Is the ankle brachial index for compression therapy necessary?

A blood pressure cuff helps determine compression therapy.

If you are OK with the status quo, then do not read any further. 

However, if you want to look at whether guidelines that have been established and promoted for years are based on evidence and science, then read on. 

For years, clinicians (including myself) have been using the ankle brachial index (ABI) as a guide to determine whether a patient is a candidate for:

  • High (therapeutic) compression
  • Low-level compression
  • No compression

It was only after listening to a colleague’s lectures on myths in wound care that inspired me to look deeper into this practice. 

Why is this a big deal? 

It is rather simple. We know therapeutic compression (30-50mmHg) is necessary to successfully heal venous leg ulcers and that lower levels of compression are not sufficient in severe or chronic venous insufficiency.

If the current guidelines are not truly accurate, many patients are condemned to ineffective levels of compression, and the likelihood of healing is poor.

This means we may need to rethink how we determine who is not a candidate for therapeutic-level compression and put more patients into the treatment to have the best chance of healing.

According to the Journal of Wound, Ostomy and Continence Nursing, the current ABI compression therapy guidelines used by clinicians and compression product manufacturers are as follows:  

  • ABI < 0.5 = No compression
  • ABI 0.5 – 0.8 = Low level compression
  • ABI > 0.8 = High (therapeutic) compression

There are some minor differences in literature and recommendations, but these are what is most commonly used.

Does it follow science and evidence?

The underlying thought for doing the ABI before compressing is that the choice of compression therapy strength may compromise arterial flow in the lower leg if it is too high.

How were these ABI compression therapy guidelines established? 

Surprisingly, I could not find any studies done to establish these guidelines.

In fact, only 15% of wound care interventions are supported by solid research leaving a wide gap between research and practice.

Let’s look at some clinical evidence and research that does exist on this topic.

For a tourniquet to completely occlude the arterial flow in the lower leg it can take 250-450mm Hg, depending on width, according to Tourniquets.org.

This begs the question, “What is 50mm Hg or less going to do to the blood flow?” I think we know the answer to that. 

Remember that diabetics have a high risk for calcified arteries at the ankle that makes the ABI an unreliable test.

If one simply pinches their own fingernail bed until it blanches, that takes about 32mm Hg.

Give it a try. Does that feel like it could compress the deep arteries?

Or even if you pressed a little harder, does it feel like you could get to 50? Do you see the point?

What should evidence-based focused clinicians do?

First, the ABI can still be helpful to determine if there is adequate blood flow.

If a clinician suspects significant arterial disease, it would benefit us to see if it is above 0.5 to determine the amount of venous compression that could be safely applied.

That’s because if it is below that level, there isn’t enough blood flow even reaching the lower leg, which creates its own problems (not because compression will cut it off further). 

Another thing to keep in mind is the big vessels may not be occluded, but the smaller vessels still could be. 

The goal should always be therapeutic-level compression for optimal outcomes. A prudent way to determine safe compression is to check toe color and temperature before application and again about 20 minutes after application. 

A significant change could indicate compromised blood flow. However, pain or discomfort in the lower leg should not be used as an indicator because it is likely because of the tight wrap (which it is supposed to be).

If better patient outcomes are the goal, then compression at 30-50mm Hg at the ankle is needed. Let’s not be so quick to go with lower compression immediately.

Take our course on “Venous Wound Care: Compression is not enough.”

wound care

Bill Richlen, PT, WCC, DWC, is a clinical instructor for the Wound Care Education Institute. As a licensed physical therapist, Richlen has experience in advanced wound care consultations in long-term care, outpatient, skilled rehabilitation and home health. He has served as a clinical instructor for physical therapy students, been the director of several large rehabilitation departments, and has been providing multi-disciplinary wound care education to nurses and therapists for more than 17 years. His expertise in diverse settings enhance his role as a clinical instructor. His dynamic and captivating teaching style keeps attendee’s attention throughout each course.

What do you think?

comments

Leave a Reply

You must be logged in to post a comment.