Your next patient is a 72-year-old man with a suddenly cold, painful right leg for 4 hours. Here's how the acute limb ischaemia case unfolds and what to pick up on the way.

An acute limb ischaemia case can be easy to misread when the story is brief and only a few hours old. Your next patient is a 72-year-old man with a suddenly cold, painful right leg for 4 hours. The patient says: "A sudden cold, painful leg since a few hours ago." The trap is stopping at pain and missing that the leg is pale and perishingly cold, the foot numb with pins and needles, and new weakness of the toes in the last hour, without any history of claudication, in a lifelong smoker.

This page walks through how it presents, what to pick up in the history, the bedside Doppler or ABPI, confirming anatomy with a CT angiogram or on-table angiogram, and finding an embolic source with an ECG for atrial fibrillation and later echocardiography. It also recaps the six P's to recognise.

How the case presents

Your next patient is a 72-year-old man with a suddenly cold, painful right leg for 4 hours. In their own words: "A sudden cold, painful leg since a few hours ago."

Observations on arrival:

Observation	On arrival
Heart rate	96 beats per minute
Blood pressure	150/90 mmHg
Respiratory rate	18 breaths per minute
Oxygen saturation	97%
Temperature	36.5 °C

What to pick up in the history

These are the findings the case is built around. Each one moves you towards or away from acute limb ischaemia, and the scorecard checks whether you found it.

Sudden severe right leg pain four hours ago.
Leg is pale and perishingly cold: pallor and poikilothermia separate arterial ischaemia from a swollen warm deep vein thrombosis.
Numb foot with pins and needles: sensory loss grades the limb as threatened rather than viable, demanding urgent revascularisation.
New weakness moving the toes in the last hour: motor loss marks an immediately threatened limb, the point at which delay costs the leg.
No previous claudication in this leg.
Lifelong smoker: establishes the atherosclerotic background and drives secondary prevention after revascularisation.
Other leg is warm with normal sensation: A normal contralateral limb argues for embolus rather than diffuse bilateral atherosclerotic disease.

Red flags you must not miss

The case marks these as must-elicit. They only come out if you ask.

New weakness moving the toes in the last hour.
The pain is now constant and severe even at rest and the foot is starting to look blotchy and purple-white.
He has had no chest pain, no sudden breathlessness and no sudden weakness of his face, arm or speech.

Investigations and what they showed

Creatine kinase: Raised and rising, from ischaemic skeletal muscle. Why it helps: A rising creatine kinase indicates muscle ischaemia/necrosis (rhabdomyolysis), it signals advancing damage and the risk of reperfusion injury and acute kidney injury after revascularisation.
Lactate: Raised. Why it helps: reflects anaerobic metabolism in the ischaemic limb; a marker of severity that rises further on reperfusion.
Urea and electrolytes: Baseline renal function; watch potassium.
Group and save: Sample sent.
CT angiogram lower limb / peripheral: An abrupt cut-off (filling defect) of the right superficial femoral/popliteal artery with no distal reconstitution, an embolic occlusion; the contralateral vessels are patent and relatively free of atheroma. Why it helps: the definitive test that confirms the occlusion, shows its level and the run-off, and plans revascularisation, the smooth cut-off in otherwise clean vessels points to an embolus rather than in-situ thrombosis.
12-lead ECG: Atrial fibrillation (irregularly irregular, no P waves).
Ankle-brachial pressure index: Absent/very low on the right (no measurable ankle pressure); normal on the left. Why it helps: A quick bedside confirmation of the severity of the arterial insufficiency and a comparison with the normal leg.
Ultrasound Doppler arterial lower limb: Absent (or monophasic) arterial Doppler signals distal to the occlusion on the right. Why it helps: A rapid bedside/portable test, a hand-held Doppler over the pedal arteries showing no signal supports the diagnosis and is used serially; an absent arterial (but present venous) signal helps distinguish it from DVT.
Inspect the soles of the feet: The affected foot is also cold to touch. Why it helps: the single most useful bedside manoeuvre in a suspected acutely ischaemic limb is to put the two feet next to each other, colour, warmth and capillary refill are only interpretable by comparison. Pallor progressing to a dusky non-blanching mottle is the 'Pallor' of the six P's and marks a limb moving from viable to threatened.
Inspect the toes: The toes are dusky violet-blue with a sharp line of demarcation across the forefoot, the skin beyond it still pink. Capillary refill in the toes is sluggish or absent and the toes will not move properly. Why it helps: A sharply demarcated line of colour change tells you the level of arterial occlusion and that the ischaemia is acute and embolic rather than a chronically shut-down limb.
Inspect the feet: The dorsum of the right foot is blotchy and marbled, patches of waxy pallor interleaved with dusky purple mottling, with dusky nail beds. There is no swelling and no warmth: the foot is pale and cold, not red and hot. Why it helps: this is the picture that separates acute limb ischaemia from its great mimic. A DVT or a cellulitis gives a swollen, warm, red leg; an ischaemic leg is pale, cold, mottled and pulseless.
Inspect the thighs: A lacy, net-like purple-red mottling (livedo) of the skin of the thigh, beginning at about mid-thigh and extending downwards; above this the skin is normally coloured. Why it helps: the upper limit of the mottling marks how far up the limb the ischaemia reaches, which in this man (mottling from the mid-thigh down) implies an occlusion at or above the superficial femoral artery. Mottling that still blanches with pressure means a threatened but salvageable limb; fixed, non-blanching mottling means irreversible ischaemia.
Inspect the lower limbs: The right leg is strikingly white and waxy compared with the normal, pink, warm left leg. The demarcation is at about the mid-thigh: above it the limb looks normal, below it the skin is bloodless and marble-like. The right leg lies absolutely still. Why it helps: the whole-limb comparison is the diagnosis.
Inspect the calves and shins: The superficial veins of the right calf and foot are empty and collapsed, so they appear as shallow grooves or gutters in the skin (venous guttering); on the left leg the same veins are comfortably filled. The right calf muscle is soft and slack, not tense.
Inspect the patient's posture and position: He is lying rigidly still, guarding the right leg and refusing to let anyone move it, and he has instinctively let it hang down over the edge of the trolley. He is sweaty, grimacing and gripping the rail, visibly in severe pain despite what he has already been given. Why it helps: dependency of the limb is an instinctive attempt to recruit gravity-assisted perfusion, and pain far beyond what the leg looks like should raise your urgency.

Imaging findings

Transthoracic echocardiogram: May show left atrial enlargement or a mural/appendage thrombus (source of embolus).
X-ray chest: Clear lung fields, no acute abnormality. Normal.

Why the diagnosis is acute limb ischaemia

The decisive diagnosis is acute limb ischaemia, the sudden onset of the six P's (Pain, Pallor, Pulselessness, Paraesthesia, Paralysis and a Perishingly cold/Poikilothermic limb), most likely embolic from atrial fibrillation (sudden onset, no prior claudication, an irregular pulse, a clean contralateral leg and a smooth cut-off on angiography) rather than in-situ thrombosis on chronic disease. It is a time-critical, limb-threatening surgical emergency: the window to revascularise is roughly 4 to 6 hours, and the presence of sensory loss and paralysis signals a threatened, near-irreversible limb. 'Peripheral arterial disease' is the correct broader umbrella but names only the chronic condition and misses the acute emergency; calling it 'DVT' or 'a trapped nerve' is a dangerous, limb-losing miss.

Acute limb ischaemia at a glance

What it is

Acute limb ischaemia is a sudden, severe reduction in blood flow to a limb, most often caused by an embolus lodging in a leg artery or a thrombus forming on top of existing arterial disease. It is a surgical emergency: without prompt revascularisation, the limb becomes irreversibly damaged.

Pathogenesis

When an artery is suddenly occluded, the tissues it supplies are starved of oxygen. Skeletal muscle and nerve are highly sensitive to ischaemia, which is why sensory and motor changes (paraesthesia and paralysis) appear early and signal a genuinely threatened limb, not just pain. As ischaemia progresses, the limb becomes pale, then mottled, then fixed and anaesthetic as tissue death sets in. An embolic occlusion typically causes sudden, severe symptoms with a clean, sharp cut-off, since the rest of the arterial tree has no time to develop collateral vessels; a thrombotic occlusion on existing disease is often somewhat less abrupt, because collaterals have already formed.

Who it affects

Embolic acute limb ischaemia typically occurs in patients with a source of clot, most often atrial fibrillation, and often with no prior history of claudication. Thrombotic acute limb ischaemia occurs on a background of pre-existing peripheral arterial disease, usually in older patients with vascular risk factors.

How serious it is

This is a time-critical emergency: the limb is usually only salvageable for around 4 to 6 hours before muscle becomes non-viable.

Causes and risk factors

Atrial fibrillation is the leading source of embolic acute limb ischaemia. Pre-existing peripheral arterial disease, smoking, diabetes and other cardiovascular risk factors predispose to the thrombotic form. A normal contralateral leg with no history of claudication points toward an embolic cause.

Investigations and lab tests

A CT angiogram (or on-table angiogram) confirms the level and extent of occlusion and guides the revascularisation plan; a bedside hand-held Doppler and ABPI support the clinical assessment. The embolic source is sought with an ECG (looking for atrial fibrillation) and later an echocardiogram.

At a glance: Confirms occlusion: CT angiogram or on-table angiogram. Bedside: hand-held Doppler, ABPI. Finds the source: ECG (AF), echocardiogram. Grade the limb: viable, threatened, or irreversible.

Teaching points

Acute limb ischaemia is a surgical emergency, recognise the six P's: Pain, Pallor, Pulselessness, Paraesthesia, Paralysis and Perishingly cold (Poikilothermia).
Confirm and plan with a CT angiogram (or on-table angiogram) and a bedside hand-held Doppler/ABPI; find the embolic source with an ECG (AF) and later echocardiography.

Practise a similar case

Reading about acute limb ischaemia is tidy, but it is not the same as asking the questions yourself with the clock running, trying to pin down that the toe weakness started only in the last hour while the foot is perishingly cold. Test your history taking under gentle pressure with another surgical patient.

Here's one from the same specialty, with the diagnosis left for you to find. Your next patient has sudden, severe tummy pain that started 3 hours ago. Take this patient's history in Diagnosica. It's free to start, no card needed.

Acute limb ischaemia case presentation: history, findings and tests