Acute limb ischaemia (ALI) describes the sudden blocking of an arterial vessel in the limb, resulting in ischaemia to the tissue and possibly necrosis – it is an emergency requiring urgent intervention.
Causes
- Thrombosis: This is usually secondary to atherosclerosis
- Embolus: For example, from atrial fibrillation or valvular disease vegetations
- Trauma
- Compartment syndrome
- Vasospasm
Risk Factors
- Smoking
- Obesity
- Diabetes
- Cardiovascular disease
- Peripheral vascular disease
- Hyperlipidaemia
- Atrial fibrillation
Clinical Features
The 6 P’s are often used in order to remember the clinical features of acute limb ischaemia. These are:
- Pain: Tends to be more sudden in the case of an embolus as opposed to a thrombus
- Pulselessness
- Perishingly cold limb
- Pallor
- Paraesthesia: Late sign
- Paralysis: May present as a foot droop and occurs secondary to peroneal nerve involvement (easy to remember as it’s another P!). Paralysis is a late sign.
Rutherford Classification
The Rutherford classification is used to categorise ALI severity and subsequently guide management.
| Classification | Motor | Sensory | Doppler | Typical Management |
| I (Viable) | No weakness | No loss | Audible | Initial work-up i.e. imaging followed by revascularisation within hours |
| IIa (Marginally threatened) | No weakness | Sensory loss to toes/no loss | Arterial doppler inaudible, venous signal audible | Urgent revascularisation |
| IIb (Immediately threatened) | Moderate weakness | More than toes sensory loss | Arterial doppler inaudible, venous signal audible | Urgent revascularisation |
| III (Irreversible) | Profound weakness/paralysis | Profound sensory loss | Inaudible | Amputation |
Differential Diagnosis
- Compartment syndrome: This is a known complication of ALI, but it can also be a potential differential. Occurs when there are increases in the pressure within fascial compartments, resulting in compression of blood flow.
- Cellulitis: Can cause leg pain but leg is usually erythematous
- DVT: Can cause leg pain but leg is usually warm and tender
Investigations
Bedside
- Palpation of pulses: Dorsalis pedis and posterior tibialis
- ECG: ?Atrial fibrillation
Bloods
- FBC, U&E, LFT: For baseline
- Coagulation studies: Treatment will likely include anticoagulation
- Lactate: Will be raised if there is an ischaemic limb
- CK: Raised in the case of muscle ischaemia
- Group and save: Patient may require surgery
Imaging
- Ultrasound Doppler: To confirm if pulses are present
- CT Angiogram: Contrast based scan that allows you to visualise the vasculature of the affected limb
Management
Patients with suspected acute limb ischaemia require urgent emergency referral to vascular surgery. Tissue will be irreversibly damaged within 6 hours, so recognition and intervention should be prompt.
Initial and Conservative Management
- IV unfractionated heparin: A bolus is usually given first to prevent further development of the clot. Patients who do not receive definitive management may receive a further infusion of UFH as a conservative management option
- Analgesia
- IV hydration if clinically indicated
- Oxygen
Definitive Management
- Percutaneous thrombectomy/embolectomy: This involves passing a Fogarty catheter into the artery to mechanically remove an thrombus/embolus
- Surgical thrombectomy: Open surgery to remove the thrombus
- Intra-arterial thrombolysis +/- angioplasty: Thrombolysis involves the use of clot dissolving drugs – this can be achieved by percutaneous passing of a catheter to deliver intra-arterial thrombolysis. Angioplasty involves the insertion of a stent in order to maintain patency of the vessel.
- Peripheral artery bypass surgery: Using a graft (typically venous) to create an arterial bypass.
- Amputation: In the case of irreversible ischaemia i.e. Rutherfords category III
- Palliation: In some instances where patients are not fit for surgery, an acute limb ischaemia can be a terminal event and palliation may be considered.
Complications
- Reperfusion Injury
- In the time the limb has been ischaemic, toxic substances such as free radicals, potassium, creatine kinase, and myoglobin build up.
- On restoration of the vasculature and blood flow, there is sudden release of these substances into the blood stream which can cause cardiovascular compromise, acute respiratory distress syndrome, renal failure etc.
- Compartment syndrome
- Can occur following revascularisation therapies – fasciotomies are sometimes performed at the time of surgery to reduce the risk of this complication.
References
https://cks.nice.org.uk/topics/peripheral-arterial-disease/management/acute-limb-ischaemia/
https://www.rcemlearning.co.uk/reference/acute-limb-ischaemia/#1567523587443-70a31fa5-f375
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6326052/#:~:text=Acute%20limb%20ischemia%20(ALI)%20is,and%20appropriate%20treatment%20is%20given.
https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-16/Clinical-presentation-of-lower-extremity-arterial-disease-LEAD#:~:text=The%20Rutherford%20classification%20is%20more,recordings%20and%20vascular%20Doppler%20ultrasound.
https://academic.oup.com/eurheartj/article/39/9/763/4095038?login=false#117577092
