Ankle-arm index (abi)

Doppler sonographic measurement of the arterial occlusion pressures of the dorsalis pedis and the posterior tibialis and, if necessary, the fibularis in a lying patient and the formation of the ankle-arm index (ABI) for a basic examination of the vascular status. Unidirectional pocket Doppler devices and the bidirectional continous wave Doppler method with acoustic and frequency-analytical flow representation are used.

An ABI value of < 0.9 is regarded as proof of the presence of a relevant PAVK.

Evaluation of the measured values

• > 1.3 - false high values (suspected mediasclerosis, peripheral edema, single-vessel supply through the fibular artery)
• > 0.9 - normal findings
• 0.75-0.9 - light PAVK
• 0.5 - 0.75 - medium PAVK
• < 0.5 - severe PAVK (critical ischemia)

• Overall, the lower the value, the more pronounced are the atherosclerotic changes in the leg and thus the obstruction of blood flow
• With well collateralized proximal occlusions or hemodynamically borderline stenoses, ABI values of >0.9 are possible, demasking by ABI measurement after loading possible - peripheral pressure values >20% below the initial resting pressure and until normalization > 1 min.
• Additive ABI measurement at rest one minute after physical exertion by repetitive toe position or ergometric stress increases the sensitivity for a crural PAVK at rest by 10% in case of inconspicuous ABI.

• The ABI is an independent marker for cardiovascular morbidity and mortality. ABI <0.9 is associated with an increased risk of death from a cardiovascular event
• The 10-year mortality is approximately doubled in patients with an ABI < 0.9.

Suspicion or exclusion of an arterial occlusive disease (PAVK) in clinical symptoms, before compression therapy or in the context of the diagnosis of patients with typical comorbidities and/or leg disorders, e.g. renal failure, diabetes mellitus, heart failure, leg ulcers

• Before the procedure: no excessive exertion (e.g. cycling, long walks), lying down in a resting position for 10 minutes
• Measurement can be performed by a doctor or trained nursing staff
• ARM: 2 systolic blood pressure measurements at the brachial artery according to Riva-Rocci right and left, averaging (exception: in case of pressure differences ≥ 10 mmHg the higher pressure is used)
• BONE: Right and left determination of the systolic blood pressure over the posterior tibial and anterior tibial artery using a 10-12 cm wide blood pressure cuff and a Doppler probe (8-10MHz). - As an alternative to the Doppler probe, semi-automatic blood pressure measurement (Dinamap) or other validated pulse sensors can also be used.
• IMPORTANT: The pressure is measured at the height of the blood pressure cuff, not at the probe!

• Calculation of the ABI: per leg "lowest ankle artery pressure divided by mean arm artery pressure". As it is a quotient, the value has no dimension or unit of measurement.

• NOTE: In previous studies, the highest measured ankle pressure was used, but now the use of the lowest foot arterial pressure value is generally accepted standard for the exclusion or proof of PAVK. It increases the sensitivity to detect relevant arterial occlusive disease to > 90% with a comparable specificity of almost 100% and reduces the rate of unidentified high risk patients.