The ankle-arm index (ABI) is the ratio of blood pressure measured at the ankle to blood pressure in the arm. Knowing your ABI is important because it can be used as an indicator of peripheral arterial disease (PAD). Peripheral arteries have the same problems as coronary arteries (those of the heart). They can become clogged with cholesterol or stiffen due to calcification. A significant difference between pressure in the lower legs and in the arms may indicate the presence of a diseased peripheral artery. Such ailments pose a risk and cause stroke and heart failure.
Steps
Part 1 of 3: Measure Brachial Artery Pressure
Step 1. Ask the patient to lie on his stomach (supine position)
Make sure the surface the patient is lying on is flat so that the arms and legs are level with the heart. Let the patient rest for at least 10 minutes before starting the procedure. Rest will normalize blood pressure, especially if it is an anxious person, and will allow the pulse of the heart, and therefore of the brachial artery, to stabilize.
Both arms of the patient must be uncovered. The sleeves must be rolled up so they don't get in the way
Step 2. Locate the brachial artery
Use the index and middle fingers of your hand to detect the pulse. Do not use your thumb, as you will feel your own pulse making it more difficult to find the patient's pulse. Brachial pulsation usually occurs at the anterior aspect of the elbow crease.
Step 3. Wrap the cuff of the blood pressure monitor around the patient's left arm
Make sure that the cuff is placed approximately 5 cm above the brachial pulse detection site, and that - to avoid inaccurate results - it is loosened enough that it can slide slightly around the arm, but not too much to allow it to slip off.
If possible, use a cuff that is approximately two thirds of the length of the patient's arm wide
Step 4. Inflate the cuff to find the systolic pressure of the arm
To measure your blood pressure, place the stethoscope's diaphragm (the circular component) on the spot where the brachial pulse is detected. Close the valve on the pump body and use it to inflate the cuff to approximately 20mmHg above normal blood pressure, or until the patient's pulse is no longer audible.
- Systolic pressure is the maximum blood pressure created by the contraction of the heart's left ventricle.
- Diastolic pressure, on the other hand, refers to the minimum pressure created when the ventricles fill with blood during the beginning of the cardiac cycle.
Step 5. Deflate the cuff
Release the pressure slowly at a rate of 2 or 3 mmHg by opening the valve while keeping a close eye on the pressure gauge (the pressure gauge). Note when the pulse returns, and also when it disappears - in the first case you will have the value of the systolic pressure, in the second the diastolic pressure. The systolic blood pressure value is what you will need to use for the ABI calculation.
Part 2 of 3: Measure Your Ankle Pressure
Step 1. Ask the patient to lie on their back
The aim is always to keep arms and legs at heart level for more accurate results. Remove the cuff from the patient's arm.
Step 2. Wrap it around your left ankle
Place the cuff about 5 cm above the malleolus (the bony protuberance of the ankle). As before, make sure the sleeve is not too tight - check how tight it is by inserting two fingers; if you can't do it, it means it's too tight.
Make sure you have the right size cuff for your patient. The width must be slightly greater than the diameter of the ankle
Step 3. Locate the dorsal artery of the foot
The dorsal artery of the foot (DP) is located on the upper surface of the foot, close to the ankle. Smear ultrasound gel on the surface. Use a Doppler probe to find where the pulse is strongest. You should be able to hear a slight rattle or rustle.
Step 4. Take note of the blood pressure of the DP artery
Inflate the cuff to approximately 20 mmHg above the patient's normal systolic pressure, or until the hiss detected by the Doppler disappears. Deflate the cuff and note when the hiss returns. This is the systolic blood pressure of the ankle.
Step 5. Find the posterior tibial artery (PT)
To determine a more accurate ABI, you should measure both the dorsal foot artery pressure and the posterior tibial artery pressure. The PT artery is located behind the medial malleolus of the foot, below the calf. Smear ultrasound gel on the area and use the Doppler probe to detect the strongest pulsation of the PT artery.
Step 6. Note the blood pressure of the PT artery
Repeat the same process you did to find the DP artery. Once finished, mark the pressure and move the cuff to the right leg, and again find the pressure values of the posterior tibial and dorsal artery of the foot.
Part 3 of 3: Calculate the Ankle-Arm Index (ABI)
Step 1. Make a note of the highest ankle systolic pressure
Compare, for each leg, the results obtained by measuring the pressure of the DP artery and the PT artery. Take into account only the highest value you have obtained, one for each of the two legs: it will be the one you will use to calculate the ABI.
Step 2. Divide the systolic blood pressure measured at the ankle by the systolic blood pressure measured on the arm
You will calculate the ABI for each leg individually. Use the highest value you got from your left ankle measurements, and divide it by the brachial artery value.
Example: The systolic blood pressure measured at the left ankle is 120, while the systolic blood pressure of the arm is 100. 120: 110 = 1.02
Step 3. Mark and interpret the result
A normal ankle-brachial index ranges from 1.0 to 1. 4. The more the result tends to 1, the better the patient's ABI will be. This means that the pressure in the arm should be as similar as possible to that of the ankle.
- An ABI of less than 0.4 indicates the presence of peripheral obliterating arteriopathies. The patient may develop untreatable ulcers or gangrene.
- An ABI between 0.41 and 0.9 reveals the likelihood of peripheral vascular disease and requires further tests (computed tomography, magnetic resonance, angiography).
- An ABI between 0, 91 and 1, 30 indicates regular vessels. However, a value of 0, 9 - 0, 99 could cause fatigue during physical activity.
- An ABI greater than 1.3 denotes stiff and often calcified vessels that raise blood pressure. Cases of long-standing diabetes and chronic kidney disease could lead to this state.
Advice
- Symptoms of peripheral obliterative arteriopathies include pain in the calves while walking, untreatable ulcers in the toes, feet or legs with associated color change and hair loss, cold and clammy skin, etc.
- Asymptomatic individuals who should measure their ABI to rule out early development of peripheral vascular disease include heavy smokers, diabetic patients over 50, people in their family with cardiovascular disease, and people with high cholesterol levels.
- If the patient has a wound on the brachial artery or foot area, use sterile gauze to protect it when wrapping the area with the cuff.
- Check for any orders from the doctor and consider everything you need to do before performing the procedure. Measuring the brachial pressure of a patient undergoing dialysis may be a contraindication for the procedure.
- Check the general condition of the patient. Other pathological conditions could affect the accuracy of the procedure.
