Is The ABI Accurate In Assessing Arterial Perfusion In Decubitus Ulcers?

A poster presented at the American Podiatric Medical Association annual meeting expresses doubt that non-invasive vascular testing is accurate and reliable in patients with heel decubitus ulcers.

The poster focuses on 92 decubitus ulcers in 83 patients, 67 of whom had an ankle-brachial index (ABI) evaluation. Authors observed non-compressible vessels in 35 of 75 feet. They added that in 46 percent of feet, the study found evidence of non-compressible vessels leading to no quantitative results or results that were potentially falsely elevated. The authors advise considering the angiosome and direct arterial supply to an area of tissue loss rather than a more general assessment of perfusion.

How can physicians effectively measure arterial perfusion in decubitus ulcers? Alexander Reyzelman, DPM, recommends assessing toe pressure and the toe brachial index (TBI) along with Doppler waveforms and an ABI in patients without diabetes.

As Dr. Reyzelman explains, there is currently no good way of measuring the perfusion of the angiosomes and there is a lot of overlap in that certain angiosomes have more than one artery supplying them. He also notes that there is no reliable way of measuring the direct arterial supply to a specific angiosome.

“ABI is not reliable for evaluating arterial perfusion to the foot in patients on dialysis and patients who are diabetic due to calcification of the arterial wall,” says Dr. Reyzelman, the Co-Director of the San Francisco Center for Limb Preservation at the University of California.

True decubitus ulcers do not necessarily need to have vascular disease as a component of the etiopathogenesis but if there is concomitant peripheral arterial disease (PAD), it will delay or prevent wound healing, according to Lee Rogers, DPM. As he points out, most consensus guidelines recommend testing for PAD in any lower extremity ulcer since its prevalence is as high as 50 percent in patients with diabetic foot ulcers.

Dr. Rogers, the Medical Director of the Amputation Prevention Centers of America, says skin perfusion pressure (SPP) is the best predictor of the actual perfusion in the skin. He argues that measuring the SPP in the angiosome for heel decubitus ulcers is preferable since one calculates the ABI by either the anterior tibial artery or the posterior tibial artery, and only the posterior tibial artery feeds the calcaneal area. Dr. Reyzelman adds that the poster authors did not take into account the fact that the peroneal artery, not just the posterior tibial artery, supplies blood to the lateral posterior heel.
In addition to the SPP, Dr. Rogers says other options to assess perfusion include transcutaneous oxygen (TcPO₂) or fluorescence angiography.

“Obtaining the SPP of the calcaneal angiosome will be more meaningful for prediction of wound healing,” maintains Dr. Rogers.

In regard to non-invasive vascular tests, Dr. Reyzelman also cites the use of fluorescence angiography (Luna, Novadaq Technologies) but concedes that it still needs validation in terms of its accuracy.
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Does NPWT Reduce Oxygenation Levels In Diabetic Feet?

By Brian McCurdy, Managing Editor

Negative pressure wound therapy (NPWT) can promote lower levels of oxygenation in the diabetic foot, according to a recent study in Advances in Skin and Wound Care.

Authors theorize the lower oxygen levels are because the foam sponge of NPWT compresses the wound bed. Researchers measured transcutaneous partial oxygen pressures (TcPO₂) in the feet of 21 patients with diabetes. The study found that mean TcPO₂ values significantly decreased from 44.6 to 40.3 mmHg after therapy.

The results of the study do not contradict the current understanding of negative pressure, according to Paul Kim, DPM, MS. As he notes, early work on NPWT and angiogenesis revealed the need for intermittency of therapy. He says this intermittent pressure results in periods of hypoxia during negative pressure, noting this may be why this therapy may be beneficial in stimulating blood vessel/capillary formation. Dr. Kim points out that the authors applied NPWT on intact skin and that the study therefore does not address any effect in the wound environment. He also notes reliability issues with TcPO₂, saying that makes the results “less conclusive.”

Dr. Kim, an Associate Professor at the Georgetown University School of Medicine, says maximizing tissue oxygenation has nothing to do with NPWT. He notes that a patient with suspected peripheral vascular compromise should have a workup by a vascular specialist, who may consider endovascular or open management.

Dr. Kim expresses concern that people who read the study will conclude that they should not use NPWT in a potential environment of ischemia. He suggests evaluating the study alongside other studies on the topic.

“Academically, studies such as these provide useful information. However, the complexity of diabetic foot ulcers precludes a common denominator,” points out Dr. Kim.

Does Postural Stability Predict Offloading Adherence?

By Brian McCurdy, Managing Editor

The success of offloading depends on patient adherence and a recent study concludes that postural instability can predict non-adherence.

The study, published in Diabetes Care, focused on 79 people with plantar diabetic foot ulcers (DFUs). Patients received removable offloading devices and the study notes that 77 percent used removable cast walkers. The study authors also noted that patients used the devices, on average, during 59 percent of their activities.

Authors note that smaller baseline DFU size and better offloading adherence predicted DFU healing at six weeks. In contrast, worse postural instability was predictive of decreased offloading adherence, according to the study. The authors advise that physicians consider postural stability when choosing an offloading device.

As postural stability is a measure of ambulatory confidence or, by inference, fall apprehension, James McGuire, DPM, PT, CPed, points out that if the offloading device makes patients more fearful, they will not use it. He says practitioners may need to alter the choice of device to maximize stability and order gait training and postural exercises to improve safety and adherence in this population.  

The study confirms a relationship between offloading and neuropathic sensation, which David G. Armstrong, DPM, MD, PhD, says clinicians have suspected in the past. It is important to take these data and incorporate them into practice, notes Dr. Armstrong, the Director of the Southern Arizona Limb Salvage Alliance and a Professor of Surgery at the University of Arizona Medical Center in Tucson, Ariz.

To that end, he suggests discussing and evaluating the level of postural stability for patients and getting them into offloading devices.

“Try to get them moving through the world and living their lives a little bit better with a little more stability,” says Dr. Armstrong.

Low profile gentle rocker sole removable walkers are effective offloading options, according to Dr. McGuire, the Director of the Leonard Abrams Center for Advanced Wound Healing and an Associate Professor in the Departments of Podiatric Medicine and Biomechanics at the Temple University School of Podiatric Medicine. He notes rocker sole shoes or extra-depth shoes with offloading insoles can give the patient the greatest sense of normal stability. In addition, Dr. McGuire says total contact cast designs may be important with patients more accepting of low profile rocker designs.