Performing a manual ankle-brachial index (ABI)
In this video, Dr Elizabeth Tenny will take you through this procedure, step-by-step, pointing out the common pitfalls and how to avoid them.
If you suspect that a patient may have peripheral arterial disease in the legs, performing an ABI is crucial to confirming your suspicions. In this video, Dr Elizabeth Tenny will take you through this procedure, step-by-step, pointing out the common pitfalls and how to avoid them.
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With the patient lying supine, apply the cuff or cuffs to the limbs starting with the brachial artery in the right arm. Hold the Doppler pen as though it is a real pen. The strongest signal is at an angle 45 degrees to the artery pointing towards the heart. Use this technique, find the right radial artery at the thumb side of the inner wrist.
Balance your wrist or ring and pinky fingers on the patient's arm or bed to keep a steady hand. Pump up the cuff 20 millimeters of mercury above when you hear the last arterial beat from the Doppler pen. Slowly release the pressure from the cuff and record the pressure at which the first arterial beat returns, which is the systolic pressure.
Remember, only the systolic pressure is obtained for ABI's. Allow three beats before knowing the sound is not artifact. Write down the right brachial pressure. Obtain the left brachial pressure using the Doppler the same way as the right arm and write it down. The higher of these is the denominator for the ABI equation.
Next, apply the cuff to the right ankle just above the bone. Find the dorsalis pedis artery (DPA) by sliding the Doppler from inner to outer ankle across the anterior ankle, it will cross the DPA. Adjust the Doppler pen angle to 45 degrees to the skin and listen for how many peaks and pits you hear. This is your first clue as to presence of disease.
Obtain the ankle pressure with the Doppler pen on the DPA. Write these pressures down. Obtaining this pressure is similar to the brachial pressure, only the systolic portion is recorded. If you have trouble finding the DPA at the anterior ankle, starting between the great and second toes, and slide proximally in between the bones to find the pedal arch.
To find the right posterior tibial artery (PTA), start just behind the medial malleolus or inner ankle bone, and slide posteriorly toward the Achilles tendon, you will cross the PTA. Use enough gel to get good contact with the skin. Listen for the waveform and obtain the pressure. Remember, the higher systolic number is used regardless if it is the DPA or the PTA.
This number will be the numerator for the ABI equation. Repeat the exact steps to obtain blood pressure and listen to the Doppler for the left angle. In the interest of ergonomics, try using your left hand to hold the Doppler when obtaining the left PTA data. The higher of the left DPA and PTA pressures is a numerator for the left ABI equation.