Reprint of: Burn wound healing time assessed by laser Doppler imaging. Part 2: Validation of a dedicated colour code for image interpretation

Laser speckle contrast imaging, an alternative to laser doppler imaging in clinical practice of burn wound care derivation of a color code

OBJECTIVE

To develop a color code and to investigate the validity of Laser Speckle Contrast Imaging (LSCI) for measuring burn wound healing potential (HP) in burn patients as compared to the reference standard Laser Doppler Imaging (LDI).

METHOD

A prospective, observational, cohort study was conducted in adult patients with acute burn wounds. The relationship between mean flux measured with LDI and mean perfusion units (PU) measured with LSCI was expressed in a regression formula. Measurements were performed between 2 and 5 days after the burn wound. The creation of a LSCI color code was done by mapping the clinically validated color code of the LDI to the corresponding values on the LSCI scale. To assess validity of the LSCI, the ability of the LSCI to discriminate between HP < 14 and ≥ 14 days and HP < 21 and original ≥ 21 days according to the LDI reference standard was evaluated, with calculation of receiver operating characteristics (ROC) curves.

RESULTS

A total of 50 patients were included with a median age of 40 years and total body surface area burned of 6%. LSCI values of 143 PU and 113 PU were derived as the cut-off values for the need of conservative treatment (HP < 14 and ≥ 14 days) resp. surgical closure (HP < 21 and ≥ 21 days). These LSCI cut off values showed a good discrimination between HP 14 days versus ≥ 14 days (Area Under Curve (AUC)= 0.89; sensitivity 85% and specificity = 82%) and a good discrimination between HP 21 days versus ≥ 21 days (AUC of 0.89, sensitivity 81% and specificity 88%).

CONCLUSION

This is the first study in which a color code for the LSCI in adult clinical burn patients has been developed. Our study reconfirms the good performance of the LSCI for prediction of burn wound healing potential. This provides additional evidence for the potential value of the LSCI in specialized burn care.

Helpful hints in deciding what and when to operate after enzymatic debridement

INTRODUCTION

In recent years, it has become clear that the burn eschar in deep burns can be selectively removed using the enzymatically debriding agent NexoBrid® (EDNX). In deep partial-thickness burns, such selective debridement preserves all non-injured dermis, which is sometimes sufficient for spontaneous re-epithelization. Nevertheless, it can be extremely challenging to determine exactly what and when to operate after an EDNX procedure. In this manuscript, we sought to investigate the clinical aspect of the enzymatically debrided wound bed of laser Doppler imaging (LDI)-confirmed deep dermal and full-thickness burns after NexoBrid® application. This to evaluate the residual wound healing capacity and implement specific indications for surgical therapy after enzymatic debridement.

MATERIAL AND METHODS

Mainly LDI-blue areas, determined between 48 h and 5d after burn and afterwards treated with EDNX were selected. Six practical and three expert EDNX users evaluated the high-quality digital images of the wound beds immediately post NexoBrid® removal and after a 2 h wet-to-dry (WTD) dressing period.

RESULTS

One hundred and two mainly LDI-blue areas in 32 patients were analyzed. Regarding the early decision-making, there were no significant differences in the wound bed evaluations, wound healing assessment and treatment decision of all 9 EDNX users post EDNX removal versus post WTD. Moreover, there was a good to excellent consensus between the practical and expert EDNX users in the individual wound bed evaluations. Even in the evaluation of a newly developed wound bed color code, with 7 different colors/patterns to choose from, the consensus was 80%. There was also an 84% consensus on the decision whether or not to operate. All mainly LDI-blue areas with incomplete enzymatic debridement, determined during clinical investigation by expert EDNX users, required surgery. Additionally, the expert investigators demonstrated that the following wound bed characteristics were independent predictors of the need for surgical treatment: visible fat lobules (p = 0.028), translucent fat lobules (p < 0.001), dermal step-off in the wound bed (p < 0.001), visible blood vessels (p < 0.001) and coagulated blood vessels (p = 0.023). Also, higher color code ranges on our own developed wound bed classification were significantly related to a surgical intervention (p = 0.006). When including the LDI flux values, the perfusion units were significantly different (p < 0.001) between the exclusively LDI-blue areas treated conservatively (mean 145.7) and the areas ultimately treated with autografts (mean 119.5).

CONCLUSION

To the best of our knowledge, this study is the first to address the clinical wound bed evaluation of LDI-confirmed deep burns after NexoBrid® application. Based on our results, it is recommended to evaluate the wound bed twice: immediately after removing NexoBrid® to assess the viability of the wound bed and after the WTD period to reach a more complete decision. During these evaluations, wound bed characteristics such as incomplete debridement, visible and/or translucent fat lobules, visible and/or coagulated blood vessels and a dermal step-off in the wound bed combined with a higher range (4-5) in the newly developed wound bed color code should lead to an early and reliable decision for skin grafting. For burn centers using LDI, mean flux values below 119.5PU - in addition to the above-mentioned wound bed evaluation - are a clear indicator for surgical therapy.

Laser doppler imaging - the role of poor burn perfusion in predicting healing time and guiding operative management

AIM

To identify if the proportion of poor blood flow (blue) within an LDI (Laser doppler Imaging) image of a burn independently correlates with healing time.

METHODS

Patient age, gender, burn type, and burn surface area were collected from the IBID (International Burn Injury Database). All LDI images were copied from the MoorLDI2-BI- Laser Doppler (MLDI) Scanner, onto Adobe Photoshop® version 2020 for pixel counting analysis and calculation of % TBSA (Total Body Surface Area) blue. Multiple linear regression analysis determined whether a proportional relationship was present for each parameter (age, gender, % TBSA Blue and comorbidities) with healing time.

RESULTS

110 patients with 197 burns were scanned with MLDI. Median age was 5 years (IQR 1-6). Median burn surface area was 1.5% (IQR 1-2.4). 56.4% of patients were male and patients were scanned an average of 2.68 days (SD±1.37) following burn injury. Number of physical comorbidities and age were found to have a statistically significant relationship with healing time (p = 0.03, p = 0.002). Gender and %TBSA blue did not have a statistically significant relationship with healing time (p = 0.07 and p = 0.058 respectively). We found a statistically significant difference in the mean healing time between burns with and without blue (3.43 weeks vs. 2.80 weeks, p = 0.0001). % TBSA Blue was more than four times higher in the operated group (0.48% vs. 0.11%) and was shown to have a statistically significant relationship with decision to operate (p = 0.027). Positive predictive value for the presence of blue on operative rate was 71.6%. Age, gender and number of comorbidities did not have a statistically significant influence on operative rate (p = 0.07, p = 0.50 and p = 0.49).

CONCLUSION

% TBSA blue was not found to be a reliable independent indicator of burn healing time, but the presence of blue within an LDI image, advanced patient age and increased number of comorbidities did have a statistically significant relationship with healing time. This suggests their standardised inclusion into management decisions regarding intermediate depth burns is warranted.

Enzymatic debridement: past, present, and future

INTRODUCTION

Early surgical debridement of the deep second and third-degree burns is still the standard of care (SOC) to prepare the wound bed for skin grafting. However, this technique has some drawbacks that explain the growing interest in enzymatic debridement as an alternative. In this article, we provide a historic overview as well as the current state-of-the-art and future prospective of this type of non-surgical debridement.

MATERIALS AND METHODS

A narrative review of the available literature was conducted using a systematic search.

RESULTS

A total of 32 articles were included. The only enzyme mixture still used nowadays for burn eschar removal is bromelain-based. There is increasing evidence that this type of enzymatic debridement is a powerful tool to selectively remove the eschar in deep burns, thereby reducing the need for autologous skin grafting compared to surgical SOC. Moreover, off-label use of enzymatic debridement with NexoBrid^® (facial, pediatric, and >15%TBSA burns) has proven to be effective and safe.

CONCLUSION

There is increasing evidence that bedside administered NexoBrid^®, preferably under regional anesthesia, is a powerful tool for selective burn eschar removal. However, the clinical wound bed evaluation post-NexoBrid^® procedure in relation to the optimal treatment decision-conservative treatment vs. surgery-is not yet completely elucidated. More high-quality prospective clinical trials are necessary to compare enzymatic debridement of objectively confirmed deep burns with the current standard treatment and assess the effectiveness of the eschar removal, the need for surgery, the healing time of such wounds, and the long-term scar quality.

The LDI Enigma Part II: Indeterminate depth burns, man or machine?

INTRODUCTION

Laser Doppler imaging is universally considered the most evidence-based method for objective burn depth assessment by accurately predicting burn wound healing potential. This study has analyzed how exactly laser Doppler imaging measurements can be useful in the early therapeutic decision making for patients with clinically indeterminate depth burns.

MATERIAL AND METHODS

An extensive survey, by questionnaire and in-depth interviews, was conducted among 51 burn centers worldwide to gain insight on the practical use of laser Doppler imaging.

RESULTS

Twenty-seven (53%) of the 51 burn centers contacted almost completely answered the 32 questions. Fifty-two percent of these centers (14/27) had at least 10 years of laser Doppler imaging experience. laser Doppler imaging was considered to be mainly or almost completely accurate by 89%. In case of discrepancy between clinical assessment and LDI, 41% relied more on clinical diagnosis, 25% delayed decision to operate, while 16% re-scanned the next day. The centers most experienced with laser Doppler imaging (13%) relied on it more. Final decisions for treatment were based on the combination of laser Doppler imaging and clinical assessment by 74%. Seventy percent of the centers almost never operated burns with laser Doppler imaging-red and would almost always operate burns with LDI-blue. Treatment decisions for intermediate laser Doppler imaging colors (pink, yellow and green) varied, with 76% basing decisions on other factors: % Total Body Surface Area (TBSA), general health, age, location of the burn, potential for colonization/infection, patient preference, compliance with aftercare, logistics, and socio-economic factors.

CONCLUSION

Laser Doppler imaging reduces the number of clinical indeterminate depth burns. For these intermediate depth burns on laser Doppler imaging, treatment decisions are based on a combination of interpretation ('man') and laser Doppler imaging measurements ('machine'). Thorough knowledge of confounding factors and validated laser Doppler imaging color code, consideration of surrounding laser Doppler imaging colors, the use of mean flux values, and not directly burn related factors are essential. Burn centers with most laser Doppler imaging experience considered laser Doppler imaging an indispensable diagnostic tool.

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.

3D-perfusion analysis of burn wounds using hyperspectral imaging

BACKGROUND

Determination of the depth of burn wounds is still a challenge in clinical practise and fundamental for an optimal treatment. Hyperspectral imaging (HSI) has a high potential to be established as a new contact-free measuring method in medicine. From hyperspectral spectra 3D-perfusion parameters can be estimated and the microcirculatory of burn wounds over the first 72h after thermal injury can be objectively described.

METHODS

We used a hyperspectral imaging camera and extended data processing methods to calculate 3D-perfusion parameters of burn wounds from adult patients. The data processing results in the estimation of perfusion parameters like volume fraction and oxygenation of haemoglobin for 6 different layers of the injured skin. The parameters are presented as depth profiles. We analyzed and compared measurements of wounds of different degrees of damage and present the methodology and preliminary results.

RESULTS

The depth profiles of the perfusion parameters show characteristic features and differences depending on the degree of damage. With Hyperspectral Imaging and the advanced data processing the perfusion characteristics of burn wounds can be visualized in more detail. Based on the analysis of this perfusion characteristics, a new and better reliable classification of burn degrees can be developed supporting the surgeon in the early selection of the optimal treatment.

Increased burn healing time is associated with higher Vancouver Scar Scale score

Increased burn wound healing time has been shown to influence abnormal scarring. This study hypothesised that scar severity increases commensurate to the increase in time to healing (TTH) of the wound. Wound healing and scar data from burn patients treated by the Burn Service of Western Australia at Royal Perth Hospital were examined. The relationship between TTH and scar severity, as assessed by the modified Vancouver Scar Scale (mVSS), was modelled using regression analysis. Interaction terms evaluated the effect of surgery and total body surface area - burn (TBSA) on the main relationship. Maximum likelihood estimation was used to account for potential bias from missing independent variable data. The sample had a median age of 34 years, TTH of 24 days, TBSA of 3% and length of stay of five days, 70% were men and 71% had burn surgery. For each additional day of TTH, the mVSS score increased by 0.11 points (P ≤ 0.001) per day in the first 21 days and 0.02 points per day thereafter (P = 0.004). The relationship remained stable in spite of TBSA or surgical intervention. Investigation of the effect of missing data revealed the primary model underestimated the strength of the association. An increase in TTH within 21 days of injury is associated with an increase in mVSS or reduced scar quality. The results confirm that efforts should be directed toward healing burn wounds as early as possible.

Long-term scar quality in burns with three distinct healing potentials: A multicenter prospective cohort study

The laser Doppler imager is used in cases of indeterminate burn depth to accurately predict wound healing time at an early stage. The laser Doppler imager classifies burns into three estimated healing potentials as follows: high, <14 days; intermediate, 14-21 days; and low, >21 days. At this time, the relationship between these healing potentials and long-term scar quality is unknown. The objective of this study was to determine the long-term scar quality of burns with three distinct healing potentials. The secondary objectives were to compare treatment strategies in intermediate wounds, to study the effect of the timing of surgery on low healing potential wounds and to identify predictors of reduced scar quality. Hence, in a prospective cohort study, scar quality was determined in patients whose burns were assessed with laser Doppler imaging. Scar Quality was assessed with objective and subjective measurement tools, including overall scar quality (Patient and Observer Scar Assessment Scale) as a primary outcome and color and elasticity parameters. A total of 141 patients (>19 months postburn) with 216 scars were included. Wounds with high and intermediate healing potential did not significantly differ regarding scar quality. Wounds with a low healing potential had a significantly lower scar quality. Analysis of 76 surgically treated low healing potential wounds showed no significant differences in the primary outcome regarding the timing of surgery (≤14 days vs. >14). Predictors of reduced long-term scar quality were darker skin type and multiple surgeries. In conclusion, scar quality was strongly related to the healing potential category. Scar quality was very similar in high and intermediate healing potential wounds. No positive effects were found on scar quality or on healing time in surgically treated wounds with intermediate healing potential, advocating a conservative approach. Further studies should focus on the optimal timing of surgery in low healing potential wounds.

Aquacel(®) Ag dressing versus Acticoat™ dressing in partial thickness burns: a prospective, randomized, controlled study in 100 patients. Part 1: burn wound healing

INTRODUCTION

Studies comparing contemporary silver dressings in burns are scarce.

METHODS

In a prospective, randomized, controlled study, counting 50 patients/research group, we compared two frequently used silver dressings, Acticoat™ and Aquacel(®) Ag, in the management of partial thickness burns with a predicted healing time between 7 and 21 days as assessed by laser Doppler imaging between 48 and 72h after burn. Variables investigated were related to baseline research group characteristics, wound healing, bacteriology, economics, nurse, and patient experience.

RESULTS

Both research groups were comparably composed taking into account gender, age and burn characteristics. Similar results were obtained as to healing time and bacterial control with both silver dressings. A statistically significant difference in favor of the Aquacel(®) Ag dressing was found for average ease of use (p<0.001), average ease of application (p=0.001), patient pain (p<0.001), patient comfort with the dressing (p=0.017), silver staining (p<0.001), and cost effectiveness (p<0.001).

CONCLUSION

Both silver dressings resulted in comparable healing times and bacterial control but the Aquacel(®) Ag dressing significantly increased comfort for patients as well as nurses and was significantly more cost-effective than the Acticoat™ dressing for the given indication.