Surgical emergency: acute limb ischaemia

Ashok Handa, Kevin Turner, and Adam Jones examine a life threatening condition

A request to see a patient with a "cold limb" should be a priority as acute limb ischaemia has a high associated morbidity and mortality. Speed is important as complete acute limb ischaemia will lead to irreversible tissue damage within 6 hours unless the limb is revascularised.

In England and Wales approximately 5000 patients present each year with acute limb ischaemia, and the associated mor- tality is at least 20%, with a limb loss rate of 40%.¹ Mortality is higher in patients presenting with embolic causes, while limb loss is higher in those with thrombosis. All patients presenting with an ischaemic limb should be assessed by an experienced surgeon. You should contact the surgical registrar as soon as you have seen the patient.

Clinical presentation

The classical description of the features of acute limb ischaemia is the "six Ps": pain, parasthesia, paralysis, pallor, pulseless, and perishingly cold (Box 1). However, the severity of the symptoms and signs of acute ischaemia is not proportional to the degree of ischaemia. Initially there is spasm of the distal arterial tree with an associated pallor. Over the next few hours there is some vasodilatation and the deoxygenated blood gives a mottled purple appearance that blanches. As ischaemia progresses this turns darker in colour and becomes fixed.

Aetiology (Box 2)

The majority of acute limb ischaemia is caused by acute thrombosis in a vessel with pre-existing atherosclerosis (60%). Emboli account for a further 30% of acutely ischaemic limbs. The management and outcome of these two broad categories is different and thus distinguishing between them is essential. Other causes include aortic dissection, trauma, iatrogenic injury (arterial cannulation), peripheral aneurysm and injury caused by exteme cold. Important differentials may be intra-arterial drug administration and venous gangrene.

Embolism

Most emboli (80%) have a cardiac cause and arise from the left atrium in patients with atrial fibrillation or following acute myocardial infarction. Less common cardiac sources include prosthetic valves, valve vegetations in endocarditis, "paradoxical" embolus (a venous embolism from a deep venous thrombosis passes into the systemic arterial circulation through a congenital communication between the right and left cardiac circulation), and atrial myxoma. Arterial aneurysms account for a further 10% of emboli and may be in the aortoiliac, femoral, popliteal, or subclavian arteries.

In some patients no source is found. Most emboli lodge at bifurcations of arteries as the diameter of the vessel suddenly reduces here. The commonest site of embolic occlusion is the femoral bifurcation. Other sites that emboli lodge at are the brachial, popliteal, and aortic bifurcations. (An embolus lodged in the latter site is known as a saddle embolus.)

Thrombosis

In most cases thrombosis is secondary to pre-existing atherosclerosis. Predisposing factors are dehydration, hypotension, malignancy, polycythaemia, or inherited prothrombotic states. Clinical features suggestive of thrombosis are a previous history of intermittent claudication, no source for emboli, and reduced or absent peripheral pulses in the contralateral limb (Table).

Assessment

Patients who present with an ischaemic limb often have widespread arterial disease. Particular attention should be paid to pre-existing coronary, cerebrovascular, and renovascular abnormalities. General assessment of the patient requires a clear history and examination with particular regard to identifying the underlying cause of limb ischaemia. Assessment of the limb requires a judgment of the severity of ischaemia. Involve the general or vascular (if available) surgical registrar early.

Immediate management

Patients who present with limb ischaemia are potentially seriously ill. Remember to go through the ABC of resuscitation. Give 100% oxygen.

Get venous access and start slow intravenous infusion (a litre of normal saline over 8 hours, unless the patient is very dehydrated in which case it should be faster).

Withdraw blood for full blood count, measurement of urea and electrolytes, glucose in diabetics, cardiac enzymes, clotting, and group, and save. A thrombophilia screen and lipid profile are also useful.

Get a chest radiograph and an electrocardiogram, and if the patient is in atrial fibrillation arrange for cardiac monitoring.

Insert a urinary catheter to monitor resuscitation if the patient is dehydrated.

Prescribe opiate analgesia if the patient is in severe pain, and call for senior help.

Subsequent management

This will depend on the assessment of the severity of the ischaemia. There are three broad categories:

• irreversible with a non-salvageable limb
• complete with an acutely threatened limb
• incomplete with a viable limb.

This assessment can only be made by an experienced surgeon and will dictate further treatment. In the first category amputation is inevitable and often a pressing need as delay may result in death from the systemic sequelae of muscle necrosis (hyperkalaemia, acidosis, acute renal failure, and sepsis).

In the at risk and viable limb category, management usually involves initial intravenous heparinisation to prevent propagation of thrombus and prompt angiography to plan further intervention. If there are no contraindications (eg aortic dissection, multiple trauma, head injury) you should give an intravenous bolus of 5000 units of heparin and start an infusion of 1000 units per hour. Recheck the activated partial thromboplastin time (APTT) in 4-6 hours, and aim for a time 2-2.5 times the normal range.

The acutely threatened group needs expert vascular input. Thrombolysis, angiography, angioplasty, embolectomy, or urgent arterial bypass may be required depending on the individual circumstances. Detailed discussion of the therapeutic options is beyond the remit of this article.

Conclusion

Acute limb ischaemia is both life and limb threatening. It requires prompt assessment. Consider the underlying causes and arrange investigations as a matter of urgency. Call for senior help early as this may lead to improved limb salvage and survival. Remember, it is better to call someone and find that you could manage after all than to call someone too late!

Ashok Handa, clinical lecturer, Nuffield Department of Surgery, John Radcliffe Hospital, Oxford

Kevin Turner, research fellow in urology, Molecular Oncology Group, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford
Email: kevin@kkturner.freeserve.co.uk

Adam Jones, specialist registrar in urology, Churchill Hospital, Oxford


studentBMJ 2000;08:217-258 July ISSN 0966-6494

1. Hickey NC, Crowson MC, Simms MH. Emergency arterial reconstruction for acute ischaemia. Br J Surg 1990;77:680-1.