Advanced Technologies for
Skin and Tissue Assessment
Published online: ?? ??? 2026
Suggested citation
National Pressure Injury Advisory Panel, European Pressure Ulcer Advisory Panel and Pan Pacific Pressure Injury Alliance. Advanced Technologies for Skin and Tissue Assessment. In: Prevention and Treatment of Pressure Ulcers/Injuries: Clinical Practice Guideline. The International Guideline: Fourth Edition. Emily Haesler (Ed.). 2026. [cited: download date]. Available from: https://internationalguideline.com.
Introduction
The visual and tactile assessment performed by clinicians at the bedside is the most common method of assessing skin and tissue and detecting signs of pressure injury (PI) (see guideline chapter: Skin and Tissue Assessment). Although there is mixed evidence on their reliability and reproducibility, visual and tactile clinical assessment techniques for assessing skin and soft tissues are feasible, accessible and do not require advanced resources. However, the average clinician experiences several challenges in accurately assessing skin and soft tissues and detecting pressure-induced injury. This includes:
skin pigmentation or skin conditions that obscure visual evidence of early pressure damage (e.g., rashes, moisture-associated skin damage, mottling, etc.). This includes the purple or maroon color that accompanies suspected deep tissue pressure injury (sDTPI), which may be missed entirely in dark skin tones (1),
environmental factors (e.g., lighting, positioning, etc.) that can impact visibility, and
varying knowledge and clinical skills of health professionals performing visual and tactile skin and tissue assessment.
Additionally, latency between the initial onset of pressure damage and the subsequent manifestation of a visible and clinically diagnoseable PI at the skin's surface has challenged clinical practice (2, 3, 4).
Early detection of PIs using technologies (e.g., thermography and focal edema measurement) is an innovative and promising field of research and practice with a high potential to improve clinical decision making and PI prevention planning and implementation. Several new technologies are available that are intended to assist clinicians to identify early skin and tissue injury that occurs before it is visible to the naked eye. These technologies measure one or more of the early changes that occur in pathophysiology associated with PI. The following pathological changes can be measured using various advanced technologies (5, 6, 7, 8):
inflammation, which might be measured with thermographic imaging that detects temperature differentials (e.g., higher temperature in relation to normal surrounding tissues),
sub-epidermal edema, which might be measured with bioimpedance or ultrasound that detects serial changes in values,
ischemia and infarction, which might be measured with:
thermographic imaging that detects temperature differentials (e.g., focal areas of decreased temperature in relation to normal surrounding tissue) or
a variety of devices that detect changes in tissue oxygenation and perfusion (i.e., blood flow), and
tissue destruction, which might be measured with:
thermography that detects areas of cooler temperature in relation to normal surrounding tissue, and
ultrasound that detects structural changes in the tissue layers.
However, the above pathological changes can also occur with conditions other than pressure-induced tissue damage. Therefore, changes in the measures of pathological changes detected with advanced technologies should not be considered in isolation as definitive diagnostic signs of pressure-induced skin and tissue injury.
Diagnosis of a PI can only be made in the presence of the visibly detectable signs and symptoms specified in an acceptable classification system (See guideline chapter Pressure Injury Classification).
Considerations in evaluating evidence for diagnostic/assessment testing
The systematic summary and appraisal of evidence related to clinical testing methods, including those developed to detect early subclinical signs of pressure injury, is challenging, because both the measurement properties of the test results and the potential impact of the test results on clinical practice—and ultimately on clinical outcome measures—must be evaluated.
There are no perfect ‘gold standard’ reference tests for early pressure-induced tissue injury. However, since these tests are intended to measure early subclinical pressure-induced tissue damage (i.e., tissue damage that is not sufficiently severe to present definite or readily observable symptoms), a strong association with subsequent development of PI can be assumed.
Most technologies for detecting early pressure-induced injury examine the differences in measurements between a pressure-loaded anatomical location (e.g., a bony prominence) and adjacent or contralateral normal tissue. Protocols for these comparisons should be developed in the early research and testing phases and used to ensure accuracy and reproducibility in clinical settings.
With no ‘gold standard’ reference tests, several considerations need to be made in making recommendations for the use of diagnostic/assessment tests. The GRADE Working Group (2019) (9) recommends linking available evidence on testing, implementation of interventions informed by the testing and clinical outcomes. The chain of linked evidence used to evaluate, organize and summarize the evidence on advanced technologies for evaluating subclinical early pressure-induced injury requires reviewing the evidence in four steps:
Evidence on the test properties,
Evidence on clinical performance with respect to reliable administration of the test,
Evidence on clinical performance with respect to test results being applied to the development of PI prevention interventions, and
Evidence on clinical performance with respect to the impact of this on PI occurrence.
This linked chain of evidence is outlined in Figure 1 and discussed below.
Figure 1: Chain of linked evidence used to evaluate tests of early pressure-induced injury (adapted from Schünemann et. al., 2019 (9))
1: Evidence on the test properties: Does the test accurately and reliably measure one or more tissue responses to early pressure-induced injury?
Prior to clinical testing, the basic properties of the diagnostic test should be examined. Some questions that are relevant to explore include:
Is the diagnostic test logically linked to our knowledge of pressure injury etiology?
In controlled conditions, does the test accurately measure one or more of the pathophysiological changes noted above (i.e. inflammation, sub-epidermal edema, ischemia and infarction or tissue destruction).
In controlled conditions, are the test measurements reliable (e.g., consistent and repeatable) and free from absolute measurement error?
If the answer to any of these questions is ‘no’, or if there is insufficient evidence, the diagnostic test properties might be considered inadequate for use in clinical settings.
2: Evidence on clinical performance with respect to reliable administration of the test: Can the test be administered reliably under clinical conditions?
The clinical performance of the test refers to whether the results of the diagnostic test are reliable when the test is administered in usual clinical situations. Some questions that are relevant to explore with consideration to the context of the education, training and experience of clinical staff include:
What is the inter-rater and intra-rater agreement and reliability among end users?
Is there a standard protocol for performing the test?
Does the test have clear criteria for differentiating normal and abnormal results (e.g., cutoff scores, image analysis parameters).
What is the diagnostic and prognostic accuracy?
Do the test results supplement the clinician’s understanding of the individual’s condition? (Note: this is an intermediate outcome that is sufficient to answer clinical questions).
If the test is not used to alter prevention plans, does the test “predict” visible PI outcomes? (Note: In most clinical settings, standard care includes baseline implementation of PI preventive strategies, creating some confounding with respect to predictive properties).
3: Evidence on clinical performance with respect to test results informing the development of PI prevention interventions:Are test results used to alter preventive interventions?
In most situations, standard care for individuals at risk of PI development includes baseline implementation of PI preventive strategies. Alterations to the PI prevention plan based on the diagnostic test results can include initiation, modification or escalation/enhancement of preventive interventions. Interventions may also target a specific anatomical location of concern. Protocols for enhancement of PI preventive care should be developed and compliance should be monitored.
4: Evidence on clinical performance with respect to the impact of implementation of test-informed PI interventions on PI occurrence: Do rates of PI occurrence decrease?
The endpoint for clinical evaluation of a diagnostic test is whether the use of the test to inform care provision ultimately results in a favorable clinical outcome, in this case, a decrease in PI occurrence. Decrease in PI occurrence was selected by the Guideline Governance Group as the core outcome measure to evaluate all preventive interventions because it was identified as an outcome of critical importance in a Delphi survey (10) that underpinned the development of a core outcome set for PI prevention trial:
Technologies to assess non-visible or early pressure-induced skin and tissue injury
The clinical questions explored diagnostic/assessment testing technologies that are currently available for clinical use at the bedside. These technologies serve as an adjunct to standard skin and tissue assessment (see the guideline chapter Skin and Tissue Assessment), and should not be considered a replacement to performing a visual and tactile assessment of the skin and soft tissues (5). Technology-based skin and tissue assessment results should be evaluated within the overall context of the individual’s condition using clinical judgement.
More information
STA3: Recommendation
We suggest using results from a device that detects and measures focal edema as an adjunct to a visual and tactile skin and tissue assessment in individuals at risk of pressure injuries, where the technology is available and feasible to use.
Conditional recommendation; very low certainty of evidence
Clinical question: Should measurements of focal edema (e.g., subepidermal moisture) be used in addition to standard skin and tissue assessment for identifying early non-visible tissue changes consistent with early signs of pressure-induced injury to inform PI prevention and reduce PI occurrence?
Implementation considerations
Always use a PI classification system to diagnose PIs. Do not consider the detection of focal edema (i.e., delta cutoff score of ≥ 0.6) as diagnostic of a PI.
Device results should be evaluated within the context of the individual’s overall condition and based on clinical judgement and the goals of care.
Provide appropriate training to the interdisciplinary team before introducing a device that measures focal edema to the facility to promote consistency in measurement methods over time and between users.
Develop local health service-based guidance on the selection of individuals for technology-enhanced skin and tissue assessment, identifying when an individual should receive testing and how results will be integrated into care pathways. Protocols should also identify when use of a focal edema measurement device is no longer required (e.g., the individual becomes more mobile).
Monitor trends in the delta cutoff score over time for individuals identified as being at risk of PIs (43). When the delta cutoff score is ≥ 0.6, use established protocols and clinical judgment to increase/enhance PI preventive care. Target the anatomical location affected when selecting PI preventive interventions.
Explore strategies to incorporate testing and implementing the results into staff workflow and reporting systems (42)..
Implementation considerations for special populations
-
When available, a device to measure focal edema might offer an enhanced skin and tissue assessment to identify early tissue damage that is obscured (e.g., erythema or purple/maroon presentation of a DTPI).
Evidence Summary
In making this recommendation, the Guideline Governance Group considered evidence at each of the steps in the chain of linked evidence to evaluate tests of early pressure-induced injury (see Figure 1).
Evidence on the test properties
Inflammation and edema are early responses to tissue injury in an anatomical location that is subjected to pressure loading (6). Non-loaded surrounding tissues are usually not affected. When a small imperceptible voltage current is applied to the skin and reaches subepidermal layers the current moves through normal tissue with little to no resistance; however, there is resistance (i.e., bioimpedance) in tissues with inflammatory-mediated increases in interstitial fluid (i.e., focal edema). There are measurable differences between normal tissue and tissue with focal edema (11). Bioimpedance indicating focal edema increase with the progression to a visibly detectable PI (12, 13).
Proof of concept is demonstrated in a study in which an ex-vivo porcine model was used to test the ability of a bioimpedance measurement device to detect subepidermal focal edema in relation to normal tissue. The study (14) also examined the effects of increasing amounts of edema on bioimpedance measurements. One mL of isotonic fluid was injected at a depth of 3 mm beneath the surface of the skin. There was a statistically significant difference in bioimpedance measures between areas of experimentally induced focal edema and adjacent normal tissue (p = 0.0052). There were also statistically significant (p < 0.001) increases in bioimpedance corresponding with several subsequent additional fluid injections, indicating a dose-response relationship (14).
Delta cutoff scores and protocols for measuring bioimpedance in PIs and normal surrounding skin have been established. In a cross-sectional study (15) set in a nursing home with 125 individuals diagnosed with PIs and intact skin and 50 individuals without PIs, bioimpedance measures were taken at the center of the PI (or bony prominence in control subjects). For comparison, bioimpedance measurements were also taken in surrounding tissue at designated anatomical zones/rings surrounding the center of the PI or bony prominence. Center bioimpedance was compared to multiple measures at the surrounding tissue. Bioimpedance discriminated well between individuals with and without PIs at the sacrum location, but less adequately for the heel. In the group with PIs, sensitivity ranged between 76% and 91% and specificity ranged between 32% and 90% depending on delta cutoff score, anatomical location and the algorithm used for analysis of data. A delta cutoff score of ≥ 0.6 was selected to favor sensitivity over specificity (15).
At a delta cutoff score of ≥ 0.6, sensitivity was 86.82% (95% confidence internal [CI] 79.74% to 92.13%), specificity was 88.00% (95% CI 79.98% to 93.64%) and the area under the receiver operator curve [AUROC] was 0.9181 (95% CI 0.8817 to 0.9545, p < 0.0001).(15) When using fewer control points, sensitivity was 82.17% (95% CI 74.46% to 88.35%), specificity was 51.00% (95% CI 40.80% to 61.14%) and the AUROC was 0.7809 (95% CI 0.7221 to 0.8397, p < 0.001) (15).
Diagnostic accuracy studies have reported heel and sacral measurements using a device to measure focal edema (delta ≥ 0.6 as cutoff for abnormal values) (2, 15, 16). Comparisons have been made between measurements and a visual inspection leading to a categorization of “skin reddening”, Category/Stage I or II PI, or suspected DTPI. Sensitivity ranged from 62% to 91% (depending on the categorization used for the visual inspection and the anatomical location). Specificities ranged from 32% to 86% (2, 15, 16). Area under the receiver operator curve (AUROC) varied from 62.5% (95% CI 61.5% to 63.0%, p < 0.001) (16) to 0.9181 (95% CI 0.8817 to 0.9545, p < 0.0001) (15). An observational study (17) conducted in pediatric populations (aged 8 to 16 years) showed similar patterns in focal edema measurements and their relationship to skin redness and Category/Stage I PIs as in adult populations (17).
In making a conditional recommendation to use results from a device that measures focal edema to augment a standard skin and tissue assessment, the Guideline Governance Group balanced the reported data on sensitivity and specificity of measurements for the delta cutoff score of ≥ 0.6. There are strong and positive associations between abnormal focal edema readings and subsequent clinically visible full pressure ulceration. This indicates that the test results are highly sensitive to detect early non-visible PI. At the same time, reported specificities are low, including values below 50%. This indicates that the test procedures and test results may be unable to correctly identify those individuals who are not affected by early tissue damage in some clinical situations and/or at some anatomical locations. High sensitivity is important to correctly identify individuals with early tissue damage (true positives) because this information can assist in reducing PI occurrence. However, when those individuals without early tissue damage (true negatives) are not adequately distinguished by the test, there may be implications for resource allocation with respect to device acquisition and integration with existing systems (5, 18), possible over-testing, and over-implementation of PI preventive strategies. This is a consideration in determining when and in what populations to use devices that measure focal edema. Health services are encouraged to develop use cases, policies and procedures at the local level to balance early identification of individuals who require enhanced PI preventive care with over-servicing.
Inter-rater and inter-device reliability were tested in controlled laboratory conditions with three trained operators testing four anatomical sites on 31 normal volunteers. Intraclass correlation coefficient (ICC) for devices ranged between 0.828 (95% CI 0.805 to 0.850) and 0.957 (95% CI 0.950 to 0.963). ICC for trained operators (inter-rater reliability) ranged between 0.848 (95% CI 0.827 to 0.867) and 0.961 (95% CI 0.955 to 0.967) (19). Another controlled comparison of two devices in healthy volunteers (with head of bed elevation at 60) showed good agreement at baseline and at most (but not all) time points in a repeated measures design. Differences were not clinically significant (20).
Accuracy and reliability in dark skin tones have also been tested (12, 21, 22). Detection of focal edema was associated with visual detection of Category/Stage I PIs and Category/Stage II+ PIs one week following the focal edema detection in individuals in a nursing home setting with both light and dark skin tones. The association was stronger in individuals with dark skin tones (12). In an observational study conducted in a surgical intensive care unit (ICU) in which ethnicity was used as a proxy for skin tone, serial tests for focal edema were completed for 69 individuals (42% African American, 52% White). There were no significant differences for focal edema results or new PI development based on ethnicity.(21) In a third study (22), focal edema was evaluated in 140 individuals in an adult coronary care unit (90 pre-intervention, 50 post intervention, approximately 70% of subjects in each group were African American). PI prevention plans were enhanced for individuals with a delta cutoff score ≥ 0.6. Eight individuals in the pre-intervention group developed PIs, all of whom were African American. There were no hospital-acquired PIs (HAPIs) in the post intervention group (22).
An important consideration in making a conditional recommendation for using a device to measure focal edema to augment a visual and tactile skin and tissue assessment is the potential to enhance assessment of dark toned skin. Visual signs of early tissue damage (e.g., erythema) may not be detectable as early in individuals with medium and dark skin tones as in light skin tones, increasing the potential value of using a device that can detect subclinical pressure-induced tissue damage. Noting the disparity in the severity of PIs observed between individuals with different race/ethnicities (23, 24) and with different skin tones (18), the Guideline Governance Group suggest that using a device to measure focal edema might play a role in reducing health inequities, if the technology is available in the clinical setting.
Evidence on clinical performance with respect to reliable administration of the test
Reliability of contemporary devices to measure focal edema when used in clinical settings (i.e., used and interpreted by health professionals at the bedside) was not reported. Several studies (19, 20) demonstrated that testers achieve good inter-rater reliability after undergoing training, suggesting translatability to practice.
Prognostic accuracy can be estimated from studies in which focal edema was measured and correlated with subsequent occurrence of PIs (but without implementing changes to PI management plans based on the delta cutoff score). It should be noted that the baseline care provided in these studies included standard PI prevention interventions, which prevents calculation of true estimates of sensitivity, specificity and AUROC. A narrative systematic review (4) reporting four studies (2, 25, 26, 27) reported a mean sensitivity of 72% (standard deviation [SD] 23.05) and mean specificity of 51.96% (SD 20.2%) (4). A systematic review and meta-analysis reported that a delta cutoff score ≥ 0.6 increased the risk of PI cumulative incidence (risk ratio [RR] 19.53, 95% CI 9.14 to 41.72).(28) A study conducted in the ICU reported a sensitivity of 89.2%, specificity of 77.8% and AUROC of 0.88.(29) The risk of bias in these studies is unclear to high.
Several authors (29, 30) compared the prognostic accuracy of focal edema detection to the prognostic accuracy of PI risk assessment tools. The AUROC was usually better for focal edema detection. These results should be interpreted cautiously. Focal edema is a sign that early pressure-induced injury has occurred, while a risk assessment tool identifies risk factors that increase the likelihood of future PI development. The clinical utility of a risk assessment tool lies in its application to preventive planning through the identification and address of modifiable risk factors rather than as a prognostic tool (see the guideline chapter on Pressure Injury Risk for further discussion). Focal edema detection is specific to an anatomical site and can be used to prompt the immediate enhancement of anatomically-targeted interventions. It should be noted that the time lag between detection of focal edema and visually detectable and diagnoseable PIs provides a window of opportunity for enhanced prevention. One meta-analysis (4) reported that the mean time from detection of focal edema to diagnosis of a PI was 4.61 days (95% CI 3.94 to 5.28, p = 0.0001) and a second meta-analysis reported a pooled time lag of 4.08 days (95% CI 1.09 to 7.08) (28).
Evidence on clinical performance with respect to test results informing the development of PI prevention interventions, and the resulting impact on PI occurrence
A meta-analysis conducted for this guideline included eight studies (one randomized study and six non-randomized comparative studies) (22, 31, 32, 33, 34, 35, 36, 37) that reported on the impact of using a device to identify/measure focal edema and using the result to inform the adjustment/enhancement of PI prevention care. The studies compared using a device to measure focal edema versus not using such a device in adults in hospital, long term care, community and palliative care settings. In all the studies, a delta cutoff score of ≥ 0.6 was considered a measurement indicating a potential requirement for increased preventive PI care. After receiving the delta cutoff score, clinical staff implemented enhanced PI prevention interventions. The interventions made available to staff varied across the studies and included SSKIN, changing the support surface, repositioning and heel off-loading, barrier cream, preventive dressings, increased frequency of skin and tissue assessments, nutrition care planning and patient education (3).
The meta-analysis showed that using a delta cutoff score from a device that measures focal edema to inform PI preventive care was associated with a significantly lower rate of PIs (relative risk [RR] 0.36, 95% CI 0.245 to 0.53, p < 0.001). This translated to a difference of 16 fewer per 1,000 experiencing a PI, with the true effect lying between 19 fewer people and 12 fewer people. Evidence from an additional pre-post clinical study that was not appropriate for inclusion in the analysis showed that when clinical staff acted on abnormal focal edema results, there was a 93% reduction in PI (35).
The evidence was of very low quality. The evidence was downgraded due to more than half the studies having a high risk of overall bias and also downgraded for indirectness because the PI interventions available across the studies varied. It must also be considered that the results may reflect the reported high sensitivity and low specificity of measurements of focal edema, potentially leading to intensified PI prevention interventions for more individuals than truly necessary. Potential undesirable effects of using a device that measures focal edema for decision-making regarding PI preventive care are unknown, but there does not appear to be adverse effects associated with the device use itself. The desirable clinical effects of identifying an individual with delta cutoff score ≥ 0.6 and subsequently enhancing the PI prevention most likely outweighs the clinical risks associated with an inaccurate measurement. However, on a population level, over-provision of unnecessary PI prevention may have resource implications. This has yet to be fully explored in the research.
The Guideline Governance Group considered the costs associated with using a device to measure focal edema to be moderate. Costs include hardware, licenses, disposables and supplies, personnel, education and training, cost of information technology (IT) and integration of the device into the electronic health record (5). Several cost effectiveness models (38, 39) at uncertain to high risk of bias were available that suggested that integrating use of devices to measure focal edema might be cost effective. The Guideline Governance Group determined that this would probably lead to cost savings. The potential for overall unnecessary increases in PI prevention care at the population level may vary based on the clinical setting and should be explored at the local health service level. In clinical practice, health professionals appear to find using a testing device acceptable (3, 34, 40, 41). However, a more recent study (42) in the aged care setting found that that acceptability to health professionals of using devices to measure focal edema decreases over time due to the increase in work load, technical and workflow challenges and competing resource priorities (42). Feasibility depends on access to equipment and resources, and how the technology is incorporated into care pathways (42), and may vary across clinical settings.
Certainty of Evidence
ACCURACY OF DEVICES FOR IDENTIFYING/MEASURING FOCAL EDEMA
| Certainty assessment | No of patients | Effect | Certainty |
Importance |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
No of studies |
Study design |
Risk of bias |
Inconsistency |
Indirectness |
Imprecision |
Other considerations |
Device for identifying focal edema |
Various reference standards |
Relative (95% CI) |
Risk difference with sensor |
||
| 8 | Observational studies |
Extremely Serious [a] |
Serious [b] | Not serious [c] |
NotSerious | none | Not measurable | Not measurable | Not measurable | Not measurable |
Very Low |
CRITICAL |
[a] High to unclear risk of bias across the studies
[b] Studies reported variable results and used different devices and different cut-off points
[c] in all studies, individuals were at PI risk, the accuracy is not transferable to individuals who are not screened as having a PI risk
USE OF SEM SCANNER MEASUREMENT TO INFORM PREVENTIVE PI CARE TO REDUCE PI
| Certainty assessment | No of patients | Effect | Certainty |
Importance |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
No of studies |
Study design |
Risk of bias |
Inconsistency |
Indirectness |
Imprecision |
Other considerations |
Device for identifying focal edema |
Various reference standards |
Relative (95% CI) |
Risk difference with sensor |
||
| 8 | Observational studies |
Extremely Serious [a] |
Serious [b] | Not serious [c] |
NotSerious | none | Not measurable | Not measurable | Not measurable | Not measurable |
Very Low |
CRITICAL |
[a] High to unclear risk of bias across the studies
[b] Not all studies applied the exact same PI interventions or clinical pathways. This reduces reproducibility in clinical practice.
Evidence to Decision Framework
Problem:
Desirable Effects:
Undesirable Effects:
Certainty of Evidence:
Values:
Balance of Effects:
Resources Required:
Certainty of Evidence of Required Resources:
Summary of Judgements
Cost Effectiveness:
Inequity:
Acceptability:
Feasibility:
Yes
Large
Don’t know
Very low
No important uncertainty or variability
Probably favors the intervention
Moderate costs
Low
Probably favors the intervention
Varies
Probably yes
Varies
STA4: Good Practice Statement
It is good practice to assess skin and tissue temperature as a part of a comprehensive assessment. Approaches include:
Skin: tactile assessment of skin temperature or, if available, supplemented with use of a skin temperature probe, or
Skin and underlying tissue: long wave infrared thermography with imaging where the technology is available and feasible to use.
More information
Clinical question: Should temperature measurements using infrared technology be used in addition to standard clinical assessment for identifying non-visible tissue changes consistent with early signs of pressure-induced injury to inform PI prevention and reduce PI occurrence?
The role of infrared thermography with imaging as an adjunct to skin and wound assessment in routine clinical care is evolving. Where it is available, infrared thermography with imaging is being used in clinical practice in a variety of ways (see Resources), although effectiveness in leading to reduction in PI occurrence has not been fully demonstrated.
Implementation considerations
Always use a PI classification system to diagnose PIs. Do not consider temperature differential readings as diagnostic of a PI.
Device results should be evaluated within the context of the individual’s overall condition and based on clinical judgement and the goals of care.
Infrared imaging can identify warmer or cooler areas. Temperature changes in either direction can be indicative of potential of developing PI (50, 73). Warmer areas are indicative of inflammation. Cooler areas are indicative of ischemia or infarct (death of tissue).
Consult the device manufacturer to identify the clinically relevant cutoff temperature that distinguish between normal and abnormal readings, and thresholds for inflammation and infection. There is a range of abnormal temperature differentials in published studies. Be aware that these are generally device-specific (47, 50, 52, 54, 56, 67, 68, 73, 74, 75).
Develop local health service-based guidance on the selection of individuals for technology-enhanced skin and tissue assessment, identifying when an individual should receive testing and how results will be integrated into care pathways. Protocols should also identify when use of LWIT is no longer required (e.g., the individual becomes more mobile).
Ensure clinicians receive training in LWIT use and image capture and interpretation of thermal patterns to attain inter-rater reliability.
Device results should be evaluated within the context of the individual’s overall condition and based on clinical judgement. Target the anatomic area(s) affected when enhancing preventive measures.
Additional implementation considerations for special populations
-
When available, a LWIT might offer an enhanced skin and tissue assessment to identify early tissue damage that is obscured (e.g., erythema or purple/maroon presentation of a DTPI).
Supporting information
In making this recommendation, the Guideline Governance Group considered evidence at each of the steps in the chain of linked evidence to evaluate tests of early pressure-induced injury (see Figure 1).
Supporting evidence on skin temperature assessment using a temperature probe
Evaluation of skin temperature is an important component of a comprehensive skin and tissue assessment. An assessment is usually made with the clinician’s hand to identify any warm or cool to touch bony prominences that might indicate that early pressure damage is occurring (see guideline chapter Skin and Tissue Assessment). A more objective measure of skin temperature is the use of simple temperature probes or thermistors to evaluate differences in skin temperature at loaded versus surrounding unloaded anatomical locations.
Absolute skin temperature of the loaded area alone is of little value given the variation of normal skin temperature between anatomic locations on an individual and variations between individuals. If using skin temperature as an indicator of early pressure-induced injury, relative temperature (i.e., the difference in skin temperature between the loaded area (e.g., bony prominence) and surrounding normal tissue is a more accurate indicator. Under these circumstances, the individual serves as their own control and potential environmental confounders (e.g., room temperature and humidity) are addressed. A decreased relative skin temperature was associated with 16 times higher odds of developing a PI based on a meta-analysis of three studies (pooled odds ratio [OR] 16.02 (95% CI 6.38 to 40.19, I2 79.4%). Certainty of evidence was low (44). The lower relative skin temperature indicates at least some ischemia in the loaded area.
Evidence on testing properties
Data on the accuracy and reliability of various temperature probes varies among manufacturers and users. Inter-rater reliability testing of an infrared based thermometer reported an ICC of 0.99 (95% CI 0.99 to 1.00) for heels and an ICC of 0.77 (95% CI 0.32 to 0.89) for sacrum for measurements taken in volunteers without PI risk (45). Data on the accuracy of tactile assessment of skin temperature to identify early injury was not available.
Evidence on clinical performance
There was no evidence exploring the clinical performance of temperature probe measurements with respect to reliable administration in clinical settings or use of results to inform the development of a PI prevention plan. There was no evidence linking the use of a skin thermometer probe to PI occurrence.
Supporting evidence on skin and tissue temperature assessment using long wave infrared thermography (LWIT)
The use of long wave infrared thermography (LWIT) devices for assessing skin and tissue can provide a more comprehensive evaluation of temperature differences. LWIT devices with imaging provide both temperature differential readings and visual patterns of temperature at the assessed anatomical location. The advantage of infrared thermography with imaging is that it provides information on the collective heat emission of all tissues in the area, not just the skin.
Evidence on the test properties
Inflammation (producing heat) is a very early response to tissue injury in an anatomical location subjected to pressure loading. Once ischemia occurs, the affected tissue becomes cooler than surrounding tissue. Death of tissue may intensify this effect (6). Non-loaded surrounding tissues are usually not affected. LWIT with imaging is designed to identify and visualize these temperature changes.
Signs of early tissue injury are detected with LWIT by comparing the temperature differentials between pressure loaded and unloaded anatomical locations and observing thermal patterns. Loaded tissues exhibiting early injury are typically either warmer (due to inflammation) or cooler (due to ischemia or tissue death) (46) than the adjacent skin and tissue. The pressure-loaded anatomical location can appear as a distinct area of temperature difference with imaging. In contrast, normally perfused tissue has a fairly uniform temperature distribution.
Cutoff temperature differences and protocols for obtaining LWIT have been established. Cutoff scores for the temperature differential between tissue exhibiting signs of pressure-induced injury and surrounding normal tissue have varied over the course of 20 years of research on LWIT. However, research using one currently available device is converging around a cutoff of ± 1.1 to 1.2° C (30, 47, 48, 49, 50, 51). Lower cutoff scores were associated with a different device (52, 53, 54). Protocols for obtaining LWIT measurements are explained in most studies. Many of the protocols contain detailed information on positioning the individual, timing of the measurement, camera distance and angles, lighting and interpretation of results based on known cutoff scores specific to the device (49, 52, 55). Protocols have also been published for use of LWIT in the home setting, specific to individuals with spinal cord injury (SCI) (56).
Diagnostic accuracy studies have reported sensitivity and specificity for LWIT in clinical settings. In a retrospective study set in an ICU, a cohort of 25 individuals with a documented on-admission PI and LWIT readings, 92% (n = 23) of the cohort had abnormal thermographic scores (using a cutoff temperature difference of ± 1.1° C). Sensitivity in the presence of an existing PI was 92.5% and specificity was 66.7% (47). A prospective cohort study set in critical care included individuals (n = 263) who received daily LWIT readings taken at the sacrum, of whom 22% (n = 58) developed a PI. Sensitivity was 98.3%, specificity was 99% (Youden index 0.97295) and AUROC was 0.98 (95% CI 0.95 to 1.00) (54).
Inter-rater and inter-rater reliability. Under controlled laboratory conditions, retrospective intra-rater and inter-rater reliability varied by 1% and 2%, with mean temperature reading differences varying by 0.14° C to 0.29° C (57). Inter-rater reliability between two raters for eight thermographic images (three with PIs and five with diabetes-related foot disease) was 1.00 (95% CI 1.00 to 1.00). Intra-rater reliability with repeat assessments taken after five days was 1.00 (95% CI 1.00 to 1.00) (58). Inter-device reliability and device accuracy was explored in a cohort of healthy adults with representation across Monk Skin Tones (n = 35) using six different thermal imaging devices; device accuracy and psychometric properties varied by device (59). There were significant differences in temperature readings between different device brands, but minimal differences based on variations in lighting, posture and camera distance (60). This highlights the importance of developing local guidance and standardized protocols that are specific to the device being used, for example using temperature difference thresholds for the appropriate device based on reliability data and previous clinical studies. Training should be provided until acceptable levels of reliability are achieved.
Accuracy and reliability in dark skin tones is an important consideration because LWIT with imaging may be particularly useful in detecting early pressure-induced injury in medium and dark skin tones (61, 62). The international standard governing screening thermographs (63) specifies a uniform skin emissivity value of 0.98 across all humans. This parameter is scientifically justified because long wave infrared emissivity is not affected by melanin concentration. Notably, this standard does not require testing across different skin tones because the underlying physics renders such variation irrelevant (63). This distinction underscores a fundamental advantage of LWIT and has been demonstrated in human testing. In one study (n = 65 healthy participants) the mean calculated emissivity was 0.972 (range 0.96 to 0.99). No significant differences in emissivity were observed between participants when grouped by skin pigmentation categorized using the Fitzpatrick Scale (p = 0.859) or based on reflectance spectrophotometry measurements (p = 0.346) (64). In an experimental model, no significant differences were found between LWIT readings for healthy individuals categorized as having dark skin tones and light skin tones (65). Several studies have confirmed these findings in clinical settings and confirmed the ability of LWIT readings to detect early pressure-induced injury in individuals with dark skin tones (30, 49, 66). Additionally, correlation has also been reported between cooler temperature and clinically diagnosed erythema and Category/Stage I PIs in individuals with dark skin tones (67).
Evidence on clinical performance with respect to reliable administration of the test
Reliability of LWIT readings in the clinical setting were established in a prospective study conducted in a tertiary health service. The nurse researchers achieved a 95% inter-rater reliability and a 95% intra-rater reliability before and throughout the study (68).
Prognostic accuracy is reported in studies exploring LWIT readings and visual skin assessment in detecting PIs. Reported sensitivity ranged from 80% to 92% and specificity ranged from 66% to 97.2%, noting the studies were at high risk of bias (47, 52, 56). Prognostic accuracy of LWIT detection of early pressure-induced injury has also been compared to the prognostic accuracy of risk assessment tools. AUROC was usually better for LWIT detection (47, 52, 54, 69, 70). As previously noted, risk assessment tools are best use in preventive planning rather than as a prognostic tool (see the guideline chapter on Pressure Injury Risk for further discussion).
Evidence on clinical performance with respect to test results informing the development of PI prevention interventions, and the resulting impact on PI occurrence
Several studies discussed efforts to integrate LWIT measurements into PI prevention protocols and workflows. Formalized prevention bundles based on LWIT results have been developed to inform the enhanced PI prevention protocols (49, 55, 56).
The strongest evidence linking LWIT to reduced PI occurrence was established in a study (56) in which individuals with SCI (n = 89) were randomly assigned to receive an individualized plan of repositioning based on sacral and skin temperature monitoring, or to receive standard PI prevention. After initial training conducted in a health service, the intervention was carried out in the individual’s home. Pressure injury incidence was lower at 3 months (p = not significant), 6 months (p < 0.001) and 1 year (p=0.027) for individuals receiving the LWIT-enhanced protocol (56). However, results were confounded by the inclusion of interface pressure as a co-occurring prompt to enhance prevention.
One observational study focused specifically on early detection of DTPI (49), noting that injury to deeper tissues can occur 1 to 3 days before the damage is visible on the surface of the skin, and is particularly challenging to identify in individuals with dark skin tones (1). With early detection, the anatomical location can be offloaded, potentially limiting tissue damage. In the study (49), individuals were screened with LWIT on admission to an ICU. Those with identified thermal anomalies indicative of DTPI (i.e., temperature differential > 1.2° C or < 1.2° C) were enrolled in the LWIT-informed enhanced PI prevention protocol. Two of twelve thermal anomalies developed into a visible DTPI. Rate of HAPIs dropped by 60% after implementation of the LWIT (49). In a second study (55), individuals in a long-term acute care hospital were scanned with LWIT on admission and weekly as part of a quality improvement project. Individuals identified as having thermal anomalies were enrolled in a LWIT-informed enhanced PI prevention protocol. The facility reported HAPI rates dropping to zero. Both these studies were at high risk of bias and had confounding issues.
There was only a very small volume of very low certainty evidence across the full chain of linked evidence. The Guideline Governance Group considered this body of evidence to be insufficient to establish a clear link demonstrating that use of advanced technologies to evaluate skin and tissue temperature leads to a reduction in PI occurrence. However, the body of evidence is expanding (71). No cost effectiveness studies were identified. Several reviews (5, 40, 59, 72) described the feasibility and acceptability of using LWIT in clinical practice. The reviews noted the challenge of identifying a known unaffected area (normal tissue) and using its temperature as a comparator measure. Additionally, the fact that abnormal readings can be either high (from inflammation) or low (from ischemia/tissue death) contribute to challenges in interpreting results and may require different reporting and care pathways for abnormally high and low readings. Practicalities such as adequate time to reposition the individual and allow for stabilization of temperature with consideration to environmental factors (e.g. humidity and temperature) and patient factors (e.g. perspiration) before taking a LWIT reading were also noted as feasibility considerations (40, 59, 72). Factors such as standardization of photography technique, appropriate and regular calibration of equipment, and training to interpret visual imaging need consideration when introducing LWIT in the clinical setting (5, 59). Staff education on, and development of local health service policies for calibration and maintenance, protocols for use and clinical pathways are considerations when introducing any new technologies and equipment to the clinical setting. Several studies have reported detailed protocols (5, 48, 52, 59).
Resources
The role of infrared thermography with imaging as an adjunct to skin and wound assessment in routine clinical care is evolving. Its effectiveness in leading to reduction in PI occurrence has not been fully demonstrated. However, the technology has multiple potential clinical uses, some of which include identifying early subclinical tissue changes prior to visible identification of PIs (55, 76, 77, 78), monitoring progress of wound healing (55, 76, 77, 78, 79), predicting wound healing (76, 80, 81), predicting recurrent pressure injuries (82), monitoring flap perfusion (83), and guiding differential diagnosis of PIs. Table A1 provides an overview of some contexts in which infrared thermography with imaging is currently being used, and Table A2 provides some guidance on interpreting the results.
Table A1: Use of infrared thermography with imaging in pressure injury detection
Identification of early deep tissue pressure injury (DTPI) prior to visible skin changes (48, 49): early identification and implementation of preventive care has been associated with reduction in early thermographic anomalies evolving into visually identifiable DTPIs (49).
Differentiation of DTPI and shallow (skin-deep) pathologies in cases of purple discoloration of the skin: DTPI is identified with targeted cold area (due to ischemia/infarcted/dead deeper tissues) versus shallow pathophysiology (e.g., skin failure or purpura) that has warmer and more uniform thermal patterns (84).
Differentiation between blanching erythema and Category/Stage 1 PI: When the relative temperature in the anatomical area of interest is elevated, the elevation is significantly higher for Category/Stage 1 PIs, potentially indicating greater inflammation (85). Category/Stage 1 PIs may also exhibit lower temperatures in relation to surrounding skin (85), potentially indicating progression to ischemia. The reactive hyperemia of blanchable erythema produces a transient pattern of increased heat as tissues are re-perfused.
Predicting progression of discolored intact skin to necrosis: Cooler temperatures at the center of a discolored area of interest appears to be more likely to develop necrosis (50, 73). Lack of capillary refill is also a predictor of necrosis (50, 73).
Enhancing identification of early tissue injury in darkly pigmented skin: There appears to be no difference in thermal emissivity based on Fitzpatrick skin phototyping scale (64). Heat emissivity of human skin does not vary significantly across the range of skin tones (64).
Table A2: Interpreting infrared temperature patterns
Note: thermographic differences are not diagnostic of PI or infection, but rather they enhance a visual and tactile skin and tissue assessment. PIs are diagnosed through visual and tactile assessment and use of a recognized PI classification system.
Warmer temperature pattern in the loaded areas can indicate inflammatory changes that occur relatively early in the etiology of PI (85).
Very high temperature areas may indicate infection (86, 87).
Cooler/cold temperature patterns in the loaded area may indicate poor perfusion, ischemia or infarct (i.e. death of underlying tissues).
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