Is near-infrared spectroscopy a promising noninvastive vascular study to measure tissue perfusion in diabetic foot ulcers? Presenting a case study, these authors assess how an innovative device can provide clinicians a better picture of the potential for wound healing.
The debilitating triad of peripheral neuropathy, increased plantar pressures and vascular compromise creates the perfect storm for the development of chronic diabetic foot ulcers (DFU). Controlling infection, debriding devitalized tissue, decreasing inflammation, controlling glycemia, proper offloading, and maximizing vascular supply are all essential in supporting the DFU healing cascade.
It is imperative that clinicians routinely assess limb perfusion in order to ensure successful wound healing outcomes. As part of an initial wound care physical exam clinicians should evaluate the index limb for key signs of adequate tissue perfusion. These parameters include skin temperature, quality, texture, and hydration, as well as the amount and distribution of hair growth.
Pulse palpation paired with Doppler auscultation is a requisite component of a wound care screening visit. Palpable pulses alone are not a valid indicator of adequate arterial supply. A 2003 study by Bjellerup compared pedal pulse data to ankle-brachial index (ABI) values in 510 patients.1 He found that in patients without palpable pedal pulses, 39.8% had an ABI >0.9. Conversely, 15.4% of patients with palpable pedal pulses had an ABI <0.9. This study indicated that palpable pedal pulses alone resulted in a 40% false negative in the prediction of arterial disease. Bjellerup’s study went as far as to say that the utilization of a handheld Doppler should be considered mandatory at all new patient visits in those presenting with leg or foot ulcers. In patients who exhibit a weak or absent palpated pulse along with deficient or non-Dopplerable signal, a routine non-invasive vascular evaluation should be ordered.
Although a variety of clinical options exist, there is no ideal way to perform a non-invasive vascular study (NIVS). When appropriately selected, ABI and toe-brachial index (TBI) measurements, pulse waveform recordings, transcutaneous oxygen pressure measurements (TCOM), skin perfusion pressure, or duplex scanning can be helpful screening tools to determine if vascular intervention is needed.2 However, the results of NIVS can be inaccurate due to study limitations in the presence of calcinosis, scarring, wounds, edema, amputations, and/or infections.3-5
NIVS results show macrovascular patency, but don’t necessarily translate to microvascular patency and tissue perfusion to wounded tissues, especially below the ankle. Thus, NIVS results can lead clinicians to falsely believe that sufficient perfusion for wound healing is present. A study by Bunte et al examined 89 patients presenting with clinical complaints indicative of lower extremity peripheral arterial disease.6 Twenty-six percent had rest pain without ischemic loss, 33% had minor ischemic tissue loss, and 42% had major ischemic tissue loss. Nearly one-third of patients who presented with any ischemic tissue loss, indicating the presence of critical limb ischemia, had normal or only mildly reduced ABIs.
What You Should Know About Near-Infrared Spectroscopy
Adequate tissue perfusion is a known predictor of wound healing. For reasons mentioned previously, patients may appear to have adequate macrocirculation, but may actually have poor perfusion present at the area of concern. Near-infrared spectroscopy (NIRS) is an emerging technology that has been successfully used to evaluate functional tissue oxygen saturation in the management of diabetic foot ulceration.7-9
One such commercially available NIRS device is the SnapshotNIR (Kent Imaging, Calgary, AB, Canada) (Figure 1). The non-contact SnapshotNIR is handheld, mobile and offers repeatable immediate images that can be used to determine site-specific quantifiable levels of tissue oxygenation. This diagnostic tool utilizes differing optical signals based on the proportion of oxygenated hemoglobin found within the tissue capillary bed. The images obtained allow clinicians to get a better idea of microcirculation and functional blood flow to the wound as well as the surrounding tissues.
Herein, the authors present a case that highlights the ability of the SnapshotNIR to help manage a wound care patient’s treatment course where routine NIVS were inconsistent and undependable.
A 65-year-old Caucasian male presented to the wound center with a two-week history of multiple ulcerations on the left foot with devitalized tissue and necrotic changes of the fourth and fifth toes (Figure 2). He had a positive medical history of insulin dependent diabetes mellitus, coronary artery disease, peripheral vascular disease, hypertension and hypercholesterolemia.
Upon initial evaluation his left foot was cold to the touch with taut and shiny skin, an absence of hair growth, and a non-palpable and non-Dopplerable dorsalis pedis pulse. NIVS were ordered and performed that day. The results were consistent with severe arterial occlusive disease—decreased digital perfusion, monophasic flow in the posterior tibial artery, and an ABI of 0.27. He was immediately referred for vascular intervention that resulted in stent placement. Vascular service informed the patient that even with intervention he had a 75% chance of losing part of his foot or lower leg due to the severity and level of occlusion.
The patient returned to the wound center postoperatively (Figure 3). After discussing his treatment options, including transmetatarsal amputation, the patient was adamant that he wanted to avoid amputation at any level. An aggressive wound care treatment plan was then devised, which included weekly wound care visits, serial debridement of necrotic and devitalized tissue, weekly pulsed acoustic cellular expression (PACER) therapy to all open wounds, and wound dressings consisting of 0.9% cadexomer iodine pad, foam and rolled gauze changed every other day at home by the patient. Baseline SnapshotNIR images were taken in order to track wound progress. The initial NIRS images revealed a 48% oxygen saturation present in the tissues of the medial forefoot ulcer, (Figure 4A) and a 38% oxygen saturation present in the tissues of the lateral forefoot ulcer (Figure 4B).
The patient returned to his vascular surgeon 4 weeks post-op for a follow-up visit. Repeat NIVS were performed, but an ABI was unobtainable. The study results were as follows: left lower leg pressure of >220 mmHg suggests no compressibility of the vessels make absolute segmental limb pressures unreliable, decreased digital perfusion is noted, monophasic flow of the left dorsalis pedis artery, biphasic flow is noted in the left popliteal artery and left posterior tibial artery, left first toe pressure was not obtained due to wound in area of interest. The vascular service was concerned about long term tissue viability based on these results.
Two days later, at the patient’s next wound care visit, NIRS images were again obtained. In contrast to the NIVS, the NIRS images showed a vast improvement in wound tissue oxygen saturation. Oxygen levels had risen to 81% in both the medial and lateral forefoot wounds (Figures 5A and 5B). The overall clinical appearance of the foot had improved dramatically as well. There was no necrotic tissue present, very little devitalized tissue remained, several of the wounds had completely healed and the remaining wounds showed signs of increased granulation tissue with decreased wound area measurements (Figure 6). Based on the results of the NIRS images, we decided we would stay the course and continue with the current wound care treatments. Ultimately, all of the patient’s left foot DFUs completely healed 9 weeks after vascular intervention (Figure 7).
It has been the authors’ experience that use of the SnapshotNIR device to monitor and track tissue oxygenation is an effective aid in the prediction of wound healing potential. Incorporation of this near-infrared imaging technology frequently eliminates the limitations typically found with standard NIVS. In this case, the SnapshotNIR was able to track hemodynamic changes in the wound tissues after revascularization with more precision than NIVS alone. The changes noted in wound tissue oxygenation seen in this case study also correlated better with the clinical appearance of the wound compared to NIVS. Overall, the SnapshotNIR helped to determine that the current treatment protocol for this patient was appropriate and effective. The images obtained by NIRS are immediate and reproducible, providing further advantages when used in the setting of an outpatient wound care center.
The addition of the SnapshotNIR into wound care algorithms may enable clinicians to make better clinical decisions, thus reducing healing times and wound complications.
Windy Cole is an Adjunct Professor and the Director of Wound Care at Kent State University College of Podiatric Medicine in Independence, Ohio.
Stacey Coe is a Clinical Research Coordinator at Kent State University College of Podiatric Medicine.
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