What initial investigations should be performed in a patient suspected of having acute limb ischaemia?

In a patient suspected of having acute limb ischaemia, the initial investigations should include a thorough clinical assessment and measurement of the ankle brachial pressure index (ABPI). This involves asking about the presence and severity of symptoms, examining the legs and feet for signs such as ulceration, and palpating femoral, popliteal, and foot pulses. The ABPI should be measured with the patient resting and supine, using a Doppler probe to record systolic blood pressures in both arms and at the ankle arteries, then calculating the index by dividing the highest ankle pressure by the highest arm pressure. In patients with diabetes, a normal or raised ABPI does not exclude peripheral arterial disease, so clinical judgment is essential. Pulse oximetry is not recommended for diagnosis. If revascularisation is being considered, duplex ultrasound is the first-line imaging modality, followed by contrast-enhanced magnetic resonance angiography or computed tomography angiography if further imaging is needed or if MRI is contraindicated.