Abstract: The evaluation of burn depth is mainly performed by clinical assessment. Although rapid and useful, this approach is sometimes inaccurate and subjective. In this study, the reliability of subjective clinical assessment of burn depth by clinicians is compared to the reliability of a colorimetric measurement technique. Using clinical scoring and objective assessment with a tri-stimulus colorimeter, the authors evaluated 123 patients with superficial and deep partial-thickness burns. Healing time was correlated to the clinical scoring and instrumental data on burn depth. Superficial wounds had a significantly higher luminance (L*, p < 0.05) and redness (a*, p < 0.05) when compared to deep wounds. The overall accuracy of deep burn depth estimation was significantly more accurate with the colorimeter than with clinical scoring. This study shows that an overall evaluation of partial-thickness burns with a colorimeter is more reliable than clinical evaluation by observers.

E

arly and accurate assessment of burn depth is an essential element in the care of thermally injured patients. Cutaneous burn wounds are currently classified by accurate clinical estimation of depth and outcome. This classification describes 4 levels of burn injuries: superficial burns, superficial partial-thickness burns, deep partial-thickness (deep dermal) burns, and full-thickness burns.¹ Burn depth and extent assessment is a key step in determining prognosis and establishing proper treatment options.
       Early excision of devitalized tissue and grafting are the current treatments of choice for deep dermal and full-thickness burns that do not heal spontaneously within 3 weeks.² In this type of wound, surgical treatment has been shown to reduce the risk of infection, decrease hypertrophic scar formation, shorten hospital stays, and reduce costs.³
       Although clinical evaluation conducted by experienced physicians remains a rapid and simple way to detect burn wound depth and estimate the time needed for the burn wound to heal, this is often an inaccurate method, particularly in identifying indeterminate-depth dermal injuries.⁴ For this reason, various instrumental techniques have been investigated to standardize this important aspect of burn evaluation and render it more objective. Different criteria have been explored, such as detection of dead cells by skin biopsy⁵ or by the use of vital dyes,⁶ evaluation of tissue density,⁷ assessment of dermal circulation with fluorescein⁸ or with laser Doppler flowmetry,⁹ monitoring of wound temperature,¹⁰ and color coding of burn wounds with light reflectance.¹¹ In burn patient management, it is often difficult to correctly estimate depth in superficial and deep partial-thickness wounds in contrast to shallow and full-thickness lesions, which are easily detected by clinical observation.
       Since a basic foundation for diagnosis in burn care is color, tri-stimulus colorimetric analysis, a noninvasive technique, was used in this study to determine whether a correlation exists between wound color and burn depth.

Materials and Methods

       The authors prospectively evaluated 123 patients (age 12–68, mean 47) who had 2% to 15% total body surface area (TBSA) burns (mean 4.5%) and had been admitted to the Burn Unit of the Department of Dermatology, University of Pisa, as a result of superficial and deep partial-thickness burns. Only burns that had occurred within the previous 24 hours were included in the study. After wound debridement, burn sites were mapped with a transparent plastic stencil, and the points under observation were recorded. Objective assessment of wound color was made with a tri-stimulus colorimeter (Chroma Meter CR-200, Konica Minolta Italia, Milan, Italy). The L* a* b* system, as recommended by the Commission Internationale de l’Eclairage (CIE), was used for skin color assessment. The L* value represents relative color brightness ranging from total black (L* = 0) to total white (L* = 100). The a* value represents the color hue ranging from red (positive results) to green (negative results). The b* value represents the color hue ranging from blue (negative results) to yellow (positive results). For comparison, measurements were taken on the skin contralateral to the burn wounds, and these values were expressed as ΔL*, Δa*, and Δb*. Measurements were taken on Days 1 and 3 after admission. Four consecutive measurements were made for each point, and the mean ± SD was calculated. Clinical estimation of burn depth was independent from instrumental readings, and the observer was asked to define the depth of superficial and deep partial-thickness burns. Patients were treated daily with a topical antibacterial agent until Day 14, and at that time, unhealed areas were excised and grafted. Healing time was correlated to the clinical scoring and instrumental data on burn depth.

Statistical Analysis

       All measurement data were entered into 1 database for comparative evaluation. Analysis of variance (ANOVA) and a Wilcoxon signed rank test for paired observations were applied to compare the colorimetric mean values obtained with different clinical scoring. The nonparametric paired test was used for the analysis of control values versus burn wound sites.

Results

Tables 1-2

       The colorimetric characteristics of different partial-thickness burns are presented in Table 1. Superficial wounds had a significantly higher luminance (L*, p < 0.05) and redness (a*, p < 0.05) when compared to deep wounds. No significant difference was found in the b* values between deep and superficial wounds. The ΔL* and Δa* values were also statistically significant (p < 0.05) when compared to different burn depths. The overall accuracy of deep partial-thickness burn depth estimation was significantly more accurate with the colorimeter than with clinical scoring (p < 0.01) (Table 2). The same level of accuracy was not found in assessing superficial burn wounds.

Discussion

       In recent years, the incidence of severe, deep burns has been reduced as a result of improved fire safety measures and burn prevention.¹² For this reason, in clinical practice, there is an increasing need to accurately evaluate and manage small superficial burn injuries in order to achieve cost-effective treatment and proper patient management.¹³
       Assessment of burn severity is a key step in establishing a proper plan of care for patients who have sustained thermal injuries and requires correct estimation of the extent and depth of the skin injury. The first assessment of burn depth is usually dependent on the subjectivity and experience of the examiner as well as the timing of diagnosis, but it can be difficult to estimate the actual extension and depth of the lesion. Proper diagnosis of burn depth is usually simple in the case of superficial burns where erythema is the main component. Extent and depth of full-thickness burns are also simple to define. Difficulties may be encountered, however, in the differentiation between superficial partial-thickness and deep partial-thickness burns.¹⁴
       Various attempts have been made to improve the early diagnosis of burns with indeterminate depth. A technique based on indocyanine green fluorescence was used in the 1990s to determine viable tissue circulation at different levels in skin and burn tissue, but this method did not gain widespread clinical acceptance.¹⁵ Another method that may be used is a punch biopsy, which provides histological assessment of occluded blood vessels within the dermis and an estimation of burn depth.¹⁶ However, this technique, as in the case of the indocyanine method, is invasive. For this reason, there is a legitimate need for noninvasive, objective, and standardized methods to assess burn wound depth and, thereby, achieve early diagnosis.
       Several noninvasive measuring methods have been developed for the determination of burn depth, such as sonography¹⁷ and thermography,¹⁸ nuclear magnetic resonance,¹⁹ and laser Doppler flowmetry.²⁰ Laser Doppler flowmetry appears to be a major advancement in the management of burns, providing information about blood flow in the dermis in addition to predicting healing with nearly 100% accuracy within the first 48 hours after burn injury.²¹ A more advanced laser Doppler imaging technique can evaluate larger burn areas in a shorter time period, but its use is limited due to high costs.²²

Conclusion

       The purpose of this study was to determine whether the tri-stimulus colorimetric assessment of burn wounds could determine a range of colors and distinguish between superficial and partial-thickness burns. The authors believed application of this method of assessment would lead to more accurate burn depth diagnosis and earlier excision and skin grafting. The authors’ results indicate that colorimetric evaluation is more accurate than clinical scoring in diagnosing deep partial-thickness wounds. This could be useful in defining and delimiting areas that require debridement as well as in monitoring the results of treatment.
       The advantage of this method is that it can visualize subclinical and deep modifications at a time when clinical assessment cannot detect them.
       With this instrument, it is also possible to assess the whole burn while avoiding direct contact with the burn surface. This aspect is crucial to avoid cross-contamination and infection on the wound surface. The instrument also displayed good reliability in measuring scar tissue when compared to a subjective scar assessment scale because of its convenient, practical, and objective evaluation of vascularization and pigmentation.²³
       The measurement technique used in this study shows high reproducibility and can help overcome possible bias derived from clinical scoring.
       The results obtained from this study are promising, and it appears that the colorimeter system and the methodology applied can provide a relatively consistent and comparable measure of burn depth when used by different individuals. The technique is noninvasive, safe, and painless, and each measurement takes less than 30 seconds.
       When used to properly diagnose and treat burn lesions, this method of assessment may result in reduced costs, length of hospitalization, and unnecessary surgery.