Gastrointestinal & Hepatic · Topic 15 of 26
Acute Mesenteric Ischemia
Gastrointestinal · vascular emergency
Acute Mesenteric Ischemia
Severe pain with a soft abdomen is ischemic bowel until CT angiography says otherwise — lactate rises only once bowel is dying.
Key numbers
CT angiography without delay6 h delay ≈ 2× mortality
Lactate rises late; normal does not excludelactate > 2 mmol/L
01 · Look forPain out of proportion to the exam
Severe abdominal pain with a soft, barely tender abdomen should be assumed to be acute mesenteric ischemia until disproven; peritoneal signs appear only once the bowel has infarcted.
02 · DoCT angiography without delay
Order CT angiography (arterial and venous phases) without delay for any suspicion of mesenteric ischemia — delay in diagnosis drives the 30–70% mortality, and each 6 hours of delay roughly doubles it.
03 · The numberLactate rises late; normal does not exclude
No lab test rules mesenteric ischemia in or out: lactate rises with necrosis, so it is late, and a normal value does not exclude early ischemia; lactate above 2 mmol/L is associated with irreversible ischemia.
01
Causes & risk factors
Why it happensArterial embolism is the most common causeCauses: SMA embolism about 50% (atrial fibrillation, heart failure, valve disease, prior emboli), arterial thrombosis 15–25% (atherosclerosis), nonocclusive ischemia about 20%, and venous thrombosis 5–15% (hypercoagulable state, portal hypertension, abdominal inflammation).
02
Presentation
What you'll seePostprandial pain history suggests arterial thrombosisSudden pain suggests an embolus and gradual pain venous thrombosis; a history of postprandial pain (intestinal angina) suggests thrombosis on chronic mesenteric atherosclerosis.
03
Diagnosis & monitoring
Work-upInfarction is the turning point for survivalMortality is low when ischemia is treated before infarction but high afterward; bowel necrosis can begin within 6 hours of symptom onset, so clinical suspicion should outrank slow diagnostic tests.
04
Do right now
In this orderFirst moves
1
→CT angiography without delay6 h delay ≈ 2× mortality
2
→Resuscitate, heparinize, give broad antibiotics
3
Peritonitis: laparotomy; otherwise revascularize
Why each step
CT angiography without delayOrder CT angiography (arterial and venous phases) without delay for any suspicion of mesenteric ischemia — delay in diagnosis drives the 30–70% mortality, and each 6 hours of delay roughly doubles it.
Resuscitate, heparinize, give broad antibioticsOnce ischemia is diagnosed, start IV fluid resuscitation, correct electrolytes, decompress with a nasogastric tube, give broad-spectrum antibiotics immediately, and start full-dose anticoagulation (unfractionated heparin) before any procedure.
Peritonitis: laparotomy; otherwise revascularizeOvert peritonitis means immediate laparotomy to resect necrotic bowel and restore flow; without it, revascularize arterial occlusion — endovascular therapy is first choice where expertise exists, open embolectomy or bypass otherwise.
05
Management
OrdersVenous thrombosis: unfractionated heparin infusion firstMesenteric venous thrombosis without peritonitis is managed nonoperatively with a continuous unfractionated heparin infusion; systemic thrombolysis is rarely indicated, and resection is limited to clearly necrotic bowel.
Second-look laparotomy within 24–48 hoursAfter resection, use damage-control surgery with temporary abdominal closure and a planned second look within 24–48 hours to reassess questionable bowel before anastomosis or stoma.
Long-term anticoagulation after embolism or venous thrombosisAfter arterial embolism or venous thrombosis, plan long-term anticoagulation (with antiplatelet therapy after arterial stenting or bypass) and surveillance of stent or graft patency.
06
Red flags & don'ts
Avoid harmNonocclusive ischemia in vasopressor-dependent shock complicationSuspect nonocclusive mesenteric ischemia in a critically ill patient on vasopressors (shock, heart failure, after cardiac surgery) with abdominal pain or distention and organ dysfunction; treat the low-flow state, wean vasoconstrictors, and consider catheter-directed papaverine.
07
Arterial embolus or mesenteric venous thrombosis?
Commonly confused| Share of cases | About 50% — the most common |
|---|---|
| Onset | Sudden |
| Risk factors | Atrial fibrillation, heart failure, valve disease, prior emboli |
| First treatment | Revascularize — endovascular or embolectomy |
08
More detail
ReferenceShow 5 reference facts
Give antibiotics for at least 4 days in stable immunocompetent patients, longer with ongoing infection, and narrow them to culture results.
Leukocytosis occurs in over 90% and lactic acidosis in about 88%, but neither is specific; a normal D-dimer argues against intestinal ischemia.
The SMA supplies the distal duodenum to the splenic flexure; the splenic flexure is a watershed between SMA and IMA territories. Ischemic colitis is a different, small-vessel mucosal disease that mainly bleeds.
Plain radiographs mainly exclude other causes such as perforation; portal venous gas and pneumatosis intestinalis on radiograph or CT are late signs of infarction.
Massive resection leaves short bowel syndrome needing prolonged parenteral nutrition or transplant referral; with near-total necrosis, discuss goals of care, including palliation.
Waiting for the lactate means waiting for infarction — scan on suspicion.
Sources · Merck Manual Professional — Acute Mesenteric Ischemia · Acute mesenteric ischemia: updated guidelines of the World Society of Emergency Surgery. World J Emerg Surg 2022 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).