1) Taking ankle pressures using the dorsalis pedis pulse or the anterior tibial artery at the ankle adds specificity to ABI testing. 2) Proper patient preparation and technique, such as slowly inflating and deflating the blood pressure cuff, are important for obtaining accurate ABI readings. 3) Medial calcification of the arteries in patients with diabetes or other conditions can result in artificially elevated ABI readings, so toe pressures may also need to be measured.

1. Beyond the Basics Tips and Suggestions on Performing an ABI from an Expert, Norma Vandenberghe, RN, RVT

2. An alternative way for taking ankle pulses: Palpate the DP pulse (Dorsalis Pedis), but take the signals from the distal ATA (Anterior Tibial Artery) at the ankle flexure. If the ATA is occluded, the DP may still be present and even relatively normal due to collateral circulation through the pedal arch. Using the ATA adds a bit of specificity to the test.

3. Excellent ABI & PAD links: American Heart Association: http://www.americanheart.org/presenter.jhtml?identifier=2158 search: Peripheral Vascular Disease American College of Cardiology: http://www.acc.org/index.htm search: PAD American College of Physicians: http://www.acponline.org/clinical_information/journals_publications/acp_internist/jun07/extra/diagnosis.htm

4. Excellent ABI & PAD links (Continued): Diabetes Journals: http://care.diabetesjournals.org/cgi/content/extract/26/12/3333 http://intl-care.diabetesjournals.org/cgi/content/full/27/7/1591 Cleveland Clinic Journal of Medicine: http://www.ccjm.org/content/73/Suppl_4 Supplement on PAD * Note all links are current as of 09/24/09.

5. Preparing the patient is very important. Cold, nervous or uncomfortable patients will not give you accurate readings, especially of the ankles. If the feet are cold, the vessels will be vasoconstricted and may be more difficult to assess. A warm resting patient who is well prepared for the test will give you accurate readings that will provide diagnostic measurements.

6. Take your time when getting pressures; inflate the cuff slowly until the sound and waveform are suppressed, noting that pressure in your head and inflating the cuff 20-30 mm Hg above that pressure. Then deflate slowly (2-3 mm Hg per cardiac cycle) for an accurate systolic pressure. Inflating the cuff to over 200 mm Hg when it isn’t necessary just hurts the patient and doesn’t improve the accuracy of your readings. Deflating the cuff too fast may cause you to note the pressure at a lower level than the actual pressure.

7. Finding the best position over the artery and getting the best angle in order to get the best Doppler sound and waveform is worth not rushing to get the test done. It is important to be sure the Doppler stays over the vessel as the cuffs are inflated and deflated. Remember that you are listening to the blood flow towards the Doppler so the angle should point the Doppler towards the patient’s head. Having enough gel on the artery allows you to angle the Doppler while maintaining “contact” with the skin through the gel. If the gel isn’t warm, warn the patient that it is cool.

8. Use a gentle pressure over the artery, resting the heel of your hand against the bed or patient for stability. Too much pressure will not help, and may actually compress the vessel, obliterating the signal.

9. As you perform more and more exams you will become more proficient and take less time and be more accurate. It’s like roller skating, once you know how the skates become part of your foot. Excellent technique will pay off in better agreement from visit to visit and between techs.

10. When we take blood pressures using a stethoscope, we are listening to Korotkoff sounds (the sounds of the heart valves opening and closing with the cardiac contractions.) That is why we can hear both systolic and diastolic values. When we use a Doppler, we are hearing the frequency shifts caused by blood cells moving through the Doppler beam. Therefore, we hear systolic values very clearly, even far away from the heart and when the flow is quite low, but we do not hear diastolic values.

11. Often the clinician can take the first brachial (arm) pressure with the Doppler, and then take the second arm with the stethoscope in order to obtain the diastolic pressure. If you get systolic pressures that are within 4-6 mm Hg of each other, you can consider the arm pressures to be comparable (accurate and normal.) If you get a wider difference between the arm pressures, you should continue to repeat the pressure readings, usually using Doppler on both arms, until you are sure whether there really is a difference and the magnitude of the difference.

12. An abnormally low arm pressure is caused by proximal obstruction of the artery, which may be reflected in changes in the waveform contour as well. In any case, the higher arm pressure will reflect the most accurate systemic pressure and is the one to use in calculation of the ABI.

13. Irregularity in heart rhythm can create difficulty in deciding which beat to use for the systolic pressure. Beats that are stronger will come in earlier (giving a higher pressure) and the shorter cardiac cycles will produce beats that come in later (giving a lower pressure reading). As in cardiac echo and vascular duplex scanning, the best approach is to use the “normal” beats if possible. Try to catch a series of regularly spaced beats or use one that is strong and in between the long and short beats (sort of an “averaging” process). This is a time when it is even more essential to deflate the cuff slowly. Try to be consistent from site to site as to which beat you use.

14. Diabetic patients (and a small number of others, like those with chronic renal failure or long-term steroid use) may have “medial calcification” of the vessel walls. This condition occurs when the medial layer of the arteries (not the intimal layer, where plaque is deposited) become calcified; it can happen in vessels that also have obstructive plaque or in vessels where the lumen is unobstructed. In such cases, taking ankle pressures is like taking pressures on a metal pipe: the vessels do not compress at the pressures we can apply with a vascular cuff.

15. The cuff can be pumped up to 300 mmHg or even higher and Doppler signals will still be audible through the artery. Therefore, the true pressure level within the vessel cannot be measured. If the ABI is greater than 1.3, the patient is considered to have medial calcification, and the ABI is considered inadequate for diagnostic purposes. The solution to this dilemma is twofold : first, pay attention to the Doppler waveform, if it is a normal multiphasic waveform contour, chances are there are no significant obstructive lesions in the vessel. Second, to be sure of the perfusion to the foot, toe pressures should be measured (Toe Brachial Index TBI). Because medial calcification does not affect the smaller toe vessels as it does the calf vessels, toe pressures provide a good clinical addition when calcific vessels are encountered.

16. There are multiple variations in waveform appearance as the vessel reopens. Often, the initial waveform will be retrograde; this can be a normal shifting of the flow through the pedal arch, or may indicate a pattern of collateralization of a more proximal obstruction in the vessel.

17. An historical note: the terms “triphasic’, “biphasic” and “monophasic” all come from the early days when all Doppler signals were interpreted audibly. The major distinction is that of the normal reverse flow component that occurs during early diastole. It is easy to hear; it is a result of both the compliance of the vessel and the high resistance to flow that is normal in the peripheral arteries. Many practitioners prefer the term “multiphasic” to describe a signal that is relatively normal with a reverse flow component. The distinction between more normal biphasic waveforms and abnormal monophasic waveforms is made by observing both the speed of the initial upstroke (straight up is normal, sloped is abnormal) and the relative amplitude of the signal, biphasic being higher and monophasic being much lower.

18. For more information, please contact Hokanson @ www.hokanson.cc or 425-882-1689 or info@deh-inc.com