Gastrointestinal

Acute mesenteric ischemia: pain out of proportion and management

Clinical Overview and When to Suspect Acute Mesenteric Ischemia

— Arterial embolism (~50%): SMA embolus, usually from LA appendage (AFib), recent MI with mural thrombus, or valvular disease; lodges 3–10 cm distal to SMA origin, sparing proximal jejunum

— Arterial thrombosis (~15–25%): superimposed on chronic atherosclerosis at SMA origin; often history of postprandial pain, food fear, weight loss ("intestinal angina")

— Nonocclusive mesenteric ischemia (NOMI, ~20%): low-flow state from shock, sepsis, vasopressors, cocaine, ergot, digoxin; ICU patients

— Mesenteric venous thrombosis (~10%): younger patients, hypercoagulable states (Factor V Leiden, OCPs, malignancy, cirrhosis, portal HTN), more indolent course over days

Acute mesenteric ischemia (AMI) is a true surgical/vascular emergency where intestinal perfusion fails, leading to bowel infarction, sepsis, and death if not rapidly diagnosed

Mortality remains 60–80% when diagnosis is delayed beyond 12–24 hours — survival is driven almost entirely by time to revascularization

Four mechanistic subtypes (must distinguish for management):

When to suspect: older patient (>60) with sudden severe abdominal pain out of proportion to a benign exam, especially with AFib, recent MI, vascular disease, or hypercoagulability

Classic triad (only ~30% have all three): severe abdominal pain, gut emptying (vomiting/diarrhea), and a source of embolism

Lactate may be normal early — do not be reassured by normal labs in the first hours

Board pearl: "Pain out of proportion to exam" in a patient with AFib not on anticoagulation = AMI from SMA embolus until proven otherwise. Next step is CT angiography of the abdomen — not abdominal ultrasound, not plain films, not waiting for lactate. Empiric heparin, IV fluids, broad-spectrum antibiotics, and immediate vascular surgery consultation should occur in parallel with imaging.

Presentation Patterns and Key History

— Embolic AMI: abrupt, "thunderclap" pain in minutes; often with simultaneous forceful gut emptying (vomiting, diarrhea, sometimes bloody)

— Thrombotic AMI: more gradual over hours; preceded by weeks–months of postprandial pain, food fear, and weight loss (chronic mesenteric ischemia transitioning to acute)

— NOMI: insidious; the critically ill ICU patient who develops worsening ileus, abdominal distention, metabolic acidosis, or rising pressor requirement

— Mesenteric venous thrombosis: subacute, days of vague abdominal pain, nausea, anorexia; often missed initially

— AFib (especially if anticoagulation interrupted for procedure or noncompliance)

— Recent MI with LV thrombus, dilated cardiomyopathy, endocarditis

— Prior peripheral arterial disease, prior CABG, smoking, diabetes, hyperlipidemia

— Hypercoagulable history: prior DVT/PE, malignancy, JAK2 mutation, inflammatory bowel disease, recent splenectomy, OCP use

— Hypotensive event, recent cardiac surgery, dialysis, cocaine use, digoxin toxicity (NOMI risk)

Cardinal symptom: sudden, severe, poorly localized periumbilical or diffuse abdominal pain that is disproportionate to physical findings — patient writhes in agony but abdomen is soft and minimally tender early on

Onset characteristics differ by etiology:

Key historical anchors to elicit:

Late findings (means infarction): bloody diarrhea (~25%), abdominal distention, peritonitis, hypotension, altered mental status — these signal transmural necrosis, and mortality climbs sharply

Ask explicitly about postprandial pain pattern — a positive history dramatically raises pretest probability for thrombotic AMI

Key distinction: Patients with embolic AMI often have a completely soft abdomen despite 10/10 pain — this paradox is the diagnostic clue. By the time guarding and rebound appear, you are operating on dead bowel. Step 3 management: initiate workup based on history and risk factors, not on awaiting exam progression.

Physical Exam Findings and Hemodynamic Assessment

— Patient appears in severe distress, often diaphoretic, restless, unable to find comfortable position

— Abdomen is soft, nondistended, with minimal or no tenderness despite extreme pain — the hallmark "pain out of proportion"

— Bowel sounds initially normal or hyperactive (gut emptying phase)

— Heart rate may be elevated; check rhythm carefully for AFib

— Abdominal distention, rigidity, guarding, rebound tenderness — peritonitis

— Absent bowel sounds (ileus)

— Hematochezia or melena in ~25%

— Hypotension, tachycardia, fever — septic shock from translocation and necrosis

— Altered mental status, mottled skin, oliguria

— Obtain BP, HR, MAP, mental status, urine output, capillary refill, and lactate trend

— Check temperature: hypothermia is a poor prognostic sign

— Examine for AFib (irregularly irregular pulse), murmurs (endocarditis, valvular embolic source), carotid bruits, diminished femoral/popliteal pulses (suggests systemic atherosclerosis → thrombotic etiology)

— Look for stigmata of cirrhosis or hypercoagulability (splenomegaly, caput medusae) suggesting mesenteric venous thrombosis

Early exam (golden window, first 6–12 hours):

Late exam (after transmural infarction, >12–24 hours):

Hemodynamic assessment:

Rectal exam: occult or gross blood supports the diagnosis but absence does not exclude it

Document baseline neuro status before sedation/intubation for OR

CCS pearl: On the CCS case, your first orders should be: IV access ×2, NPO, NG tube if distention/vomiting, IV crystalloid resuscitation, continuous cardiac monitoring, pulse oximetry, urinary catheter, and simultaneous orders for CBC, BMP, lactate, coags, type and cross, ABG, and CT angiography. Move the clock forward in 15–30 minute increments; do not "observe" — every hour of delay raises mortality.

Diagnostic Workup — Initial Labs, Imaging, Biomarkers

— CBC: leukocytosis often >15,000, left shift; hemoconcentration from third-spacing

— BMP: anion-gap metabolic acidosis, AKI from hypoperfusion

— Lactate: elevated lactate supports diagnosis but normal lactate does NOT exclude early AMI — lactate rises only after significant bowel necrosis; it is a late marker

— ABG/VBG: metabolic acidosis with respiratory compensation

— LFTs, lipase: rule out hepatobiliary/pancreatic mimics; AST/LDH may rise from infarction

— Coags (PT/INR, PTT): baseline before heparin

— Troponin, BNP: assess cardiac substrate for embolism

— Type and crossmatch: anticipate operative intervention

— Blood cultures ×2: before antibiotics if not delaying

— Lactate dehydrogenase, amylase, D-dimer (elevated D-dimer is sensitive but nonspecific; a normal D-dimer has reasonable NPV)

— Plain abdominal films: usually normal early; late findings include thumbprinting, pneumatosis intestinalis, portal venous gas, free air — all are late and ominous

— Abdominal ultrasound: limited by bowel gas, not the test of choice

— CT angiography of the abdomen and pelvis with IV contrast (arterial + portal venous phases) is the diagnostic test of choice — sensitivity and specificity >90%

— Findings: SMA filling defect, lack of bowel wall enhancement, bowel wall thickening, mesenteric edema, pneumatosis, portal venous gas, SMV thrombus

Initial labs (order all together, do not wait sequentially):

ECG: identify AFib, recent MI, LV aneurysm — embolic source

Imaging:

Board pearl: Do not delay CT angiography to "first check creatinine" in a hemodynamically threatened patient with suspected AMI — the risk of contrast nephropathy is far outweighed by the risk of missed mesenteric infarction. Hydrate, proceed with contrast CT, and address renal recovery later. Step 3 management: lactate is for prognosis, not exclusion.

Diagnostic Workup — Advanced and Confirmatory Studies

— Arterial phase: identifies SMA embolus (filling defect, often 3–10 cm from origin, sparing proximal branches) vs. thrombosis (ostial occlusion with heavy calcified plaque)

— Portal venous phase: identifies SMV/portal vein thrombus (mesenteric venous thrombosis)

— Bowel findings: wall thickening, decreased enhancement (most specific), pneumatosis intestinalis, portal venous gas, mesenteric fat stranding, ascites

— Vascular reconstruction (3D) helps surgical planning

— Historically the gold standard; now reserved for cases proceeding to endovascular intervention (thrombolysis, thrombectomy, stenting)

— Can be both diagnostic and therapeutic in the same setting

— Useful when CTA equivocal, especially in NOMI where it shows segmental vasospasm with "string of sausages" appearance and may guide intra-arterial papaverine infusion

— Alternative when iodinated contrast contraindicated, but slower acquisition limits use in acute setting

— Indicated when peritonitis is present — do not delay surgery for imaging if patient has frank peritoneal signs

— Allows direct assessment of bowel viability and concurrent revascularization plus resection

CT angiography (CTA) of the abdomen/pelvis remains the gold standard for noninvasive diagnosis:

Catheter-based mesenteric angiography:

MR angiography:

Exploratory laparotomy:

Diagnostic laparoscopy: limited role; cannot reliably assess mesenteric vasculature or full bowel viability

Echocardiography (after stabilization): identify embolic source — LA thrombus, LV thrombus, vegetations, PFO

Key distinction: Peritonitis = OR, not CT. A patient with rigid abdomen, hypotension, and a story consistent with AMI goes directly to laparotomy with intraoperative revascularization. Imaging is for the patient who is still in the diagnostic window without frank peritoneal signs. CCS pearl: order surgical consult before completing the imaging workup — parallel processing saves bowel.

Risk Stratification and First-Line Management Logic

— ABCs, two large-bore IVs, aggressive crystalloid resuscitation (avoid vasopressors if possible — they worsen mesenteric vasoconstriction; if essential, norepinephrine preferred over phenylephrine/vasopressin)

— NPO, NG tube for decompression

— Foley catheter for UOP monitoring

— Correct electrolytes and acidosis

— Empiric broad-spectrum antibiotics: piperacillin-tazobactam, or ceftriaxone + metronidazole, to cover gut flora and prevent translocation sepsis

— Therapeutic anticoagulation with IV unfractionated heparin (bolus 80 U/kg, infusion 18 U/kg/hr) unless contraindicated — applies to embolic, thrombotic, and venous etiologies; hold in active GI bleed or imminent OR per surgeon preference

— Vascular surgery + general surgery + interventional radiology consults

— Peritonitis present → emergent laparotomy with embolectomy/bypass + bowel resection

— No peritonitis + embolic SMA occlusion → endovascular thrombectomy/thrombolysis OR open embolectomy

— No peritonitis + thrombotic SMA occlusion → endovascular stenting OR open bypass (mesenteric revascularization)

— NOMI → treat underlying low-flow state (optimize cardiac output, withdraw vasoconstrictors, treat sepsis); selective intra-arterial papaverine infusion

— Mesenteric venous thrombosis without peritonitis → systemic anticoagulation alone (heparin → warfarin or DOAC); surgery only if infarction

Immediate priorities the moment AMI is suspected (within minutes, all in parallel):

Triage by etiology and clinical state:

Avoid digoxin, vasopressin, alpha-agonists when possible — all worsen mesenteric perfusion

Step 3 management: the management algorithm hinges on two binary questions: (1) Is there peritonitis? (2) What is the etiology (embolic, thrombotic, NOMI, venous)? These determine OR vs. endovascular vs. medical management. Anticoagulation, fluids, and antibiotics are universal first moves.

Pharmacotherapy — First-Line Drug Regimens

— Unfractionated heparin IV: 80 U/kg bolus then 18 U/kg/hr infusion, titrate to aPTT 1.5–2.5× control or anti-Xa 0.3–0.7

— Preferred over LMWH acutely because of titratability and reversibility (protamine) prior to surgery

— In mesenteric venous thrombosis, anticoagulation is the primary therapy; transition to warfarin (INR 2–3) or a DOAC (apixaban, rivaroxaban) for ≥3–6 months; lifelong if persistent hypercoagulable state, recurrent event, or unprovoked with thrombophilia

— Piperacillin-tazobactam 4.5 g IV q6–8h, OR

— Ceftriaxone 2 g IV daily + metronidazole 500 mg IV q8h, OR

— Carbapenem (meropenem) if recent broad-spectrum exposure or septic shock

— Add vancomycin if MRSA risk

— Balanced crystalloid (LR, Plasma-Lyte); avoid large NS volumes (hyperchloremic acidosis)

— Target MAP ≥65, UOP ≥0.5 mL/kg/hr, lactate clearance

— Norepinephrine is preferred — least mesenteric vasoconstriction at typical doses

— Avoid vasopressin, phenylephrine, high-dose dopamine when possible

Anticoagulation (cornerstone):

Empiric antibiotics (gut flora coverage to blunt bacterial translocation):

Fluid resuscitation:

Vasopressors (if needed):

Papaverine intra-arterial infusion via SMA catheter (30–60 mg/hr): vasodilator, mainstay of NOMI management; also adjunctive after embolectomy to reduce reperfusion vasospasm

Thrombolytics (catheter-directed alteplase): selected non-peritonitic embolic AMI in patients without contraindications, when endovascular team available

Analgesia: IV opioids (fentanyl, hydromorphone); do not withhold for fear of masking exam — the diagnosis should already be established

Board pearl: Heparin + fluids + antibiotics + surgical/IR consult is the universal opening combo. Do not give NSAIDs (renal injury), avoid digoxin (mesenteric vasoconstriction), and avoid vasopressin.

Procedures and Revascularization

— SMA embolectomy via transverse arteriotomy with Fogarty catheter — for embolic disease

— Mesenteric bypass (aortomesenteric or iliomesenteric, using saphenous vein or prosthetic) — for thrombotic disease at SMA origin

— Concurrent resection of frankly necrotic bowel; questionable segments left, with planned second-look laparotomy in 24–48 hours to reassess viability and minimize short bowel syndrome

— Intraoperative assessment: color, peristalsis, mesenteric pulses, Doppler, fluorescein/indocyanine green if available

— Catheter-directed thrombolysis (alteplase) — for embolic AMI without infarction signs

— Mechanical thrombectomy / aspiration thrombectomy

— Angioplasty + stenting — for thrombotic AMI on atherosclerotic lesion (SMA origin)

— Lower morbidity, shorter ICU stay, but requires patient stability and skilled IR

— Selective SMA catheter with continuous papaverine infusion 30–60 mg/hr for 24 hours; reassess with repeat angiography

— Optimize cardiac output, treat sepsis, withdraw offending vasopressors/digoxin

— Primarily medical (anticoagulation); thrombectomy/TIPS or transhepatic thrombolysis reserved for progressive thrombosis despite anticoagulation

Open surgical revascularization (gold standard when peritonitis present):

Endovascular revascularization (preferred when no peritonitis and timely access available):

Hybrid approach (increasingly common): laparotomy for bowel assessment + retrograde open mesenteric stenting (ROMS)

NOMI-specific:

Mesenteric venous thrombosis:

Second-look laparotomy: planned re-exploration at 24–48 hours after initial damage-control surgery — preserves bowel length, identifies delayed necrosis

CCS pearl: After revascularization, anticipate reperfusion injury — worsening acidosis, hyperkalemia, hypotension, AKI, compartment syndrome. Continue ICU monitoring, anticoagulation, and order a second-look laparotomy at 24–48 hours if any bowel viability was uncertain at index operation.

Special Populations — Elderly and Renal/Hepatic Impairment

— Vast majority of AMI occurs in patients >60 years; mean age ~70

— Comorbidities (CAD, CHF, CKD, AFib, PAD) raise both pre-test probability and operative risk

— Atypical presentations: less dramatic pain, more delirium, falls, "failure to thrive" — lower threshold to image

— Higher mortality (>70%) reflects delayed diagnosis and frailty

— Frailty assessment (Clinical Frailty Scale) informs goals-of-care discussion preoperatively

— Anticoagulation requires careful balance: fall risk, polypharmacy, GI bleeding history

— Iodinated contrast for CTA: in suspected AMI, proceed with contrast — benefit far outweighs nephropathy risk; pre-hydrate with isotonic crystalloid; avoid nephrotoxins (NSAIDs, aminoglycosides)

— Avoid metformin around contrast (hold 48 hours if eGFR <30)

— Heparin dose unchanged in renal failure (preferred over LMWH/fondaparinux)

— Postoperatively: monitor for contrast-induced AKI and reperfusion-related rhabdo/AKI

— DOAC dosing for long-term anticoagulation (in MVT) requires CrCl-based adjustment; apixaban most renally forgiving

— Cirrhosis with portal hypertension is a major risk factor for mesenteric venous thrombosis

— Baseline coagulopathy is not truly "auto-anticoagulated" — these patients still clot; anticoagulation is indicated for MVT even with elevated INR

— Warfarin difficult to monitor (baseline elevated INR); LMWH or apixaban often preferred

— Avoid hepatotoxic antibiotics; dose-adjust as needed

Elderly patients (the typical AMI demographic):

Renal impairment:

Hepatic impairment / cirrhosis:

Consider goals-of-care discussion early in frail elderly with extensive necrosis — short bowel syndrome with TPN dependence may not align with patient values

Step 3 management: in an elderly patient with AFib not on anticoagulation who presents with severe abdominal pain, AMI is the diagnosis until imaging proves otherwise — do not delay CTA for renal function.

Special Populations — Pregnancy, Younger Patients, and Hypercoagulable Subgroups

— AMI is rare but described, typically mesenteric venous thrombosis in third trimester or postpartum (hypercoagulable state of pregnancy, OCPs, hyperemesis dehydration)

— Imaging: MR angiography preferred to limit fetal radiation; if CTA needed for life-threatening suspicion, the maternal benefit justifies it (single CT abdomen ~25–30 mGy, below teratogenic threshold)

— Anticoagulation: LMWH (enoxaparin) is the agent of choice — does not cross placenta; warfarin and DOACs are teratogenic/contraindicated

— Multidisciplinary care: OB, MFM, vascular surgery, hematology

— Mesenteric venous thrombosis from inherited thrombophilia (Factor V Leiden, prothrombin G20210A, protein C/S deficiency, antithrombin deficiency, antiphospholipid syndrome)

— Acquired: malignancy (pancreatic, colon), myeloproliferative neoplasms (JAK2 V617F → polycythemia vera, essential thrombocytosis), PNH, IBD flare, recent splenectomy, OCP use, smoking, hyperhomocysteinemia

— Order thrombophilia workup (ideally after acute phase and off anticoagulation, but JAK2 and antiphospholipid can be drawn acutely): protein C/S, antithrombin, factor V Leiden, prothrombin gene, antiphospholipid panel, JAK2

— Indefinite anticoagulation often indicated

Pregnancy and postpartum:

Younger patients (<50) — almost always one of:

Pediatric AMI is exceptionally rare; consider intestinal volvulus, intussusception, vasculitis (HSP), sickle cell vaso-occlusion instead

Cocaine/methamphetamine users: drug-induced mesenteric vasoconstriction → NOMI-like picture; supportive care, cessation counseling, benzodiazepines

Board pearl: A young woman on OCPs with subacute abdominal pain and ascites → think mesenteric venous thrombosis. Stop OCPs, start anticoagulation, search for underlying thrombophilia or malignancy. Key distinction: in pregnancy, the anticoagulant is LMWH, never warfarin or DOACs.

Complications and Adverse Outcomes

— Transmural necrosis → perforation → fecal peritonitis → septic shock

— Requires emergent resection; massive resection may produce short bowel syndrome (<200 cm small bowel remaining → lifelong TPN dependence in severe cases)

— Bacterial translocation across ischemic mucosa; gram-negatives and anaerobes predominate

— Refractory hypotension, multiorgan dysfunction

— Oxidative stress, hyperkalemia, lactic acidosis surge, myocardial stunning, AKI, ARDS

— Compartment syndrome of bowel/abdomen → abdominal compartment syndrome (bladder pressure >20 mmHg + organ dysfunction) → decompressive laparotomy

— Loss of >50% small bowel; loss of terminal ileum → B12/bile acid malabsorption

— Management: TPN, enteral rehab, teduglutide (GLP-2 analog), intestinal transplant in select

— If embolic source (AFib, LV thrombus) not addressed with anticoagulation, recurrence is high

— Recurrent MVT in untreated thrombophilia

— Overall in-hospital mortality 40–70%; embolic > thrombotic survival; MVT lowest mortality (~20–30%)

— Time-dependent: <12 hours from onset to revascularization markedly improves survival

Bowel infarction and perforation:

Septic shock:

Reperfusion injury (after revascularization):

Short bowel syndrome:

Anastomotic leak, intra-abdominal abscess, enterocutaneous fistula after resection/anastomosis

Recurrent thrombosis/embolism:

Postoperative AKI, MI, stroke, VTE, pneumonia, delirium — typical major surgical morbidity, compounded by frailty

Mortality:

Long-term: chronic mesenteric ischemia recurrence, malabsorption, malnutrition, depression, deconditioning

CCS pearl: After revascularization, order serial abdominal exams q4–6h, lactate trend, ABG, CBC, and bladder pressure monitoring. Rising lactate, worsening acidosis, or peritoneal signs post-op = return to OR for second look.

When to Escalate Care — ICU, Consultation, Triage

— Vascular surgery (or general surgery if vascular unavailable) — definitive revascularization

— Interventional radiology — endovascular options

— Critical care — perioperative resuscitation, ICU admission

— Anesthesia — preoperative optimization

— If the receiving facility lacks vascular surgery or 24/7 IR capability, initiate transfer immediately — call ahead, start heparin, fluids, antibiotics, and image at the sending facility only if it does not delay transfer

— Use EMTALA-compliant transfer with accepting physician and capability match

— Hemodynamic instability, pressor need

— Severe metabolic acidosis (pH <7.2, lactate >4)

— Post-revascularization (open or endovascular)

— Mechanical ventilation, AKI requiring CRRT

— NOMI requiring intra-arterial papaverine

— Cardiology (AFib source control, anticoagulation, post-MI thrombus)

— Hematology (thrombophilia workup, MVT long-term plan)

— Nutrition support (early enteral when possible post-resection; TPN if extensive resection)

— Palliative care (in frail patients with extensive necrosis or poor reserve, early goals-of-care)

— Cardioversion or rate control for AFib once stable

— Echocardiogram to identify and address embolic source

— Long-term anticoagulation plan before discharge

Every confirmed or strongly suspected AMI is an ICU-level admission — not floor, not stepdown

Immediate (within minutes) consults:

Transfer considerations:

ICU admission triggers:

Multidisciplinary care:

Source control:

Step 3 management: the moment CTA confirms AMI (or peritonitis is present), the patient is NPO, on heparin, on antibiotics, fluid-resuscitated, and going to OR or IR within the hour. There is no "admit and observe" pathway for AMI. CCS pearl: parallel orders save bowel — do not serialize consults.

Key Differentials — Same-Category (Vascular/Intra-abdominal Catastrophes)

— Older male smoker, sudden severe back/abdominal pain, hypotension, pulsatile mass

— Bedside aortic ultrasound or CTA confirms; emergent vascular surgery

— Tearing chest/back pain radiating to abdomen, asymmetric pulses, widened mediastinum

— CTA chest/abdomen; can cause secondary AMI by occluding visceral branches

— Sudden pain, peritonitis, free air on upright CXR/CT

— Distinction: AMI early has soft abdomen; perforation has rigid abdomen from onset

— Epigastric pain radiating to back, vomiting, lipase >3× ULN; gallstones/alcohol history

— CT shows pancreatic edema/necrosis; can coexist with mesenteric vein thrombosis

— Prior surgery, hernia, distention, vomiting, obstipation

— CT: transition point, dilated loops, mesenteric edema; if closed loop with ischemia, surgical emergency

— RUQ pain, fever, Murphy sign, Charcot triad; US/HIDA

— Usually involves watershed colon (splenic flexure, rectosigmoid), often after AAA repair, hypotension, or in elderly

— Milder pain, more bloody diarrhea early, often self-limited; supportive care, bowel rest, antibiotics

— Key distinction: ischemic colitis = colon (IMA territory or watershed), more LLQ pain, bloody stools early; AMI = small bowel (SMA), severe periumbilical pain out of proportion

Ruptured abdominal aortic aneurysm (AAA):

Aortic dissection (Stanford A or B) with mesenteric malperfusion:

Perforated viscus (peptic ulcer, diverticulitis, appendicitis):

Acute pancreatitis:

Small bowel obstruction with strangulation/closed-loop:

Acute cholecystitis / cholangitis:

Ischemic colitis (often confused with AMI):

Splenic infarct, renal infarct: focal flank pain, AFib history; CT diagnosis

Key distinction: AMI's hallmark is pain >> exam findings early, while perforation, obstruction-with-strangulation, and ruptured AAA usually present with prominent exam findings or hemodynamic collapse from the start. CTA distinguishes all of them simultaneously.

Key Differentials — Other-Category (Medical Mimics)

— Can present with epigastric pain, nausea, vomiting, diaphoresis — easily mistaken for abdominal pathology

— Always obtain ECG in any older patient with abdominal pain

— Right-sided ECG leads if inferior MI to detect RV involvement

— Abdominal pain (especially in young T1DM), nausea, vomiting, Kussmaul respirations

— Anion gap acidosis with hyperglycemia and ketones — but lactate not markedly elevated

— Resolves with insulin + fluids

— Diffuse crampy pain, vomiting, diarrhea, fever; viral exposure; self-limited

— Misleading in early AMI where gut emptying mimics gastroenteritis — age and risk factors are the differentiator

— Abdominal pain, hypotension, hyponatremia/hyperkalemia in known or undiagnosed adrenal insufficiency

— Empiric hydrocortisone if suspected

Inferior myocardial infarction:

Diabetic ketoacidosis:

Gastroenteritis:

Adrenal crisis:

Sickle cell vaso-occlusive crisis (abdominal/splenic sequestration)

Porphyria (acute intermittent porphyria): episodic severe abdominal pain, neuropsych symptoms, dark urine; rare but classic

Lead poisoning, black widow envenomation, scorpion sting: rare toxic causes of severe abdominal pain with benign exam

Hereditary angioedema: episodic abdominal pain from bowel wall edema; C1 esterase inhibitor deficiency

Spontaneous bacterial peritonitis (cirrhotic): diffuse pain, fever, ascites; paracentesis with PMN >250

Retroperitoneal hematoma (on anticoagulation): flank/back pain, drop in hemoglobin

Familial Mediterranean fever: recurrent serositis episodes in young patients with Mediterranean ancestry

Board pearl: A diabetic with severe abdominal pain may have DKA, MI, or AMI — order ECG, lactate, glucose/ketones, and CTA simultaneously. Step 3 management: never anchor on gastroenteritis in an older patient with AFib or vascular disease and severe pain — the cost of missing AMI is bowel and life.

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Embolic AMI (AFib source): lifelong oral anticoagulation. DOAC preferred (apixaban, rivaroxaban, dabigatran, edoxaban) over warfarin for non-valvular AFib; warfarin (INR 2–3) for mechanical valves or rheumatic mitral stenosis. CHA₂DS₂-VASc score already meets threshold given the embolic event itself

— Embolic AMI (LV thrombus post-MI): warfarin or DOAC for at least 3 months, then reassess with echo; lifelong if persistent thrombus or recurrent

— Thrombotic AMI on atherosclerosis: dual antiplatelet therapy (aspirin + clopidogrel) for 1 month post-stenting then aspirin lifelong; high-intensity statin; smoking cessation; BP and DM control

— Mesenteric venous thrombosis: anticoagulation for 3–6 months if provoked; indefinite if unprovoked, persistent thrombophilia, malignancy, or recurrent

— High-intensity statin (atorvastatin 40–80, rosuvastatin 20–40); LDL goal <70

— BP control to <130/80; ACEI or ARB preferred

— Diabetes: A1c individualized, typically <7%

— Smoking cessation (most important modifiable factor) — varenicline, NRT, counseling

— Aspirin 81 mg daily

— Dietitian consult; small frequent meals; B12 supplementation if terminal ileum resected

— If short bowel syndrome: home TPN, teduglutide, GI/nutrition follow-up

Anticoagulation is the cornerstone of preventing recurrence:

Atherosclerosis risk factor management (thrombotic etiology):

AFib management: rate control (β-blocker, diltiazem) ± rhythm control; cardiology follow-up; consider LAA closure (Watchman) only if true anticoagulation contraindication

Nutritional support post-resection:

Vaccinations: pneumococcal, influenza, COVID, RSV per age

Step 3 management: discharge the AMI survivor on anticoagulation + statin + antiplatelet + BP/DM control + smoking cessation, with cardiology, vascular surgery, and PCP follow-up scheduled before they leave the hospital.

Follow-Up, Monitoring Parameters, and Rehabilitation

— Confirm anticoagulation regimen, dose, duration, monitoring needs

— Medication reconciliation; teach-back of new meds, signs of bleeding, signs of recurrence

— Schedule follow-up before discharge: vascular surgery 2 weeks, PCP 1–2 weeks, cardiology 4 weeks, hematology if MVT/thrombophilia

— Wound check, drain management if applicable

— Duplex ultrasound or CTA at 3, 6, 12 months post-revascularization to assess patency of bypass/stent, then annually

— Repeat echo at 3 months if LV thrombus, to confirm resolution and guide anticoagulation duration

— Warfarin: INR weekly until stable, then monthly (target 2–3)

— DOAC: annual CBC, CMP, renal function (more frequent if CKD); no routine drug levels

— Statin: lipid panel at 4–12 weeks; LFTs only if symptomatic

— Diabetes: A1c q3 months

— Nutrition labs if short bowel: B12, iron, vitamin D, magnesium, fat-soluble vitamins

— Early mobilization in hospital; PT/OT consult to assess functional status

— Cardiac rehab if concomitant MI/CAD

— Pulmonary rehab if prolonged intubation

— Nutrition rehab and counseling; consider intestinal rehabilitation program if extensive resection

— Recognize recurrence symptoms (recurrent postprandial pain, weight loss, abdominal pain)

— Anticoagulation adherence and bleeding precautions

— Smoking cessation reinforcement

— Mental health screening — PTSD/depression after critical illness is common; refer to behavioral health

Pre-discharge planning:

Imaging surveillance:

Lab monitoring:

Rehabilitation:

Counseling:

Advance care planning: document preferences after this sentinel event

CCS pearl: Move time forward in CCS to capture scheduled imaging surveillance, INR checks, A1c, lipid panel, and outpatient visits — Step 3 rewards demonstrating longitudinal care, not just acute stabilization.

Ethical, Legal, and Patient Safety Considerations

— In a peritonitic, hemodynamically unstable AMI patient, life-threatening necessity may justify emergency exception to formal consent if no surrogate is immediately reachable — document the emergency, attempt to reach next of kin, and obtain consent as soon as feasible

— When time permits, discuss high mortality (40–70%), risk of short bowel syndrome, possible second-look laparotomy, possible ostomy

— In frail elderly with extensive necrosis discovered intraoperatively, consider whether massive resection aligns with the patient's previously expressed values

— Document POLST/MOLST, advance directives; engage palliative care early

— Surrogate decision-making hierarchy (spouse → adult children → parents → siblings, varies by state)

— ED → OR → ICU → floor → home transitions each carry medication error risk

— Use structured handoffs (SBAR, I-PASS)

— Anticoagulation bridging at discharge is a common failure point — explicit written instructions

— Heparin dosing errors are sentinel events — use weight-based protocols and standardized order sets

— Warfarin/DOAC at discharge: confirm pharmacy fill, education, and follow-up INR appointment before discharge

— AMI is among the most commonly missed diagnoses in the ED; if delay occurred, transparent disclosure to patient/family is ethically and (in many states) legally required

— Root cause analysis for missed/delayed cases

— Cocaine-induced NOMI: counsel and offer substance use treatment; not mandatorily reportable in adults

— Suspected elder neglect contributing to missed AFib/anticoagulation noncompliance → consider Adult Protective Services

— Disparities exist in time-to-revascularization; ensure equitable triage protocols

Informed consent for emergency surgery:

Goals-of-care discussion:

Transitions of care (high-risk handoffs):

Medication safety:

Diagnostic error and disclosure:

Mandatory reporting:

Health system equity:

Board pearl: Missed AMI is a high-liability diagnosis. The Step 3 expectation is early CTA, early anticoagulation, early consultation, and transparent disclosure when errors occur.

High-Yield Associations and Rapid-Fire Clinical Facts

AFib + sudden severe abdominal pain + soft abdomen = SMA embolus

Postprandial pain + food fear + weight loss + sudden worsening = thrombotic AMI on chronic mesenteric ischemia

ICU patient on pressors + worsening acidosis + abdominal distention = NOMI

Young woman on OCPs + subacute pain + ascites = mesenteric venous thrombosis

Cirrhosis with portal HTN + new abdominal pain = think MVT

Pneumatosis intestinalis + portal venous gas on CT = bowel infarction (late, ominous)

Lactate is a late marker — normal lactate does not exclude early AMI

D-dimer: sensitive (~95%) but nonspecific; useful negative predictive value

CTA is the diagnostic test of choice; do not delay for creatinine

Heparin + fluids + broad-spectrum antibiotics + surgical/IR consult = universal opening orders

Norepinephrine is the preferred vasopressor; avoid vasopressin and phenylephrine

Papaverine intra-arterial = NOMI mainstay

Second-look laparotomy at 24–48 hours preserves bowel length

SMA embolus lodges 3–10 cm distal to origin, sparing proximal jejunum (vs. thrombosis at ostium)

Ischemic colitis = colon (often watershed), bloody diarrhea early, usually self-limited — distinct from AMI

Avoid digoxin, NSAIDs, vasopressin in suspected AMI (mesenteric vasoconstriction or renal injury)

Short bowel syndrome if <200 cm small bowel remaining; loss of terminal ileum → B12 and bile acid malabsorption

Lifelong anticoagulation for AFib-related embolic AMI; DOAC preferred for non-valvular AFib

Embolic source workup post-AMI: ECG, telemetry, TTE, consider TEE; treat AFib, LV thrombus, endocarditis as found

Mortality time-dependent: <12 hours to revascularization dramatically improves survival

Pregnancy MVT: LMWH (enoxaparin), never warfarin or DOACs

Hypercoagulable workup in young/unprovoked MVT: protein C/S, antithrombin, factor V Leiden, prothrombin gene, antiphospholipid, JAK2 V617F

Step 3 management: memorize "pain out of proportion + AFib → CTA + heparin + consult" as a single reflex.

Board Question Stem Patterns

Stem 1: 72-year-old man with AFib on warfarin (held 5 days ago for colonoscopy) develops sudden 10/10 periumbilical pain. Exam: distressed, soft abdomen, mild tenderness. Labs: WBC 18, lactate 2.4. Next step? → CTA abdomen/pelvis, start IV heparin, consult vascular surgery

Stem 2: 68-year-old smoker with 6 months of postprandial pain, 30-lb weight loss, presents with severe constant abdominal pain. CT shows ostial SMA occlusion with calcified plaque. Diagnosis? → Thrombotic AMI on chronic mesenteric ischemia. Management? → Endovascular stenting or mesenteric bypass + lifelong antiplatelet + statin + smoking cessation

Stem 3: ICU patient on norepinephrine and vasopressin for septic shock develops abdominal distention, worsening acidosis, rising lactate. Angiography shows segmental SMA vasospasm without filling defect. Diagnosis/treatment? → NOMI; intra-arterial papaverine, optimize cardiac output, wean vasoconstrictors

Stem 4: 34-year-old woman on OCPs with 4 days of vague abdominal pain, ascites. CT shows SMV thrombus. Management? → Anticoagulation (heparin → warfarin or DOAC), stop OCPs, thrombophilia workup (factor V Leiden, JAK2, antiphospholipid)

Stem 5: 75-year-old with peritonitis, hypotension, lactate 8, on AFib. Next step? → Emergent laparotomy, not CTA — do not delay surgery in peritonitis

Stem 6: Post-revascularization patient develops worsening acidosis, hyperkalemia, oliguria, abdominal distention, bladder pressure 25 mmHg. Diagnosis? → Abdominal compartment syndrome + reperfusion injury; decompressive laparotomy

Stem 7: Discharge planning for AFib patient s/p SMA embolectomy. Best anticoagulant? → Apixaban (or other DOAC) lifelong, unless mechanical valve or moderate–severe mitral stenosis (warfarin)

Stem 8: 28-year-old pregnant woman, 32 weeks, with severe abdominal pain and SMV thrombus on MRA. Anticoagulant? → LMWH (enoxaparin) — avoid warfarin and DOACs

Board pearl: Step 3 stems often test the next step after diagnosis — anticoagulation, antibiotics, imaging, consult, or OR. Anchor on peritonitis (→ OR) vs. no peritonitis (→ CTA + endovascular/medical).

One-Line Recap

Acute mesenteric ischemia is a time-critical vascular emergency defined by pain out of proportion to exam in a patient with embolic, thrombotic, low-flow, or venous risk factors, diagnosed by CT angiography, and managed with immediate IV heparin, fluids, broad-spectrum antibiotics, and emergent revascularization — endovascular or open — with peritonitis mandating direct passage to the operating room.

Recognize: sudden severe abdominal pain + soft abdomen + AFib/vascular disease/hypercoagulability + late lactate elevation → suspect AMI; do not be falsely reassured by a benign exam or normal lactate early

Diagnose: CT angiography of the abdomen and pelvis is the test of choice; do not delay for creatinine; peritonitis bypasses imaging and goes straight to laparotomy

Treat: parallel orders — IV heparin (80 U/kg bolus, 18 U/kg/hr), balanced crystalloid resuscitation, broad-spectrum antibiotics (pip-tazo or ceftriaxone/metronidazole), NPO, NG decompression, simultaneous vascular surgery and IR consults; norepinephrine if pressors needed; papaverine for NOMI; second-look laparotomy at 24–48 hours when bowel viability uncertain

Prevent recurrence: lifelong DOAC for AFib-related embolic AMI, warfarin for mechanical valves, antiplatelet + high-intensity statin + smoking cessation for thrombotic etiology, 3–6 months or indefinite anticoagulation for mesenteric venous thrombosis based on provocation and thrombophilia; LMWH in pregnancy; scheduled vascular imaging, INR/A1c/lipid follow-up, and nutrition rehab for short bowel survivors

Step 3 management: "Pain out of proportion + risk factor → CTA + heparin + surgical consult, all at once." Time is bowel; time is life.