Revascularization – Preserve as Much Viable Bowel as Possible
    • Massive Gut Necrosis May Be Best Managed By Comfort Care Measures and Evaluation of Underlying Comorbidities and Advanced Directives Should Be Considered Prior to Resection 10
  • Low Threshold for Leaving an Open Abdomen and Second Look in 24-48 Hours to Reassess Bowel Viability if Questioned 30-32

Exposure of the SMA

  • The SMA May or May Not Have a Palpable Pulse and May Be Difficult to Identify
  • Anterior Approach:
    • Retract the Transverse Colon Cephalad and the Small Bowel to the Right
    • Palpate the SMA at the Root of the Transverse Colon Mesentery at the Inferior Margin of the Pancreas
    • Carefully Dissect Down to Isolate the Artery
    • Multiple Small Venous Branches from the SMV May Cross Over the SMA and Require Division (SMA Lies to the Left of the SMV)
  • Lateral Approach:
    • Take Down the Ligament of Treitz
    • Retract the Entire Small Bowel to the Right
    • Carefully Dissect Down to Isolate the Artery

SMA Embolectomy

  • Expose the SMA – Through an Anterior Approach
  • Obtain Proximal and Distal Control of the Artery
  • Make a Proximal Transverse Arteriotomy
  • Perform the Embolectomy Using a 3-4 mm Fogarty Balloon Catheter
    • Insert Both Proximally and Distally to Extract Embolus
    • Repeat Passage as Needed to Ensure All Clot is Removed
  • Flush with Heparinized Saline
  • Close Arteriotomy Primarily with 6-0 Prolene Sutures
  • *Rarely May Consider Longitudinal Incision with Patch Angioplasty if Concerned for Small Caliber Vessel and Resulting Stricture

SMA Bypass

  • General Technique:
    • Expose the SMA – Through a Lateral Approach
    • Expose the Inflow Site
    • Anastomose the Bypass After Obtaining Proximal and Distal Control at Each Site Sequentially
    • Cover the Graft with an Omental Buttress to Protect and Decrease the Risk of Kinking
  • Inflow Bypass Route:
    • Right Common Iliac Artery to SMA – The Preferred Route in Emergent Situations
      • Retrograde in “Lazy-C” Configuration
      • Avoids Aortic Cross Clamping and Provides Good Positioning with Minimal Kinking
    • Other Retrograde Sources if Right Common Iliac is Diseased:
      • Left Common Iliac Artery
      • Infrarenal Aorta
    • Antegrade Supraceliac Bypass
      • Technically More Difficult Dissection and Increases the Physiologic Insult from Aortic Cross Clamping
      • Only if Infrarenal Aorta and Iliacs are Diseased
    • May Consider Bifurcated Prosthetic Conduit to Both the Celiac and SMA if Both are Diseased in Select Circumstances – More Often Used in a Chronic Mesenteric Ischemia
  • Graft Options:
    • Synthetic Graft (Dacron) – Generally Preferred
      • Benefits:
        • Better Patency
        • Better Size Match
        • Easier Handling
        • Kink Resistant
        • Avoid Additional Time Required for Vein Harvesting
      • Generally Avoided in the Setting of Bowel Necrosis or Perforation
    • Autogenous Vein
      • Preferred if Bowel is Necrosed or with Peritoneal Spillage
      • Requires a Vein of Suitable Size and Quality – Most Commonly the GSV
      • Higher Risk of Kinking and Requires Extra Time for Harvesting

SMA Bypass with C-Loop Graft 33

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