The Role of Vascular Testing in Chronic Wound Management
Peripheral arterial disease (PAD) is a leading justification for lower-limb amputations; a condition prevalent in high-income countries and patients aged 55 and above. PAD occurs when there is poor circulation to the lower extremities, often resulting in chronic non-healing ulcers. It indicates a narrowing of the arteries due to the internal build-up of fatty deposits, aka arteriosclerosis. Common symptoms of PAD include ulcers on the legs or feet that are slow to heal, pain in the thighs, hips, or calf muscles relieved during rest (claudication), and leg numbness or weakness.
Chronic wounds affecting the lower extremities contribute significantly to the number of limb amputations performed annually in the United States, placing an immense strain on healthcare resources. The SAGE group puts the cost of lower-limb amputations in the country at $43 billion annually, with Medicaid covering most of the bills, although amputation is not always needed.
According to Mary L. Yost, SAGE GROUP president, the probability of undergoing a major amputation "depends on who you are, where you live, and the outcome of the "Amputation Lottery." Amputation rates vary by race, socioeconomic status, age, sex, hospital, and geographic location.” “Amputation is undesirable for patients and the economy. It reflects in its high costs, lower cost-effectiveness than revascularization, and abysmal patient outcomes." Vascular testing can help to salvage limbs and prevent unnecessary amputations.
What is Vascular Testing?
Vascular testing is a systematic, non-invasive approach that measures circulation through blood vessels using ultrasound and other emerging technologies. Methods for vascular assessment of limbs having chronic wounds include the Ankle-Brachial Index (ABI) test, transcutaneous oximetry, duplex arterial ultrasound, Magnetic resonance angiography (MRA), and Spatial frequency domain imaging. Most of these methods have been endorsed by the Wound Healing Society. Vascular testing should not be a one-off approach but done on an ongoing basis.
Why Comprehensive Vascular Testing is Essential
Unfortunately, many decisions to perform a limb amputation rest on the judgment of clinicians and are not necessarily an outcome of a thorough vascular assessment. Left untreated, PAD can progress into critical limb ischemia (CLI), a severe complication with a high rate of long-term mortality. Simple checking of pulses in typical clinical settings is not ideal for determining arterial insufficiency. According to Dr. Lee Rogers, DPM, a podiatric surgery specialist, "during a foot examination, absent pulses can be an indicator of no flow, but palpable pulses are never an indicator of sufficient flow." A good understanding of vascular testing techniques and objective analyses of results will aid clinicians in salvaging more limbs and preventing unnecessary amputations.
Ankle-Brachial Index (ABI) Test
The ABI test assesses the level of tissue perfusion in a limb by comparing the difference in systolic blood pressure at the brachium and ankle. A low ABI number is an indication of constricted or blocked vessels that reduce circulation to the lower extremities. The ABI test is carried out similar to a blood pressure test. The clinician may utilize a hand-held Doppler probe with the patient in a prone position. An ABI value lower than 0.9 indicates very poor perfusion, likely due to peripheral arterial disease.
Transcutaneous Oximetry (TCPO2)
Measures the oxygen content of a limb to assess perfusion. It is an especially helpful test for determining the severity of blood flow deprivation due to advanced PAD. To perform the procedure, a clinician first removes any wound dressings, cleans the site with alcohol, and applies an electrically-conductive gel onto the limb. The clinician uses a sensory apparatus to measure the number of oxygen molecules present. Electrodes in the gel warm the subcutaneous layer of the skin to improve oxygen flow for a more accurate reading. Radiometer provides a very useful visual aid for transcutaneous oxygen measurement ("TCP02 Decision Tree") clinicians can use to assess circulation, monitor treatment, and evaluate outcomes. TCPO2 causes minimal discomfort to the patient and the test can be done within 15 minutes.
Duplex Arterial Ultrasound
This technique uses high-frequency (Doppler and B-mode) ultrasound to assess the circulation and structure of arteries in the affected limbs. The Doppler ultrasound creates a color map of blood flow through the vessel while B-mode (brightness mode) ultrasound creates a 2D representation of the artery structure. The clinician uses transducers; small microphone-like devices that generate ultrasound sound waves that reflect off bones and tissues and are converted into electrical signals displayed on a monitor. The devices are placed on a patient's limbs while in a prone position.
Magnetic Resonance Angiography (MRA)
Despite its relatively high costs, Magnetic Resonance Angiography (MRA) is an effective technique for detecting PAD with a high level of specificity. This non-invasive approach creates 3-dimensional imaging of the arterial structure of the limbs without the use of ionizing radiation and iodinated contrast materials as in computed tomography angiography and digital subtraction angiography.
Spatial Frequency Domain Imaging
Spatial frequency domain imaging (SFDI) is a new technique for assessing arterial insufficiency that has grown in popularity over the last decade. It is based on the principle that beamed light reflected off arterial structures and tissues provides information about their state. SFDI estimates levels of tissue perfusion by analyzing absorption, scattering, and fluorescence. This technique measures tissue hemoglobin and tissue oxygen saturation (StO2) to assess the amount of circulation in the lower extremity to a high degree of accuracy.