Synopsis
Differentiate likely embolic from in-situ thrombotic acute limb occlusion while preserving identical emergency assessment and limb-salvage priorities.
- Sudden maximal symptoms, a normal opposite limb, absent prior claudication and atrial fibrillation favour embolism; previous claudication, diffuse pulse loss and bilateral PAD favour thrombosis in situ.
- Do not let cause-finding delay limb rescue: map sensory loss and weakness, contact vascular surgery immediately, and give intravenous unfractionated heparin unless active bleeding or current or previous HIT contraindicates it.
- Neurological deficit requires emergency revascularisation and imaging only when it will not delay treatment; profound anaesthesia, paralysis and absent arterial plus venous signals suggest Rutherford III.
Key red flags
Any new motor weakness or sensory loss beyond the toes means immediate limb threat irrespective of whether embolism or thrombosis is more likely.
Profound anaesthesia, paralysis or rigor with absent arterial and venous Doppler signals suggests irreversible tissue injury and major reperfusion hazard.
Chest or back pain, pulse asymmetry or haemodynamic instability raises aortic dissection or proximal aortic occlusion rather than an isolated leg lesion.
Massive swollen cyanotic limb with preserved arterial inflow can indicate phlegmasia and also requires emergency vascular assessment.
Active major bleeding or known immune HIT changes initial anticoagulation choice, but the vascular referral remains immediate.
Instantaneous, maximal-at-onset pain and dysfunction favour embolism, whereas thrombosis may worsen over hours on a background of chronic symptoms, although either mechanism can present abruptly.
Sensory loss beyond the toes or any motor weakness identifies an immediately threatened limb requiring emergency revascularisation regardless of aetiological confidence.
Investigation priorities
Define occlusion morphology, background arterial disease, inflow and distal runoff.
Management branches
A patient presents with acute painful cold limb and the cause is uncertain.
- Grade Rutherford viability from symptom duration, sensory loss, motor power and Doppler signals while contacting the vascular service immediately.
- Give analgesia and intravenous unfractionated heparin unless contraindicated; arrange emergency treatment without waiting to prove embolism or thrombosis.