Acute Limb Ischemia

Definition

By definition, acute limb ischemia is an acute interruption of blood supply to an organ or extremity.

It is an emergency that requires immediate treatment.

Ischemia beyond 6 hours is usually irreversible and results in limb loss.

Etiology

1. Arterial embolism

2. Thrombosis

3. Traumatic

4. Acute aortic dissection

5. Rare causes:

a) Low flow states e.g. cardiogenic shock/sepsis

b) Drugs (cocaine, vasopressors)

c) Vasculitis

Embolism

The most common.

Secondary to:

1. Cardiac causes (80–90%): most common

a) Arrhythmias

b) Myocardial Infarction

2. Non-Cardiac causes:

a) Athero-embolism

b) Aneurysms

3.Cryptogenic emboli: 5–10%.

Thrombosis

Thrombosis occurs mainly in the abdominal aorta, distal superficial femoral artery, and popliteal artery.

In absence of stenotic lesion, it can be due to:

i. Intra-arterial injections

ii. Hypercoagulable states: e.g. malignancy, etc.

Thrombosis of bypass grafts (kinking, stenosis, anastomotic lesions)

Pathophysiology

By pathophysiology, an embolus originates from the heart or dilated diseased arteries e.g. aneurysm and suddenly occludes a relatively healthy arterial tree.

It usually arrests at arterial bifurcations.

And atherosclerosis causes progressive narrowing of the arterial trees and thus stimulates the development of collaterals.

Its severity depends on the degree of obstruction, Site of occlusion, Presence of collaterals, and affected tissues.

Different tissues can tolerate ischemia at different rates. Nerves are the first to be affected, Muscles are more tolerant they can last up to 6–10 hours. And Skin is the last to show necrosis.

Diagnosis

Diagnosis is made mainly clinically, starting from the history.

Embolic ischemia is usually seen in previously cardiac patients. whereas other risk factors for atherosclerosis are assessed e.g. if the patient is a smoker or diabetic.

The clinical picture mainly shows 6 Ps which include:

1. Pain(sudden / acute onset, severe, steady, starts most distal).

2. Pallor or cyanosis

3. Paraesthesia(numbness)

4. Pulselessness(sudden loss of previously palpable pulse).

5. Poikelothermia(cooling of the limb)

6. Paralysis(fine movement first due to motor nerve ischemia then because of nerve and muscle).

Investigations

1. Doppler US is done to detect the blood flow.
2. Contrast Imaging is done to know the site of occlusion.

Treatment

For reversible ischemia:

1. Immediate anticoagulation

-Unfractionated heparin or LMWH

-Oral anticoagulation

2. Open surgical treatment

-Embolectomy/thrombectomy

-Bypass

For irreversible ischemia

1. Anticoagulation

2. Amputation

Amputation level is planned for ideal functional outcome starting from toe amputation up to hemipelvectomy.