Acute lower limb ischaemia is in most cases caused by sudden obstruction of an artery due to an embolus or thrombosis. Rare causes that should be kept in mind include aortic dissection and thrombosis of a popliteal aneurysm.
Chronic lower limb ischaemia is a slowly progressing disease process that is usually caused by an obliterating arterial disease.
Acute lower limb ischaemia must be recognized and the patient immediately referred for further management.
Chronic lower limb ischaemia must be diagnosed and its severity (stage) assessed, as the severity of the condition will determine management approach.
Mild ischaemia is asymptomatic, but is suggestive of an increased overall cardiovascular risk.
Moderate ischaemia causes intermittent claudication which, as such, is a benign but troublesome complaint. Claudication may be treated conservatively, but if the condition threatens the work or functional capacity of the patient, a referral to a vascular surgeon is indicated.
Critical ischaemia manifests itself as pain at rest and may lead to a non-healing chronic leg ulcer and eventually to gangrene. Patients with critical limb ischaemia require urgent referral to a vascular surgeon. If limb ischaemia is complicated by an infection or if a gangrene has developed fast, an emergency referral is indicated.
If ischaemia is suspected it should be verified by measuring the ankle and brachial pressures with Doppler ultrasonography in all suspected cases of ischaemia. Examination of the patient, see Doppler Stethoscopy in Diagnostics.
A patient suffering from lower extremity ischaemia always has atherosclerosis also elsewhere than in the arteries of the lower extremities (ASO). Consequently, the prevention of coronary heart disease and ischaemic cerebrovascular disorders should be taken care of by controlling the risk factors (hypertension, dyslipidaemia, smoking, diabetes). This has the greatest impact on the patient's prognosis.
In all stages of ischaemia, the patient will complain of cold feet and the skin is cold to touch.
Intermittent claudication: repeated pain in the lower limbs, usually in the calves, which develop during walking. Pain is relieved by a rest of 5-15 minutes, after which the patient is again able to walk the same distance.
The severity of intermittent claudication does not correlate with the stage of the disease. Of the patients with critical ischaemia, 50% present with no previous history of intermittent claudication; the mobilisation of many elderly patients is very limited.
In Leriche's syndrome the occlusion is situated in the distal aorta, and the patient will have claudication pain in both limbs up to the buttocks. Men may also have erectile dysfunction.
Occlusion at the iliac artery results in thigh and calf claudication. Occlusion at the superficial femoral artery leads to claudication in the calf, and popliteal occlusion to foot numbness during exercise.
Leg pain at rest, which is relieved by standing upright or hanging the limb over the edge of the bed, is suggestive of severe ischaemia; pain in the foot, ankle brachial index (ABI) often < 0.5.
Ischaemic tissue damage: necrosed areas or ulcers which may be dry and localised or become infected and may, at the worst, lead to a septic infection.
In patients with diabetes, 10% of all tissue damage is of pure ischaemic origin and 50% of combined neuropathic and ischaemic origin. A warm and dry neuropathic skin may mislead the clinical assessment. It is therefore safest to presume skin damage to be of ischaemic origin until proven otherwise.
Palpation for foot pulses
First-line examination. The arteries to palpate are the dorsalis pedis artery and the posterior tibial artery.
Oedema will hamper the palpation.
The examiner's own capillary pulse may interfere with the palpation.
If both the dorsalis pedis artery and the posterior tibial artery can definitely be palpated, significant arterial stenosis is improbable. An inconclusive finding is always an indication for a Doppler study.
Measurement of peripheral pressure and ankle brachial index (ABI)
The measurement of the peripheral pressure with the Doppler technique (see Doppler Stethoscopy in Diagnostics; video Measurement of Ankle Pressure and Abi) is the most important diagnostic tool. ABI is calculated by dividing the ankle pressure by the brachial pressure. The result will also be indicative of the severity of the disease. The measurement of the ankle pressure will usually suffice in general practice; the normal ABI is > 0.9. The pulse usually is not palpable if ABI < 0.7.
At the threshold value of 0.9, the sensitivity and specificity of ABI is about 95%. ABI of 0.9-0.7 is usually indicative of mild ischaemia, ABI 0.7-0.4 of moderate ischaemia and ABI < 0.4 of severe ischaemia.
ABI > 1.3 is indicative of incompressible arteries due to mediasclerosis, and the measurement will yield no information about the presence of ischaemia. Mediasclerosis is common in persons with diabetes.
ABI < 0.9 and ABI > 1.3 are also associated with an increased overall cardiovascular risk.
Cessation of smoking is the most important single measure in conservative management, and it will slow down the disease progress.
If the patient continues to smoke, the risk of amputation will increase. The patient should be advised to choose between “cigarettes or legs”.
Exercise
The patient should be advised to walk for an hour every day.
If leg pain develops, the patient should rest and then continue walking.
Results should be evident after about three months.
However, an exercise regime is usually not effective in patients who develop claudication after walking less than 50 metres or if the symptom is caused by stenosis of the iliac artery (femoral pulse in the groin is absent).
Drug treatment
Aspirin 100 mg daily. Its effect in the prevention of complications in peripheral arterial obstructive disease (PAOD) has not been conclusively proven, but its use is justified as it will be beneficial in the treatment of coronary heart disease, which is common in these patients. Its efficacy has been established in the post-operative care following vascular reconstruction surgery.
Clopidogrel may be used in patients who are hypersensitive to aspirin, and in patients who develop new occlusions during aspirin therapy. Warfarin and low-molecular heparin are of no benefit in the treatment of chronic lower limb ischaemia.
Lipid-lowering medication . The progression of co-existing coronary heart disease may be slowed down with statins. Moreover, statins are also likely to slow down the progression of PAOD. As a rule, statin medication is always started, with LDL concentration of < 1.8 mmol/l as the target.
The efficacy of pentoxiphylline has not been established. The clinical response is either of short duration, slight or insignificant.
Vitamin E has no effect on intermittent claudication.
A selective beta-blocker may usually be used with no adverse effects, unless the patient has critical ischaemia. A beta-blocker may be indicated for the treatment of coronary heart disease or hypertension. The choice of an ACE inhibitor as an antihypertensive agent in PAOD is justified, as it will also have a beneficial effect on other co-existing vascular diseases.
Tight glucose control in diabetes will reduce vascular complications. The target is HbA1c< 53 mmol/mol (< 7%).
Foot care
Particularly important in patients with diabetes; a dusky or discoloured heel is at risk of developing an ulcer, and the heel must be protected against pressure.
The patient must avoid trauma to the foot as well as too cold or too hot baths.
In order to reach and maintain good treatment results, a patient with diabetes should wear specialist footwear (moulded inserts, custom made shoes etc.) at all times to relieve pressure on the feet.
Intermittent claudication, induced by chronic ischaemia, is a troublesome complaint but seldom poses a serious risk. Risks arise from co-existent coronary heart disease and cerebral vascular disease, which determine the patient's prognosis.
Initially, the treatment of PAOD should consist mainly of conservative management, i.e. "Stop smoking and keep walking"
Where intermittent claudication threatens the patient's work or functional capacity, vascular surgery should be considered.
The choice between an endovascular procedure and surgical revascularisation is made individually for each patient according to the results of imaging studies.
In patients with PAOD, percutaneous transluminal angioplasty (PTA) is a simple and effective treatment form, and a vascular surgeon should be consulted about the feasibility of the procedure in patients whose symptoms worsen. Proximal occlusions should be identified and treated even if they are only mildly symptomatic. Proximal occlusions are typical in persons who smoke and distal occlusions in patients with diabetes.
Prognosis in chronic ischaemia: deterioration in 25% of cases, revascularisation in 5% of cases and amputation in 1-2% of cases.
The term critical ischaemia is used to denote the worsening of chronic ischaemia leading to the threat of gangrene in the lower extremity. Symptoms include rest pain and/or gangrene or an incurable ulcer in the foot area.
Should be suspected if a leg ulcer shows no signs of improvement in two weeks. A typical sign of ischaemia is distal gangrene ("toe infarct") as well as an ulcer outside the usual pressure areas, which are the heel and ball of the foot. An ulcer must not be treated blindly, and the cause of the problem should be established.
The limb will feel cool or cold to touch and have abnormal colouring.
50% of patients with critical ischaemia have diabetes.
The patient may perceive the ischaemia as numbness.
Concomitant deep venous insufficiency and a venous ulcer may make the diagnosis difficult. It should be kept in mind that in the background there may be insufficiency of both arterial and venous circulation, and ABI should be measured in a patient with a leg ulcer as well.
Ischaemia should be considered critical if
the patient has severe pain during the night, when at rest
the patient has foot gangrene or a foot ulcer that does not improve, and the ankle brachial index (ABI) is < 0.85. In a patient with diabetes, the reading taken with a Doppler stethoscope may be falsely high, but the presence of ischaemia will be revealed by a faint, monophasic flow signal.
Critical ischaemia requires urgent by-pass surgery or extensive endovascular recanalisation in order to avoid amputation (above or below knee).
If critical ischaemia is suspected, the patient should be referred without delay, even as an emergency case, to a vascular surgery unit where all potentially mobile patients will either undergo angiography or immediate vascular reconstruction.
Critical ischaemia is often associated with long occlusions in the thigh and leg arteries. The patients are often elderly and have multiple co-existing illnesses and poor life expectancy. However, an attempt should be made to salvage the limb even in elderly patients if the choice is between independent living and amputation followed by institutional care.
Primary amputation is carried out in patients in poor general health who no longer are able to mobilise independently and in cases where the gangrenous tissue covers at least half of the foot.
A patient who has undergone amputation due to ischaemia is not likely to learn to walk with a prosthesis, and reconstructive vascular surgery should therefore be the management of choice whenever possible.
Symptoms and diagnosis of acute ischaemia
Acute limb ischaemia may be caused by an acute thrombotic occlusion of a pre-existing atherosclerotic artery (acute-on-chronic) (40% of cases), by reocclusion of a previous vascular reconstruction site (20%) or by an embolus (40%) which is in most cases of cardiac origin.
Symptoms
The rule of the "five P's": pain, pallor, pulselessness, paraesthesia, paralysis
The affected limb may also feel colder to the touch than the unaffected side. A distinct line between the cold and warm zones may be evident on the skin.
If the foot is cyanotic or there is motor and/or sensory loss (test the dorsiflexion of the foot and toes), circulation must be restored within 6 hours.
Diagnosis
Embolic occlusion has an acute onset. The primary cause is often atrial fibrillation, myocardial infarction etc.
The onset of acute-on-chronic ischaemia is slower. The patient often has a history of intermittent claudication and the other limb is also affected by PAOD.
Massive iliofemoral venous thrombosis must be borne in mind in differential diagnosis; the signs and symptoms include limb oedema, cyanosis and venous congestion.
Ischaemic paralysis may mimic a neurological illness.
If the entire limb is cyanotic and stiff, emergency above-knee amputation must be carried out in order to save the patient's life.
The treatment of acute-on-chronic ischaemia is in most cases intra-arterial thrombolytic therapy with tPA (tissue-type plasminogen activator). After the fresh thrombus has been lysed, endovascular surgery or vascular reconstruction is often needed in order to correct the cause of the occlusion.
Embolectomy is the first-line treatment in case of an embolus. If needed, it can also be carried out under local anaesthesia even if the patient is elderly or in poor general health. Intra-arterial thrombolysis is an alternative treatment approach. If a differential diagnosis cannot be made, thrombosis should be considered as the cause of acute ischaemia.
Angiographic studies may be carried out during the initial phase, provided that the mobility and sensation of the toes and ankle are normal, the ankle pressure is > 30 mmHg measured with a Doppler stethoscope and no cyanosis or muscle tenderness is present. If the foot is cyanotic or the motor function impaired, circulation must be restored immediately with emergency surgery.
References
Girolami B, Bernardi E, Prins MH, Ten Cate JW, Hettiarachchi R, Prandoni P, Girolami A, Büller HR. Treatment of intermittent claudication with physical training, smoking cessation, pentoxifylline, or nafronyl: a meta-analysis. Arch Intern Med 1999 Feb 22;159(4):337-45. [PubMed]
Vuorisalo S, Venermo M, Lepäntalo M. Treatment of diabetic foot ulcers. J Cardiovasc Surg (Torino) 2009;50(3):275-91. [PubMed]
European Stroke Organisation., Tendera M, Aboyans V et al. ESC Guidelines on the diagnosis and treatment of peripheral artery diseases: Document covering atherosclerotic disease of extracranial carotid and vertebral, mesenteric, renal, upper and lower extremity arteries: the Task Force on the Diagnosis and Treatment of Peripheral Artery Diseases of the European Society of Cardiology (ESC). Eur Heart J 2011;32(22):2851-906. [PubMed]