Evaluating Tissue Perfusion To Assess Wound Healing In Patients With PAD

Given that peripheral arterial disease can slow or prevent wound healing, tissue perfusion can be a valuable indicator of the progression of wound resolution. Accordingly, these authors evaluate the efficacy of various diagnostic methods for assessing tissue perfusion.

Peripheral arterial disease (PAD) presents a tremendous challenge in the field of wound care. Not only can PAD result in delayed wound healing or a failure to heal, PAD usually presents in varying degrees that may go unnoticed for extended periods of time in a patient who fails to present with advanced symptoms.

Evaluation of the patient should start with a thorough history and physical exam, and continue with more comprehensive testing as one deems necessary. Tissue perfusion assessment is a critical component to successful wound healing.

Risk factors should alert a physician to the possible existence of PAD. Some of the most common risk factors include diabetes mellitus, hypertension, hyperlipidemia and cigarette smoking. Oftentimes, patients will relate signs and symptoms of intermittent claudication, which present as reproducible leg pains. Some patients relate that their legs tire quickly while others report painful cramping. The classical presentation of intermittent claudication includes pain or cramping in the posterior calf after walking a short distance causes pain and rest relieves the pain. Claudication pain may also occur in the posterior thigh, hip, buttocks and even in the foot. Ischemic rest pain occurs in an advanced state of PAD and presents when the patient is supine or when the patient elevates the legs above the level of the heart.

Pain is usually reduced when the lower extremities are in a state of dependency. Patients relate leg cramps or pain when resting or sleeping, and state that hanging their legs over the side of the bed or getting out of bed to walk achieves relief. This typically indicates an advanced state of PAD.

Physical examination of the patient is a key component to assessing tissue perfusion. Most noted findings include atrophic skin changes, which indicate decreased arterial perfusion. Other findings associated with decreased arterial perfusion include thinning or loss of hair on the foot and leg, skin that is pale and cool to the touch, and delayed capillary refill times. In these patients, toenails usually become thick, discolored and dystrophic.

Buerger’s sign, which is characterized by rubor of dependency and pallor with elevation, presents in affected extremities. This is a result of chronic dilatation of the vascular system caused by loss of vasomotor control and presents in advanced cases of PAD. With a patient seated on the examination table, have him or her place the lower extremities in dependency hanging over the side of the exam table with the patient in the supine position. The feet and legs will show a deep, dusky red “flushing” after a short period of time. Elevate the legs to 45 degrees and after a brief period, pallor replaces the flushing red color.

Keys To Clinical Recognition Of Lower Extremity Ulcers
Lower extremity ulcers fall into different categories and distinguishing the etiology is critical in establishing an effective wound care regimen. Key categories of lower extremity ulcerations include ischemic, venous, neuropathic, traumatic and mixed origin ulcerations. Failing to categorize the ulcer usually results in unsuccessful treatment.

A key to differentiating between the different types of ulcers is their location. Venous type ulcerations typically appear around the ankle on either the medial or lateral side near the distal site of the saphenous veins. This area is commonly referred to as the “gaiter area.” Neuropathic ulcerations typically occur over bony prominences and areas of pressure. Traumatic ulcerations can occur anywhere where trauma has occurred. Mixed type ulcerations are the most difficult to categorize and require both an astute clinician and a patient who can relate a comprehensive history of the lesion.

Ischemic ulcerations, or ulcerations with noted arterial disease, typically occur over distal portions of the toes, forefoot and areas with bony prominences. They may also occur spontaneously due to minor trauma. Most ischemic ulcers present at the tips of the toes, on the dorsum of the foot, around the heel or under the metatarsal heads. Many have a “punched out” appearance or smooth demarcated edges. The wound base is usually fibrotic with white or gray tissue, a lack of surrounding edema, inflammation and usually has absent or minimal drainage.

What You Should Know About The Value Of The ABI
Usually, the primary care physicians are the first caregivers to come in contact with PAD patients, whether they present with or without a foot ulcer at the time. It is crucial to assess the patient’s symptoms for early detection and if they coincide well with PAD, one should subsequently obtain an ankle-brachial index (ABI).

For a current algorithm for vascular testing in patients whom you suspect of having PAD, see “A Quick Guide To The Diagnostic Workup For Patients With Suspected PAD” at left.¹

The history and physical exam are important components in establishing the diagnosis of PAD, but may have poor sensitivity. Most patients with ischemic ulcers have already received a preliminary diagnosis of PAD but the ABI is a simple and inexpensive exam that offers relatively high accuracy in confirming the diagnosis.

Though bedside ABI is not sensitive or specific enough to distinguish the severity of the disease, there is a correlation between the symptomatology and the ABI values. Claudication occurs between ABI of 0.4 and 0.9, rest pains occur anywhere from 0.2 and 0.4 and tissue loss occurs at 0 to 0.4.² In general, an ABI <0.9 with the appropriate history of leg pain is diagnostic of PAD with 95 percent sensitivity in identifying arteriogram-positive PAD and nearly 100 percent specificity in ruling out PAD in healthy individuals.

Ankle systolic pressure should be greater than 60 mmHg for adequate perfusion in a lower extremity wound to heal. In patients with diabetes, this systolic pressure should be greater than 90 mmHg. In fact, when there is an ABI of less than 0.5 in a patient with a foot ulcer, he or she must undergo arterial revascularization in order for the ulcer to heal.³

The symptoms of PAD are a manifestation of systemic atherosclerosis. Therefore, a low and a high ABI could be indicative of increased cardiovascular risk. Calcified vessels may falsely elevate an ABI value. However, a clinician must be cautious in distinguishing other etiologies of abnormal ABI as other non-atherosclerotic diseases could also produce abnormal results.

What Are The Options For Additional Vascular Testing?
If the physical exam and ABI are indicative of PAD, one should consider additional vascular testing along with a vascular consult. These vascular testing options include duplex ultrasound, computed tomography angiogram (CTA), magnetic resonance angiography (MRA) and other advanced techniques.

Duplex ultrasonography. This offers a noninvasive imaging modality that is helpful in visually evaluating the site and severity of vascular disease, and is relatively inexpensive in comparison to other advanced testing. The images produced as a result of reflected sound waves evaluate the blood velocity. Duplex scanning has demonstrated sensitivity and specificity of 80 and 98 percent respectively for a greater than 50 percent stenosis of femoropopliteal arteries.⁴ A drawback to using ultrasound is that it is heavily technician dependent and requires a certain level of expertise in its use. Duplex ultrasonography is very sensitive to small movements and usually has poor detection of perforating vessels in my experience.

Transcutaneous oxygen pressure (TcPO₂). Also known as transcutaneous oximetry, the TcPO₂ is another non-invasive technique for determining the level of skin perfusion. It is extremely effective in evaluating ischemic wounds and predicting their ability to heal. Wounds are expected to have full healing potential when the TcPO₂ pressure is at least 30 to 40 mmHg. In a patient with diabetes, a pressure higher than 40 mmHg is required for healing. If the pressures are below 20 mmHg, the wound is severely deprived of oxygenation and has a poor prognosis for appropriate wound healing.

The TcPO₂ has become an important tool in determining if a patient has the healing potential at the wound site, the need for amputation and if there is a need for revascularization surgery that could benefit the patient. One can also use this technique as a screening tool to see if the patient is a good candidate for hyperbaric oxygen therapy (HBOT) for an ischemic, nonhealing ulcer. During the oxygen challenge, one should observe a 100 percent increase in the TcPO₂ level of the ischemic wound or an increase greater than 100 mmHg for effective wound healing to occur with HBOT.

One would obtain the TcPO₂ pressure by placing platinum oxygen electrodes over the chest and the lower extremities. Normally, the foot is 60 mmHg and a chest/foot ratio is 0.9.^5-6 However, the results of this test can be erroneously influenced by factors such as skin edema, a rise in temperature, vasoconstriction, inflammation and some specific medications.

Contrast arteriography. Considered one of the primary and gold standard imaging techniques in the vascular medicine, contrast arteriography offers the advantage of instantaneous intraoperative intervention. It has been the standard among vascular surgeons for decades. However, it is an invasive technique and with rising healthcare costs and declining revenues, physicians are utilizing it less than before.

Additionally, many patients are unable to tolerate the radiation, the contrast dye and the potential damage to the already weakened, tortuous vessel. One alternative is to use CO₂ gas instead of contrast dye although image quality is degraded. In other cases, plain computed tomography (CT) and magnetic resonance imaging (MRI) could offer detailed vascular imaging without the detrimental effects of the contrast.

Computed tomography angiogram. The computed tomography angiogram (CTA) utilizes X-rays with computerized 3-D analysis with iodinated contrast. There are several advantages to using the CTA over magnetic resonance angiography (MRA). It is less costly to the patient and widely available. Further, the spatial resolution for CTA is superior to that of the MRA. The time patients spend in the CT scanner is also comparably short, ranging from 10 to 15 minutes. Bear in mind though that the iodinated contrast with this testing modality may be harmful in patients with renal impairment and those with an allergy to the dye.

Magnetic resonance angiography. The MRA produces rapid 3-D imaging sequences combined with a gadolinium contrast agent. One of the major advantages of the MRA is the use of a magnetic field instead of ionizing radiation. However, as we mentioned before, it is more costly, time-consuming (as it takes 30 to 40 minutes in the MRI machine) and uses a contrast agent that the patient may not be able to tolerate.

Laser angiography. This is a relatively new technology that offers high quality, real-time images intraoperatively to visually evaluate the blood flow and tissue perfusion of a specific site while using indocyanine green. One can perform laser angiography in a clinic setting instead of the operating room. When clinicians inject indocyanine green via peripheral or central intravenous access, it binds to the plasma proteins with a short half-life of three to five minutes, rapidly clearing from the body. The liver excretes indocyanine green so laser angiography may be beneficial to use in patients with renal impairment.

In specific settings, laser angiography using indocyanine green can improve clinical outcomes and help guide surgical decisions for flap design, tissue resections and other procedures.7 Laser angiography has been associated with reduced rates of postoperative necrosis and flap loss in comparison to clinical judgment alone. While laser angiography is associated with high costs, invasive technique and bulky equipment, it does offer an alternative method for imaging and assessment of our patients. While some hail this technology as new, laser angiography has in fact been around for decades in ophthalmology and only recently got FDA approval for cardiovascular, plastic and reconstructive surgical procedures in the care of lower extremity ulcers.

In Summary
Peripheral arterial disease is extremely prevalent, especially in the aging population and could seriously hinder appropriate wound healing. Therefore, it is important to recognize the signs and symptoms of early and atypical PAD by doing a thorough physical exam, especially if the patient presents with a lower extremity wound. One can further assess adequate vascular perfusion to the wound site with the aforementioned various vascular exams in the appropriate setting. The ABI and duplex ultrasonography are the most prevalent, non-invasive initial methods followed by the TcPO₂ studies.

Alongside podiatric physicians, vascular specialists are an integral part of the interdisciplinary team who can help prevent the worsening of ischemic wounds. Accordingly, timely vascular consults are essential for these patients. The lack of vascularity to the wound site could lead to amputation, which poses a serious problem to the patient’s lifestyle, functionality and overall prognosis.

As clinicians, the foremost goal is to improve the patient’s outcome and his or her quality of life. In order to do so, one must understand and expedite the wound evaluation as carefully as possible.

Dr. Espensen serves as the Co-Director of the Amputation Prevention Center and Clinical Education Coordinator at Valley Presbyterian Hospital in Van Nuys, Calif. He is a Clinical Assistant Professor in Surgery at the Western University of Health Sciences in Pomona, Calif. Dr. Espensen also oversees the Hyperbaric Oxygen Treatment program at Valley Presbyterian Hospital.

Dr. Ahmed is a first-year resident with the Veterans Affairs West Los Angeles Medical Center residency program, and graduated from the Western University of Health Sciences in Pomona, Calif. She is currently working on additional research programs.

References
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2.    Norgren L, Hiatt WR, Dormandy JA, et al. Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II). J Vasc Surg. 2007; 45(Suppl S):S5.
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4.    Koelemay MJ, den Hartog D, Prins MH, et al. Diagnosis of arterial disease of the lower extremities with duplex ultrasonography. Br J Surg. 1996; 83(3):404-9.
5.    Bowers BL, Valentine RJ, Myers SI, et al. The natural history of patients with claudication with toe pressures of 40 mm Hg or less. J Vasc Surg. 1993; 18(3):506-11.
6.    Byrne P, Provan JL, Ameli FM, Jones DP. The use of transcutaneous oxygen tension measurements in the diagnosis of peripheral vascular insufficiency. Ann Surg. 1984; 200(2):159-65.
7.    Gurtner G, Jones G, Neligan P, et al. Intraoperative laser angiography using the SPY system: review of the literature and recommendations for use. Ann Surg Innov Res. 2013; 7(1):1.

Additional Reference
8.    Holtman D, Gahtan V. Peripheral arterial perfusion: is it adequate for wound healing? Wounds. 2008;20(8):230-235.