The ‘6 Ps’

Now explore the six presenting ‘Ps’ associated with acute limb ischaemia:


In most cases pain will occur at rest, although a patient with a viable limb may present with acute onset, short distance claudication.

Rest pain is usually worse in the most distal part of the limb (toes) since this has the worst perfusion, and may be relieved on dependency (by hanging the patients’ legs over the bed).

Calf pain that is worse on passive movement of the muscles indicates potential compartment syndrome and is a poor prognostic sign.


Pallor is especially useful as a comparison with the opposite limb. It is also useful to check venous filling.

Acutely ischaemic limbs are classically of a white pallor rather than blue. Chronic critically ischaemic limbs may appear pink due to compensatory vasodilation – the so-called ‘sunset foot’.

In this situation, Buerger’s test – pallor on elevation of the limb, with erythema on dependency – may also be useful.


Click on the image to enlarge.


Paraesthesia is present in over 50% of cases [1]. Sensory nerves are smaller than motor nerves and more sensitive to ischaemia so tend to be affected first.


Paralysis is a poor prognostic sign and indicates an element of irreversible ischaemia.

Perishingly cold

Perishingly cold is a useful sign if used in comparison to the opposite (‘normal’) limb. Check temperature using the back of your hand.


Checking pulses is notoriously unreliable. Arterial Doppler signals should be checked in anyone with suspected acute limb ischaemia [3].

Audible arterial Doppler signals do not eliminate the diagnosis of acute limb ischaemia.

Learning bite

Arterial Dopplers should be performed on all patients with suspected acute limb ischaemia. Classical signs (the ‘6 Ps’) may be attenuated in a patient with pre-existing peripheral arterial disease and collaterals.

Compartment syndrome

Compartment syndrome occurs when the pressure increases within a fascial compartment and compromises blood flow. This can result in tissue necrosis once the intra-compartmental pressure is greater than the arterial pressure. It commonly occurs following trauma, and the anterior compartment in the leg is particularly at risk.

Following ischaemia or reperfusion of an ischaemic leg, compartment syndrome may occur. It presents with severe pain and tenderness in the affected compartment associated with pain on passive movement of the muscles, and later neurosensory loss.

The treatment is fasciotomy to release the muscle, which should be performed following reperfusion, if there is any question of compartment syndrome.