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The Role of Near-Infrared Spectroscopy (NIRS) in Treating Hard-to-Heal DFUs
Diabetic wounds, particularly those classified as diabetic foot ulcers (DFUs), are a common complication of diabetes mellitus. Approximately 15% of patients diagnosed with diabetes will develop a foot ulceration at some point, in which approximately 14% of DFUs lead to some level of amputation.1
A hallmark feature of DFUs is impaired healing due to various factors, including neuropathy, poor blood circulation, and immune system dysfunction.2 The pathophysiology of hard-to-heal diabetic foot wounds involves a complex interplay of ischemia, infection, and inflammation. Reduced blood flow to the affected area hampers the delivery of essential nutrients and oxygen, leading to delayed wound healing and increased risk of infection.3 Addressing diabetic foot ulcers with appropriate intervention measures could ultimately assist in lowering the rate of further diabetes complications in patients, such as amputations and morbidity in the long term.4
Near Infrared Spectroscopy Imaging and Perfusion
Despite the complexities of wound healing, one important requirement is not simply the movement of blood through the lower extremity, but the perfusion of oxygenated blood to the wound. Clinicians have several tools to evaluate limb blood flow, including the ankle-brachial index (ABI), infrared spectrography, and laser Doppler flowmetry.
Near-infrared spectroscopy (NIRS) imaging has gained attention for its ability to measure tissue oxygen saturation in both the wound bed and periwound area. NIRS is a noninvasive optical technique that measures the absorption and scattering of near-infrared (IR) light by tissues. The fundamental principle behind NIRS involves the interaction of light with tissue chromophores, such as hemoglobin and myoglobin. These chromophores absorb light at specific wavelengths, and the amount of light absorbed can be correlated with the concentration of these molecules in the tissue.5 NIRS can provide real-time data on tissue oxygenation and hemodynamics, offering valuable insights into the perfusion status of wounds.
NIRS has been used in a wide variety of industries including agriculture, food, and pharmaceutical. The use of NIRS in the medical field dates as far back as 1977, when Jobsïs studied the changes in oxygenated and deoxygenated hemoglobin for the analysis of brain function.6 This landmark study found that we can measure oxygenation of tissue noninvasively. Since then, physicians have utilized NIRS in the treatment and research of cancers, neurological conditions, heart disease, and diabetes mellitus, and now in the management of lower extremity wounds.7
Physicians can utilize NIRS in the treatment course for a variety of wound types including chronic diabetic wounds, venous leg ulcerations, traumatic wounds, post-surgical incisions, and can also augment treatment of wounds undergoing hyperbaric oxygen therapy (HBOT).1 Through the data obtained from NIRS, physicians can analyze tissue oxygenation levels, which can indicate if a wound has the capability to heal. When interpreting this data, it is vital to understand alternative causes of lower tissue oxygenation aside from vascular perfusion8; it is important to address other factors such as infection, the general health of the patient, offloading areas of concern, and how frequently clinicians perform debridements for nonhealing wounds.
Wound healing is composed of a multi-stage process including inflammation, proliferation, and maturation.1,9 The inflammation state begins following wound debridement and the latter stages follow during the healing journey.8 Incorporation of NIRS during wound debridement clinic visits can provide valuable data for clinicians in efforts promote wound healing, as hard-to-heal wounds oftentimes arrest in the inflammatory stage, where there is an increase in oxygenated blood delivered to the wound site due to angiogenesis.1,8 IR thermography offers significant potential as a complementary technique for diabetic foot assessment. Elevated temperature, for instance, is a reliable indicator of inflammation and/or infection.10
A Guide to Clinical Application of NIRS
Debridement is crucial in treating chronic wounds, such as diabetic foot ulcers, by removing fibrin, necrotic debris, and stimulating the hemostatic phase, which facilitates the healing process. Clearing these barriers promotes granulation tissue formation and supports angiogenesis and vasculogenesis, creating a more favorable environment for wound closure.11 By performing NIRS imaging pre- and post-debridement, clinicians can assess and confirm the effectiveness of the intervention, aiding in decision-making and improved wound management outcomes.
In our wound care center, we utilize NIRS and IR thermography imaging to monitor wound healing by tracking patients’ oxygenation and skin surface temperature levels in both the wound and periwound areas throughout their treatment journey. This longitudinal tracking of the healing trajectory helps us better understand each patient’s healing potential and their response to treatment, allowing for more informed and personalized care. We begin by capturing predebridement images using a handheld mobile device that collects multispectral NIRS, IR thermal, and digital images in under one second (Mimosa Pro, Mimosa Diagnostics, Inc.).
This mobile NIRS imaging device allows us to assess areas of the wound with insufficient oxygenation (Figure 1, predebridement). From these images, we can perform targeted debridements to improve oxygen supply to the affected areas. The device enables us to highlight specific wound regions to analyze both oximetry and thermal data. By identifying areas with low oxygenation, we can debride nonviable tissue more precisely. We then take postdebridement images (Figure 1, post-debridement), allowing us to evaluate whether the procedure has successfully increased oxygenation in the wound.
One can also use this technology in conjunction with other wound care products such as biologic grafts, wound care dressings, and hyperbaric oxygen therapy.9 By comparing pre- and posttreatment measurements, clinicians can assess whether interventions are improving tissue oxygenation and blood flow, thereby adjusting treatment protocols based on objective data. In our clinic, we have been collecting images before and after HBOT to assess treatment response and longitudinally track the healing trajectory. See Figure 2 for the longitudinal tracking after HBOT for the same patient shown in Figure 1.
From the patient’s perspective of treatment for their hard-to-heal wounds, NIRS offers comprehensible visual data to formulate a better understanding of their healing progression. Oftentimes, it is difficult for patients to gauge how their wounds are improving after every visit or understand why a wound might have stalled in healing. Typical assessment of wounds involves its measurements over time, odor, drainage, and pain level.9 With a NIRS device, clinicians can help patients better visualize the healing process by showing them real time imaging about the oxygenation levels of their wound in addition to the other physical findings.9 By having easily comprehensible and readily available imaging, it allows patients to be active participants in their own health.
As wound healing continues to be a challenging aspect of treating diabetic foot ulcers, physicians have used NIRS to predict wound prognosis in this population with multiple studies in the literature. An observational study by Lin and colleagues in 2020 focused on NIRS in a population of patients with diabetes with and without peripheral arterial disease (PAD).12 Another subgroup of this study was patients with PAD who underwent angioplasty. This study aimed to assess the effect of Buerger exercises on healing potential of DFUs using wearable NIRS.
The results of this study highlighted some expected results such as high concentration of oxyhemoglobin (HbO2) and tissue blood volume (HbT) in the group with DFU with no PAD and lowest in the group with DFU with PAD but no intervention.12 It also revealed that most non-healing patients in the two groups with PAD had higher HbO2, Hb, and HbT concentration and lower StO2 at rest. It implied that populations with PAD experience inflammation that results in higher blood flow and oxygen consumption to their lower extremities. Additionally, the nonhealed patients in the group with DFUs without PAD had higher HbO2 and HbT concentrations than the patients who healed at the end of the study.12 Despite having higher oxyhemoglobin and tissue blood volume, these patients did not heal as quickly. This finding reiterates that there may be other factors involved in wound healing.
Although further research is necessary to efficiently predict wound prognosis using NIRS, these earlier studies are useful in assisting in mapping important patterns in wound healing. These patterns in turn can assist clinicians with targeted therapeutic treatments for certain patient populations.
In Conclusion
Near-infrared spectroscopy represents a valuable tool in the management of nonhealing diabetic wounds, offering real-time insights into tissue oxygenation and blood flow. Its noninvasive nature and ability to provide objective data make it an attractive option for clinicians seeking to optimize wound care and improve patient outcomes. While challenges remain, ongoing research and technological advancements hold promise for further enhancing the role of NIRS in diabetic wound management. By integrating NIRS into clinical practice, healthcare providers can aim to better address the complex needs of patients with diabetes.
Anthony Tickner, DPM, FRCPS, FACCWS, FAPWCA, FAPWH, FADFS, is the Medical Director at Saint Vincent Hospital Wound Healing Center in Worcester, MA.
Jeesha Patel, DPM, is a second-year resident at Saint Vincent Hospital Wound Healing Center in Worcester, MA.
Rida Kayani, DPM, is a second-year resident at Saint Vincent Hospital Wound Healing Center in Worcester, MA.
Allison Salvadore, DPM, is a first-year resident at Saint Vincent Hospital Wound Healing Center in Worcester, MA.Chandni Parmar, DPM, is a first-year resident at Saint Vincent Hospital Wound Healing Center in Worcester, MA.
References
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