The ankle-brachial pressure index (ABPI) is a non-invasive method of assessing the extent of chronic peripheral arterial disease in the lower limbs. It is a ratio composed of the blood pressure in the brachial artery and the pressures in the foot arteries (dorsalis pedis and the posterior tibial artery). This guide provides a step by step approach to performing ABPI measurement in an OSCE setting.
Introduce yourself – state your name and role
Confirm patient details – name / DOB
Explain the procedure:
- “I would like to measure the pressures in your arm and ankle”
- “This will involve inflating a cuff around your arm and ankle briefly and listening to your pulse with this probe”
- “It shouldn’t be painful, but it may feel a little tight temporarily, please let me know if you want to stop at any point”
Check understanding: “Do you understand everything I’ve mentioned? Do you have any questions?”
Check if the patient currently has any pain: “Do you have any pain anywhere?”
Rule out diabetes: “Do you suffer from diabetes?” (see reasoning below)
Gain consent: “Are you happy for me to continue with the assessment?”
Calcified vessels in diabetes sufferers will lead to artificially high ABPI values due to vessels which are not compressible. In such cases measure the Toe pressure (with a special toe cuff) rather than the ankle pressure. This is called the Toe Brachial Pressure Index (TBPI).
If the patient has leg ulcers these can be covered in sterile cling-film and the cuff applied as above, provided the patient doesn’t feel discomfort
- Doppler probe
- Ultrasound gel
Check probe is functioning correctly (battery / sound volume)
Measuring the brachial pressure
1. The patient must be lying supine for the measurements on an examination couch.
2. Place the sphygmomanometer cuff over the left arm proximal to the brachial artery (avoiding any cannulas) and position the doppler probe on the brachial artery at a 45° angle (medial to the biceps tendon at the antecubital fossa).
3. Inflate the cuff 20-30 mmHg above the pressure at which the doppler pulse is no longer heard. Deflate the cuff slowly and note the pressure at which you first detect a pulse from the doppler. This is the systolic pressure in that vessel.
4. Now repeat this process on the right brachial artery.
5. The higher of the two readings will be used as part of the ratio.
Measuring the ankle pressure
1. Place the sphygmomanometer on the left ankle and position the doppler probe over the posterior tibial artery (behind the medial malleolus of the foot). Measure the pressure in the same way as for the brachial artery: inflate and deflate the cuff slowly to detect the pressure at which blood returns to the posterior tibial artery.
2. Repeat this process (keep the sphygmomanometer in the same place) at the dorsalis pedis artery of the left foot (lateral to the extensor hallucis longus tendon).
3. Use the highest of the two pressures obtained from the posterior tibial artery (PTA) and dorsalis pedis (DP) for the ratio of the left ABPI.
4. Repeat the same process on the right ankle to work out the ratio for the right ABPI.
To complete the procedure…
Thank the patient
Record left and right ABPI in the patient’s notes
Suggest further assessments and investigations
- Take a thorough history from the patient
- Perform a full peripheral arterial exam
- Bloods: FBC, U&Es, glucose, cholesterol
- Further imaging – duplex ultrasound / CT or MRI angiogram
Examiner question: “If you find an abnormal ABPI result, what would be the next steps in investigation and management?”
Answer: “If mild disease is present, this may be managed conservatively. If further imaging is needed, then a duplex ultrasound of the lower limb arteries can be undertaken. Prior to surgical or endovascular interventions a CT or MR angiogram may be needed.“
Left ABPI = (Highest pressure of either left PTA or DP) ÷ (Highest brachial pressure)
Right ABPI = (Highest pressure of either right PTA or DP) ÷ (Highest brachial pressure)
- Right brachial artery: 120 mmHg
- Left brachial artery: 125 mmHg
- Right DP: 80 mmHg
- Right TP: 75 mmHg
Right ABPI = 80/125 = 0.64
|>1.2||Abnormally hard vessel (e.g. calcified) – this can often be a false negative as there is likely significant peripheral vascular disease but the hardened vessels give a higher ABPI reading, so correlation with clinical findings is advised.|
|0.8-0.9||Mild arterial disease: mild claudication|
|0.5-0.79||Moderate arterial disease: severe claudication|
|<0.5||Severe arterial disease: rest pain, ulceration and gangrene (critical ischaemia)|
Errors can occur due to:
- Irregular pulse (AF)
- Cuff positioned incorrectly
- Calcified vessels (diabetes)
. Mo Al-Qaisi, David M Nott, David H King, and Sam Kaddoura. (2009). Ankle Brachial Pressure Index (ABPI): An update for practitioners. Vasc Health Risk Manag. 5, 833–841.
. McDermott MM, Criqui MH, Liu K, Guralnik JM, Greenland P, Martin GJ, Pearce W (2000). “Lower ankle/brachial index, as calculated by averaging the dorsalis pedis and posterior tibial arterial pressures, and association with leg functioning in peripheral arterial disease”. J Vasc Surg. 32 (6): 1164–71
. Gogalniceanu P, Pegrum J, Lynn W. (2015) Physical Examination for Surgeons – a guide to the MRCS OSCE. Cambridge University Press, UK.
CONTENT REVIEWED BY
Mr Peter Gogalniceanu – Surgeon