Authors: Juan Torregrosa Valls, Andreu Jaume Rigo Monserrat y Julio A. Ceniza Villacastín

Introduction

Ulcers, defined as "A lesion or break in the continuity of the skin and/or underlying tissue as a result of various internal, external, and patient comorbidity factors," present a significant challenge in the field of healthcare. These wounds, which can be acute (short duration) or chronic (long evolution with alterations in any of the different healing phases in time and form), affect a wide range of patients, especially those with comorbidities or conditions such as chronic venous insufficiency, peripheral arterial diseases, neuropathy caused by diabetes mellitus, or autoimmune diseases, among others.

The diagnosis, classification, and treatment of long-term wounds are essential to improve the quality of life of patients and reduce associated costs, both economically and humanly.

The most common types of long-term wounds faced by professionals in both primary care and hospitals are lesions with venous, arterial, or mixed etiology, pressure ulcers, and neuropathic or neuro-ischemic lesions within the "complex context of the diabetic foot." Each type of lesion requires individualized treatment and a set of specific resources.

Context of Thermography in Wound Treatment

Infrared thermography is based on detecting thermal radiation emitted by an object, allowing the visualization of temperature patterns that can reveal underlying processes in tissues. This technology, applied to medicine, offers significant advantages in terms of speed, non-invasiveness, and precision in detecting changes in wound status. Thermography applied to wounds, especially in the context of long-term lesions, is based on measuring the skin's surface temperature to identify and monitor inflammatory processes, infections, and blood perfusion status.

Infrared thermography offers multiple benefits in the clinical context, including:

• Early Detection of Infections and Necrosis: Infrared thermography allows the early detection of complications, such as incipient or deep infections, which may not be visible to the naked eye. In the case of diabetic feet, for example, infrared thermography has proven useful in identifying areas of high temperature that may indicate the presence of infections before visible ulcers develop.
• Identification and Evaluation of Inflammatory Processes: Measuring the skin's surface temperature allows us to detect an increase in temperature in inflamed areas due to increased blood flow and the local immune response. It also helps assess the wound's progression and evaluate the treatment's response by comparing different images taken over time. This allows for more precise visualization of inflamed areas, which may be related to pain, and infected wounds, as inflammatory and infectious processes cause a local temperature increase.
• Early Detection of Nervous or Neuropathic Alterations: Serial temperature control allows the early detection of peripheral nervous system alterations in patients with diabetes mellitus or neurological disorders. The onset of neuropathy directly or indirectly affects skin thermoregulation, often resulting in a sustained increase in temperature compared to the contralateral region.
• Monitoring the Healing Process: Monitoring wound temperature allows evaluating the effectiveness of the applied treatment. Wounds that are healing correctly usually show a gradual decrease in temperature, approaching the normal temperature of the surrounding skin (±32ºC). Conversely, an increase in temperature or stabilization of this increase over time may indicate an infection or a complication in the healing process.
• Evaluation of Blood Perfusion and Venous Insufficiency: Thermography is also useful for assessing blood perfusion in the skin. Adequate perfusion is essential for wound healing as it ensures the supply of oxygen and nutrients needed for tissue repair. Thermography can identify areas with poor perfusion where there is a decrease in local temperature, helping professionals adjust treatments to improve blood flow and, consequently, healing. Additionally, one of the great utilities of this technology is in detecting and assessing venous insufficiency, where the increase in skin surface temperature due to the different pathophysiological mechanisms in this condition makes thermography a very valuable tool for its assessment.
• Prevention of Pressure Ulcers: In the hospital and home care settings, thermography is used to prevent pressure ulcers. By identifying areas with temperature increases indicating pressure, excessive friction, shear, or a sustained inflammatory state, preventive measures can be taken to redistribute pressure and avoid ulcer formation.
• Objectivity and Precision: Unlike subjective visual methods, thermography provides quantifiable and reproducible data, improving the accuracy of diagnosis and the assessment of healing progress. This precision greatly depends on the type of camera used and the applied protocol. Currently, the accessibility of cameras connected to smartphones as well as professional ones (see images) allows more professionals to use thermography.

Common Types and Thermal Responses

Wounds, particularly long-term lesions, often present alterations in local temperature due to different processes. The thermal response in wounds can manifest as:

• An increase in temperature in the affected area and/or the perilesional skin due to inflammation, which is a natural body mechanism to combat infection and facilitate healing. Additionally, it may result from alterations in various mechanisms controlling surface temperature, such as Arteriovenous Shunts in diabetic neuropathy.
  • This temperature increase is mainly observed in the perilesional skin of incipient pressure ulcers of grade I, II, in venous lesions due to the skin's inflammatory process, and in lesions with a neuropathic component as a result of vasomotor reflex and nitric oxide release.
• A decrease in temperature in the wound bed due to the loss of all cutaneous insulation mechanisms or the progressive necrosis of different tissues, allowing excessive evaporation or alteration of local blood flow (hypoxia) and therefore an alteration in temperature maintenance.
  • This temperature decrease is mainly observed in the wound bed of ischemic lesions, in the bed of venous lesions caused by the effect of present fibrin, or in pressure ulcers grade III and IV due to necrosis and alteration of deep tissues (fat, tendons, ligaments, muscles, and bone).

The temperature difference between the wound bed and the perilesional region (±3cm around the wound) can be a crucial indicator of the presence of infection. According to several authors, a significant increase of ±2ºC in this temperature difference may indicate the need for interventions aimed at reducing and controlling the bacterial load or changes in treatment.

Temperature variations can be accurately detected using infrared thermography, allowing healthcare professionals to assess the severity and status of the wound..

Practical Applications

Some practical applications could be:

• Wound Care: In wound care, especially in diabetic foot ulcers, TI allows the early detection of neuropathy, infections, and inflammations. Thermal images can identify temperature differences between the wound bed and perilesional skin, providing valuable information about the wound's condition and the need for medical intervention.
• Treatment Evaluation: In cases where the pre and post temperature difference is significant. In revascularization interventions, the effect of the intervention can be clearly observed with local temperature changes. Additionally, we can assess the local effect of different dressings and barrier creams used in wound treatment; excessive temperature may suggest excessive occlusion when good moisture control is sought, allowing treatment optimization.
• Surgery: In the surgical field, TI is useful for evaluating the viability of skin flaps and detecting infections at the surgical site. For example, in reconstructive surgery, TI can monitor blood perfusion in real-time, ensuring transplanted tissues receive an adequate blood supply. Additionally, with new techniques like "seal grafts," the viability of their application can be assessed.

Conclusions:

• Thermography is a non-invasive and painless technique that presents itself as an innovative tool for evaluating wounds and their comorbidities.
• In wounds, the use of a meticulous and systematic protocol is essential to obtain accurate and reliable data.
• Understanding and evaluating temperatures and their local and contralateral thermal asymmetries are fundamental to obtaining relevant information about the wound's status or the pathology under study.
• It is a technology that, although the results obtained cannot be used alone for diagnosis, provides very valuable information to guide professional evaluations and streamline subsequent treatment..

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