B-mode ultrasonic echo determination of depth of thermal injury

Evidence Based Burn Depth Assessment Using Laser-Based Technologies: Where Do We Stand?

Early clinical assessment of burn depth and associated healing potential (HP) remains extremely challenging, even for experienced surgeons. Inaccurate diagnosis often leads to prolonged healing times and unnecessary surgical procedures, resulting in incremental costs, and unfavorable outcomes. Laser Doppler imaging (LDI) is currently the most objective and accurate diagnostic tool to measure blood flow and its associated HP, the main predictor for a patient's long-term functional and aesthetic outcome. A systematic review was performed on non-invasive, laser-based methods for burn depth assessment using skin microcirculation measurements to determine time to healing: Laser Doppler flowmetry (LDF), LDI and laser speckle contrast imaging (LSCI). Important drawbacks of single point LDF measurements are direct contact with numerous small points on the wound bed and the need to carry out serial measurements over several days. LDI is a fast, "non-contact," single measurement tool allowing to scan large burned areas with a 96% accuracy. LDI reduces the number of surgeries, improves the functional and aesthetic outcome and is cost-effective. There is only limited evidence for the use of LSCI in burn depth assessment. LSCI still needs technical improvements and scientific validation, before it can be approved for reliable burn assessment. LDI has proven to be invaluable in determining the optimal treatment of a burn patient. For unclear reasons, LDI is still not routinely used in burn centers worldwide. Additional research is required to identify potential "barriers" for universal implementation of this evidence-based burn depth assessment tool.

The LDI Enigma, Part I: So much proof, so little use

INTRODUCTION

Laser Doppler imaging (LDI) is still not an ubiquitous part of burn care worldwide despite reported accuracy rates of more than 95%, which is significantly higher than clinical assessment alone (50-75%). The aims of Part I of this survey study are: to identify the most important barriers for the use of LDI and to provide useful recommendations for efficient implementation in routine burn care. The actual interpretation and use of LDI measurements is discussed in the Enigma Part II article.

MATERIAL AND METHODS

1. Informative interviews with 15 representatives of burn centers without LDI. 2. A survey among 51 burn centers with LDI by means of an extensive questionnaire. 3. In-depth interviews with 21 of the participating centers.

RESULTS

1. All 15 centers without LDI indicated that cost of purchase in combination with maintenance of the LDI device, as well as personnel costs were the reason for not buying, while 12 (80%) also rated the current scientific evidence as insufficient. 2. Twenty-seven burn centers with an LDI (53%) participated and filled in almost the entire questionnaire. In 5 centers, cost delayed the purchase of LDI. The hospital/department paid for the LDI device in 62% of the burn centers and in 88% also for maintenance and salaries. The LDI operators were mainly surgeons (47%) or nurses (42%). In more than half of the burn centers (52%), between 2 and 5 people were trained and certified to use an LDI. In 50% of burn centers, the interpretation of the LDI scan was done by the same person doing the actual measurements. Eighty-nine percent of the burn centers considered the accuracy of the LDI scan as mainly to almost completely accurate. In case of real discrepancy between clinical diagnosis and LDI, in 48% of the burn centers (13/27) the surgeon still relied more on the clinical diagnosis despite reporting this high or almost complete accuracy rate of the LDI.

CONCLUSIONS

Barriers for the routine implementation of LDI were: 1. cost of purchasing and using an LDI combined with health care systems that inadequately reimburse non-surgical management; 2. lack of awareness of or ongoing skepticism towards the scientific evidence supporting LDI use; and 3. organizational constraints combined with logistical limitations. Our recommendations for wider use of LDI technology include: 1. a cost-effective reimbursement of LDI use combined with a more appropriate valuation of expert conservative management compared to surgical therapy; 2. increased use of LDI for every mixed depth burn and; 3. specialized LDI teams to improve burn procedural flexibility and to enable embedding LDI use in the burn care routine. Implementing these measures would promote the highest standards for LDI measurements and interpretation resulting in optimal care with mutual benefits for the hospital, for burn care teams and, most importantly, for the patients.

Real-time Burn Classification using Ultrasound Imaging

This article presents a real-time approach for classification of burn depth based on B-mode ultrasound imaging. A grey-level co-occurrence matrix (GLCM) computed from the ultrasound images of the tissue is employed to construct the textural feature set and the classification is performed using nonlinear support vector machine and kernel Fisher discriminant analysis. A leave-one-out cross-validation is used for the independent assessment of the classifiers. The model is tested for pair-wise binary classification of four burn conditions in ex vivo porcine skin tissue: (i) 200 °F for 10 s, (ii) 200 °F for 30 s, (iii) 450 °F for 10 s, and (iv) 450 °F for 30 s. The average classification accuracy for pairwise separation is 99% with just over 30 samples in each burn group and the average multiclass classification accuracy is 93%. The results highlight that the ultrasound imaging-based burn classification approach in conjunction with the GLCM texture features provide an accurate assessment of altered tissue characteristics with relatively moderate sample sizes, which is often the case with experimental and clinical datasets. The proposed method is shown to have the potential to assist with the real-time clinical assessment of burn degrees, particularly for discriminating between superficial and deep second degree burns, which is challenging in clinical practice.

Hyperspectral index-based metric for burn depth assessment

Burn depth objective classification is of paramount importance for decision making and treatment. Despite the wide variety of burn depth assessment methods tested so far, none of them have gained wide clinical application. Here, we introduce a new approach for burn depth assessment based on hyperspectral imaging combined with a spectral index-based technique that exploits specific spectral bands to map skin areas with different burn degrees. The spectral index amplifies the contrast between normal skin and areas with different degrees of burn, taking advantage of the differences in spectral amplitudes that occur as a result of the morphological and physiological changes occurring in burned skin. We demonstrate that by using the new measurable spectral index, it is possible to generate accurate burn classification maps showing spatial distribution of burn types in the affected body areas, facilitating the decision-making process and prognosis evaluation. The results highlight the potential of the new hyperspectral metric in the field of burn depth classification and its applicability in hospital settings seems promising.

Imaging Techniques for Clinical Burn Assessment with a Focus on Multispectral Imaging

Significance: Burn assessments, including extent and severity, are some of the most critical diagnoses in burn care, and many recently developed imaging techniques may have the potential to improve the accuracy of these evaluations. Recent Advances: Optical devices, telemedicine, and high-frequency ultrasound are among the highlights in recent burn imaging advancements. We present another promising technology, multispectral imaging (MSI), which also has the potential to impact current medical practice in burn care, among a variety of other specialties. Critical Issues: At this time, it is still a matter of debate as to why there is no consensus on the use of technology to assist burn assessments in the United States. Fortunately, the availability of techniques does not appear to be a limitation. However, the selection of appropriate imaging technology to augment the provision of burn care can be difficult for clinicians to navigate. There are many technologies available, but a comprehensive review summarizing the tissue characteristics measured by each technology in light of aiding clinicians in selecting the proper device is missing. This would be especially valuable for the nonburn specialists who encounter burn injuries. Future Directions: The questions of when burn assessment devices are useful to the burn team, how the various imaging devices work, and where the various burn imaging technologies fit into the spectrum of burn care will continue to be addressed. Technologies that can image a large surface area quickly, such as thermography or laser speckle imaging, may be suitable for initial burn assessment and triage. In the setting of presurgical planning, ultrasound or optical microscopy techniques, including optical coherence tomography, may prove useful. MSI, which actually has origins in burn care, may ultimately meet a high number of requirements for burn assessment in routine clinical use.

A systematic review of the evolution of laser Doppler techniques in burn depth assessment

Aims. The introduction of laser Doppler (LD) techniques to assess burn depth has revolutionized the treatment of burns of indeterminate depth. This paper will systematically review studies related to these two techniques and trace their evolution. At the same time we hope to highlight current controversies and areas where further research is necessary with regard to LD imaging (LDI) techniques. Methods. A systematic search for relevant literature was carried out on PubMed, Medline, EMBASE, and Google Scholar. Key search terms included the following: “Laser Doppler imaging,” “laser Doppler flow,” and “burn depth.” Results. A total of 53 studies were identified. Twenty-six studies which met the inclusion/exclusion criteria were included in the review. Conclusions. The numerous advantages of LDI over those of LD flowmetry have resulted in the former technique superseding the latter one. Despite the presence of alternative burn depth assessment techniques, LDI remains the most favoured. Various newer LDI machines with increasingly sophisticated methods of assessing burn depth have been introduced throughout the years. However, factors such as cost effectiveness, scanning of topographically inconsistent areas of the body, and skewing of results due to tattoos, peripheral vascular disease, and anaemia continue to be sighted as obstacles to LDI which require further research.

Histological Assessment of Tangentially Excised Burn Eschars

BACKGROUND

The burn eschar serves as a medium for bacterial growth and a source of local and systemic infection. To prevent or minimize these complications, it is important to debride the eschar as early as possible.

OBJECTIVE

To identify the presence of viable skin within the excisions by examining tangentially excised burn eschars.

METHODS

A total of 146 samples of burned human tissue were removed during 54 routine sharp tangential excision procedures (using dermatomes). The samples were histologically examined to identify the relative thickness of the dead, intermediate and viable layers.

RESULTS

The mean (± SD) thickness of the excised samples was 1.7 ± 1.1 mm. The sacrificed viable tissue (mean thickness 0.7+0.8 mm) occupied 41.2% of the entire thickness of the excision. In 32 biopsies (21.8%; 95% CI 16.0 to 29.3), the excision did not reach viable skin. Only eight biopsies (5.4%; 95% CI 2.8 to 10.1) contained all of the necrotic tissue without removing viable tissue.

CONCLUSIONS

The thickness of a single tangentially excised layer of eschar is not much greater than the actual thickness of the entire skin and often contains viable tissue. Because surgical debridement is insufficiently selective, more selective means of debriding burn eschars should be explored.

Critical review of burn depth assessment techniques: Part I. Historical review

The assessment of burn depth, and as such, the estimation of whether a burn wound is expected to heal on its own within 21 days, is one of the most important roles of the burn surgeon. A false-positive assessment and the patient faces needless surgery, a false-negative one and the patient faces increased length of stay, risks contracture, and hypertrophic scar formation. Although many clinical signs can aid in this determination, accurate assessment of burn depth is possible only 64 to 76% of the time, even for experienced burn surgeons. Through the years, a variety of tools have become available, all attempting to improve clinical accuracy. Part 1 of this two-part article reviews the literature supporting the different adjuvants to clinical decision making is, providing a historical perspective that serves as a framework for part 2, a critical assessment of laser Doppler imaging.

Accuracy of early burn depth assessment by laser Doppler imaging on different days post burn

BACKGROUND

Accurate diagnosis of burn depth is essential in selecting the most appropriate treatment. Early assessment of burn depth by clinical means only has been shown to be inaccurate, resulting in unnecessary operations or delay of grafting procedures. Laser Doppler imaging (LDI) was reported as an objective technique to determine the depth of a burn wound, but the accuracy on very early days post burn has never been investigated yet.

METHODS

In 40 patients with intermediate depth burns, we prospectively evaluated and compared the accuracy of the LDI measurements with the clinical assessments on days 0, 1, 3, 5, 8. Clinical evaluation of the depth of the burn was performed by two observers blinded to the LDI images. Accuracies were assessed by comparison with outcome: healing times longer than 21 days were considered to be equivalent to a biopsy finding of a deep dermal wound. Obviously superficial and full thickness wounds were excluded. LDI flux level was used for LDI prediction of outcome: less than 220PU to predict non-healing at day 21.

RESULTS

The accuracies of burn depth assessments on the day of burn and post burn days 0, 1, 3, 5 and 8 using LDI were 54%, 79.5%, 95%, 97% and 100% compared with clinical assessment accuracies of 40.6%, 61.5%, 52.5%, 71.4% and 100%, respectively. LDI accuracy was significantly higher than clinical accuracy on day 3 (p<0.001) and day 5 (p=0.005). Burn depth conversion was also considered. This is the first study to quantify the advantage of LDI scanning over clinical assessments during these important early after burn days.

Assessment of burn depth and burn wound healing potential

The depth of a burn wound and/or its healing potential are the most important determinants of the therapeutic management and of the residual morbidity or scarring. Traditionally, burn surgeons divide burns into superficial which heal by rapid re-epithelialization with minimal scarring and deep burns requiring surgical therapy. Clinical assessment remains the most frequent technique to measure the depth of a burn wound although this has been shown to be accurate in only 60-75% of the cases, even when carried out by an experienced burn surgeon. In this article we review all current modalities useful to provide an objective assessment of the burn wound depth, from simple clinical evaluation to biopsy and histology and to various perfusion measurement techniques such as thermography, vital dyes, video angiography, video microscopy, and laser Doppler techniques. The different needs according to the different diagnostic situations are considered. It is concluded that for the initial emergency assessment, the use of telemetry and simple burn photographs are the best option, that for research purposes a wide range of different techniques can be used but that, most importantly, for the actual treatment decisions, laser Doppler imaging is the only technique that has been shown to accurately predict wound outcome with a large weight of evidence. Moreover this technique has been approved for burn depth assessment by regulatory bodies including the FDA.

Biomechanical monitoring of cutaneous sulfur mustard-induced lesions in the weanling pig model for depth of injury

BACKGROUND/PURPOSE

A sulfur mustard (SM)-induced cutaneous injury model was developed in weanling swine to evaluate the efficacy of candidate treatment regimens. Lesions were assessed clinically and histopathologically. Histopathologic evaluation of lesions was a subjective and invasive assessment. Biomechanical engineering methods offer an objective and less invasive method to evaluate lesions. The purpose of this study was to use biomechanical engineering instruments to assess SM-induced lesions for depth of injury and to correlate those assessments with histopathology.

METHODS

Two groups of six animals each were exposed to 400 microL undiluted SM applied at each of six abdominal sites for either 2 or 30 min. An additional seven animals received a sham treatment (control; 400 microL deionized water applied to each of six sites for 30 min). Each site was evaluated before exposure and 2 days after exposure. Biomechanical engineering techniques used to assess each lesion were reflectance colorimetry, evaporimetry [transepidermal water loss (TEWL)], laser Doppler perfusion imaging, and high-frequency (20 MHz) two-dimensional ultrasound. Injury depth and lesion severity were assessed and correlated to biomechanical methods using special histopathologic staining techniques.

RESULTS

Two- and 30-min cutaneous lesions were significantly different from controls at the 0.05 probability level for redness (chroma meter) and TEWL (evaporimeter), but were not significantly different from each other. The 2-min lesions had a significant increase (2.11 AU, SE=0.06) and the 30-min lesions had a decrease (0.96 AU, SE=0.04) from controls (1.31 AU, SE=0.03) in microcirculatory blood flux (laser Doppler). The 2-min lesions and controls were significantly different at the 0.05 level from 30-min lesions in skin thickness (ultrasound). The 2- and 30-min groups were significantly different from controls and from each other at the 0.05 level in histopathologic assessment of injury depth, basal cell necrosis, depth of necrosis, and vascular necrosis, with the 30-min injuries being most severe.

CONCLUSION

There was mixed evidence that the bioengineering techniques tested could differentiate between controls, 2-min (partial-thickness) cutaneous injuries and 30-min (full-thickness) cutaneous injuries at day 2. Both biomechanical and histopathologic assessments are useful methods of characterizing SM lesions in the weanling pig model. Biomechanical methods are non-invasive and quantitative, and multiple readings over shorter and longer periods of time may improve differentiation in depth of injury. Histopathologic assessments are important for confirmation of lesion depth and severity, and for assisting interpretation when a single assessment using bioengineering methods is used.

Fire and smoke injuries

The successful management of burns and related injuries requires a comprehensive team approach at a designated burn center. This team should consist of burn surgeons, burn nurses, respiratory therapists, physical therapists, occupational therapists, clinical nutritionists, social workers, chaplains, and other clinical consultants. This article focuses specifically on the management of thermal burns and inhalational injuries, with an emphasis on assessment, resuscitation, and critical care management. It also discusses special considerations related to burned trauma patients.

A general overview of burn care

The majority of burn victims do not need to be treated in a burn centre. Adequate care can be given by non specialised medical personnel, provided that proper guidelines are followed. The article outlines and reviews these guidelines.

Prediction of burn healing time using artificial neural networks and reflectance spectrometer

BACKGROUND

Burn depth assessment is important as early excision and grafting is the treatment of choice for deep dermal burn. Inaccurate assessment causes prolonged hospital stay, increased medical expenses and morbidity. Based on reflected burn spectra, we have developed an artificial neural network to predict the burn healing time.

PURPOSE

Our study is to develop a non-invasive objective method to predict burn-healing time.

METHODS AND MATERIALS

Burns less than 20% TBSA was included. Burn spectra taken on the third postburn day using reflectance spectrometer were analyzed by an artificial neural network system.

RESULTS

Forty-one spectra were collected. With the newly developed method, the predictive accuracy of burns healed in less than 14 days was 96%, and that in more than 14 days was 75%.

CONCLUSIONS

Using reflectance spectrometer, we have developed an artificial neural network to determine the burn healing time with 86% overall predictive accuracy.

Burn wound assessment and surgical management

Ideally, in a burn-traumatized patient, nonviable skin and tissues should be excised early in the course of treatment and replaced with a graftable material that mimics the properties of normal skin in function,texture, sensation, and appearance. The difficulty in identifying indeterminate-depth dermal injuries requires further studies to establish the line between extending injury and delaying the progressive excision of nonviable tissue. Recent studies have shown that molecularly the process of wound healing is an interaction among multiple macromolecules and therefore requires in-depth studies of growth factor symptoms, the extra-cellular matrix, and the immunologic response to wounds [8788].The survival of patients with major thermal injuries (Fig. 35) has dramatically increased in recent years. Therefore, greater emphasis must be placed on improving the overall treatment process and the quality of the end result for these patients. Surgically directed and laboratory-based investigations into the cellular components of wound repair and the development of alternative methods of final wound closure are continuing to evolve, and bum specialists are,optimistic that new alternatives will become available for their patients.

Laser Doppler imaging determines need for excision and grafting in advance of clinical judgment: a prospective blinded trial

INTRODUCTION

Clinicians' judgment as to which burns require excision and grafting remains one aspect of burn care without objective measurements. This study presents a prospective, blinded trial to assess decision to operate by laser Doppler imaging (numerical criteria) versus the clinical judgment of an experienced burn surgeon.

METHODS

A number of 23 patients were enrolled in this prospective trial and 41 representative wounds of indeterminate depth were selected for observation. Daily determination of need to operate (burn depth) was made by a single burn surgeon. Laser Doppler imager (LDI) scans of the same wounds were simultaneously obtained, and not revealed to the clinician. Data analysis compared quickness of decision to operate by LDI to the clinician's judgment. Concurrence of decisions by either method was compared.

RESULTS

A total of 23 patients and 41 wounds were analyzed. LDI and the surgeon agreed in determination of wound depth 56% of the time (23/41, P=0.031). Biopsy confirmation was obtained for 21 wounds. The surgeon's determination of burn depth was accurate in 71.4% of wounds biopsied (15/21). When the LDI scan median flux indicated need for excision, it was 100% accurate (7/7). When both the surgeon and the LDI were correct in assessing wound depth, LDI would have saved median number of 2 days (minimum=0, maximum=4).

CONCLUSION

LDI allowed for earlier, objective determination of need to operate. Concurrence with clinical judgment in this blinded study was excellent. LDI should be seen as an effective aid to clinical judgment when contemplating excision of burns with indeterminate depth.

Measurement of depth of burns by laser Doppler perfusion imaging

Laser Doppler perfusion imaging (LDPI), is a further development in laser Doppler flowmetry (LDF). Its advantage is that it enables assessment of microvascular blood flow in a predefined skin area rather than, as for LDF, in one place. In many ways this method seems to be more promising than LDF in the assessment of burn wounds. However, several methodological issues that are inherent in the LDPI technique, and are relevant for the assessment of burn depth, must be clarified. These include the effect of scanning distance, curvature of the tissue, thickness of topical wound dressings, and pathophysiological effects of skin colour, blisters, and wound fluids. Furthermore, we soon realised that to examine the perfusion image generated by LDPI adequately the process of analysis was appreciably improved by the simultaneous use of digital photography. In the present investigation we used both in vitro and in vivo models and also examined burned patients, and found that the listed factors all significantly affected the LDPI output signal. However, if these factors are known to the examiner, most of them can be adjusted for. If the technique is further improved by minimizing such effects and by reducing the practical difficulties of applying it to a burned patient in the burns unit, the technique may find uses in everyday clinical decision-making.

Diagnosis of burn depth using laser-induced indocyanine green fluorescence: a preliminary clinical trial

Clinical assessment of burn depth is frequently inaccurate. In order to effectively plan the treatment of burn wounds, an accurate diagnosis of burn depth is desirable. A new method for evaluating the depth of burns by imaging the blood flow through the burned tissue using fluorescence from intravenously injected indocyanine green (ICG) dye illuminated with a 785-nm, near-infrared diode laser array was evaluated. Nine patients and 15 individual burn sites were studied. Five sites were classified by the ICG study as superficial second degree, four were deep-dermal second degree, and six were third degree. Etiology of the injuries included flame, contact burns, and scalds. The date postburn of the study ranged from 1 to 11 days. In all cases, the relative fluorescence levels (e.g. superficial second-degree burns yielded relatively bright fluorescence, third-degree burns appeared much darker than surrounding normal skin) were found to correlate well with actual burn depth as determined by histologic examination of biopsies and intraoperative clinical assessment.

An audit of the use of laser Doppler imaging (LDI) in the assessment of burns of intermediate depth

This is the first report of an evaluation of the use of a laser Doppler imager (LDI) scanner in the assessment of burn depth in patients. It is based on a 6-month, prospective audit of 76 burns of intermediate depth. Clinical and LDI assessments of burn wound depth were recorded at 48-72 h post-injury. Histological confirmation of depth was obtained from those burns requiring surgery. A healing time of less than 21 days was taken as confirmation of the injury being an superficial dermal burn. The accuracy of LDI in the assessment of burn depth was 97%, compared with 60-80% for established clinical methods. This audit confirms that LDI is a very accurate measurement tool for the assessment of burn wound depth. We recommend that all burns of intermediate depth should be analysed in this way in order to ensure appropriate management of the burn, to avoid unnecessary surgery and to reduce hospital stay and costs.

Standardized burn model using a multiparametric histologic analysis of burn depth

OBJECTIVE

Burn depth and extent determine prognosis and therapy. The current classification into first-, second-, and third-degree burns is crude, making comparisons between studies difficult. The authors standardized a reproducible burn model and a precise histopathologic method for describing burn depth in swine.

METHODS

This was a prospective, cross-sectional interventional animal study. Eighteen paired sets of burns were inflicted on the clipped flank skin of two anesthetized domestic pigs with a 2.5 cm by 2.5 cm by 7.5 cm aluminum bar preheated in water to 50 degrees C, 60 degrees C, 70 degrees C, 80 degrees C, 90 degrees C, degrees C or 100 degrees C. The bar was applied for 10, 20, or 30 seconds. Full-thickness skin biopsies were obtained 30 minutes after injury for blinded histopathologic evaluation using hematoxylin and eosin staining. Two dermatopathologists made two sets of measurements and were masked to each other's evaluations. The depth of injury was measured with an ocular microtome for each of five dermal parameters: collagen discoloration, intercollagen basophilic material, endothelial cell necrosis, epithelial cell necrosis, and mesenchymal cell necrosis. The correlation between burn depths of the paired sets of experiments was calculated to assess the reliability of the model. Inter- and intraobserver correlations were calculated to assess the reliability of the scale. Analysis of variance (ANOVA) was used to assess the relation between temperature and exposure times on burn depth.

RESULTS

Depth of injury for all five dermal elements was related to temperature and exposure times (ANOVA, p < 0.001 for each). The depth of injury in the paired sets of burns was highly consistent (Pearson correlation, range = 0.88-0.95). Inter- and intraobserver correlations were excellent for all measured elements (range = 0.91-0.97 and 0.95-0.99, respectively).

CONCLUSIONS

The authors describe a simple and reproducible animal burn model and histopathologic scale for measuring burn depth that they believe will facilitate standardization and comparison within future burn studies.

Use of laser Doppler flowmetry for estimation of the depth of burns

The trend for treatment of deep second degree burns and third degree burns is toward early excision and skin grafting. The ability to predict burn depth accurately as early as possible is important for early excision and skin grafting. This study, prospectively evaluated the ability of laser Doppler flow measurements, obtained within 72 hours after burn injury, to predict the depth of burn wounds. A Periflux system 4001 laser Doppler flowmeter was used to measure the cutaneous microflow circulation of 100 selected points of burn wounds on 44 inpatients and of 1680 selected points on 120 volunteers from March of 1993 to February of 1994. The mean value of superficial second degree burns checked by laser Doppler was 194.6 perfusion units (PU). The value of deep second degree burns was 59.7 PU, and the value of third degree burns was 5.1 PU. The mean normal cutaneous blood flow of 120 volunteers (control group) was between 4 and 9 PU, except on the head, neck, hand, and foot. Blood flow of more than 100 PU correctly predicted (90.2 percent of cases) a superficial second degree burn. Blood flow between 100 and 10 PU correctly predicted (96.2 percent of cases) a deep second degree dermal burn. That of less than 10 PU correctly predicted (100 percent of cases) a third degree burn. There was also a significant correlation between initial flow measurements and the depth of burn wounds. We conclude that laser Doppler flow measurements performed early after burn injury are useful in predicting the depth of burn wounds. Laser Doppler flowmetry has the advantage of being easy to use and noninvasive and of providing immediate results for early determination of burn depth. Laser Doppler flowmetry is useful in selecting patients for early excision and grafting of burn wounds.

Determination of Teflon thickness with laser speckle. I. Potential for burn depth diagnosis

A quantitative method for determining the depth of burn eschar would aid surgeons in determining whether to excise and subsequently graft a burn wound. We hypothesize that tissue viability could be assessed by an analysis of the spatial modulation of near-field laser speckle by flowing blood. A feasibility study of the technique was performed with two-layer tissue phantoms used to simulate a burn wound. A sheet of polytetrafluoroethylene (PTFE) was used to simulate nonperfused burn eschar, and tissue perfusion within deeper layers was represented by Brownian motion from a scattering solution. A low-power He-Ne laser was focused onto the target, and the resulting speckle image was captured with a CCD camera and stored on a computer for further processing. The diameter of the speckle pattern was found to be directly proportional to the thickness of the overlying layer. These data suggest that the thickness of PTFE can be determined to ±100-μm accuracy with 95% confidence and may be suitable for burn depth detection in vivo.

Improved accuracy of burn wound assessment using laser Doppler

The utility of the laser Doppler for determining burn depth has been questioned because of problems with technology and methodology. This study prospectively evaluates the ability of a new laser Doppler technique to predict burn healing time. Using the Periflux System 4000 laser Doppler, readings were taken on 305 burns (147 patients) on postburn day 3 or 4. Sixty-six wounds were used to derive a predictive function (phase I) and 152 wounds were used to test the function (phase II). Blood flow dynamics (flux), microvascular dilation capacity of the wounds to beat stress, and flow motion wave pattern (vasomotion) were studied using the laser Doppler, and seven parameters were evaluated to determine their relative contribution to the prediction of healing time. These parameters are hyperemic flux (flux value after heating to 42 degrees C), average hyperemic wave amplitude (AHWA), number of average flux units >100(F100), number readings with wave amplitude 75 (A5), average flux change (AFC), percentage of average flux increase, and relative flow capacity (RFC = AFC/average hyperemic flux). After readings were made, the wounds were observed and divided into two groups: those that healed in less than 14 days and those that healed or were grafted after 14 days. A step-wise discriminant analysis was used to assess the relative contribution of the Doppler-derived measures to healing time prediction. AHWA, F100, and RFC were included in the final discriminant function explaining 72% of the healing time variance (Wilks' lambda value 0.28; p value <0.0001). Predicted outcome = 0.05(AHWA) + 0.31(F100) + 5.0(RFC) - 2.3. With this derived function, there is 94% accuracy in the prediction of burn wound healing time compared with a physician predictive accuracy of 70%.

New laser Doppler scanner, a valuable adjunct in burn depth assessment

A new medical instrument is presented that produces a doppler blood flow image from a laser beam in a raster pattern and the results of a pilot study which shows this technique to be highly accurate in assessing burn depth is described.

Burn depth: a review

Despite the plethora of technologic advances, the most common technique for diagnosing burn depth remains the clinical assessment of an experienced burn surgeon. It is clear that this assessment is accurate for very deep and very shallow burns. But since clinical judgment is not precise in telling whether a dermal burn will heal in 3 weeks, efforts to develop a burn depth indicator are certainly warranted to accurately determine which dermal burns to excise and graft. This review summarizes the considerable literature in which a variety of techniques to determine burn depth have been used.

Cutaneous 10 MHz ultrasound B scan allows the quantitative assessment of burn depth

Alterations in the epidermis and dermis after a scald burn (deep dermal wound) are sonographically displayed by different echo reflections. Histological slide preparations from various layers of healthy skin were studied to check the ultrasound analysis. Echo reflections of high and low density showed a close correlation to real anatomical structures in the histological slides. The 10-MHz B scan allows the differentiation of 0.1 mm. Heat causes an increase in dermal thickness of between 50 and 100 per cent for the period between 1 and 6 h after injury. Identifying the layers corresponding to the histological slides makes it is possible to measure the distance between the interfaces. This improves the quantitative assessment of both the depth and the area of thermal injury.