Acute Limb Ischaemia

What's Actually Going On

An artery supplying the limb blocks abruptly. Usually a clot travels from elsewhere, most often the heart in an irregular rhythm, and lodges where the vessel narrows. Or a clot forms directly on existing furring in the artery wall. Less often the cause is a clotted aneurysm behind the knee, a tear in the main artery of the abdomen, injury, or a clotting tendency driven by cancer or acute infection.

Downstream of the block, blood flow stops. Muscle is the bulk of a limb and the least tolerant tissue in it. Irreversible muscle cell death begins after roughly 3 hours and is nearly complete at 6.

Two consequences are counterintuitive and both change what you look for. Nerve fails before muscle dies, which is why numbness and weakness, not how much it hurts, decide how urgent this is. A patient can be in less pain and be worse. And once tissue is dead, swelling stops, because flow through the smallest vessels ceases altogether. The most advanced limb can look the calmest.

How to Identify It

Every test below is available to a physical therapist. Every accuracy figure behind them was measured in long-standing, slow-building artery disease, not in this sudden condition. Across 134 papers, zero studies have measured any of these signs in acute limb ischaemia.

• Temperature comparison, cool skin LR+ 5.90 CHRONIC DISEASE ONLY — how much a cool limb raises the odds, measured in slow-onset disease
• Pulse palpation, any abnormality LR+ 4.70 | LR− 0.38 CHRONIC DISEASE ONLY
• Audible handheld Doppler Sn 42.8% | Sp 97.5% | LR− 0.59 DIFFERENT REFERENCE TEST — catches 43% of cases, correctly clears 98% of people without it

Three warnings follow, and they are the practical content of this page.

1. The strongest bedside tool rules in, not out. An abnormal Doppler signal is powerful evidence. A normal one is close to worthless, and that holds even inside the disease it was actually tested on.

2. The ankle pressure test does not weaken here, it inverts. It needs a measurable ankle pressure to give a number. In a severely blocked limb there may be no signal at all, so it returns nothing rather than a low reading. Read as a technical glitch, that non-result is falsely reassuring. The failure of the test is the finding.

3. Combinations do not rescue individual findings. Stacking three normal-ish tests does not build a rule-out, because combining examination findings was shown not to raise the likelihood beyond the individual findings.

The single most useful discriminator: every warm-leg diagnosis in the differential is something else. A clot in a vein, a skin infection, a calf strain and a ruptured cyst all give a leg that is warm or hot. This one gives a leg that is cold.

The Debate

Honest Limitations

The Nuance

No branch of the decision path ends in a physical therapy treatment. Check temperature and pulses in both limbs first. Cold with absent or reduced pulses moves on. Warm with normal pulses moves to the ordinary differential: a clot in a vein, a skin infection, a calf strain, a ruptured cyst, a nerve root problem. Cool or dusky but pulses seem present does not stop the process, because a present signal does not clear it.

Then one question: any new numbness or weakness? Yes means emergency services now. No still means same-day emergency vascular assessment. The absence of weakness is the favourable side of the line, not a reason to wait.

And three overrides checked every time, even when the first step looked reassuring. Diabetes with nerve damage means the pain may be absent, so judge on colour, temperature and pulse. Both legs weak means check pulses before accepting a nerve cause. Active cancer, recent viral illness, a known aneurysm behind the knee or an irregular heartbeat all lower the threshold further.

Where this profession actually contributes sits either side of the emergency. Before diagnosis, someone assesses this patient first, and the misdiagnosis literature names orthopaedic surgeons, neurologists and general practitioners as the specialties involved in initial assessment. Physical therapy does not appear in that list, and the honest reading is that nobody has studied it rather than that it performs well. The window is real either way, and it is measured in hours. After treatment, both the saved limb and the amputated limb come back into rehabilitation, and only one of those two pathways has an evidence base behind it.

On the definitive treatments themselves, there is less certainty than most people assume. A Cochrane review of five randomised trials in 1,292 patients found no clear difference between clot-dissolving drugs and surgery for limb salvage, amputation or death, at low certainty, and no new trials have been identified since 2018. That comparison is not a physical therapy decision, and it is recorded here so nobody repeats a superiority claim that the evidence does not support.