PLAB 2 Surgery OSCE: Acute Limb Ischaemia Complete Guide

Why Acute Limb Ischaemia Is a High-Yield PLAB 2 Station

Acute limb ischaemia (ALI) is one of those time-critical surgical emergencies that PLAB 2 examiners love. It tests multiple domains simultaneously: your ability to recognise a surgical emergency, take a focused history, perform a targeted examination, initiate immediate management, and communicate urgency — all within an 8-minute station. What makes ALI particularly attractive to examiners is that the window for limb salvage is narrow (typically 6–8 hours), meaning a candidate who delays or mismanages the case demonstrates poor clinical judgement — an automatic fail criterion.

If you are preparing for PLAB 2, you must be able to manage this station with the same confidence you would bring to a patient collapsing in front of you. This guide walks you through everything you need to know.

Understanding Acute Limb Ischaemia: Core Knowledge

Definition

Acute limb ischaemia is defined as any sudden decrease or worsening of limb perfusion lasting less than 14 days that threatens the viability of the limb. It is distinct from critical limb ischaemia (CLI), which is a chronic condition.

Rutherford Classification

The Rutherford classification is the framework examiners expect you to know. It categorises ALI into three broad categories:

Key exam tip: Category IIb and III require immediate surgical involvement. If you fail to escalate these urgently, you will fail the station.

Causes: Embolic vs Thrombotic

The two main mechanisms are:

Embolic (most common):

• Atrial fibrillation (the single most common cause — always ask about this)

• Post-myocardial infarction (mural thrombus)

• Prosthetic heart valves

• Aortic/iliac aneurysm with mural thrombus

• Paradoxical embolus (DVT with PFO)

Thrombotic:

• Pre-existing peripheral arterial disease (PAD) with acute-on-chronic occlusion

• Graft thrombosis (previous bypass surgery)

• Buerger's disease

• Hypercoagulable states (malignancy, antiphospholipid syndrome)

• Trauma (popliteal artery entrapment, supracondylar fracture)

The OSCE Scenario: What to Expect

A typical PLAB 2 ALI station may present in one of two formats:

Format 1: History and Management (Station 2 Style)

You are asked to assess a 72-year-old patient brought to A&E with sudden onset right leg pain. The patient is anxious and in significant discomfort. You have 8 minutes to take a focused history, initiate management, and discuss the plan.

Format 2: Structured Clinical Assessment (Station 4 Style)

You are given a brief about a patient with a cold leg and asked to assess and manage. An examiner may ask structured questions between your interaction with the patient.

History Taking Framework

Use a structured approach. Start with the presenting complaint and work outward:

1. Pain Assessment (SOCRATES)

• Site: Which part of the leg? (Calf vs foot vs whole leg — this matters for localisation)

• Onset: When did it start? (Exact time is critical — the 6-hour clock starts ticking)

• Character: Cramping? Sharp? Burning? Numbness?

• Radiation: Does it move anywhere?

• Associated symptoms: Numbness, paraesthesia, paralysis, coldness

• Timing: Sudden or gradual? (Sudden = embolic; gradual worsening = thrombotic)

• Exacerbating/relieving: Does elevation help? (Elevation worsens ischaemic pain)

• Severity: Score out of 10

2. The Six Ps Screen

Ask explicitly about the six classical features:

1. Pain — where and when?

2. Pallor — has the leg gone pale or white?

3. Paraesthesia — any pins and needles or numbness?

4. Paralysis — can they move their toes/foot?

5. Pulselessness — have they noticed absent pulses?

6. Perishingly cold — does the leg feel cold compared to the other?

Critical point: Paraesthesia and paralysis indicate Category IIb or worse. This is a surgical emergency requiring immediate escalation.

3. Risk Factor Assessment

• Cardiac history: atrial fibrillation, recent MI, heart failure, valvular disease

• Vascular history: previous claudication, previous bypass/angioplasty, known PAD

• Smoking history (pack-years)

• Diabetes mellitus

• Hypertension and hyperlipidaemia

• Previous thromboembolic events

• Medications: anticoagulants (warfarin, DOACs) — if on warfarin, ask about INR compliance

• Recent trauma or prolonged immobilisation

4. Past Surgical History

• Previous vascular surgery (bypass grafts, stents)

• Previous amputations

• Recent cardiac or vascular procedures

Examination: What Examiners Want to See

1. General Assessment

• ABCDE approach first (the patient may be in AF or have cardiac compromise)

• Vital signs: pulse (check for irregularity → AF), blood pressure (both arms — consider subclavian stenosis or aortic dissection), temperature (sepsis?)

• Glucose (diabetic patients may have neuropathy masking pain)

2. Limb Examination — Compare Both Sides

This is where candidates lose marks. Always examine the contralateral limb as your baseline.

Inspection:

• Colour: pale, white, mottled, cyanotic, or gangrenous?

• Skin changes: blisters, skin breakdown, necrosis?

• Muscle bulk: wasting suggesting chronic disease?

• Any surgical scars from previous vascular procedures?

Palpation:

• Temperature: compare proximal to distal, and side to side

• Capillary refill time (normal < 2 seconds)

• Pulses: femoral, popliteal, posterior tibial, dorsalis pedis — grade as 0 (absent), 1 (weak), 2 (normal)

• Sensation: light touch and pinprick (loss = Category IIb+)

• Motor function: can they wiggle toes, dorsiflex, plantarflex? (Paralysis = Category IIb/III)

• Tenderness and calf tenderness (calf tenderness with pulselessness may indicate phlegmasia cerulea dolens — a venous emergency)

3. Use a Handheld Doppler

If available (and in PLAB 2, it may be provided):

• Check for audible arterial signals at the ankle

• Check for venous signal (absence of venous signal = severe ischaemia)

• Measure ABPI if possible (ABPI < 0.5 suggests severe ischaemia; ABPI > 1.3 may indicate calcified, non-compressible vessels in diabetics)

Immediate Management: The OSCE Action Plan

This is where PLAB 2 candidates often falter. Management must be simultaneous, not sequential. Here is your action plan:

Step 1: ABCDE and Resuscitation

• High-flow oxygen (if hypoxic — do not give oxygen routinely to non-hypoxic patients per NICE guidance, but in an emergency resuscitation context, assess and treat)

• Two large-bore IV cannulae

• Bloods: FBC, U&E, CRP, clotting (PT/INR, APTT), group and save, crossmatch (2 units), D-dimer, troponin (if cardiac cause suspected), lactate

• ECG (look for AF — the most common cause)

• IV analgesia: morphine 2.5–5 mg titrated with antiemetic (e.g., metoclopramide 10 mg IV)

Step 2: Anticoagulation

This is a non-negotiable immediate action:

• IV unfractionated heparin — bolus 80 units/kg (or as per local protocol), then infusion at 18 units/kg/hour

• Why unfractionated and not LMWH? Because it is rapidly reversible with protamine sulphate if surgery is needed, and dosing can be titrated to APTT

• Do not wait for imaging to start heparin — it prevents clot propagation while awaiting definitive management

Common OSCE pitfall: Prescribing LMWH instead of IV unfractionated heparin. Examiners specifically look for this distinction.

Step 3: Urgent Vascular Referral

• Category I (viable): Refer within a few hours; imaging can be semi-urgent

• Category IIa (marginally threatened): Refer immediately; intervention within hours

• Category IIb (immediately threatened): Refer immediately as a surgical emergency; intervention needed within 1–2 hours

• Category III (irreversible): Urgent referral; debridement or amputation likely

In the OSCE, if the patient has paraesthesia or paralysis, say out loud: "This patient has Category IIb acute limb ischaemia. I need to refer urgently to the on-call vascular surgeon."

Step 4: Imaging

• CT angiography is the gold standard (fast, comprehensive, identifies the level and extent of occlusion)

• Duplex ultrasound may be used if CT is unavailable or contraindicated

• Do not delay referral while waiting for imaging — refer first, image as directed by the vascular team

Step 5: Definitive Management

The vascular team will decide between:

1. Surgical embolectomy (Fogarty catheter) — for embolic causes, especially with a clear embolic source (e.g., AF)

2. Catheter-directed thrombolysis — for thrombotic causes, graft occlusion, or if the patient is not fit for surgery (contraindications: recent surgery, recent stroke, active bleeding, pregnancy)

3. Endovascular intervention — angioplasty and stenting for underlying stenotic lesions

4. Surgical bypass — for chronic underlying disease with acute-on-chronic occlusion

5. Fasciotomy — prophylactic or therapeutic if reperfusion injury is anticipated

6. Amputation — if the limb is non-viable (Category III)

Communication: Scoring High in the OSCE

With the Patient

1. Acknowledge the urgency without causing panic: "This is a serious condition that needs urgent treatment. I've already started blood thinning medication and I'm contacting the specialist surgeon now."

2. Explain what will happen next: "The vascular surgeon will assess your leg and may arrange a CT scan to see exactly where the blockage is. Depending on what they find, you may need a procedure to remove the clot or improve the blood flow."

3. Discuss potential outcomes honestly: "There is a possibility that we may not be able to save the limb, but we are doing everything we can to act quickly. The sooner we treat this, the better the chances."

4. Obtain consent for heparin: "I'd like to give you a blood-thinning medication called heparin through your drip to prevent the clot from getting worse. Are you allergic to anything or have you had a reaction to heparin before?"

With the Examiner

When speaking to the examiner (if asked structured questions):

• Be concise and structured

• State the Rutherford category explicitly

• Justify your management decisions with evidence

• Demonstrate awareness of time sensitivity

• Discuss the need to investigate the underlying cause (ECG for AF, echocardiogram for thrombus, AAA screen)

Common OSCE Pitfalls and How to Avoid Them

Post-Management Considerations

After the acute episode, the OSCE may ask about ongoing management:

1. Investigate the cause:

   • ECG and echocardiogram (cardiac source of embolus)

   • CT abdomen (AAA as source)

   • Thrombophilia screen (if young or recurrent)

2. Secondary prevention:

   • Anticoagulation (warfarin or DOAC) if embolic cause — typically for life if AF persists

   • Antiplatelet therapy (aspirin 75 mg or clopidogrel 75 mg) if thrombotic/PAD cause

   • Statin therapy (atorvastatin 80 mg per NICE guidance for PAD)

   • Blood pressure and diabetes control

   • Smoking cessation — this is critical and must be addressed

3. Follow-up:

   • Vascular outpatient clinic

   • ABPI monitoring

   • Consider supervised exercise programme if underlying PAD

Time-Sensitive Checklist for the OSCE

Use this mental checklist during the station:

• [ ] Confirm time of onset (calculate hours remaining)

• [ ] Screen for six Ps (especially paraesthesia and paralysis)

• [ ] Examine both limbs — compare side to side

• [ ] Check pulses with Doppler if available

• [ ]ABCDE approach

• [ ] Bloods including clotting and group/crossmatch

• [ ] ECG — check for atrial fibrillation

• [ ] IV morphine for analgesia

• [ ] IV unfractionated heparin (not LMWH)

• [ ] Urgent vascular surgery referral (state the Rutherford category)

• [ ] CT angiography (arranged with vascular team)

• [ ] Communicate urgency and possible outcomes to patient

• [ ] Mention investigating underlying cause

Summary

Acute limb ischaemia is a must-know station for PLAB 2. The keys to success are:

1. Recognise the emergency early — the six Ps are your screening tool

2. Stratify severity — use the Rutherford classification and say it out loud

3. Act immediately — heparinise, analgesia, bloods, and refer to vascular surgery

4. Communicate clearly — with the patient about urgency and possible outcomes, and with the examiner about your clinical reasoning

5. Avoid common traps — especially LMWH instead of IV UFH, and delaying referral for imaging

Remember: in ALI, time is limb. Every minute of delay reduces the chance of limb salvage. Examiners want to see a candidate who acts decisively, communicates effectively, and demonstrates safe clinical judgement. Master this station, and you will demonstrate the competence expected of a doctor entering UK practice.

This blog is intended for educational purposes for PLAB 2 candidates. Always refer to the latest NICE and Vascular Society guidelines for current clinical practice.