Early Detection of Pressure Injury Using a Forensic Alternate Light Source

Objective. This study aimed to determine if an alternate light source (ALS) can be used to detect tissue trauma before visible manifestations of tissue injury are evident with the naked eye. Materials and Methods. Ten participants were recruited and gave consent, and 7 completed the study. Researchers examined and photographed participants’ heels in ambient light to establish baseline. A series of photographs using ALS and camera were taken as follows: violet wavelength at 415 nm to 445 nm with yellow lens; blue wavelength at 455 nm to 515 nm with orange lens; and green wavelength at 535 nm to 575 nm with red lens. Participants were examined weekly for 6 consecutive weeks to ascertain skin changes in ambient light and through the ALS. Results. Overt tissue changes were noted when viewed with the ALS and camera compared with visual screens in ambient light. Descriptive statistics were calculated for all wavelengths. Two chi-square tests of independence were run to look for relationships between wavelength and the number of detected injuries (absorption). Conclusions. Participants presenting with nonblanching erythema in ambient light showed significant tissue absorption under ALS and camera, depicting the actual scope and magnitude of the tissue trauma. Participants with scars, areas of previous injury, and pigmentary changes also showed significant absorption at those sites. These combined findings indicate that ALS can detect tissue trauma and areas at risk not readily visible by the naked eye. This noninvasive tool could help identify patients in the early stages of tissue trauma as well as screen for sites of previous injury that are at risk for subsequent breakdown, saving significant health care dollars and improving outcomes and quality of life.

Pressure ulcers or injuries are defined by the National Pressure Ulcer Advisory Panel (NPUAP) as “localized damage to the skin and/or underlying soft tissue usually over a bony prominence or related to a medical or other device. The injury can present as intact skin or an open ulcer and may be painful. The injury occurs as a result of intense and/or prolonged pressure or pressure in combination with shear. The tolerance of soft tissue for pressure and shear may also be affected by microclimate, nutrition, perfusion, comorbidities, and condition of the soft tissue.”¹ Pressure ulcers are a common condition affecting all clinical settings and represent a costly cycle of recurrent hospitalizations, surgeries, office visits, and homecare needs.² Estimates of pressure ulcer prevalence range from 10% to 18% in acute care, 2.3% to 28% in long-term care, and 0% to 29% in homecare.³ According to the Agency for Healthcare Research and Quality, pressure ulcers cost $9.1 to $11.6 billion per year in the United States, with individual patient care costs ranging from $20,900 to $151,700 per pressure ulcer.⁴ 

Early detection of pressure ulcers is vital because of the socioeconomic burden placed upon the health care system, the difficulty in treating later stage ulcers, and the importance of skin integrity and its relation to function, mobility, and quality of life for patients. Currently there are very few clinically useful tools to assist with early pressure ulcer detection and prevention. As far as prevention strategies for pressure ulcers, the standard of care involves the use of a risk assessment tool to identify people at higher risk for developing ulcers in conjunction with interventions for prevention. According to the American College of Physicians’ 2015 Clinical Practice Guideline on Risk Assessment and Prevention of Pressure Ulcers, the current evidence does not show a difference between risk assessment scales and clinical judgement in reducing pressure ulcer incidence.⁵ Further, the guideline indicated there is moderate quality evidence that specific scales can predict which patients are more likely to develop a pressure ulcer (Braden, Cubbin and Jackson, Norton, and Waterlow scales), yet the accuracies of the scales do not differ significantly and all have low sensitivity and specificity.⁵

There is a critical and apparent need to develop new and valid clinical tools for pressure ulcer prevention and early detection. Current prevention interventions include repositioning, skin care (lotions, dressings, management of incontinence), nutritional support, and support surfaces for pressure redistribution (mattresses, overlays, cushions, integrated bed systems).⁶ Given these interventions, there is no standardized or recommended early detection device for pressure ulcers. 

Multiple investigational detection devices have been studied with various results. There is research involving monitoring oxygen saturation in the skin, functional infrared (IR) imaging, enhanced imaging, multiwavelength imaging, tissue reflectance spectroscopy, and even thermal imaging. However, no technique has been proven to be superior.

Forensic science has routinely used ultraviolet (UV) and infrared (IR) as alternate light sources (ALSs) to collect evidence such as latent finger prints, body fluids, hair, fibers, and soft tissue injuries. More recently, ALS has been employed to detect intradermal bruising and strangulation injuries.⁷ Consisting of a powerful light source that emits UV, visible, and IR wavelengths, ALS filters light into wavelengths to visually enhance evidence by light interaction techniques such as fluorescence, absorption, and oblique lighting.⁷ In soft tissue injuries under ALS, blood presents as evidence that darkens (absorption). The visible portion of the electromagnetic spectrum extends from UV wavelengths (190–400 nm) to visible wavelengths (400–700 nm) and to IR wavelengths (>700 nm). These light sources can reveal details in the skin that are invisible under normal white-light illumination. When attempting to detect soft tissue injuries, multiple wavelengths are necessary as different colors penetrate to different depths in the skin. The wavelengths used to detect soft tissue trauma tend to be in the visible portion of the electromagnetic spectrum (violet, blue, green); therefore, ALS does not carry any safety concerns. Examiners using ALS wear goggles as a filter to allow visualization of absorption or fluorescence, and because the wavelengths are so bright, it is recommended the patient wear blackout goggles during the examination to protect their eyes from the luminosity.

The objective of this study is to determine if ALS can be used to detect tissue trauma related to pressure ulcer pathophysiology before visible manifestations of tissue injury become evident with the naked eye. Utilization and implementation of ALS to detect tissue trauma related to pressure ulcer formation has the potential to provide a simple, noninvasive, clinically applicable tool for the detection and prevention of pressure ulcers in the medical field. The development of a valid prevention tool is vital for not only preventative measures but also to understand the clinical course of pressure ulcers and intervention outcomes and further refine health care policies to improve standards of care.

Institutional Review Board approval was obtained at Nova Southeastern University (Fort Lauderdale, FL). A prospective, single-institution, repeated-measures design was employed to collect participant data. The study was conducted at a long-term care facility (MorseLife, West Palm Beach, FL). Potential participants were referred by the Director of Nursing to the Primary Investigator (PI). Study participation was limited to residents who were medically stable with at least 1 intact lower extremity, given that the body region under investigation involved the heels. 

Study equipment included SPEX Forensics Mini-CrimeScope (Edison, NJ); single-lens reflex (SLR) camera; tripod; yellow, orange, and red camera lenses; yellow, orange, and red goggles; blackout goggles (for participants and research assistants); 2 black sheets; 2 foam rolls; white board with dry erase marker; and a photographic grid. The study protocol involved positioning the participants in bed, side-lying on their preferential side. Prior to data collection, the ALS equipment was plugged in to a wall socket and turned on to warm up for maximum luminosity. The camera, tripod, lenses, and goggles were arranged for easy access during data collection.  

Various colored goggles were worn by the PI taking the photographs and Research Assistant 1 operating the light source to view the ALS findings. The violet spectrum was viewed using 415-nm and 445-nm wavelengths with a yellow camera lens and yellow goggles. The blue spectrum was viewed using 455-nm, 475-nm, 495-nm, and 515-nm wavelengths with an orange camera lens and orange goggles. The 455-nm and 475-nm wavelength were also viewed under the yellow lens and goggles, as these combinations effectively showed absorption. The green spectrum was viewed using 535-nm, 555-nm, and 575-nm wavelengths with a red camera lens and red goggles. The colored lenses were used on the SLR camera to photograph the findings viewed with the ALS equipment. The investigators’ goggles and the SLR camera lenses were changed as described above for each of the 3 wavelengths. The participants’ heels were first exposed to the violet, then blue, then green wavelengths through the ALS equipment. When illuminated with each wavelength, the PI took the photograph using the appropriate colored lens to capture photographic evidence of any absorption if present.

The camera aperture was set as low as possible to allow the proper light and ranged from F2.8 to F8. The exposure time was set at 1/100 seconds, and the camera distance from the photographed area was set at 24 in. Data were collected in the evening to allow for minimal natural light and for participant convenience.  

A black sheet was placed under the participant’s legs, and the lower extremities were supported with foam rolls to position and provide comfort during data collection. One roll was placed beneath the lower leg to elevate above the bed surface, and the other was placed between the medial malleoli to separate the feet and heels to maximize viewing area. The second black sheet was used to provide a backdrop and to maximize contrast for the photographs. A white board and photographic grid was placed next to the participant’s feet containing the following information included in for each photograph: position indicated by L or R (left side-lying or right side-lying), participant number, date, and wavelength (nm).

The participant’s heels were photographed first in ambient light. Next, a series of photographs were taken using the ALS equipment and SLR camera under the various wavelengths as described above. Window shades were drawn and room lights were turned off for the ALS data collection. A minimum of 12 photos were taken per participant per week. If absorption was noted, it was documented on the data collection sheet by the respective wavelength.

The roles and responsibilities of the research team were as follows: the PI took photographs and managed the camera; the co-PI recorded findings on data collection sheets; Research Assistant 1 handled the ALS equipment, which provided the light source for data collection; Research Assistants 2 and 3 draped the second black sheet to provide contrast and supported/guarded the participant during data collection. The PI and Research Assistant 1 verified whether absorption was present. It took about 30 minutes to complete data collection per visit per participant. In addition, the PI had full access to all study data and took responsibility for the integrity of the data and the accuracy of the data analysis.

Seven participants completed the study. The findings from the data collection sheets were transferred into an Excel spreadsheet (Microsoft Corporation, Redmond, WA) for statistical analysis. Participant data were entered into the spreadsheet for each week data were collected. Findings were reported for each wavelength and noted as either “M” for missing (photo not clear or unable to obtain), “Y” for yes indicating absorption, or “N” for no indicating no change or no absorption.

Descriptive statistics were calculated for all wavelengths. Two analyses were conducted to look for relationships between wavelength and detecting injury (absorption). For the first analysis, different wavelengths were grouped into 2 categories: (1) 455 Y and 475 Y versus (2) Other. For the second analysis, the groups were extended: (1) 455, 455 Y, 475, 475 Y, 495, and 515 versus (2) Other. To look for differences under both scenarios, 2 chi-square (c²) tests of independence were run to look for relationships between wavelength and the number of detected injuries (absorption). Results are as follows: 

• For the first analysis, the percentage of findings did not differ by grouping (c² [2, N = 1540] = 2.71, P = .257).
• For the second analysis, the percentage of findings did differ by grouping (c² [2, N = 1540] = 11.95, P = .002). Significantly more tissue damage (absorption) was visible under the wavelength grouping 455, 455 Y, 475, 475 Y, 495, and 515 than other combined wavelengths.

Participants who presented with nonblanching erythema and existing ulceration in ambient light (Stage 1 pressure ulcer, Unstageable pressure ulcer) showed significant tissue absorption indicating the actual scope and magnitude of the tissue trauma under ALS. Figure 1 shows a participant’s heels in ambient light with visible tissue erythema. Figure 2 is of the same participant’s heels as viewed under ALS using 415-nm violet wavelength. Note the marked absorption (or darkening) in the tissues indicates the presence of blood in the subcutaneous tissues. This provides greater detail as to the extent of tissue trauma not visible to the naked eye in ambient light. Additionally, in the body region observed for this study, participants with scars, areas of previous injury, and pigmentary changes also showed significant absorption at those sites beyond what was noted in ambient light. Figure 3 depicts a participant’s foot with visible yet faint scar tissue and pigmentary changes in ambient light. Figure 4 shows the same participant’s foot under ALS using 475-nm blue wavelength with a yellow lens. The areas of scar tissue and previous injury are well demarcated and more visible under the ALS than in ambient light alone. This is clinically relevant because noting areas of scar tissue or previous injury is important, as these areas are at greater risk for subsequent breakdown or reinjury due to reduced tensile strength. Figure 4 also depicts yellow patches of fungus that fluoresce under ALS; this was not visible in Figure 3 when viewed in ambient light alone.

These combined findings indicate that ALS can detect tissue trauma not readily visible to the naked eye, providing further details regarding extent and magnitude of tissue involvement. This noninvasive tool could help identify patients in the early stages of tissue trauma as well as screen for sites of previous injury that are at risk for subsequent breakdown.

There are numerous factors associated with increased risk of pressure ulcer development, including people of African descent, of an older age, with a poor nutritional status, who are underweight or malnourished, with physical or cognitive impairment, with incontinence, and with specific medical comorbidities that affect circulation such as diabetes or peripheral vascular disease.⁶ There are several instruments available to assess for the risk of pressure ulcers such as the Braden Scale, the Norton Scale, and the Waterlow Scale; however, there are no reliable tools to detect tissue trauma before visible manifestations are evident on the skin.

A study by Rowan et al⁷ conducted within the field of forensic medicine has relevant implications within this study. Blunt force trauma may not show visual skin effects initially, but the subdermal breakdown may still be occurring.⁷ This is similar to the pathophysiology that takes place with pressure ulcers. This study noted that these changes beneath the skin may be revealed by other tools, and Rowan et al⁷ looked into the detection of previous blunt force injury after the resolution of skin changes were no longer visible to the naked eye. Just as with pressure ulcers, many times the damage is not visible to the naked eye. In their study,⁷ the investigators used an adapted digital camera and a standard Nikon camera (Tokyo, Japan) to photograph 10 volunteers over a 6-month period. There was no statistically significant difference between groups of bruises photographed with both the IR digital camera adapted to capture only IR light and the standard camera with the same lens fitted to it. The 2 groups were not significantly different in regard to detectable skin changes. The use of the near-IR spectrum, with wavelengths longer than the human eye can detect, did not reveal significant evidence of bruising after it had faded from view to both the naked eye and to a standard camera.⁷ While this was an innovative idea, it is implied that further work is needed to create a device that is more effective at detecting subdermal tissue destruction.

Also within the realm of forensic innovation in medicine is the study of ALS in crime scene investigations to detect soft tissue injuries not seen under visible light. In a study by Holbrook and Jackson,⁸ ALS was used to determine its value as a tool for visualizing acute trauma in cases of suspected strangulation. The ALS emits UV, IR, and visible light wavelengths to enhance the visualization of marks on the skin and is also able to reveal bruising and pattern induced by, but not limited to, a shoelace or belt. The Holbrook and Jackson study⁸ provides insight into the use of different wavelengths when utilizing ALS to detect injuries at various depths in the skin. It also presented evidence of use in individuals with darker skin tones, although specifics about the effects of the wound visualization in darker skin tones would be preferable. 

In the methods of Holbrook and Jackson’s study,⁸ different wavelengths are discussed as beneficial in visualizing wound depth. For example, the study determined that most of the bruising caused by strangulation trauma was best seen using wavelengths 415 nm to 515 nm and multiple colored protection goggles. For subcutaneous wounds, the researchers recommend using IR light to best visualize the wound because of the depth of tissue involved. Ultimately, the wavelength used depends on the depth of the injury. Further research needs to be done to determine if different areas of the body affect the quality of the pattern that can be visualized under the ALS. Moreover, the researchers suggested using ALS in medical settings to aid health care providers in detecting tissue breakdown before the visible manifestation of a wound or injury becomes evident in white or ambient light.⁸ Alternate light source has been used in autopsies and during crime scene investigations, and from this work,⁸ it has been proposed to aid living patients as well. Based upon the findings of this study,⁸ it appears that ALS could be an important tool for prevention and early detection of pressure ulcers.

Absorption occurs when light of a given wavelength is absorbed by a molecule’s electrons, and thus the molecule appears darker than the surrounding environment; this absorbed light transfers its energy into the electrons of the molecule. Everyday colored objects, such as paint, cloth, human skin, and plastic, all absorb some wavelengths of light and reflect or transmit others. Without being bound to a particular theory, it is believed that tissue damage which has or may develop into a pressure ulcer/injury may damage deep tissue structures first, including bone, muscle, and tendon, before the skin is disrupted, given that skin has the highest resistance to hypoxia. Accordingly, it is expected that the damage from pressure and/or shear will cause microtrauma and myocutaneous infarction, leading to tissue death and the release of blood products into the tissues. The ALS, using one or more wavelengths, should detect this tissue trauma by the extravasated blood molecules absorbing the light. It is noted that the depth of the skin involved is typically between 3 mm and 7 mm and is therefore reachable at the greatest depth by, at least, IR light, and to varying depths by the shorter wavelengths generated by the forensic ALS as well.

The study and protocol had several limitations. Every attempt was made to voluntarily enroll as many participants as possible with the goal of including 30 participants. Although 10 enrolled, only 7 participants completed the study. Despite participants residing in long term care, many were not interested in participating and others had cognitive limitations negating consent.

With respect to the ALS equipment used in the study, it is rather large and cumbersome given its primary usage at crime scenes. It requires robust fans to keep the equipment cool due to the power needed to provide the necessary luminosity for the respective wavelengths. A follow-up study is being designed to explore the use of a handheld ALS device to determine if the luminosity provided by the handheld device is powerful enough to detect tissue trauma changes as shown with the equipment used herein. A handheld ALS device may provide a simple, user-friendly, and clinically relevant screening tool for early detection of pressure injury.

The study protocol inherently had several limitations. To maximize visualization with the ALS, data were collected in the evening to reduce the potential for natural light to interfere with the ALS. This was also more convenient for the participants. Black sheets were employed to isolate the participants’ heels for photography. The protocol and equipment used in this study required 5 people to collect data: 1 person to manage the ALS equipment, 1 to take the photographs, 1 to record the data, and 2 to manage the sheets and maintain participant positioning. Further, the ALS equipment used for this study is costly and may not be financially feasible in its current format for clinical use. This further justifies the need for an additional study to explore the use of less expensive, handheld ALS devices.  

Because ALS utilizes different wavelengths than white light, it can reveal acute trauma and interstitial bleeding of the skin that would otherwise be invisible to the naked eye. Crime scene investigators and forensic science utilizes ALS readily, but it has only recently been utilized as a tool in medicine. As a skin and wound assessment tool, ALS appears to be beneficial in identifying early destructive tissue changes as well as sites of previous injury much sooner than just using white or ambient light and the naked eye. The ability to witness negative or deleterious tissue changes before visual and physical manifestations appear on the skin is a breakthrough in pressure ulcer detection.

The ALS device has the potential to be used as a quick screening tool to assess the overall health of a patient’s skin. It is well established that early detection of tissue trauma can lead to better outcomes for patients while reducing health care costs. Alternate light sources provide a noninvasive approach to early detection and intervention of pressure ulcers, resulting in improved health outcomes and quality of life for patients while potentially saving substantial resources spent on managing pressure ulcers. Alternate light sources may prove invaluable in clinical practice for detecting early tissue trauma that is time efficient, user friendly, and cost effective.