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Current Concepts In Vascular Assessment Of Wounds
Given the increasing prevalence of lower extremity wounds and peripheral arterial disease (PAD), proper evaluation is crucial to prevent worsening complications. This author discusses vascular examination methods ranging from the ankle brachial index to emerging modalities such as spatial frequency domain imaging.
Next month will mark Peripheral Arterial Disease (PAD) Awareness month, which is observed every September. The ever increasing number of patients with diabetes in our country mirrors a global increase in comorbidities commonly associated with diabetes. One of these comorbidities is PAD.
The team approach to lower extremity amputation prevention and wound management is a necessity due to the complex nature of patients afflicted with limb-threatening PAD or critical limb ischemia (CLI), the more advanced form of peripheral arterial disease.
Communication within the interdisciplinary team is critical in expediting care for this group of patients. However, an even larger challenge is the early detection of PAD and the prevention of PAD subsequently deteriorating into CLI cases.
The first steps in lower extremity amputation prevention lie in a greater understanding of the disease and how to better assess these high-risk patients throughout the course of their disease management. Simply stated, regular and ongoing assessment are essential in treating any patient with lower extremity wounds, regardless of the underlying etiology. Knowing how to assess these patients better will certainly improve outcomes in addition to reducing potential pain and suffering.
A Closer Look At The Epidemiology Of Chronic Lower Extremity Wounds
Chronic lower extremity ulcers affect 0.6 to 3 percent of those over 60 years of age in the general population and this prevalence increases to over 5 percent of those over 80 years of age.1,2 Chronic lower extremity ulcers are a common cause of morbidity and their prevalence in the community ranges from 1.9 to 13.1 percent.1,2 In the course of a lifetime, almost 10 percent of the general population will develop a chronic wound with a wound-related mortality rate of 2.5 percent.1,3
The prevailing thinking is that the incidence of ulceration is rising because of the aging population and increased risk factors for atherosclerotic occlusion such as smoking, obesity and diabetes.
Physicians perform approximately 65,000 to 75,000 major amputations (above-the-knee and below-the-knee) annually for critical limb ischemia (CLI).4 Within five years of these major amputations, approximately 70 percent of patients with CLI die. These amputations cost $11 billion with Medicare and Medicaid paying almost 80 percent of the bill.
Researchers have determined that at least 50 percent of lower extremity amputations in the U.S. are a first-line intervention and surgeons perform them without prior vascular testing.5 The decision to amputate, then, is often based on subjective opinion versus objective findings. Therefore, a patient’s fate, when amputation is a consideration, rests upon whether the patient’s provider is cognizant of the importance of lower extremity preservation. I have referred to this as “the amputation lottery.”
The SAGE Group further validated the economic impact that amputation has on the health care system.4 The SAGE Group also found that people who have minor amputations experience adverse events (reamputation and cardiovascular death) at the same rate as those having major amputations.
Key Insights On Endovascular Interventions
To better appreciate the perspective of the interventionists, whether they be vascular surgeons, cardiologists or radiologists, a review of some basic terminology will help bridge a gap between podiatrists and vascular specialists. Having a better understanding of some of these basics will help in overall vascular assessment skills as well as in knowing the type of tests to perform and order. A further examination of inflow and outflow disease, the antegrade and retrograde approaches (to endovascular intervention) and the Rutherford Classification are all warranted for a greater understanding of the vascular assessment process.
Inflow disease refers to aortoiliac occlusive disease, also known as Leriche’s syndrome. This disease is characterized by diminished pulses bilaterally and wounds, when present, that are slow to heal. Other symptoms of inflow disease are impotence and gluteal or thigh claudication. Conceptually, inflow disease occurs in the thighs and above with pain in the hip, thigh and buttock as key indicators.
Outflow disease is also referred to as iliofemoral occlusive disease and is associated with arterial segments found below the superficial femoral artery (SFA). Outflow disease is characterized by a unilateral leg with diminished pulses. Buttock claudication may be present in cases of outflow disease.
Femoropopliteal occlusive disease is characterized by thigh and calf claudication, and normal femoral pulses in the groin. Rest pain is an indicator of outflow disease. Rest pain upon elevation is indicative of advanced stenosis or occlusion, leading to CLI.
The Rutherford (or Rutherford-Becker) classification categorizes the severity of PAD, based on the clinical presentation and symptoms of the patient. The Rutherford classification levels of symptom and severity are:
0- Asymptomatic
1- Mild
2- Moderate
3- Severe
4- Ischemic rest pain
5- Minor tissue loss (toe ulcer, focal gangrene)
6- Major tissue loss (above transmetatarsal level)
When physicians utilize endovascular intervention to restore blood flow to a stenotic or occluded lower extremity artery, they typically access the diseased vessel through the use of a wire-guided approach with balloon angioplasty, stents and atherectomy to restore flow. How the interventionist gains access will be through the traditional antegrade approach and, where warranted, the retrograde approach. The antegrade approach is into the leg and foot, originating with access to an artery, typically in the groin. With the retrograde approach, the interventionalist accesses a pedal artery in the foot. The dorsalis pedis and posterior tibial arteries would be the typical vessels with targeted lesions for such procedures.
What You Should Know About Angiosome-Based Revascularization
Taylor and Palmer introduced the concept of angiosomes.5 Conceptually analogous to neurological dermatomes, angiosomes provide a vascular mapping of the body, showing anatomical regions between the skin and bones that are supplied by specific arteries and veins.6,7 The location of an ulcer can help determine the likely location of an arterial stenosis or occlusion when considering the corresponding angiosome.
Angiosome-based revascularization is the concept in which the target artery for reperfusion is the one associated with the ischemic angiosome. This direct revascularization approach is associated with higher limb salvage rates than indirect revascularization, in which a non-angiosome vessel is the target.5,7 Whether the treating surgeon uses angiosomes in conjunction with attempts at revascularization or not, angiosomes may provide an initial screening modality for arterial (and ulcer) assessment.
A Guide To Common Arterial Testing Methods
Before examining specific lower extremity testing methods, it is worth reviewing the guidelines published by the Wound Healing Society for assessing vascular status in the diabetic foot.8
• Guideline 1.1: Rule out clinically significant arterial disease (Level I).
• Guideline 4.1: Examination of the patient as a whole is important to evaluate and correct causes of tissue damage. This includes factors such as: (A) systemic diseases and medications, (B) nutrition, and (C) tissue perfusion and oxygenation (Level I).
• Risk status: Consider age, sex, ethnicity, tobacco use, diabetes, previous coronary, stroke or “leg event,” body mass index and hypertension.
• Clinical foot exam: Examine the condition of distal hair growth, skin texture and color as well as changes in skin color with elevation and dependence, skin temperature as well as femoral/popliteal/pedal pulses.
• Non-invasive vascular testing exams: These include the ankle brachial index (ABI), pulse volume recordings (PVR), skin perfusion pressure (SPP), and transcutaneous oximetry (TCOM).
The Wound Healing Society endorses several modalities for arterial testing, most of which have been readily available and in use for a significant time. That said, one may not utilize simple palpation of pulses in a typical clinical setting. Clinicians should ascertain a baseline vascular assessment during evaluation of any new patient with a wound. Repeat vascular testing should be ongoing in the high-risk patient with PAD or CLI. Pre- and post-revascularization assessment should also be regular parts of the encounter with a wound patient with more extensive testing such as arterial Doppler and waveform testing occurring every three to four months post-revascularization.
Palpation and general assessment. The presence of dusky digits, dependent rubor or a suspicious-appearing ulcer or eschar on a digit raise concerns for worrisome PAD. I cannot emphasize enough the following statement by Lee Rogers, DPM. He stated that during a foot examination, “absent pulses can be an indicator of no flow but palpable pulses are never an indicator of sufficient flow.”9
Ankle brachial index. The ABI is a widely endorsed non-invasive test, which is simple and easy to perform in an office setting. That said, there are problems that are inherent with the ankle-brachial index. To review, the ABI compares pressures in the brachial arteries to lower extremity pressures in the posterior tibial and dorsalis pedis arteries. The ratio between these pressures is the ABI. Where the ABI loses its usefulness is when non-compressible (calcified or blocked) vessels falsely elevate pressure readings. This phenomenon occurs in many patients with PAD and diabetes. Also, variations in the administration of ABI testing make the results less reliable than other available tests.
Duplex arterial ultrasound. The duplex arterial ultrasound is a non-invasive test that allows for visualization and quantification of a lesion. It is user-dependent and calcification may limit the quality of the image.
Pulse volume recordings. This test utilizes cuffs at multiple levels including the toes, transmetatarsals, calf and thigh to assess the quality of blood flow through arteries. Pulse volume recordings evaluate changes in arterial blood volume during each cardiac cycle. The PVR reveals the level as well as the absence, presence and severity of arterial disease, and is a qualitative assessment. Perform the test on both legs for comparison as well as for future reference.
Transcutaneous oximetry and skin perfusion pressure (SPP). Fife provides an excellent in-depth overview and comparison of both TCOM and SPP, and concludes they are complementary in obtaining objective information regarding tissue perfusion.10 In short, TCOM measures oxygen molecules present in tissue (TcPO2) while SPP is a pressure measurement or measure of reactive hyperemia. Both TCOM and SPP hold value in assisting in the prediction of potential success of an amputation and optimal amputation level, and for pre- and post-revascularization efficacy.
Magnetic resonance angiography (MRA), computed tomographic angiography (CTA) and digital subtraction angiography. When one suspects advanced PAD or has already confirmed PAD by clinical presentation (for example, a patient with Rutherford level 3 through 6 PAD), additional vascular assessment is required to determine with greater specificity the location(s) of arterial stenosis or occlusion.
Magnetic resonance angiography, computed tomographic angiography and digital subtraction angiography are three such methods physicians typically utilize. Each has pros and cons.
Digital subtraction angiography is the “gold standard” of arterial imaging. It has high resolution and typically guides intervention. The greatest drawbacks are that the technique uses ionizing radiation and iodinated contrast dye. Digital subtraction angiography produces two-dimensional images.
Computed tomographic angiography is non-invasive and provides three-dimensional imaging. The CTA uses ionizing radiation and iodinated contrast material. Imaging is limited in the presence of densely calcified vessels.
Magnetic resonance angiography is non-invasive and does not use radiation or contrast dye. It produces three-dimensional images. Drawbacks include lower spatial resolution than that of CTA. Prior stent placement may cause an image artifact.
Emerging Modalities For Vascular Assessment
There are a number of new and emerging technologies that can evaluate the lower extremities of patients with PAD.
Fluorescence angiography. One of the recent technological advancements in lower extremity vascular assessment has been the use of fluorescence angiography to assess tissue perfusion. Fluorescence angiography uses indocyanine green, a water soluble injectable dye that is roughly 98 percent protein bound after intravenous injection. The benefits of this technology are the quality and specificity of the images produced in determining tissue perfusion.
Applications in diabetic foot wounds have enabled surgeons to determine with greater accuracy the comparative success of pre- and post-revascularization procedures. When amputation is indicated, fluorescence angiography can provide a greater predictability of the outcome, based on uptake of indocyanine green by viable tissue.
Novadaq has been the developer and distributor of this technology via SPY Fluorescence Imaging with applications extending into areas beyond cardiovascular disease and wound care.
Spatial frequency domain imaging. The reflection of light off an object or material can provide information about that material. This concept enables the measurement of oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR) amounts, and reports an accurate measure of mixed arterial/venous oxygenation in the tissue below the epidermis. With this comes the ability to determine the true health status of tissue.
The Ox-Imager CS (Modulated Imaging) measures important indicators of tissue health, specifically tissue blood oxygen saturation (StO2), oxyhemoglobin and deoxyhemoglobin as well as providing a surface color photograph. The Ox-Imager CS is indicated for use to determine oxygenation levels in superficial tissues for patients with potential circulatory compromise.
In Conclusion
Timely vascular assessment is critical in high-risk populations with lower extremity wounds as it can go a long way toward facilitating appropriate treatment interventions and preventing unnecessary amputations. Thorough knowledge of the strengths and limitations of current and emerging vascular testing options can help us achieve optimal outcomes for our patients.
Dr. Bell is a board-certified wound specialist of the American Academy of Wound Management and a Fellow of the American College of Certified Wound Specialists. He is the founder of the “Save a Leg, Save a Life” Foundation, a multidisciplinary, non-profit organization dedicated to the reduction of lower extremity amputations and improving wound healing outcomes through evidence-based methodology and community outreach.
References
1. Agale SV. Chronic leg ulcers: epidemiology, aetiopathogenesis and management. Ulcers. 2013; 413604. Available at https://dx.doi.org/10.1155/2013/413604
2. Rayner K, Carville J, Keaton J, et al. Leg ulcers: atypical presentations and associated co-morbidities. Wound Practice Res. 2009; 17(4):168–85.
3. Sasanka CS. Venous ulcers of the lower limb: where do we stand? Ind J Plast Surg. 2012; 45(2):266–74.
4. SAGE Group. The SAGE Group estimates the economic cost of critical limb ischemia amputations at $25 billion. Available at https://thesagegroup.us/pages/news/amp-2014.php . Published Aug. 15, 2014.
5. Taylor GI, Palmer JH. The vascular territories (angiosomes) of the body: experimental study and clinical applications. Br J Plast Surg. 1987; 40(2):113-141.
6. Singh K. New treatment paradigm: the angiosome concept. Podiatry Today. 2012; 25(Suppl2):4-7.
7. Bell D. Can angiosome-based revascularization have an impact in limb salvage? Podiatry Today. Available at https://www.podiatrytoday.com/can-angiosome-based-revascularization-have-impact-limb-salvage . Published March 2012.
8. Lavery L, Davis K, Berriman SJ, et al. WHS Guidelines update. Diabetic foot ulcer treatment guidelines. Wound Repair Regen. 2016; 24(1):112–26.
9. Rogers L. Centralizing your knowledge of testing for PAD. Podiatry Management. 2013; 32(6):123-126.
10. Fife C. Non-invasive vascular testing in the wound clinic. Today’s Wound Clinic. 2010; 4(8):16–18.
For further reading, see “Can Angiosome-Based Revascularization Have An Impact In Limb Salvage?” at https://tinyurl.com/ybe8dvcq or “Current Concepts In Revascularization For Limb Salvage” in the September 2015 issue of Podiatry Today.
