To perform a manual ankle-brachial index (ABI), you’ll need to measure bilateral systolic blood pressures at three specific locations:
- Right and left brachial arteries
- Right and left dorsalis pedis arteries
- Right and left posterior tibial arteries
When taking systolic pressures in each of these areas, you follow four basic steps:
- Apply the blood pressure cuff.
- Listen for waveforms with the Doppler pen.
- Pump up the cuff (20 mmHg above when you hear the last arterial beat).
- Slowly release the pressure and record when the first arterial beat returns.
Let’s cover these steps again in each specific arterial location.
Four steps for recording brachial systolic pressures
- With the patient lying supine, apply the cuff (or cuffs) to each arm, starting with the brachial artery in the right arm.
- Hold the Doppler pen as if it’s a real pen. The strongest signal is at a 45° angle to the artery with the pen pointing towards the heart. Using 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.
- Inflate the cuff, watch the pressure gauge, and listen for the point at which you stop hearing arterial beats with the Doppler pen. Keep inflating to a pressure that is 20 mmHg higher than the pressure was at the time when you heard the last arterial beat.
- Slowly release the pressure from the cuff and record the pressure when the first arterial beat returns, which is the right brachial systolic pressure. Remember, only the systolic pressure is obtained for ABI tests. Allow three beats to ensure that the sound is not an artifact.
Check out this video from our Ultrasound Masterclass: Arteries of the Legs Course to see steps three and four in action:
Repeat these steps to obtain and write down the left brachial pressure. The highest brachial pressure (from the left or right arm) is the denominator for the ABI ratio equation.
Four steps for recording the dorsalis pedis artery (DPA) pressures
- Apply the cuff to the right ankle just above the malleolus.
- Find the dorsalis pedis artery (DPA) by sliding the Doppler from the inner to the outer ankle across the anterior ankle. The Doppler will cross the DPA. If you have trouble finding the DPA at the anterior ankle, start between the big toe and the second toe and slide proximally in between the bones to find the pedal arch. Adjust the Doppler pen at a 45° angle to the skin and listen for how many peaks and pits you hear. This is your first clue to the presence of a disease.
- Pump up the cuff (as you did for the brachial pressures) to 20 mmHg above when you hear the last arterial beat with the Doppler pen on the DPA.
- Slowly release the pressure from the cuff and record the pressure when the first arterial beat returns. Again, only record the systolic portion. This is the right systolic DPA pressure.
Four steps for recording the posterior tibial artery (PTA) pressure
- Keep the blood pressure cuff in place on the right ankle.
- Position the Doppler pen just behind the right medial malleolus (e.g., inner ankle bone) at a 45° angle and slide posteriorly towards the Achilles tendon. You will cross the posterior tibial artery (PTA). Use enough gel to get good contact with the skin. Listen for the auditory waveforms.
- Pump up the cuff to 20 mmHg above when you hear the last arterial beat.
- Slowly release the pressure from the cuff and record when the first arterial beat returns. This is the right systolic PTA pressure.
For an example of auditory waveform peaks and pits you can hear using a Doppler pen, check out this video from our Ultrasound Masterclass: Arteries of the Legs Course:
Remember, the highest systolic number of the two arteries (DPA or PTA) is used to calculate the right ABI ratio. This number will be the numerator for the ABI equation.
Repeat the steps on the left ankle to obtain the left DPA and PTA blood pressures, and listen to the Doppler waveforms. In the interest of ergonomics, try using your left hand to hold the Doppler when obtaining the left PTA data.
As with the right side, the highest reading from the left DPA and PTA pressures is the numerator for the left ABI equation.
That’s it for now. If you want to improve your understanding of key concepts in medicine, and improve your clinical skills, make sure to register for a free trial account, which will give you access to free videos and downloads. We’ll help you make the right decisions for yourself and your patients.
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