Introduction
This topic covers acute arterial obstruction, a sudden fall in blood flow to a limb or organ caused by occlusion of an artery. It explains the two main mechanisms, acute arterial thrombosis and arterial embolism, and the types of embolism. Because the limb may be lost within hours, recognising the picture and acting quickly is the central exam point.
Definition and clinical picture
Acute limb ischaemia is a sudden reduction of arterial perfusion of a limb, usually with onset within about two weeks, that threatens the viability of tissues. The classic signs are summarised by the six Ps:
- Pain of sudden onset, often severe and out of proportion, worse on passive movement of the muscles
- Pallor, later mottling or cyanosis of the skin
- Pulselessness distal to the occlusion
- Paraesthesia and numbness, an early sign of nerve ischaemia
- Paralysis (motor weakness), a late and ominous sign
- Poikilothermia, the limb feels cold to touch
Loss of the sensory and motor function, rather than pallor alone, best predicts irreversible damage. The degree of ischaemia is graded by the Rutherford classification: category I (viable), IIa (marginally threatened), IIb (immediately threatened) and III (irreversible).