Early Detection of Pressure Injury Using a Forensic Alternate Light Source

Heather Hettrick, PT, PhD, CWS, CLT-LANA, CLWT; Cheryl Hill, PT, PhD, DPT; Patrick Hardigan, PhD


Wounds. 2017;29(8):222-228. 

In This Article

Abstract and Introduction


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.