Vascular: Acute Arterial Occlusion Flashcards
What is ischemia-reperfusion syndrome?
Once several hours have passed before reperfusion of a limb/tissue, metabolic substances get released into the blood as the limb is reperfused.
Locally, causes endothelial damage, capillary permeability, transudative swelling, cellular damage. May go on to cause compartment syndrome (pain out of proportion to exam, pain with dorsiflexion, paresthesia).
Systemic: lactic acidosis, hyperkalemia, myoglobin, inflammatory cytokines. Together may cause cardiopulmonary complications.
Discuss pharmacology of antithrombin, heparin, coumadin.
All inhibit clot formation.
Antithrombin: binds to thrombin, forms an inactive complex.
Heparin: accelerates inhibition of thrombin and factor Xa by antithrombin. Causes immediate anticoagulation and accelerates inhibition and stops clot formation.
Coumadin: inhibits reduction of vitamin K in the liver –> non-functional clotting factors. Takes time to work as functional proteins must be cleared first.
Discuss pharmacology of urokinase, tissue plasinogen activator, reteplase.
All act to breakdown clots. Normally, plasminogen broken down to plasmin. Then plasmin cleaves fibrin to form d-dimer and alpha chains. These drugs act to increase intrinsic activity of plasmin.
Urokinase: directly activates plasminogen.
tPA: acts at vascular endothelium to activate plasminogen.
Reteplase: recombinant tPA, catalyzes cleavage of endogenous plasminogen to form plasmin.
6 “P’s” of arterial occlusion.
Paraesthesias (main, early sign, nerves are the first thing injured in ischemia), pain, pallor, poikilohtermia, pulselessness, paralysis.
Natural history of acute arterial occlusion and its irreversible effects.
Progresses to irreversible ischemia in 6-8 hrs.
Presentation: sudden onset, extreme pain, loss or reduction in pulses.
Paraesthesias and paralysis are hte most important signs b/c nerves are the most sensitive.
Progresses to muscle damage.
Skin mottling and no longer blanching–> sign of irreversible tissue ischemia.
Color change: extravasation of blood from capillaries into dermis.
Causes of acute arterial obstruction.
Embolus: cardiogenic or any proximal artery. Hx of afib, MI, valvular disease. Atheroembolism may come from aorta, iliac or femoral vessel. No hx of PVD, digital ischemia, palpable pulses. Normal contralateral exam
Thrombosis: atherosclerosis, aneurysm. Underlying stenosis from atherosclerosis. All pts should have angiogram unless ischemia is severe and rapidly progressive. Ask about Hx of PVD, popliteal/aortic aneurysm. Look for evidence of PVD (skin changes, lack of distal pulses on contralateral side).
Trauma: e.g. posterior knee dislocation, long bone #, penetrating trauma. If there are signs of ischemia with fracture, always try to reduce it.
Iatrogenic causes.
Comparison of embolic vs thrombotic disease
Embolic: sudden onset, no prior hx claudication, hx of Afib, AAA or arrythmias, other leg usually normal and angiogram will show sharp cut off.
Thrombus: Less dramatic onset, hx of claudication, no obvious source, other leg usually abnormal (signs PVD), angiogram will show diffuse disease.
When to do angiography for acute arterial ischemia.
If diagnosis certain by Hx/PEx (cold, newly pulseless, painful extremity) –> no further w/u.
Angiography if: need to confirm site of lesion, underlyign atherosclerosis, aneurysm, aortic dissection. Allows for determination of etiology (thrombus vs emboli). If time permits, allows to plan revascularization but should not delay getting to OR.
Mgmt acute arterial ischemia
Immediate anticoagulation: heparin bolus and continuous infusion. Helps prevent clot propagation and relieve associated vessel spasm. Improves symptoms but revascularization still required.
Thrombolytic therapy (tPA): activation of plasmin system to cause fibrinolysis and clot dissolution. Advantages- opens collaterals/buys time, avoid sudden reperfusion, reveals underlying stenosis. Indicated for early occlusion presentation, clots <14 days, large clot burden. Often takes 24+ hours to fully lyse thrombus. Not done if severe ischemia is present since takes time to dissolve the clot.
Surgery: revascularize via embolectomy or thrombectomy.
