LIMB ISCHAEMIA: WHEN CAN THE LEG BE SAVED?

By PHILIP COLERIDGE SMITH DM MA BCh FRCS Consultant Vascular Surgeon, Medical Director of the British Vein Institute and Emeritus Reader in Surgery at UCL Medical School

[LOWER LIMB ISCHAEMIA is a common problem, especially in elderly patients. Total disease prevalence has been evaluated in several epidemiological studies and is in the range of 3%-10%, increasing to 15%-20% in persons over 70 years. Modern surgical and endovascular treatments are available which will avoid amputation in patients with severe limb ischaemia.

The causes of limb ischaemia

Ischaemia most commonly affects the lower limb and usually arises as the result of atheroma (hardening) of the arteries. The main causes of this are a smoking history and diabetes. Diabetes currently affects about 4.9m people in the UK, 90% of whom have type 2 diabetes. This disease may lead to narrowing of the leg arteries, especially those vessels in the calf and foot. Poorly-controlled diabetes is more likely to cause narrowing of arteries than well-controlled diabetes. The calf is a region which is more difficult to treat than the proximal arterial system where techniques such as balloon angioplasty and open surgical bypass operations are effective in most cases.

Chronic limb ischaemia

The development of atheroma gradually narrows the affected arteries which eventually become blocked as thrombosis develops in the diseased vessels. Where arteries gradually become blocked there is an opportunity for an alternative circulation to develop to supply the limb. Less active patients may not notice the reduced blood flow but others may notice that they have developed pain in the calf on walking known as ‘intermittent claudication’. Surgical treatment is often not necessary for this condition which does not threaten the limb. It may progress to more severe arterial disease in about one quarter of cases.

Acute limb ischaemia

In some cases a blood clot forms within the vascular system and then detaches from its source to become an embolism. This travels with blood flow before blocking the artery where is comes to rest. Common sources of embolism include the heart where an irregular heart rhythm or recent heart attack may allow thrombus to develop on the wall of the heart. Atheromatous arteries may also accumulate thrombus on their irregular walls.

The clinical presentation of embolism of thrombus into the leg arteries is often more dramatic than when arteries narrow gradually. Sudden occlusion of a major artery leads to acute limb ischaemia. The main presenting symptom is severe and excruciating pain, often not relieved by opiate analgesic drugs. The limb is described as painful, pale, pulseless, perishing with cold and paralysed.

Trauma to the limb may also give rise to disruption of the artery which supplies the leg. Arterial occlusions may occur with fractures of the lower limb or dislocation of the knee. Occasionally, the trauma can arise from iatrogenic sources such as following knee replacement surgery. Traumatic interruption of the blood flow to the leg can leave the limb in great jeopardy.

In contrast to patients in whom the arteries have narrowed gradually, no alternative circulation has had an opportunity to develop and the damaged vessel has to be repaired expediently before the limb is severely damaged by ischaemia.

Diagnosis of limb ischaemia

In general the diagnosis in patients presenting with acute limb ischaemia due to sudden cessation of blood flow in the limb is readily made. The patient complains of very severe pain in the limb, which is usually cold, white and pulseless. This problem commonly presents to doctors in A&E departments who are readily able to make the correct diagnosis based on clinical examination alone.

In patients who have a reduced level of consciousness the diagnosis may not be so obvious to the attending clinicians. Patients who have suffered multiple trauma and are sedated or unconscious may have loss of the lower limb circulation associated with lower limb fractures. Some patients remain sedated following major surgery and opiate analgesics are required to provide post-operative analgesia. Examples of this include lower limb arterial surgery, cardiac surgery and knee replacement surgery. Failure to check or regularly monitor the blood flow to the lower limb in these contexts may lead rapidly to severe ischaemic damage to the limb if the circulation fails following surgery.

I have advised in cases where failure to monitor the blood flow to the lower limb following vascular, cardiac and orthopaedic surgery permitted undetected limb ischaemia to develop. By the time the diagnosis was identified, the limb was beyond salvage.

An uncommon presentation of acute lower limb ischaemia is with sudden onset of paralysis in one or both limbs. Pain may not be reported by the patient because failure of blood flow to the main nerves supplying the limb prevents pain sensations being felt. This presentation occurs when the abdominal aorta or the iliac arteries in the pelvis are suddenly occluded.

If the emergency medical team does not consider limb ischaemia as a possible diagnosis and instead investigates the neurological system, severe ischaemic damage to the lower limbs may result before the correct diagnosis is established. The diagnosis is readily established by palpation of the lower limb pulses on initial hospital attendance. Failure to complete this part of the clinical examination may fall below an acceptable standard of medical care in such cases.

Critical limb ischaemia

In patients presenting with gradual and insidious occlusion of the lower limb vessels, the diagnosis may only be established after several consultations with doctors. Where much of the blood supply to the lower limb has been blocked off, the condition is referred to as ‘limb threatening ischaemia’ or ‘critical limb ischaemia’. The symptoms are gradual onset of pain in the toes and foot. This is worse a night and is relieved by hanging the affected leg out of bed. Ulceration of the foot and toes may also arise due to the ischaemia – see photo opposite.

Diagnosis of critical limb ischaemia

The diagnosis of critical limb ischaemia can be established by palpation of the lower limb pulses, which are absent in this condition and associated with a low blood pressure measured at the ankle. However, pain in the toes is sometimes misdiagnosed as gout or some other condition of the foot. In diabetic patients, ulceration of the feet or toes may be mistakenly thought to be the result of loss of sensation in the foot due to diabetic neuropathy. In critical limb ischaemia expediency of appropriate investigation and treatment is required.

However, the timescale over which this should be done is greater than for acute limb ischaemia. The Vascular Society recommends that patients with this condition should be investigated and treated within two weeks of diagnosis, where feasible. NICE Guideline 19 on the subject of diabetic foot ulcers advocates referral to a diabetic foot multidisciplinary team within 24 hours for patients presenting with the diagnosis of a new diabetic foot ulcer. Failure to comply with these recommendations may fall below an acceptable standard of care.

Patients with limb-threating ischaemia have a 80-90% chance of avoiding amputation within 30 days of treatment with referral before irreversible damage has arisen to the limb. Delayed treatment allows progressive ischaemic damage to arise which may be complicated by uncontrolled infection in diabetic patients. Delayed referral to a vascular service in such cases may be considered to comprise substandard care.

Can the leg be saved?

In patients presenting with acute limb ischaemia, especially in those where vascular trauma has occurred and there is no preceding arterial disease, the limb will survive 4-8 hours without severe damage commencing in the muscles and nerves of the limb. These patients require expedient diagnosis and treatment. This will usually lead to avoidance of the need for limb amputation. Substandard delays in diagnosis leading to delayed treatment and adverse outcomes, including the need for limb amputation, may lead to allegations of substandard care.

For patients with insidious onset of limb-threatening ischaemia, urgent management is required, preferably within two weeks of the onset of symptoms. Vascular surgery to improve the blood supply to the limb will lead to avoidance of the need for amputation in about 90% of cases providing that the limb is still viable at the time of consideration for surgery. This type of ischaemia may lead to extensive gangrene and limb amputation where delays in diagnosis and treatment have occurred.

Causation – the main issues

My experience is that delays in surgical or endovascular intervention being commenced leading to an amputation may lead to allegations of substandard care. However, these cases are usually defended on causation.

In some cases, tiny emboli travel to the foot and toes leading to ischaemia confined to the toes or forefoot. It may not be feasible to remove the emboli from such tiny arteries, even with the best of care. The toe or forefoot may already have become irreversibly ischaemic at the time of presentation. Amputation of the toes would always have been a likely outcome in such cases.

Patients with diabetes tend to have severe disease in the arteries below the knee and in the foot. Sometimes all of the three main arteries below the knee are occluded over most or all of their course. Modern endovascular treatments such as balloon angioplasty may be effective in a limited number of cases but severe distal arterial disease often limits the efficacy of treatment. It may not be possible to restore any useful blood flow in the leg where extensive disease is present. The surgeon has no alternative but to advise amputation in these cases. The defence advanced in these cases is likely to be along the lines that the arterial disease was untreatable with any currently available method and amputation was the only feasible treatment.

In cases where delayed diagnosis and treatment has resulted in extensive gangrene of the tissues, there is no prospect of saving the limb and amputation will be advised. In these cases the claimant can argue that the limb would have been saved with timely treatment. His case is likely to succeed in this scenario.

Conclusion

The modern vascular surgical team can offer several options to restore the blood flow to severely ischaemic limbs. Delays in referral to hospital prejudice the outcome since ischaemic limbs very rapidly become non-viable if neglected. However, not all limbs can be saved. Sometimes the arterial disease is too extensive or severe to permit restoration of blood flow and an amputation is the only solution. q