Annals of Burns and Fire Disasters - vol. XII - n° 4 - December 1999

EARLY TANGENTIAL EXCISION WITH THE GUIDANCE OF METHYLENE BLUE APPLICATION

Celikoz B, Deveci M, Nisanci A.

Gulhane Military Medical Academy, Ankara, Turkey

SUMMARY. The difficulty of distinguishing devitalized tissues from vital tissues in the early post-burn period has long been a deterrent to adequate debridement. Clinical observation is still the only standard method for estimating what is to be excised, but it cannot reliably identify the critical zone of vascular stasis that separates necrotic from viable tissue. In our present clinical study we have evaluated the reliability of a practical method in which methylene blue is used to predict burn depth. The mechanism underlying this procedure exploits the metabolism of methylene blue in vital tissues, where it is converted into leucomethylene by the enzyme reductase. Pre-operative application of methylene blue enabled us to make an accurate prediction of the depth of thermal injuries while performing early tangential excision. The mean value of graft take rates was found to be 98% in all patients treated by skin grafting following tangential excision performed with the method of pre-operative methylene blue application. Acceptable wound healing, increased graft survival, and diminished intra-operative blood loss appear to be the main advantages provided by this procedure compared with conventional early tangential excision. In conclusion, we highly recommend performing early tangential excision with the guidance provided by the application of methylene blue.

Introduction

The extent and depth of thermal injury, the presence of a pre-morbid pathology, and the patient's age are the primary determinants of mortality and morbidity following thermal injury. Among these, burn depth deserves special consideration in terms of the patient's long-term appearance and functioning. In recent years, with better understanding of burn shock pathophysiology, the resuscitation of burn shock patients is successfully carried out by most surgeons. However, mortality and morbidity rates remain high with respect to extent and depth of the burn wound.
Treatment of burn shock and early tangential excision with autografting are the mainstay of management in deep burns. Inadequate eschar excision leads to skin graft loss, which results in enlargement of the total area of open wounds with the addition of graft donor areas and inevitable subsequent additional operations. Although small burns in the hands and feet are not a life-threatening risk for patients, such wounds have to be treated in the early post-burn period if patients are to return to their daily and social activities as soon as possible. First- and second-degree superficial burn wounds in the extremities are treated by non-surgical methods such as hydrotheraphy, but the treatment of deep burn wounds, i.e. second- and thirddegree, requires effective surgical treatment techniques. Appropriate eschar excision in deep burns prevents not only the loss of functional ability but also the non-cosmetic appearance of the hands, feet, and other parts of the body. The modem treatment of deep burns therefore entails early surgical excision rather than waiting for spontaneous eschar separation.
Because of the importance of burn depth in burn treatment, several methods have been suggested to enhance the accuracy of burn depth prediction. However, despite the advances of modem technology, there is as yet no method for the precise determination of burn depth, clinical observation still being the standard method. During conventional tangential excision, the surgeon considers punctuate capillary bleeding in order to delineate underlying viable tissue Bleeding points may not be seen during the excision stage when a tourniquet is used, while blood loss is extensive when the tourniquet is deflated. It is thus crucial that this aggressive surgical procedure must depend on accurate recognition of burn depth in order to prevent the unnecessary excision of healthy tissue and significant blood loss that may jeopardize the patient's chances of survival. A method that can provide a precise indication of burn depth has thus become a subject of primary consideration for surgeons.
In our present clinical study, we have evaluated the reliability of a practical method in which methylene blue is used for predicting burn depth during the early tangential excision stage. This method consists of the application of methylene blue over the burned area one day prior to the operation.

Materials and method

Between January 1997 and March 1998, 42 patients with full-thickness or deep partial-thickness burn injuries were treated by early tangential excision associated with an autograft procedure in which a new method of predicting burn depth was employed. Thii~y-one male patients (74%) and eleven female patients (26%) with a mean age of 24 yr and a mean burn extent of 27% T13SA underwent early tangential excision between 4 and 7 days post-burn.
Gauze impregnated with a 5% concentration of methylene blue was wrapped over the burned areas 12 h before the operation (Fig. 1).

Fig. 1 - Appearance of burned leg 12 h after application of methylene blue dye. Notice the variable coloration of the burn surface in relation to the variable depth of the thermal injury.

Tourniquets were applied to prevent bleeding in all the patients subjected to operation. The blue-stained eschar tissues were excised by deepening the excision until the unstained tissue border was reached. After completion of the excision at the upper level of the unstained tissue, the tourniquet was deflated and bleeding was controlled by electrocautery. It was observed that there was less bleeding, as evidenced by the scarcity of bleeding points, when this method was compared with conventional excision techniques (Fig. 2).

Fig. 2 - Same leg after burn wound excision aided by intra-operative application of methylene blue. Notice the sparse bleeding, less than that usually occurring following conventional excision performed without the guidance of methylene blue.

Autograft procedures were performed to cover the excised areas followed by conventional dressing with vaseline-impregnated gauze. Blood transfusions were not necessary for any of the patients, owing to the diminished blood loss with our method.

Results

The average percentage of the full-thickness burn areas treated with the procedure of pre-operative methylene blue application followed by early tangential excision and auto2raftinR was 23%. The mean graft take rate was 98% (Fig. 3).

Fig. 3 - Final acceptable result after grafting of excised areas.

One patient underwent secondary skin grafting because of minimal graft loss. No live tissue was encountered in histopathological studies. The application of methylene blue thus enabled us to discriminate necrotic tissue from viable tissue.

Discussion

The extent and depth of burns are essential determinants of mortality and morbidity following thermal injury. A number of techniques have been defined for the determination of burn depth, such as wound biopsy, the pin prick test, ultrasound, vital dyes, laser Doppler perfusion monitoring (LDPM), laser Doppler imaging (LDI) magnetic resonance imaging (MRI), thermal imaging, and light reflectance or spectroscopic techniques.
Histological dermal biopsy has been reported to diagnose dermal burn depth accurately. One or more punch biopsies are taken from regions of clinically indeterminate burn depth. Although histological dermal wound biopsy seems to be the most precise method, the technique is not without its drawbacks. First, the technique requires an experienced pathologist to distinguish live collagen from denatured collagen and living cells from dead cells. Second, since a burn wound continues to have dynamic properties for several days, wound biopsy is not practical with regard to early tangential excision within the first 5-7 days of burn injury; it therefore generally takes 7 days to obtain reproducible results. Third, biopsies leave permanent scars in partial-thickness wounds. Fourth, biopsies are expensive and time-consuming techniques. For all these reasons, wound biopsy is rarely used in clinical practice.
B-mode ultrasound scanning was first used by KaluS7 to assess burn depth by observing the presence of dermal boundaries. Watchel et al. however reported that ultrasonic studies failed to show burn depth in controlled studies using clinical evaluation and histological parameters. It was shown that collagen denatures at 65 °C while the epidermal cells from which burns heal are killed at about 47 °C. Nevertheless, the use of ultrasound in the determination of burn depth presents some technical difficulties. The requirement of tissue contact is a further limitation of the ultrasound technique. As a result, apparent depth is likely to be underestimated by ultrasound.
Laser Doppler or light reflectance has been reported to be effective in the estimation of full-thickness burn injury. LDPM and LDI have been used for determination of burn depth. Excellent results were reported in early studies. However, laser Doppler flowmetry, as also thermography, is highly dependent on certain external conditions, such as room and body temperature, the patient's anxiety and stress level, and the body area considered. Laser Doppler flowmetry is non-invasive, easy to use, but expensive, and it has not been used routinely in clinical applications. It is also time-consuming and too slow for clinical decision-making.
MR1 depends on the water content of tissues. Koruda et al. reported that in the immediate post-burn period MR1 could distinguish the higher water content in partial- and full-thickness rat burns from that in adjacent normal skin. They found that within 48 h partial-thickness burns returned to control values, while full-thickness burn remained oedematous. MR1 could therefore be used to distinguish full-thickness burns from partial-thickness burns. Clinically speaking, however, MR1 is still not very practical.
Vital dyes such as India ink, blue V, toluidine blue, trypan blue, Evans blue, and disulphine blue have been used to provide sharp demarcation between living and necrotic tissues. The clinical use of these techniques has however shown that they do not produce sharp enough demarcation to guide excision Fluorescein flowmetry can be used for the determination of burn depth since fluorescein, injected systemically, can be detected by ultraviolet light. It has however been reported by Heimbach et al., Gatti et al., and Black that the technique can diagnose only very deep and very superficial burns, while the distinction between intermediate and deep dermal burns cannot not be made, a distinction that is crucial in operative planning.
In the present study, methylene blue was used to distinguish vital tissue from necrotic tissue in patients subjected to early tangential excision. Methylene blue is mainly used to treat methaemoglobinaemia. It has a mildly antiseptic activity and is also used as a dye in diagnostic procedures such as fistula detection. Methylene blue is metabolized and converted into leucomethylene by vital tissues following application. Since leucomethylene is a colourless dye, it is easy to distinguish non-vital tissues from vital tissues, as described here. During the application procedure, methylene blue impregnated gauze was wrapped over the burned area 12 h prior to the operation. It can also be mixed with silver sulphadiazine or other topical burn agents, although impregnated gauze application alone proves easier than other applications. We observed that at the time of surgery necrotic tissue was coloured but viable tissue was not. All non-vital tissues were therefore removed when coloured tissues were completely excised. This procedure helped us to determine the demarcation zone and minimize vital tissue excision and blood loss.
In conclusion, none of the above-mentioned techniques for the determination of burn depth is a precise indicator of burn depth at the excision stage, while on the contrary the application of methylene blue is such an indicator. Pre-operative methylene blue application enabled us to predict the depth of burn injury accurately while performing early tangential excision. A precise tissue excision level, appropriate wound healing with living tissue, increased graft survival, and diminished intraoperative blood loss appear to be the main advantages of this procedure compared with other techniques. We therefore highly recommend performing early tangential excision with the guidance provided by the application of methylene blue.

RESUME. La difficulté de distinguer entre les tissus dévitalisés depuis longtemps et les tissus vitaux décourage les chirurgiens d'effectuer un débridement adéquat. L'observation clinique reste la seule méthode pour évaluer les parties qu'il faut exciser, même si elle ne peut pas identifier avec certitude la zone critique de la stase vasculaire qui sépare le tissu nécrotique du tissu vital. Les Auteurs de cette étude se sont proposés d'évaluer la fiabilité d'une métode pratique où le bleu de méthylène est employé pour prédire la profondeur de la brûlure. Les mécanismes de cette méthode dépendent du métabolisme du bleu de méthylène dans les tissus vitaux où il est converti en leucométhylène par l'enzyme réductase. L'application préopératoire du bleu de méthylène a permis aux Auteurs de prédire précisément la profondeur des lésions thermiques pendant qu'ils effectuaient l'excision précoce tangentielle.
Ils ont trouvé que le taux moyen de prise des greffes était 98% dans tous les pateints traités avec la greffe cutanée suivie par
l'excision tangentielle effectuée avec l'application préopératoire du bleu de méthylène. Les principaux avantages offerts par cette
méthode confrontés avec ceux de l'excision précoce conventionnelle étaient la guérison acceptable des lésions, la survie augmentée
de la greffe, et la réduction des pertes interopératoires de sang. En conclusion, les Auteurs recommandent chaleureusement la
technique de l'excision tangentielle précoce avec l'assistance de l'application du bleu de méthylène.