acute limb ischaemia

introduction

acute limb ischaemia is a time critical condition which requires rapid recognition, assessment and management to save the limb and perhaps the patient's life.
it is not an uncommon cause of diabetic ketoacidosis (DKA) and in this scenario is often over-looked with dire consequences
it is characterized by a rapid decrease in limb perfusion which usually produces new or worsening symptoms or signs, and often threatens limb viability.

local blood flow = (arterial pressure - venous pressure) / arterial resistance
ischaemic inflammation produces tissue oedema (and potentially, compartment syndrome) which increases venous pressure, compresses arteries increasing resistance and reducing arterial pressure which is further exacerbated by sympathetic drive being activated causing further vasospasm creating a vicious cycle of deterioration¹⁾

patients with collateral circulation with peripheral vascular disease (PVD or PAD) who develop thrombosis or reconstruction (graft or stent) occlusion

Pain - time of onset, variation over time, location, intensity
Pulselessness - absence of pedal pulses suggests acute limb ischaemia which can be confirmed on Doppler USS, and measurement of ankle-brachial index (ABI)
Pallor (may be absent if collaterals present, and instead may have ischaemic rubor)
Paraesthesiae - if more than just in the toes, suggests limb viability is becoming critical
Paralysis - if present suggests probable non-viable limb
Prostration is Pratt's 6th P - hypotension and shock

category I: no sensory loss and no muscle weakness
category IIa: paraesthesiae confined to toes or not present suggests limb is viable and potentially salvageable
category IIb: more extensive paraethesiae with rest pain and only mild-moderate muscle weakness, but perhaps tender muscles and pain on passive movement suggests advanced acute limb ischaemia which may still be salvageable with immediate revascularisation
category III: profound anaesthesia and paralysis indicate major tissue loss and nerve damage which is probably irreversible and require amputation

the shocked hypotensive patient especially in a patient with peripheral vascular disease (PVD or PAD)
phlegmasia cerulea dolens
acute compressive neuropathy

iv access, FBE, U&E, glucose, clotting profile, CK
ECG
early vascular surgical consult is imperative
early anticoagulation with iv heparin is usually indicated to prevent extension of thrombosis
rapid confirmation with Doppler USS and/or CT angiography may be indicated
category I and IIa patients can usually have angiography to decide further Mx such as:
- catheter directed thrombolytic Rx
- percutaneous aspiration thrombectomy (PAT) +/- thrombolysis
- percutaneous mechanical thrombectomy (PMT) +/- thrombolysis
category IIb patients will usually need immediate assessment for revascularisation procedure
- 10–15% of patients’ limbs thought to be salvageable ultimately require major amputation
category III patients will generally require amputation or palliation depending upon pre-existing co-morbidities and likelihood of survival from surgery if presentation is severely delayed.

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