Acute limb ischaemia

Causes and risk

The causes are classified as thrombic or embolic. Three features point to an embolic cause: an irregularly irregular pulse, a sudden unilateral onset, and an absent pulse (pulse is present in embolism). The most common site of arterial embolus lodgment is the femoral bifurcation, where the common femoral divides into the SFA and profunda, rather than the popliteal, the tibial arteries or the deep femoral artery.

How it presents

The symptoms are the 6 Ps, but they do not carry equal weight, and reading them as a flat list is the error:

• Pain: may be absent in complete acute ischaemia, and severe pain is also a feature of chronic ischaemia
• Pallor: also a feature of chronic ischaemia
• Pulseless: also a feature of chronic ischaemia
• Perishing cold: unreliable, as the ischaemic limb takes on the ambient temperature
• Paraesthesia and paralysis: loss of function is the most important feature of acute limb ischaemia, and it denotes a threatened limb that is likely to be lost unless it is revascularized within a few hours

So the 2 that matter are paraesthesia and paralysis, and a motor and sensory examination has to be done in every patient with ALI.