Acute Limb Ischaemia
Acute limb ischaemia is defined as the sudden decrease in limb perfusion that threatens the viability of the limb.
Complete or even partial occlusion of the arterial supply to a limb can lead to rapid ischaemia and poor functional outcomes within hours. In this article, we shall look at the causes, clinical features and management of a patient with acute limb ischaemia.
The causes of acute limb ischaemia can be classified into 3 main groups:
- Thrombosis in situ (60%) – whereby an atheroma in the artery ruptures and a thrombus forms on the atheromatous plaque’s cap
- Can present as an acute presentation or an acute-on-chronic.
- Embolisation (30%) – whereby a thrombus from a proximal source travels distally to occlude the artery. The original thrombus source may be as a result of AF, post-MI mural-thrombus, abdominal aortic aneurysm, or prosthetic heart valves.
- Trauma (10%) – including compartment syndrome.
It has an incidence of around 1.5 per 10,000 person years. Acute limb ischaemia has a mortality rate of around 20%.
In this history, the causes of potential embolisation should be explored. These include chronic limb ischaemia, atrial fibrillation, recent MI (resulting in a mural thrombus), or a symptomatic AAA (ask about back/abdominal pain) and peripheral aneurysms.
Classically, the signs and symptoms of acute limb ischaemia can be described using the 6 P’s:
- Perishingly cold
Acute limb ischaemia is often characterised by a sudden onset of these symptoms. A normal, pulsatile contralateral limb is a sensitive sign of an embolic occulsion.
The later the patient presents to a hospital, the more likely that irreversible damage to the neuromuscular structures will have occurred (more common >6hrs post-symptom onset), which will ultimately result in a paralysed limb.
|Category||Prognosis||Sensory Loss||Motor Deficit||Arterial Doppler||Venous Doppler|
|I – Viable||No Immediate threat||None||None||Audible||Audible|
|IIA – Marginally Threatened||Salvageable, if promptly treated||Minimal (toes) or none||None||Inaudible||Audible|
|IIB – Immediately Threatened||Salvageable if immediately revascularised||More than toes, rest pain||Mild/Moderate||Inaudible||Audible|
|III – Irreversible||Major tissue loss, permanent nerve damage inevitable||Profound||Profound, paralysis (rigor)||Inaudible||Inaudible|
Table 1: Clinical Categories of Acute Limb Ischemia, adapted from Rutherford et al., 2009
The differential diagnoses for acute limb ischaemia include critical chronic limb ischaemia, acute DVT (can present as Phlegmasia cerulea dolens and Phlegmasia alba dolens) spinal cord or peripheral nerve compression.
- U&Es (monitor for electrolyte imbalances)
- Serum lactate (to assess the level of ischemia)
- Thrombophilia screen (if <50yrs without known risk factors)
- Doppler ultrasound scan (both limbs)
- Consider CT angiography
If the limb is considered to be salvageable, a CT arteriogram may be undertaken prior to intervention to provide more information regarding the anatomical location of the occlusion. This can help decide the operative approach (e.g femoral or popliteal incision).
Acute limb ischaemia is a surgical emergency. Complete arterial occlusion will lead to irreversible tissue damage within 6 hours. Early senior surgical support is vital.
Start the patient on high-flow oxygen and ensure adequate IV access. A therapeutic dose heparin or heparin infusion should be initiated as soon as is practical.
Prolonged course of heparin may be the most effective non-operative management of acute limb ischemia.
Any patient started on conservative management via heparin will need regular assessment and re-examination to determine its effectiveness. Surgical interventions may be warranted if no significant improvement is seen.
If the cause is embolic, the options are:
- Embolectomy via a Fogarty catheter
- Local intra-arterial thrombolysis
- Bypass surgery (if there is insufficient flow back)
If the cause is due to thrombotic disease, the options are:
- Local intra-arterial thrombolysis
- Bypass surgery
Irreversible limb ischaemia (mottled non-blanching appearance, hard woody muscles) requires urgent amputation OR palliative care. Most post-operative cases require a high level of care, typically at a surgical high dependency unit.
Long Term Management
Reduction of the cardiovascular mortality risk in this patient group is key. Promoting regular exercise, smoking cessation, and weight loss as necessary. Most cases should be started on low-dose aspirin or clopidogrel unless there is absolute contraindications to this.
Any underlying conditions predisposing to the acute limb ischemia should be treated, for example uncontrolled AF.
Cases resulting in amputation will require occupational therapy and physiotherapy, with a long term rehabilitation plan discussed and transfer to an intermediate rehabilitation centre.
One possible complication of acute limb ischaemia is reperfusion injury, whereby a sudden increase in capillary permeability can result in:
- Compartment syndrome
- Release of substances from the damaged muscle cells, such as:
- K+ ions causing hyperkalaemia
- H+ ions causing acidosis
- Rhabdomyolysis, resulting in significant AKI
The 30-day mortality rate following the surgical treatment of acute limb ischaemia is 15-25%.