Acute Mesenteric Ischemia: Arterial & Venous
Comprehensive emergency evaluation and protocolized resuscitation of Acute Mesenteric Ischemia (AMI): four distinct pathophysiologic etiologies (Superior Mesenteric Artery [SMA] Embolism [50%], SMA Thrombosis [25%], Non-Occlusive Mesenteric Ischemia [NOMI/vasospasm, 20%], and Mesenteric Venous Thrombosis [MVT, 5–10%]), pathognomonic physical finding ('pain out of proportion to physical examination'), serum lactate limitations, CT Angiography of the mesenteric vessels (biphasic CTA protocol), systemic anticoagulation, and emergent vascular revascularization.
Resuscitation Quick Actions • First 2 Minutes
Pain Out of Proportion
Agonizing severe visceral abdominal pain with a SOFT, completely NON-TENDER abdomen is MESENTERIC ISCHEMIA until proven otherwise
Lactate Trap
DO NOT wait for lactate to rise! Normal serum lactate does NOT rule out early reversible ischemia; elevated lactate = bowel gangrene
Diagnostic Gold Standard
Biphasic CT Angiography (CTA) of Abdomen and Pelvis with IV contrast; DO NOT give oral contrast (delays scan and obscures vessels)
Immediate Anticoagulation
Unfractionated Heparin 80 units/kg IV bolus + 18 units/kg/hr infusion stat upon suspicion to halt thrombus propagation
Avoid Vasopressors
Avoid pure alpha-vasopressors (phenylephrine, high-dose norepinephrine); induces catastrophic splanchnic vasoconstriction
NOMI Management
Non-occlusive mesenteric ischemia (cardiogenic shock/ICU): resuscitate cardiac output and infuse intra-arterial Papaverine
Bottom-Line Clinical Pearl
Acute Mesenteric Ischemia (AMI) is a catastrophic vascular emergency with an overall mortality rate exceeding 50% to 70%, where survival is determined entirely by time to revascularization before transmural bowel gangrene develops. The classic pathognomonic presentation is severe, agonizing abdominal pain completely OUT OF PROPORTION TO PHYSICAL EXAMINATION (the patient writhes in severe pain, but the abdomen is soft and non-tender on palpation). A normal serum lactate DOES NOT rule out early mesenteric ischemia; elevated lactate is a LATE sign indicating irreversible transmural necrosis and gangrene! The diagnostic study of choice is BIPHASIC CT ANGIOGRAPHY (CTA) OF THE ABDOMEN AND PELVIS (IV contrast without oral contrast). Immediately administer Unfractionated Heparin (80 units/kg IV bolus) and broad-spectrum antibiotics, and alert Vascular Surgery for emergent catheter-directed embolectomy, stenting, or open surgical bypass.
The Superior Mesenteric Artery (SMA) supplies the entire small intestine from the ligament of Treitz to the mid-transverse colon. Acute interruption of blood flow leads to mucosal ischemia within 1–2 hours, followed by full-thickness transmural necrosis, bacterial translocation, sepsis, and death within 8–12 hours:
| Subtype & Frequency | Etiology & Risk Factors | Anatomical Site of Occlusion | Clinical Presentation & Onset |
|---|---|---|---|
| SMA Embolism (50%) | Cardioembolism from Atrial Fibrillation, post-MI mural thrombus, or endocarditis | Lodges 3 to 8 cm distal to SMA origin at vascular branch points (typically spares the proximal jejunum via the inferior pancreaticoduodenal artery) | Sudden, hyperacute onset of excruciating abdominal pain, forceful bowel evacuation (vomiting and diarrhea); rapid progression. |
| SMA Thrombosis (25%) | Acute in situ thrombosis superimposed on severe pre-existing chronic mesenteric atherosclerosis | Occurs at the ostium/origin of the SMA; compromises collateral circulation, causing massive pan-intestinal infarction | History of 'intestinal angina' (postprandial dull pain, food fear, weight loss) followed by sudden acute worsening; slower, insidious progression. |
| Non-Occlusive Mesenteric Ischemia (NOMI) (20%) | Profound splanchnic vasoconstriction in low-flow states (cardiogenic shock, dialysis, severe sepsis, high-dose vasopressors, cocaine) | Diffuse, non-occlusive narrowing of secondary and tertiary SMA branches throughout the mesenteric arcade | Critically ill ICU patient with unexplained worsening lactic acidosis, abdominal distension, and sepsis. |
| Mesenteric Venous Thrombosis (MVT) (5–10%) | Thrombus in mesenteric or portal veins due to hypercoagulable states (Factor V Leiden, malignancy, oral contraceptives, cirrhosis) | Superior mesenteric vein; produces severe venous engorgement, edema, and secondary arterial inflow failure | Indolent, progressive vague abdominal pain over several days to weeks prior to emergency presentation. |
1. The Serum Lactate Trap: In early, potentially reversible mesenteric ischemia, serum lactate is completely normal in up to 25% of cases! Do not be reassured by a normal lactate. An elevated lactate is a late marker that signals irreversible transmural bowel gangrene and imminent perforation.<br>2. Biphasic CT Angiography (CTA): The definitive imaging modality is a CT Angiogram of the Abdomen and Pelvis with IV contrast (thin-slice arterial and portal-venous phases). DO NOT administer oral contrast, as positive oral intraluminal contrast obscures vascular enhancement and mucosal wall evaluation.<br>3. Key CT Angiography Findings: Vascular filling defect in the SMA; bowel wall thickening or thinning ('paper-thin' wall in arterial infarction); lack of mucosal enhancement; mesenteric fat stranding; bowel dilation; and late signs: pneumatosis intestinalis (gas inside bowel wall), portal venous gas, and free intraperitoneal air.
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