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Vascular Assessment Enters the 21st Century

New, non-invasive vascular technologies are the key to better outcomes and efficient management of wound care patients. These expert panelists discuss innovative technologies for vascular evaluation, also comparing the efficacy of tests such as the ankle-brachial index (ABI), toe-brachial index (TBI), transcutaneous oxygen measurement (TCOM), and skin perfusion pressure (SPP).

New, non-invasive vascular technologies are the key to better outcomes and efficient management of wound care patients. These expert panelists discuss innovative technologies for vascular evaluation, also comparing the efficacy of tests such as the ankle-brachial index (ABI), toe-brachial index (TBI), transcutaneous oxygen measurement (TCOM), and skin perfusion pressure (SPP).

Worldwide, the incidence of diabetes and peripheral arterial disease (PAD) continues to rise, with more than 30 million Americans now carrying the diagnosis of type 2 diabetes mellitus, and more than 8 million Americans diagnosed with PAD.1

Marcus Gitterle, MD, FACCWS, recently had the opportunity to lecture on the topic of “New Technologies in Non-Invasive Vascular Evaluation” at the Undersea and Hyperbaric Medicine Society conference in Dallas, Texas on September 7, 2019. He notes it was evident from the response that there is keen interest in the subject.

“It’s easy to understand why, because never has there been a more pressing need to quickly and reliably assess the vascular status of our patients,” says Dr. Gitterle. “Seasoned wound clinicians know that without a clear and early assessment of vascular status, it is impossible to make appropriate and timely wound care decisions and assure optimal outcomes.”

Caroline E. Fife, MD, FAAFP, CWS, FUHM, details her approach to a vascular assessment. She notes ankle brachial index (ABI), toe brachial index (TBI), transcutaneous oximetry (TCOM) and skin perfusion pressure (SPP) can all help answer whether a wound has failed to heal due to poor perfusion. Each one has advantages and disadvantages and it is important to think through what the results of each test mean. 

For example, Dr. Fife says a very high ABI can be due to severe calcification in the vessels and that is why it is “perhaps the least reliable” of the screening technologies. While it is possible to deduce anatomical information from TCOM and SPP, they are physiological tests. TCOM measures skin oxygen tension whereas skin perfusion pressure measures the blood pressure in the skin capillaries. A low transcutaneous oxygen value may not be due to arterial disease. Tissue oxygen can be low due to arterial hypoxemia, a diffusion barrier like edema, severe anemia or heart failure. That does not mean the TCOM is wrong because it is correctly telling you that the wound is unable to heal due to tissue hypoxia. 

Dr. Fife notes you can’t conclude that a low TCOM is due to arterial disease unless you  employ a provocative maneuver like breathing 100% oxygen. If the TCOM breathing 100% oxygen is less than 100 mmHg, the patient probably has arterial disease. Similarly, she notes a low SPP value may not be due to arterial disease. SPP can be low as a result of heart failure, which is why it is usually paired with a PVR (pulse volume recording) (e.g., SensiLase PAD-IQ, Vasomed). A dampened PVR in conjunction with a low SPP indicates arterial disease. If you don’t understand what you are actually measuring, Dr. Fife notes you may conclude the patient needs a peripheral angiogram when, in fact, he or she is in heart failure.  

Dr. Fife also outlines her approach to vascular assessment:

1. Is the wound adequately perfused to heal?

2. Is there enough oxygen to heal?

3. If no to questions 1 and 2, is it because there’s occlusion in a large vessel?

4. If the patient has an angioplasty, is there now enough flow to heal?

5. Is the problem due to hypoxia from a cause that is not vascular?

Q: What are the advantages and disadvantages of ABI and TBI?

A: The ABI and TBI may be relatively quick to perform, notes Dr. Fife. She says the tests are easy to learn and do not require expensive equipment. Depending on the setting and who actually performs the test, she says it may not be possible to bill for the test unless the person who performs it has a specific certification and there is a printed report. We have addressed these topics in previous TWC articles. 

As Dr. Gitterle notes, clinicians evaluate vascular status “in a hit-or-miss fashion, to the detriment of patients.” He notes that some wound care centers have proactive vascular evaluation policies, where at minimum, clinicians perform ABI testing on new patients who present with a lower extremity wound and any risk factors for PAD, whereas many wound care programs do not have consistent policies for such testing. Dr. Fife adds that the U.S. Wound Registry has a CMS-recognized arterial screening quality measure reportable for credit under the Merit Based Incentive Payment System. To pass the measure, arterial screening is performed at the initial visit, something that a hospital-based outpatient department should be able to accomplish. The arterial screening quality measure was chosen by CMS to be depicted on the Physician Compare website in 2019.

One of the reasons for inconsistent testing policies in wound care centers, notes Dr. Gitterle, is that commonly available vascular screening methodologies such as the ABI and TBI suffer from significant limitations in the diabetic populations common in wound centers. Dr. Gitterle says factors such as vascular calcification, which is common in patients with diabetes, render ABI data difficult to interpret. The TBI addresses some of these limitations, but he says it can be very difficult to administer the test reliably in a significant percentage of patients.

“More importantly, ABI and TBI do not tell us anything about microvascular flow in the wound bed, and certainly nothing about tissue oxygenation—an essential factor for wound healing,” says Dr. Gitterle. 

ABI and TBI are anatomical tests, not physiological tests. A patient with a normal ABI or TBI could still have a hypoxic wound due arterial hypoxemia, heart failure or severe anemia, according to Dr. Fife. 

Q: What are the advantages and disadvantages of TCOM?

A: Although TCOM is long accepted as the “gold standard” for assessing tissue oxygenation (and collaterally, microvascular blood flow) and thereby assessing the potential for wound healing, Dr. Gitterle says the test also suffers from “very significant limitations in clinical practice.” Importantly, he notes TCOM cannot be used to directly assess the perfusion of plantar skin—the site of some of the most challenging wounds—nor are the TCOM electrodes in common use suitable for assessing perfusion in the toe. Dr. Fife adds that TCOM can be used on the plantar foot in areas without significant callus and can often be used on the great toe if the electrode can be placed on a flat area that is 0.9 cm wide. That means it can be used on the dorsal aspect of the great toe of most men and some women.

In addition to technical limitations, Dr. Gitterle and Dr. Fife both say TCOM is an expensive technology to purchase and maintain. Dr. Gitterle notes typical devices cost more than $50,000 to purchase, and his group recently received a $76,000 quote for maintenance costs for 6 devices. Dr. Gitterle and Dr. Fife say TCOM devices also require a significant training investment to use effectively, and testing can consume valuable technician time and bed minutes in the clinic.

Q: What technologies for vascular assessment do you feel are promising?

A: In an era of decreasing margins and increasingly stringent demands for efficient, optimal utilization, Dr. Gitterle says the limitations and expenses associated with ABI and TCOM are forcing clinical leaders and clinic owners to look to new technologies offering a better cost–benefit ratio. 

As Dr. Gitterle pointed out in a recent lecture, one technology is generating enthusiasm for a new paradigm in non-invasive vascular evaluation in the wound clinic, which may help overcome the current technical limitations and cost burdens imposed by existing technologies. This technology is hyperspectral imaging (Snapsho2t, Kent Imaging, and HyperView, HyperMed).

“While hyperspectral imaging and skin perfusion pressure are very different from a technological perspective, each of these new devices addresses the imperative to quickly, repeatably, and cost-effectively assess the vascular status of our patients, so that treatment decisions can be optimized from the point of care, on the first visit,” says Dr. Gitterle. 

Hyperspectral imaging technology is not fundamentally new, but Dr. Gitterle says the use of hyperspectral imaging to assess skin blood flow is a recent development. He notes many wound care clinicians have seen one or more of these devices demonstrated at industry trade shows, such as the Symposium on Advanced Wound Care (SAWC), and those who have seen these devices are typically intrigued by what they see. He notes hyperspectral units are just a bit bigger than an iPad, and are capable of capturing an image that provides direct, quantitative visualization of oxygenated hemoglobin, deoxygenated hemoglobin, and oxygen saturation, superimposed on a visual image of the wound and surrounding skin.

Dr. Gitterle says hyperspectral images can be obtained in seconds, without expendable costs, by a technician or provider with as little as 5 minutes of training, and they are compelling to look at. How do hyperspectral devices fare clinically? The literature is meager right now, but Dr. Gitterle says several groups are publishing clinically oriented papers assessing the utility of the technology for wound care and vascular medicine. Dr. Gitterle says such studies have looked at the predictive value of hyperspectral imaging in patients with vascular ulcers and diabetic foot ulcers, and what has been consistently evident is that deoxyhemoglobin imaging data correlates reasonably well with TcPO2.2

Dr. Gitterle notes hyperspectral imaging also correlates with angiosomal anatomy. One study notes “Deoxyhemoglobin values for the plantar metatarsal, arch, and heel angiosomes were significantly different between patients with and without PAD (P <.005)”3

Finally, Dr. Gitterle cites a study of 73 diabetic foot ulcers in 66 patients.4 Over a 24-week period, hyperspectral imaging correctly predicted healing with 80% sensitivity, and non-healing with 74% specificity. “Thus as a predictor of healing, hyperspectral imaging compares quite favorably with TCOM, whose generally accepted sensitivity for prediction of healing is 72%,” says Dr. Gitterle.

Having evaluated a hyperspectral imaging unit in a wound clinic setting, Dr. Gitterle finds the information helpful, but difficult to integrate into the practice patterns necessitated by Local Coverage Determination (LCD) strictures, and commonly accepted treatment pathways. He intends to watch the devices evolve and champion their promise. “They likely represent a future evolutionary step in wound care and vascular medicine, but I don’t think they are a compelling replacement for TCOM at this time,” says Dr. Gitterle.

Dr. Fife notes there are a lot of promising vascular technologies but they can’t necessarily tell you if the patient needs an angiogram or provide an estimation of whether the wound is able to heal with the perfusion it now has. “None of the new tests seem to have quantifiable data that allows me to say, ‘the perfusion may not be  normal, but it is enough to heal,’” says Dr. Fife.

Q: What are the advantages and disadvantages of SPP?

A: If hyperspectral imaging is not ready for prime time, Dr. Gitterle says SPP may be ready to step into the breach and meet the need for timely and cost-effective evaluation of tissue perfusion in the critical DFU and vascular ulcer population. While not a new technology, he notes SPP is now available in the form of an “integrated, elegant device called SensiLase PAD-IQ (Vasomed), capable of providing rapid, repeatable, predictive test results in the challenging lower extremity wound population.”

By combining ABI testing with pulse volume recording (PVR), Dr. Gitterle says the PAD-IQ can deliver 100% sensitivity for identification of PAD, and 100% negative predictive value for absence of the disease. As he notes, integrative SPP allows clinicians to perform accurate and repeatable “perfusion maps,” much like those obtained using multi-channel TCOM testing, but unlike TCOM, users can assess perfusion at the toe, as well as plantar skin.

Having used a PAD-IQ in the wound clinic for 6 weeks, Dr. Gitterle “can say unequivocally that I am ready to give up my TCOM device and embrace a new way of assessing skin perfusion.”

Dr. Gitterle calls the PAD-IQ “a well-designed device that meets multiple needs in one unit.” He says his nurses and technicians were quickly trained to use the device and started performing studies. He says the perfusion sensor is easy to apply, and the interface is “about as elegant as any (he has) seen on a medical device.” Printouts of the PAD-IQ are easy to read, and the information is rich; “the kind of reports one is proud to send to a referral source, or consultant.” He adds that the results are unambiguous and graphically clean.

Dr. Gitterle says a PAD-IQ test can be completed in less than half the time as TCOM. Like TCOM, he notes the interpretation of SPP is straightforward. Using a cutoff of 30 mmHg (capillary opening pressure, not TcPO2), one can readily predict non-healing status and determine the need for intervention.

“I stopped doing TCOMs routinely more than 10 years ago and began using SPP with PVR for all my initial vascular screening. It is easier for staff to learn, provides information on both large vessels and small vessels and is fast to perform. More importantly we can assess the perfusion in specific angiosomes,” says Fife. If used with pulse volume recordings, SPP can help determine whether a patient needs an angiogram, and can also offer information on whether the problem with perfusion is due to a failure of the pump and not the vessels. 

Dr. Fife adds that the reliability of SPP is not impacted by arterial hypoxemia or severe anemia. 

How does SPP compare to TCOM in clinical trials? Lo and colleagues found that SPP alone successfully predicted wound outcome in 87% of the cohort compared to TcPO2 at a rate of 64% (P <0.0002).5 In addition, Dr. Gitterle says the study found SPP was more sensitive in predicting wound healing than TcPO2 (90% versus 66%; P <0.0001).

“These are impressive results, and I feel just what we need to move the management of lower extremity ulcers, and particularly diabetic foot ulcers forward,” says Dr. Gitterle. “Too many programs are confounded by unsystematic, subjective vascular evaluation heuristics. It is as though we were evaluation these fraught, challenging cases using ‘Magic 8 Balls.’ Until we are assessing every lower extremity wound patient with PAD risk factors early, and definitively, we will be running in place, and generating inconsistent, suboptimal outcomes.”

“It is time, I feel, to make vascular testing simple, reliable, and something that happens at the bedside at the point of consultation in the wound clinic,” says Dr. Gitterle. “I for one am ready to embrace change.” n

Caroline E. Fife is chief medical officer at Intellicure Inc., The Woodlands, TX; executive director of the U.S. Wound Registry; medical director of St. Luke’s Wound Clinic, The Woodlands; and co-chair of the Alliance of Wound Care Stakeholders.

Marcus Gitterle is the Chief Medical Officer of WoundCentrics, LLC. 

To read about the differences between TCOM and SPP with PVR, see Non-invasive Vascular Testing and the Wound Care Clinic at https://tinyurl.com/tq7r2l6.

To read about SPP and TCOM and the oxygen challenge, see “Addressing the Need for Noninvasive Vascular Testing in the Outpatient Clinic: A Case Study” at https://tinyurl.com/qtnmtg5.

Here is the CMS approved quality measure for performing arterial screening at the first visit: https://tinyurl.com/u7epevt.

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Panelists: Caroline E. Fife, MD, FAAFP, CWS, FUHM, and Marcus Gitterle, MD, FACCWS
PDF
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References

1. Centers for Disease Control and Prevention. Diabetes quick facts. Available at https://www.cdc.gov/diabetes/basics/quick-facts.html . 

2. Jafari-Saraf L, Wilson SE, Gordon IL. Hyperspectral image measurements of skin hemoglobin compared with transcutaneous PO2 measurements. Ann Vasc Surg. 2012;26(4):537–548.

3. Chin JA, Wang EC, Kibbe MR. Evaluation of hyperspectral technology for assessing the presence and severity of peripheral artery disease. J Vasc Surg. 2011;54(6):1679–1688.

4. Bolton L. Hyperspectral imaging: early warning of low tissue perfusion. Wounds. 2012;24(10):A8-A10.

5. Lo T, Sample R, Moore P, Gold P. Prediction of wound healing outcome using skin perfusion pressure and transcutaneous oximetry: a single center experience in 100 patients. Wounds. 2009; 21(11):310-6.

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