Limb Ischaemia Flashcards
Define acute limb ischaemia.
Acute limb ischaemia is defined as a sudden decrease in limb perfusion that causes a potential threat to limb viability.
What are the causes of acute limb ischaemia?
-
Embolus - most common cause.
- When material from somewhere more proximal lodges in a blood vessel and causes a sudden occlusion.
- Thrombosis - 2nd most common cause.
- Trauma
- E.g. femoral fracture (may have injury to superficial femoral artery). ALWAYS check circulation in a trauma situation. ?pulses.
- Dissection
- Haemorrhage in the media of the vessel wall.
Describe the pathophysiology of how an embolus causes acute limb ischaemia.
- Often a cardiac source.
- AF - ventricles not emptying properly and thrombus can form.
- Valvular heart disease - valve replacement that are not adequately anticoagulated.
- Mural thrombus - develops on the wall of the ventricle. Post MI, often raw area of ventricular muscle which is pro-thrombotic. Thrombus can form on this wall and it can embolise and cause ischaemia.
- Endocarditis - can have vegetations attached to the wall of the heart. These infected vegetations can break off and travel around the body. Can cause ischaemic limbs or strokes. Can als end up with septic emboli which means you are also dealing with infection. Can cause vessel wall to break down.
- Atrial myxoma - RARE.
- Aortic and peripheral artery aneurysms - as an arterial wall dilates up to form an aneurysm, the blood flow is turbulent and thrombus formation around the walls of the aneurysm.
- Atherosclerotic plaque with plaque rupture - can rupture and expose the endothelium of the vessel wall – very pro-thombotic. Thrombus forms on the top of this; this is very unstable and can easily break off and lodge in a more distal vessel, causing an acute episode of ischaemia.
Describe the pathophysiology of how thrombosis can cause acute limb ischaemia.
- Plaque rupture and occlusion of pre-existing stenosis.
- Usually background of claudication / PVD - more complicated pattern of disease. There is collateral angiogenesis
- Causes a sudden deterioration of the symptoms.
Describe the typical presentation of an acutely ischaemic limb.
- Elderly patient
- Often new AF, or AF without adequate anticoagulation.
- Signs:
- Pallor
- Pain
- Polar (cold) - early sign
- Pulseless - early sign
- Paraesthesia
- Paralysis - late sign
- However:
- Progressive signs - may be irreversible muscle damage by 6 hours.
- Pre-existing PVD or thrombosis in situ will modify presentation.
Describe how to assess a patient with ?acute ischaemic limb.
- History (risk factors).
- Pulses (+ contralateral).
- Capillary refill / veins.
- Sensation.
- Motor function.
- Squeeze calf - calf tenderness.
- Ask to wiggle toes on BOTH feet. They may be able to move toes on ischaemic side, but if bilaterally, it is not the same, THIS IS ABNORMAL.
- Sensorimotor deficit requires prompt intervention.
- Fixed mottling and paralysis are irreversible changes.
- Fixed (unblanching) mottling and paralysis = irreversible change.
- If they have a thrombus in one leg, they may have thrown a clot down the other leg too. So, while 1 leg is acutely ischaemic, the other may be a little ischaemic too. If the contralateral leg is completely normal, this makes embolus a much more likely cause of ischaemia in the symptomatic leg.
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What should you consider once you have treated and blood has rushed back into the ischaemic limb?
- Consider fasciotomy because the patient is at risk of compartment syndrome.
- Releasing the fascia surrounding the muscles to allow them to swell.
How would you manage a patient with an acutely ischaemic limb?
- Analgesia - often opioid required.
- Sometimes necessary before you can assess px.
- Hydration - very high risk of renal failure. As ischaemia develops, there is breakdown of muscle so high levels of CK and myoglobin and myolobinuria (rhabdomyolysis) so be KIDNEY CAREFUL.
- It is a fine balance between renal protection and fluid overload and the risk of heart failure so catheterise to monitor UO and hang fluids.
- LMWH or IV UF heparin.
- This is not to dissolve clot, but rather to stop it propagating further.
- Imaging (if required).
- Intervention.
Describe endovascular repair of acute limb ischaemia.
- Good option if this is an acute problem ont op of a background chronic condition.
- Takes time to organise - class 1 or 2a acute ischaemia.
- Thrombolysis and angioplasty or stent.
- Risk of distal embolisation.
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Under what circumstances would a fem-pop / fem-distal bypass be appropriate?
- Acute thrombosis on a background of chronic disease.
- Suitable if more extensive pattern of disease.
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Why should you investigate the cause of embolus even after limb ischaemia has been treated?
- The embolus has come from somewhere.
- INVESTIGATE THIS.
- Unless you do this and anticoagulate if necessary, the patient is at risk of further emboli and stroke.
Define chronic limb ischaemia.
- Decrease in limb perfusion which may or may not threaten the viability of the limb of duration > 2 weeks.
What is the cause of chronic limb ischaemia?
- Due to atherosclerosis.
- Build up of lipid, calcium and fibrous tissue within the intima of the arterial wall.
- Once >50% of th arterial cross-sectional diameter is occupied with atheromatous plaque, this becomes flow limiting and may lead to symptoms.
- Fibrous plaque is vulnerable to rupture - if the endothelium is exposed, thrombosis may cause an acute deterioration in symptoms due to sudden narrowing of the lumen.
Describe peripheral arterial disease.
- Progressive disorder charaterised by stenosis or occlusion of large and medium sized arteries (other than coronary or cerebral arteries).
- 10-20% of patients >60 have PAD.
- Over half are aymptomatic.
- Increased risk of CV mortality (~5% risk of mortality, MI or stroke per year).
- Underdiagnosed and undertreated.
What are the risk factors for peripheral arterial disease?
- Smoking
- Age
- Male
- Hypertension
- Hyperlipidaemia
- Diabetes
- Ethnicity
- Less common in Chinese than Caucasians, more common in African Americans.