Ankle Brachial Index (ABI) Test: How to Perform

Summary

In this Stanford Medicine 25 video, Dr. John Cooke demonstrates how to detect peripheral arterial disease (PAD) using the Ankle Brachial Index (ABI). The ABI is calculated by comparing ankle pressure to brachial pressure using a handheld Doppler and blood pressure cuff. The video explains the step-by-step process of measuring pressures at both the arm and ankle, including identifying pulse waveforms, and interpreting results to diagnose PAD. Dr. Cooke highlights the importance of ABI screening for those over 60 or with risk factors like diabetes or smoking, as early detection can guide effective treatment to prevent severe complications.

Takeaways

• 😀 The Ankle Brachial Index (ABI) is a simple test used to detect peripheral arterial disease (PAD) by comparing ankle pressure to brachial pressure.
• 😀 Around 8 million people in the U.S. have PAD, but only about 30% are diagnosed.
• 😀 Everyone over 60 and anyone over 50 who is diabetic or a smoker should have an ABI test to check for PAD.
• 😀 The ABI test involves using a handheld Doppler, a blood pressure cuff, and ultrasonic gel to measure pressure at the arm and ankle.
• 😀 The test is performed in a quiet, dimly lit room, allowing the patient to relax for about 10 minutes before measurements.
• 😀 For the arm measurement, the blood pressure cuff is inflated until no pulse is detected, and then slowly released to record the pressure.
• 😀 The ABI is calculated by dividing the highest ankle pressure by the highest brachial pressure.
• 😀 The ABI values help assess the severity of PAD: 1.0 to 1.4 is normal, 0.9 to 1 indicates no intervention needed, 0.8 to 0.9 suggests early arterial disease, and values below 0.5 suggest severe arterial disease.
• 😀 If ABI results indicate moderate or severe PAD, or vessel calcification (ABI > 1.4), the patient should be referred to a vascular specialist.
• 😀 The ABI test can also help detect venous insufficiency, but this would require a separate venous exam using the Doppler device.

Q & A

What is the Ankle Brachial Index (ABI) and how is it used to detect peripheral arterial disease?

The Ankle Brachial Index (ABI) is a simple test that measures the ratio of the ankle pressure to the brachial (arm) pressure. It helps detect peripheral arterial disease by indicating the blood flow to the extremities. A low ABI suggests reduced blood flow, which can indicate peripheral arterial disease.

Why is it important for people over 60, and those over 50 who are diabetic or smokers, to get an ABI test?

People over 60, and those over 50 who are diabetic or smokers, are at increased risk of peripheral arterial disease. The ABI test can help detect early signs of the condition, allowing for the initiation of life-saving medical treatments such as ACE inhibitors, statins, and antiplatelet agents.

What equipment is needed to perform an ABI test?

To perform an ABI test, you need a handheld Doppler, ultrasonic gel, and a blood pressure cuff. The test is typically done in a quiet, dimly lit room to ensure accurate measurements.

What is the role of the handheld Doppler in the ABI test?

The handheld Doppler is used to listen for the pulse waveforms in the brachial artery and the arteries in the legs (dorsalis pedis and posterior tibial arteries). It helps detect the presence of blood flow and allows the measurement of systolic blood pressure in these areas.

What should you do if you cannot feel the dorsalis pedis artery in a patient?

If the dorsalis pedis artery cannot be felt bilaterally, it can be a normal finding. However, if the posterior tibial artery is also not palpable, it is considered abnormal and may indicate arterial disease.

What are the normal and abnormal ABI values?

An ABI between 1.0 and 1.4 is considered normal. An ABI between 0.9 and 1.0 is acceptable with no intervention required. An ABI between 0.8 and 0.9 suggests mild arterial disease, while 0.5 to 0.8 suggests moderate arterial disease. An ABI below 0.5 indicates severe arterial disease, and a value above 1.4 suggests vessel calcification or hardening.

How do you calculate the ABI?

To calculate the ABI, you divide the highest ankle pressure by the highest brachial pressure. This is done separately for each leg, using the highest values of the posterior tibial or dorsalis pedis arteries for the ankles.

What should be done if a patient has an ABI less than 0.9?

If a patient has an ABI less than 0.9, it suggests the presence of arterial disease, and it is advisable to treat the patient's risk factors, such as managing diabetes, smoking cessation, and other lifestyle changes. Referral to a vascular specialist may also be necessary for further evaluation.

What does an ABI greater than 1.4 indicate?

An ABI greater than 1.4 can indicate vessel calcification or hardening, which is also a concern that should be referred to a vascular specialist for further examination.

Why is venous return sometimes heard during the ABI test, and how can you distinguish it from the arterial signal?

Venous return is the sound caused by the movement of blood through the veins, often heard when pressure is released from the blood pressure cuff. It can be distinguished from the arterial signal by squeezing the foot, which will amplify the venous return sound. The arterial signal is typically a clear pulse sound, while venous return has a different sound.