Cardiovascular

Acute limb ischemia: 6 Ps and revascularization decision

Clinical Overview and When to Suspect Acute Limb Ischemia

— Incidence ~1.5 per 10,000 person-years; rises sharply after age 60.

— 30-day mortality 10–15%; amputation rate 10–30% even with revascularization.

— Mortality driven by underlying cardiac disease (AF, recent MI, heart failure), not the limb itself.

— Embolic (~30%): Cardiac source in 80% (AF, post-MI mural thrombus, endocarditis, mechanical valve, LV aneurysm, paradoxical embolus via PFO). Often a previously asymptomatic, normal-caliber contralateral limb.

— Thrombotic (~60%): In situ thrombosis of an atherosclerotic plaque, bypass graft occlusion, popliteal aneurysm thrombosis, hypercoagulable states, or aortic dissection extending into iliacs. Patient usually has prior claudication and bilateral PAD findings.

— Other: trauma, iatrogenic (arterial line, catheterization), phlegmasia cerulea dolens, vasospasm, ergotism, COVID-related arteriopathy.

— Sudden onset of severe unilateral leg or arm pain with pallor and absent pulses, especially in an AF patient off anticoagulation.

— Postoperative patient with new cold, mottled foot after femoral access.

— Known PAD patient whose "claudication" becomes rest pain over hours.

Definition: Acute limb ischemia (ALI) is a sudden decrease in limb perfusion (<2 weeks) that threatens limb viability. Distinguished from chronic limb-threatening ischemia (CLTI) by abrupt onset and absence of well-developed collaterals.

Epidemiology and burden:

Two dominant mechanisms — the etiology drives the workup:

When to suspect on the boards / floor:

Step 3 management: ALI is a time-critical emergency — the window from onset to irreversible muscle/nerve injury is roughly 4–6 hours. The first three orders on a CCS case should be: IV heparin bolus + infusion, vascular surgery consult, and STAT arterial imaging (CTA most commonly), before completing the labs. Do not wait for creatinine to start heparin.

Presentation Patterns and Key History

— Pain (earliest, often distal, severe, constant, worse with passive movement)

— Pallor (mottling progresses to fixed cyanosis as ischemia advances)

— Pulselessness (compare bilaterally and to baseline; Doppler if not palpable)

— Poikilothermia / Perishingly cold (the cool line marks ~1 joint below the occlusion)

— Paresthesias (small sensory fibers fail first — light touch and proprioception are early warnings)

— Paralysis (latest finding; motor loss = stage III, threatened irreversibility)

— Seconds to minutes, dramatic pain, no prior claudication → embolic, usually at bifurcations (common femoral most common in the leg, brachial in the arm).

— Hours to days, less dramatic, preexisting claudication, bilateral disease → thrombotic on plaque.

— After recent endovascular procedure or central line → iatrogenic dissection/embolism.

— Migratory phlebitis, abdominal pain, then leg ischemia in a young smoker → consider Buerger disease.

— Atrial fibrillation, anticoagulation status and adherence, recent INR.

— Recent MI, cardioversion, endocarditis symptoms, valvular disease.

— Prior bypass grafts, stents, claudication distance, rest pain, tissue loss.

— Hypercoagulable history: malignancy, prior DVT/PE, miscarriages (APS), HIT.

— Trauma, IV drug use, ergot or cocaine use, COVID infection.

— Tobacco, diabetes, dyslipidemia, family history of AAA/PAD.

Board pearl: A patient in AF off warfarin with a suddenly cold, painful, pulseless leg and a normal contralateral pulse exam is embolic ALI until proven otherwise — the saddle of the common femoral bifurcation is the most common site.

The classic 6 Ps — memorize the order they appear in time:

Tempo of onset is diagnostic:

Targeted history (cover these in any CCS or stem):

Time of symptom onset must be documented to the hour — it determines candidacy for catheter-directed thrombolysis (best within 14 days but ideally <2 weeks and limb still viable).

Physical Exam Findings and Hemodynamic Assessment

— Inspect: pallor, mottling (blanching vs fixed), demarcation line, capillary refill, tissue loss, prior bypass scars.

— Palpate temperature with the dorsum of your hand from thigh to toes; note the transition point — occlusion is typically one joint level above it.

— Pulses: femoral, popliteal, dorsalis pedis, posterior tibial. Use handheld continuous-wave Doppler if not palpable; document monophasic vs biphasic vs triphasic.

— Motor: dorsi/plantarflexion, intrinsic foot muscles. Weakness = advanced ischemia.

— Sensory: light touch between first and second toes (deep peroneal) often lost first.

— Calf: tense, tender compartments suggest impending or established compartment syndrome.

— Normal 1.0–1.4. ABI <0.4 in acute setting = severely threatened limb.

— Inaudible ankle signals = profoundly ischemic; rely on clinical category, not numbers.

— I — Viable: No sensory loss, no motor weakness, audible arterial and venous Doppler. Not immediately threatened. Time for workup.

— IIa — Marginally threatened: Minimal (toes) sensory loss, no motor deficit, inaudible arterial but audible venous Doppler. Salvageable with prompt revascularization.

— IIb — Immediately threatened: Sensory loss beyond toes, mild–moderate motor deficit, inaudible arterial Doppler. Emergent revascularization required.

— III — Irreversible: Profound anesthesia, paralysis (rigor), absent arterial and venous Doppler, skin marbling that does not blanch. Primary amputation; revascularization causes lethal reperfusion injury.

Key distinction: IIa vs IIb is the single most tested decision — IIb has motor deficit and demands the OR/cath lab now; IIa allows targeted imaging and possibly thrombolysis.

Systematic vascular exam — always bilateral and documented:

Ankle-brachial index (ABI) at bedside:

Rutherford classification — the exam IS the staging:

Don't miss the heart and abdomen: irregular pulse (AF), new murmur (endocarditis, valvular embolus), pulsatile abdominal mass (AAA), tender popliteal mass (popliteal aneurysm — bilateral in 50%).

Diagnostic Workup — Initial Labs, Imaging, and Bedside Studies

— Handheld arterial and venous Doppler at ankle/wrist — defines Rutherford class.

— 12-lead ECG: atrial fibrillation, recent MI, LV strain — establishes embolic source.

— Pulse oximetry on the affected digit (often unreadable — itself a sign).

— CBC (leukocytosis, polycythemia as thrombosis risk).

— BMP — baseline creatinine before contrast; watch potassium.

— CK, LDH, myoglobin, urinalysis — rhabdomyolysis with myoglobinuria precedes AKI and hyperkalemia.

— Lactate — elevation suggests advanced ischemia or systemic compromise.

— Coags (PT/INR, aPTT), fibrinogen, type and crossmatch — needed before heparin titration, lysis, or OR.

— Troponin, BNP — coexistent MI is common and drives mortality.

— Lipid panel, A1c, TSH — for outpatient secondary prevention later.

— Hypercoagulable workup (antiphospholipid, factor V Leiden, JAK2, protein C/S, antithrombin) — send before heparin or after anticoagulation washout; especially in young patients, recurrent events, or no embolic source.

— CT angiography (chest-abdomen-pelvis with runoff): first-line in most centers — fast, defines level of occlusion, embolus vs thrombus morphology, identifies AAA or dissection. Requires iodinated contrast.

— Duplex ultrasound: useful when CTA is contraindicated; operator-dependent.

— Catheter angiography: both diagnostic and therapeutic — go directly to angio suite for Rutherford IIb if the team can intervene immediately.

— MRA: rarely first-line acutely (too slow); useful if iodinated contrast contraindicated and patient is Rutherford I.

— Echocardiogram (TTE → TEE): after stabilization to find cardiac embolic source (LAA thrombus, vegetation, PFO).

CCS pearl: On the CCS interface, the correct early order set is IV heparin, vascular surgery consult, CTA aorta with runoff, CBC/BMP/coags/CK/lactate/type & screen, and ECG — clustered, not sequential.

Order in parallel with heparin and surgical consult — never delay anticoagulation for labs.

Bedside / immediate:

Laboratory panel:

Imaging — pick based on stability and Rutherford class:

Diagnostic Workup — Advanced and Confirmatory Studies

— Remains the gold standard for arterial anatomy and provides a therapeutic platform (aspiration thrombectomy, catheter-directed thrombolysis, angioplasty, stenting).

— In Rutherford IIa, go to angio suite for diagnosis + intervention in one trip.

— Identifies "meniscus sign" (embolus at a bifurcation with no collaterals) vs irregular plaque-based occlusion (in-situ thrombosis).

— TTE first for LV thrombus, EF, valvular vegetations.

— TEE if TTE unrevealing — far superior for left atrial appendage thrombus, PFO with bubble study, aortic arch atheroma, prosthetic valve thrombus, endocarditis.

— Holter / ambulatory monitor / implantable loop recorder if paroxysmal AF suspected and surface ECG is normal.

— CT or MR of aorta if mobile atheroma or aneurysmal source suspected.

— Blood cultures ×3 if endocarditis is plausible (fever, new murmur, IVDU, Janeway/Osler).

— Indicated in age <50, no atherosclerotic risk factors, recurrent thrombosis, family history, unusual location, or no embolic source on cardiac imaging.

— Send antiphospholipid antibodies (lupus anticoagulant, anti-β2GP1, anticardiolipin), JAK2 V617F (especially if elevated hematocrit/platelets), homocysteine, protein C/S, antithrombin, factor V Leiden, prothrombin G20210A.

— Note: heparin lowers antithrombin; warfarin lowers protein C/S — interpret accordingly.

— Consider HIT panel (PF4 antibody, serotonin release assay) if platelet count drops >50% after 5–10 days of heparin (or sooner with prior exposure).

Board pearl: A young patient with bilateral lower-extremity arterial thromboses and prior miscarriages — order antiphospholipid panel, confirm with repeat testing ≥12 weeks apart, and anticoagulate long-term with warfarin (not a DOAC for triple-positive APS).

Catheter-based digital subtraction angiography (DSA):

Source-of-embolus workup (after limb is stabilized):

Hypercoagulable evaluation — when and what:

Compartment pressure measurement: indicated when calf is tense or after revascularization of prolonged ischemia. >30 mmHg or ΔP (DBP – compartment pressure) <30 mmHg = fasciotomy.

Risk Stratification and First-Line Management Logic

— Class I (viable): Heparinize, admit, complete imaging and source workup, plan elective revascularization within 6–24 hours or even conservative management if collaterals are robust.

— Class IIa (marginally threatened): Heparinize immediately; catheter-directed thrombolysis (CDT) or percutaneous mechanical thrombectomy is preferred if onset <14 days. Surgical embolectomy is an alternative.

— Class IIb (immediately threatened): Emergent surgical or endovascular revascularization — typically open embolectomy/thrombectomy with Fogarty catheter because it is faster than lysis. Thrombolysis is too slow (hours to lyse) when motor function is failing.

— Class III (irreversible): Primary amputation. Attempting revascularization releases potassium, myoglobin, lactate, and inflammatory mediators causing hyperkalemic arrest, AKI, ARDS, and death.

— Two large-bore IVs, NPO, telemetry, hourly neurovascular checks with marked pulse sites.

— IV unfractionated heparin — 80 U/kg bolus, then 18 U/kg/hr (or institutional weight-based protocol); target aPTT 2–2.5× control or anti-Xa 0.3–0.7.

— Adequate analgesia (IV opioids); avoid NSAIDs (renal, bleeding).

— IV fluids to support kidneys against contrast and rhabdomyolysis.

— Treat precipitants: rate-control AF, correct dehydration, hold offending agents (e.g., ergot).

— Embolic lesion → Fogarty embolectomy through groin/arm cut-down is highly effective; minimal underlying disease.

— In-situ thrombotic on diseased plaque → endovascular lysis ± angioplasty/stent, or bypass if extensive disease. Embolectomy alone often fails.

Step 3 management: When the stem says "motor weakness" or "sensory loss above the toes," the answer is OR/endovascular suite now, not "obtain CT angiogram and observe."

The Rutherford category drives the algorithm — commit it to memory:

Concurrent priorities — start these in the first 15 minutes:

Decision branching for embolic vs thrombotic:

Pharmacotherapy — Heparin and Adjunctive Agents

— Bolus 80 U/kg IV, then 18 U/kg/hr infusion; goal aPTT 1.5–2.5× control (or anti-Xa 0.3–0.7 U/mL).

— Prevents propagation of thrombus, protects collaterals, and reduces recurrent embolization.

— Preferred over LMWH acutely because of titratability, reversibility (protamine), and compatibility with surgery or thrombolysis.

— Continue through revascularization; transition to long-term anticoagulant once etiology is defined.

— Alteplase (tPA) 0.5–1 mg/hr intra-arterial via multi-side-hole catheter for 12–24 hours, with serial angiograms.

— Alternatives: reteplase, tenecteplase, urokinase (where available).

— Absolute contraindications: active internal bleeding, recent (<3 mo) hemorrhagic stroke or intracranial neoplasm/AVM, recent major surgery (<14 days), aortic dissection, severe uncontrolled HTN.

— Relative: recent CPR, GI bleeding <10 days, pregnancy, recent ophthalmic surgery, severe hepatic/renal disease.

— Monitor fibrinogen — hold or reduce dose if <150 mg/dL; stop if <100 mg/dL or any major bleeding.

— Initiate aspirin 81 mg daily during admission; continue indefinitely for atherosclerotic disease.

— Clopidogrel 75 mg daily is added or substituted after stenting; DAPT for 1–3 months post-peripheral stent, then aspirin monotherapy.

— Rivaroxaban 2.5 mg BID + aspirin 81 mg (COMPASS/VOYAGER PAD) reduces MALE and MACE after lower-extremity revascularization for atherosclerotic PAD.

Board pearl: A platelet drop >50% on day 5–10 of heparin with new thrombosis = HIT — stop heparin, send PF4 ELISA + SRA, start argatroban, and bridge to warfarin only after platelets >150k.

Unfractionated heparin (UFH) — cornerstone, start immediately:

Catheter-directed thrombolytics (intra-arterial, not systemic):

Antiplatelets:

If HIT: stop all heparin, use argatroban (preferred in renal disease) or bivalirudin; do not start warfarin until platelets recover.

Statin: high-intensity (atorvastatin 40–80 mg or rosuvastatin 20–40 mg) — initiate during admission; reduces MACE and improves graft patency.

Procedures — Revascularization Decisions

— Indication: Rutherford IIb, suspected large embolus at a bifurcation, failed endovascular therapy, or contraindication to lysis.

— Technique: cut-down on common femoral (or brachial) artery, transverse arteriotomy, pass Fogarty balloon catheter proximally and distally; completion angiogram is mandatory to confirm runoff.

— Pair with on-table thrombolysis or bypass if underlying atherosclerotic disease unmasked.

— Indication: Rutherford I or IIa with onset <14 days, viable limb, no bleeding contraindication.

— Advantages: lyses thrombus in small distal vessels surgery cannot reach; unmasks culprit lesion for angioplasty/stent.

— Disadvantages: slower (hours), bleeding risk, requires monitored unit.

— Newer aspiration/mechanical devices (AngioJet, Indigo, Inari ClotTriever) shorten lysis time and reduce bleeding.

— Reserved for thrombotic ALI on chronic atherosclerotic disease, popliteal aneurysm thrombosis, or failed lysis/thrombectomy.

— Conduit: autologous saphenous vein preferred; prosthetic (PTFE) for above-knee when no vein.

— Completion angiography to verify distal flow.

— Four-compartment fasciotomy if ischemia time >4–6 hours, tense compartments, or after restoration of flow in a markedly swollen calf — err toward fasciotomy; missed compartment syndrome is a board favorite.

— Aggressive fluid resuscitation, bicarbonate or mannitol if myoglobinuria, telemetry for hyperkalemic arrhythmias.

— Rutherford III, prolonged ischemia with rigor, non-salvageable limb, or systemic instability where reperfusion would be lethal.

— Level selected to maximize healing and rehabilitation potential.

CCS pearl: After successful revascularization, order continuous telemetry, q1h neurovascular checks, serial K+/CK/Cr, IVF with isotonic crystalloid, urinary alkalinization if myoglobinuria, and prophylactic fasciotomy assessment — reperfusion injury kills patients who survive the OR.

Open surgical embolectomy / thromboembolectomy:

Catheter-directed thrombolysis (CDT) ± mechanical thrombectomy:

Bypass surgery:

Adjuncts at the time of revascularization:

Primary amputation:

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher prevalence of AF, HF, polypharmacy, frailty, and concurrent CAD/CVA.

— Mortality after ALI approaches 25–30%; amputation-free survival is the more meaningful outcome.

— Endovascular-first strategies often preferred (lower physiologic stress, no general anesthesia required) when limb category allows.

— Pre-procedure: assess functional status, cognition, and goals of care. A bedbound, demented patient with Rutherford III may be best served by comfort-focused care or primary amputation, not heroic revascularization.

— Heparin dosing unchanged but bleeding risk higher; monitor aPTT closely. Avoid LMWH if CrCl <30 unless dose-adjusted enoxaparin (1 mg/kg daily).

— Iodinated contrast for CTA/angiography risks contrast-associated AKI — hydrate with isotonic saline (1 mL/kg/hr for 6–12 hr pre/post), minimize volume, use iso-osmolar agents. Do not withhold lifesaving imaging for moderate CKD.

— CO₂ angiography is an alternative below the diaphragm in dialysis patients or advanced CKD.

— Avoid NSAIDs, aminoglycosides, and ACEi initiation during the acute phase.

— Argatroban is the anticoagulant of choice in HIT with renal failure (hepatic clearance); bivalirudin if both hepatic and renal disease.

— Coagulopathy (elevated INR) does not mean the patient is "auto-anticoagulated" — thrombosis risk persists.

— Reduce or avoid argatroban (hepatic clearance); use fondaparinux or dose-adjusted bivalirudin.

— Thrombolysis carries higher bleeding risk; reassess fibrinogen frequently.

— Multilevel infrapopliteal disease, calcified vessels — ABI may be falsely normal; use toe-brachial index (<0.7 abnormal) or pulse volume recordings.

— Strict glycemic control (target 140–180 mg/dL inpatient), foot exam daily, offloading.

Board pearl: Don't avoid CTA in CKD when the limb is at stake — hydrate and image; renal recovery is likely, but a dead limb is permanent.

Elderly (≥75 years):

Chronic kidney disease:

Hepatic impairment:

Diabetes:

Special Populations — Pregnancy, Pediatrics, and Hypercoagulable Subgroups

— Rare but devastating; hypercoagulable state plus mechanical compression by gravid uterus or iliac compression syndrome.

— Imaging: duplex ultrasound first; MRA without gadolinium if needed. CTA only if essential — abdominal shielding limited.

— Anticoagulation: LMWH (enoxaparin 1 mg/kg q12h) is the agent of choice — does not cross the placenta. Warfarin contraindicated in weeks 6–12 (embryopathy) and near term. DOACs not recommended in pregnancy or lactation.

— Thrombolytics: relative contraindication; reserved for life- or limb-threatening events with multidisciplinary input.

— Postpartum: continue therapeutic anticoagulation for at least 6 weeks, longer if APS or recurrent thrombosis.

— Most pediatric ALI is iatrogenic (umbilical or femoral arterial catheters in neonates/ICU).

— Other causes: congenital heart disease with paradoxical embolism, Kawasaki disease with coronary/limb aneurysms, trauma, sickle cell disease, malignancy, antiphospholipid syndrome.

— Management: systemic heparin with weight-based dosing; tPA for non-resolving cases; surgical thrombectomy is technically difficult in small vessels and reserved for failure of medical therapy.

— Long-term anticoagulation depends on etiology — often LMWH because of better predictability and easier dose adjustment than warfarin in children.

— Suspect in young patients, recurrent arterial and venous thromboses, recurrent fetal loss, livedo reticularis, thrombocytopenia.

— Diagnosis: persistent (≥12 weeks apart) lupus anticoagulant, anti-β2GP1, or anticardiolipin antibodies.

— Warfarin (INR 2–3, or 3–4 in arterial/triple-positive) is preferred — DOACs failed non-inferiority trials (TRAPS) in triple-positive APS.

— Young male/female smokers, distal extremity ischemia, migratory thrombophlebitis. Smoking cessation is the only therapy that alters course; revascularization rarely durable.

Key distinction: In APS, warfarin beats DOACs for arterial events — this is one of the few remaining "warfarin wins" scenarios on Step 3.

Pregnancy:

Pediatrics:

Antiphospholipid syndrome (APS):

Buerger disease (thromboangiitis obliterans):

Complications and Adverse Outcomes

— Reoxygenation generates ROS, intracellular Ca²⁺ overload, mitochondrial dysfunction, and a systemic inflammatory response.

— Hyperkalemia from muscle lysis → peaked T waves, widened QRS, cardiac arrest. Treat with calcium gluconate, insulin/dextrose, β2-agonist, bicarbonate, dialysis if refractory.

— Myoglobinuria → AKI: CK often >5,000–10,000 U/L; tea-colored urine, dipstick blood positive but few RBCs on micro. Treat with isotonic crystalloid to target UO 200–300 mL/hr; bicarbonate to alkalinize urine (pH >6.5) is reasonable; mannitol controversial.

— Metabolic acidosis with high anion gap (lactate).

— ARDS from systemic inflammatory cascade.

— Risk rises sharply after >4–6 hours of ischemia or extensive swelling post-reperfusion.

— Diagnosis is clinical — pain out of proportion, pain on passive stretch, tense compartments; sensory loss and pulselessness are late.

— Compartment pressure >30 mmHg or ΔP <30 mmHg confirms; don't delay fasciotomy for measurements if exam is convincing.

— Four-compartment fasciotomy of the leg (anterior, lateral, superficial posterior, deep posterior) via two-incision technique.

— Up to 15% within 30 days; mitigate with therapeutic anticoagulation and definitive treatment of source (warfarin/DOAC for AF, surgical correction of aneurysm).

Step 3 management: New altered mental status during catheter-directed thrombolysis = stop tPA, reverse with cryoprecipitate, STAT noncontrast head CT.

Reperfusion injury — the silent killer:

Compartment syndrome:

Recurrent embolization / rethrombosis:

Limb loss: 10–30% even with revascularization; higher with delayed presentation, IIb/III at presentation, infrapopliteal disease.

Cardiovascular: Concurrent MI, stroke, or decompensated HF are leading causes of in-hospital death. Maintain telemetry, troponin trends, and aggressive BP/HR control.

Bleeding: thrombolysis-related ICH (1–2%), GI bleed, access-site hematoma/pseudoaneurysm. Monitor neuro checks during lysis; stop infusion for any major bleeding.

When to Escalate — ICU, Consults, and Inpatient Triage

— Class I (viable): Vascular ward or step-down with continuous telemetry, hourly neurovascular checks, vascular surgery consult, planned imaging.

— Class IIa: Step-down or ICU during thrombolysis — bleeding and neuro monitoring required.

— Class IIb: Straight to OR or angio suite; postoperatively to ICU.

— Class III: OR for amputation; ICU postoperatively if systemic compromise.

— Vascular surgery — primary decision-maker; call within minutes, not hours.

— Interventional radiology — if endovascular approach planned and IR is the local service.

— Cardiology — concurrent MI, severe AF, suspected endocarditis, valvular source.

— Hematology — suspected HIT, APS, or other hypercoagulable disorder.

— Nephrology — established AKI, hyperkalemia, possible CRRT for rhabdomyolysis.

— Anesthesia / pain service — high opioid requirement, regional blocks for fasciotomy pain.

— Palliative care / ethics — non-revascularizable limb with poor prognosis or surrogate decision-making conflict.

— Hemodynamic instability, vasopressor requirement.

— Active thrombolytic infusion.

— Severe hyperkalemia (>6.0), arrhythmia, or ECG changes.

— CK rising rapidly with oliguria.

— Post-fasciotomy with large fluid shifts.

— Sepsis from infected/necrotic limb.

— Community hospitals without 24/7 vascular surgery or interventional capability should transfer urgently after starting heparin — do not wait for "stable" because every hour increases tissue loss.

— Document onset time, exam, imaging, drugs given, and Rutherford class on transfer summary.

CCS pearl: On Step 3 CCS, time advances in real and simulated minutes — order heparin and consults before ordering imaging, because consults take simulated time to arrive and limb viability is on a 4–6 hour clock.

Disposition by Rutherford class:

Mandatory consults at presentation:

ICU triggers:

Transfer considerations:

Key Differentials — Other Vascular Causes

— Type B (or A extending) dissection can occlude an iliac and present as unilateral leg ischemia with tearing chest/back pain, BP differential between arms, mediastinal widening on CXR.

— Workup: CTA chest/abdomen/pelvis; do not thrombolyse — anticoagulation and lysis worsen dissection.

— Management: control HR (esmolol) and BP, then dissection-directed surgery or TEVAR with branch-vessel fenestration.

— Massive iliofemoral DVT with venous outflow obstruction → secondary arterial compromise.

— Leg is swollen, cyanotic, painful, not pale. Pulses may be diminished from edema.

— Often associated with underlying malignancy.

— Management: anticoagulation, leg elevation, catheter-directed venous thrombolysis or thrombectomy, fasciotomy if needed.

— From crush, fracture, prolonged immobilization (e.g., found-down patient), reperfusion.

— Pain out of proportion, tense compartments — distinguish by mechanism and presence of palpable distal pulses initially.

— Most common peripheral aneurysm; 50% bilateral, often coexists with AAA.

— Acute thrombosis presents as ALI in an older man with a pulsatile popliteal mass.

— Manage with thrombolysis to clear runoff, then bypass with vein.

— Young athletes, exercise-induced ischemia; ALI rare but reported.

— Reversible with removal of agent and calcium channel blockers.

— Post-catheterization, IABP, ECMO cannulation — recognize the temporal link.

Key distinction: A swollen, blue, painful leg is phlegmasia (venous); a pale or mottled, cold, pulseless leg is arterial ALI. The colors and the swelling pattern separate them at the bedside.

Acute aortic dissection with limb malperfusion:

Phlegmasia cerulea dolens:

Compartment syndrome (primary):

Popliteal artery aneurysm thrombosis:

Popliteal entrapment / cystic adventitial disease:

Vasospasm / ergotism / cocaine-induced ischemia:

Iatrogenic dissection or embolism:

Key Differentials — Non-Vascular Mimics

— Cauda equina syndrome or acute lumbar disc herniation: bilateral leg weakness, saddle anesthesia, urinary retention; pulses intact and limb is warm. MRI lumbar spine is diagnostic.

— Stroke with hemiparesis: confined to one body side, cortical signs, intact pulses.

— Peripheral neuropathy flare (e.g., diabetic): chronic, bilateral, with normal pulses and warm feet.

— Acute compartment syndrome from trauma (see ch. 13) — exam dominated by pain and pressure, not pulselessness.

— Septic arthritis or necrotizing fasciitis: systemic toxicity, erythema, crepitus, rapidly progressive; arterial pulses preserved early. Surgical emergency in its own right — do not delay debridement for imaging.

— Acute gout / pseudogout: monoarticular, warm, red joint; pulses normal.

— Cellulitis / erysipelas: warm, red, swollen — opposite of cold, pale ALI.

— Cholesterol embolization syndrome ("blue toe syndrome"): livedo, palpable pulses, eosinophilia, AKI, often after recent catheterization or warfarin initiation. Manage atherosclerosis aggressively; statin; address source aneurysm/plaque.

— Giant cell arteritis (upper extremity claudication, jaw, headache, ESR/CRP up).

— Takayasu arteritis in young women — pulseless upper extremities, bruits, BP differentials.

— Polyarteritis nodosa: digital ischemia, hypertension, renal involvement.

— COVID-19-associated thrombotic arteriopathy.

— Conversion symptoms can mimic paralysis, but objective signs (temperature, pulses, Doppler) are normal.

Board pearl: Blue toe with palpable pulses + recent cath/AAA + AKI + eosinophilia = cholesterol (atheroembolic) embolization — not ALI. Anticoagulation may worsen it; treat with statin and source control, not heparin.

Acute neurologic causes:

Musculoskeletal:

Dermatologic / soft tissue:

Systemic / vasculitic:

Functional / psychogenic:

Secondary Prevention and Discharge Plan

— AF / atrial flutter: Lifelong DOAC (apixaban, rivaroxaban, edoxaban, dabigatran) if non-valvular; warfarin (INR 2–3) for mechanical valves, moderate–severe mitral stenosis, or APS.

— LV thrombus post-MI: Warfarin or DOAC for at least 3 months; reassess with echo.

— APS (triple positive): Warfarin INR 2–3 (some recommend 3–4 for arterial events).

— Hypercoagulable disorder: Indefinite anticoagulation in most arterial events.

— Atherosclerotic thrombotic ALI: Aspirin 81 mg + rivaroxaban 2.5 mg BID (VOYAGER PAD) reduces recurrent MALE/MACE after revascularization.

— Post-angioplasty/stent: DAPT (ASA + clopidogrel) 1–3 months, then ASA monotherapy.

— Post-bypass with vein graft: ASA indefinitely; consider adding low-dose rivaroxaban.

— High-intensity statin (atorvastatin 80 mg or rosuvastatin 40 mg); target LDL <70 mg/dL (consider <55 in very high risk). Add ezetimibe then PCSK9 inhibitor if not at goal.

— BP target <130/80; ACEi/ARB preferred in PAD with HTN, DM, or CKD.

— Diabetes: A1c <7% individualized; SGLT2 inhibitor and GLP-1 RA preferred for CV/renal benefit.

— Smoking cessation — varenicline or combination NRT + bupropion; counseling at every visit.

— Supervised exercise therapy for residual claudication.

— Influenza, COVID, pneumococcal vaccines.

— Anticoagulant (etiology-specific), aspirin ± clopidogrel, high-intensity statin, ACEi/ARB, β-blocker (if MI/HF), GLP-1/SGLT2 if DM, smoking cessation aid, analgesia, wound care supplies.

Step 3 management: After embolic ALI in an AF patient, do not discharge on aspirin alone — start a DOAC or warfarin as the primary stroke/limb prevention agent.

Etiology-directed long-term anticoagulation:

Antiplatelet plan after intervention:

Aggressive atherosclerosis risk-factor modification:

Discharge medication checklist (CCS-style):

Cardiac rehab / vascular rehab referral improves walking distance and mortality.

Follow-Up, Monitoring, and Counseling

— Vascular surgery follow-up within 1–2 weeks post-discharge (or 1 week for stents/bypass) — wound check, pulse exam, ABI.

— Primary care follow-up within 1–2 weeks for medication reconciliation, risk-factor management, and chronic disease titration.

— Cardiology follow-up within 2–4 weeks if AF, recent MI, or HF.

— Duplex ultrasound at 1, 3, 6, 12 months and annually after bypass or stent — assess graft patency; intervene on peak systolic velocity ratios >2 or new symptoms.

— Echocardiogram at 3 months post-MI to reassess LV thrombus.

— Surveillance imaging for known popliteal aneurysm contralateral side, AAA per guidelines.

— INR weekly until stable, then every 4 weeks (warfarin).

— Anti-Xa or no monitoring needed for DOACs; check renal function every 6–12 months and reassess DOAC dose.

— Lipid panel 4–12 weeks after statin initiation, then annually; A1c every 3 months until controlled.

— CBC, BMP, LFTs at 1 month for medication effects.

— Recognize recurrence: sudden cold, pale, painful limb — call 911, do not drive in.

— Medication adherence — anticoagulation must not be interrupted without bridging.

— Bleeding precautions — soft toothbrush, electric razor, report black stools, hematuria, headache.

— Foot care — daily inspection (especially diabetics), well-fitted shoes, podiatry for callus/nail care.

— Smoking cessation is the single highest-yield intervention.

— Exercise: walk to near-maximal claudication 3–5×/week, 30–45 min.

— Post-amputation: prosthetics evaluation, PT/OT, psychosocial support — depression rates are high.

Board pearl: A patient who stops their DOAC for a dental procedure and returns with recurrent ALI illustrates the danger of interrupting anticoagulation without bridging or risk assessment — at-risk patients should continue DOACs through minor procedures.

Inpatient → outpatient transition:

Imaging surveillance:

Laboratory monitoring:

Patient education and counseling:

Rehabilitation:

Ethical, Legal, and Patient Safety Considerations

— A Rutherford IIb limb has minutes-to-hours before irreversibility. Consent must be obtained for revascularization, possible amputation, fasciotomy, and possible bypass.

— If patient is delirious from pain/opioids or septic, use surrogate decision-maker per state hierarchy; if no surrogate and life/limb is at imminent risk, the emergency exception to informed consent applies — document carefully.

— Always discuss the possibility of primary amputation ahead of time so that intraoperative findings of nonviable muscle do not require waking the patient for re-consent.

— Frail elderly with dementia and Rutherford III: discuss whether revascularization aligns with prior expressed wishes. Palliative-focused management (pain control, comfort) may be appropriate.

— Document advance directive, code status, surrogate, and prior conversations.

— Transition-of-care risk: Anticoagulation errors are the leading source of post-discharge harm — use teach-back, written instructions, pharmacist counseling, and follow-up call within 72 hours.

— Heparin order-set safety: weight-based protocols with double-check, avoid concurrent IM injections, monitor platelets at baseline and day 4 for HIT.

— Time-out and site marking before fasciotomy/amputation; wrong-site surgery is a never-event.

— VTE prophylaxis for non-operative limb and during prolonged immobilization.

— Iatrogenic ALI (e.g., from arterial line) must be disclosed to the patient and family per Joint Commission and ethical standards; document the event and root-cause analysis.

— Suspected elder abuse or self-neglect contributing to delayed presentation triggers adult protective services referral.

— After amputation, formal driving evaluation may be required before return to driving; certain occupations (commercial driving, aviation) have anticoagulation restrictions.

Step 3 management: When a patient lacks capacity, no surrogate is available, and the limb is irreversibly ischemic with sepsis, proceeding with life-saving amputation under the emergency doctrine is ethically and legally appropriate — document the rationale contemporaneously.

Informed consent in time-critical scenarios:

Goals-of-care conversations:

Patient safety / system issues:

Mandatory reporting / disclosure:

Driving and work:

High-Yield Associations and Rapid-Fire Facts

CCS pearl: If the stem says "warm leg with intact pulses" anywhere, ALI is not the answer — pivot to neurologic, infectious, or musculoskeletal differential.

6 Ps order of appearance: Pain → Pallor → Pulselessness → Poikilothermia → Paresthesia → Paralysis (last and worst).

Most common embolic source: left atrial appendage in AF (~80% of cardioembolic ALI).

Most common embolic site (lower limb): common femoral bifurcation; (upper limb): brachial bifurcation.

Time window for muscle viability: ~4–6 hours; nerve injury starts even earlier.

Catheter-directed lysis works best when symptoms <14 days.

Rutherford IIa = lyse; IIb = cut (OR or thrombectomy device now); III = amputate.

Popliteal aneurysm: 50% bilateral, 40–50% associated AAA — always image both legs and the aorta.

Blue toe syndrome: cholesterol emboli, palpable pulses preserved, eosinophilia, recent catheterization or warfarin start.

Phlegmasia cerulea dolens: venous etiology, swollen blue leg, often malignancy.

HIT timing: platelet drop 5–10 days after heparin start (or within hours if prior exposure); switch to argatroban (renal-friendly) or bivalirudin.

Reperfusion labs: ↑ K⁺, ↑ CK, ↑ myoglobin, ↑ lactate, ↓ pH, ↑ Cr.

Fasciotomy compartments (leg): anterior, lateral, superficial posterior, deep posterior.

APS: warfarin, not DOAC, for arterial thrombosis (especially triple positive).

Buerger disease: young smokers; only cessation alters course.

VOYAGER PAD regimen: aspirin 81 + rivaroxaban 2.5 BID post-revascularization.

High-intensity statin LDL target: <70 mg/dL (consider <55 if very high risk).

Surveillance ABI/duplex after bypass: 1, 3, 6, 12 months, then annually.

DOAC reversal: idarucizumab for dabigatran; andexanet alfa (or 4F-PCC) for factor Xa inhibitors.

Heparin reversal: protamine sulfate 1 mg per 100 U heparin (max 50 mg).

Mortality at 1 year after ALI: 15–25% — driven by cardiac disease, not the limb.

Board Question Stem Patterns

Board pearl: The right answer almost always pairs "start IV heparin" with "vascular surgery consult" in the first move — pick that combination over "obtain MRI" or "warfarin loading."

Classic embolic ALI: "72-year-old with AF stopped warfarin 1 week ago presents with sudden severe left leg pain. Exam: cold, pale leg to mid-calf, absent femoral pulse, normal right leg." → IV heparin + emergent surgical embolectomy (likely IIb).

Thrombotic on chronic PAD: "65-year-old smoker with bilateral claudication develops worsening left foot pain over 24 hours; sensation intact, mild motor weakness in toes, faint Doppler signal at ankle." → Rutherford IIa → CDT or endovascular thrombectomy with imaging of culprit lesion.

Irreversible: "Found down 24 hours; leg is mottled, rigor of calf muscles, no Doppler signals arterial or venous." → Rutherford III → primary amputation, do not revascularize (reperfusion will kill).

HIT: "Post-op patient on heparin × 7 days; platelets 320 → 110; new right leg ischemia." → Stop heparin, send HIT panel, start argatroban, do not transfuse platelets prophylactically.

Cholesterol embolization: "After cardiac cath: livedo, blue toes, palpable pulses, AKI, eosinophilia." → Statin, supportive care, treat source — not heparin or surgery.

Phlegmasia: "Cancer patient with massive swollen, cyanotic leg, faint pulses." → DVT with venous gangrene → anticoagulation + CDT/thrombectomy.

APS in young woman: "32-year-old with prior miscarriages and DVT now with cold pulseless arm." → Anticoagulate; long-term warfarin INR 2–3.

Aortic dissection: "Tearing back pain → unilateral cold leg, BP differential." → CTA → dissection management; avoid lysis.

Compartment syndrome post-revascularization: "After successful femoral embolectomy, increasing calf pain and tense compartments." → Four-compartment fasciotomy.

Reperfusion hyperkalemia: "After thrombectomy, peaked T waves, K⁺ 6.8." → Calcium gluconate, insulin/dextrose, β2-agonist, bicarb, dialysis if refractory.

Ethics: "Demented nursing-home patient with Rutherford III and no advance directive — family wants comfort care." → Honor surrogate; palliative approach is appropriate.

One-Line Recap

Acute limb ischemia is a time-critical vascular emergency where the 6 Ps and Rutherford category dictate everything: heparinize immediately, image emergently, and match revascularization strategy (lyse, cut, or amputate) to whether the limb is viable, marginally threatened, immediately threatened, or irreversibly lost.

The 6 Ps and Rutherford classes are the bedside language of ALI — IIa lyses, IIb cuts, III amputates; missing a motor deficit (IIb) and choosing thrombolysis instead of OR costs the limb.

First three orders, always: IV unfractionated heparin (80 U/kg bolus, 18 U/kg/hr), STAT vascular surgery consult, and CT angiography with runoff — in parallel, not in series.

Etiology dictates long-term plan: AF → DOAC or warfarin; LV thrombus → anticoagulation ×3 months; atherosclerotic thrombotic → aspirin + low-dose rivaroxaban + high-intensity statin + smoking cessation; APS → warfarin (not DOAC); HIT → argatroban or bivalirudin.

Reperfusion can kill the patient who survived the ischemia — anticipate hyperkalemia, rhabdomyolysis-driven AKI, metabolic acidosis, and compartment syndrome; have a low threshold for four-compartment fasciotomy after >4–6 hours of ischemia or any tense calf.

Step 3 framing: do not stop at limb salvage — set up vascular and primary care follow-up within 1–2 weeks, surveillance duplex at 1/3/6/12 months for grafts and stents, lifelong risk-factor modification, and clear teach-back on anticoagulation continuity and recurrence warning signs; nearly half of ALI patients have a cardiac event within a year, so the heart is the next limb to save.