This work was supported by grant No. 4368-3 from the Grant Agency of the Ministry of Health of the Czech Republic.
SUMMARY Early excision and grafting changed dramatically topical wound treatment, but are restricted by difficulty in diagnosing burn depth, by limited donor sites and by technical skills to excise special areas (perineum, face). In addition to the extent of burn and the age of the patient the depth is determinant of mortality, morbidity and of patient's quality of life. It results from the time-temperature relation and is further influenced by local and systemic causes of conversion: dehydration, edema, infection and shock hypoxia, metabolic derangements, peripheral vessels diseases may contribute do deepening of burn wound. Superficial burn on day one appears deep dermal by day three, where spontaneous epithelization lasts much longer than 21 days and results in hypertrophic scarring. To prevent this sequelae deep dermal burn may be treated like full-thickness injury with excision and autografting. Another way is removal of dead layers of corium and using biological or synthetic cover. We have found a more effective way to reach wound closure (not only cover) in the method of „upside-down" application of recombined human/pig skin (RHPS), composed of allogeneic human keratinocytes cultured on cell-free pig dermis. The allogeneic epidermal cells temporarily „take", „close" the excised wound and simultaneously encourage epithelization from adnexa remnants in the wound bed. Thus definitive closure is achieved.
Die Deckung and der Verschluß der Verbrennungsflächen
Königovä R., Matouskovä E, Broz L.
Die frühe Exzision and Autotransplantation beeinflußen dramatisch die Lokalbehandlung der Verbrennungsfläche, aber sie werden beschränkt durch die Diagnose der Verbrennungstiefe, den Mangel an den Entnahmeflächen and die technische Geschicklichkeit die speziellen Gebiete (Perineum, Gesicht) zu exzidieren. Außer des Verbrennungsumfangs and des Patientenalters entscheidet über die Mortalität and Lebensqualität des Patienten gerade die Tiefe der Verbrennungsfläche. Die Lokal- and Systemursachen der Konversion - Dehydratation, Ödem, Infektion and Schockhypoxion, metabolische Störungen and Erkrankungen der peripheren Adern - tragen zur Vertiefung der Verbrennungswunde bei. Die am ersten Tag festgestellte oberflächliche Ergreifung erweist sich am dritten Tag als tiefe dermale Ergreifung, wann die spontane Epitelisation mehr als 21 Tage dauert and dessen infolge die hypertrophischen Narben entstehen. Die Konversion and Vernärbung kann man durch die frühzeitige Beseitigung der nekrotischen Schicht des Koriums and durch die Anwendung der effektiven biologischen Deckung vorbeugen. An unserer gemeinsamen Arbeitsstelle wurde die rekombinierte Haut entwickelt, die aus den allogenen menschlichen Keratinozyten entsteht. Diese Keratinozyten wurden am zellenlosen Schweindermis kultiviert. Die rekombinierte Haut appliziert man „umgekehrt" - also die Keranozyten werden in die Wunde fläche gerichtet. Das Schweindermis liefert der Deckung die Hautkonzistention and deckt die Wunde and epidermahlen Zellen von außen. Die allogennen Keratinozyten heilen zeitweilig an, verschließen die Wunde and stimulieren die allmähliche Epitelisation aus den Andexüberresten in der frühen Fläche. Dadurch erreicht man eine fließende and dauerhafte Deckung.
Key words: burn wound conversion, delivery system for cultured keratinocytes, recombined human/pig skin
Traumatic wound management has always subsequent events observed in the patient reprebased on the fundamental surgical principle of sent a continuum without any clear points of immediate debridement of necrotic tissue and pri- separation (6). Although early excision and graftmary wound closure. Burns have been the excep- ing changed dramatically local care, this procetion to this principle. A burn wound and all the dure is still restricted by difficulty in diagnosing burn depth, by limited donor sites and by technical skills to excise certain areas (face, perineum). The depth of the burn wound is determinant of the late prognosis causing fatal outcome in very extensive burns and influencing quality of life due to scar formation in survivors. Depth is variable factor being altered by many additional insults.
Wound which appears superficial on day one may appear deep on day three or four (Fig. 1, 2).
| <% immagine "Fig. 1","gr0000009.jpg","Superficial partial-thickness burn on day one (on admission).",230 %> | <% immagine "Fig. 2","gr0000010.jpg","Deep partial-thickness burn on day three. ",230 %> |
Superficial partial-thickness (superficial dermal) burn wound in confined to the papillary dermis, epidermis is destroyed, but the fat domes remain uninvolved. The prick test is positive, blisters appear above pink coloured burn area, which blanches with pressure (capillary refill is positive). The blood flow to the dermis is increased over that of normal skin. Surface healing with the reepithelization is achieved in less than 21 days from skin appendages (hair shafts, sebaceous and sweat glands) without hypertrophic scar formation or contraction.
The nature of dermis-fat interface is important in differentiating between superficial and deep partial-thickness burn.
Deep partial-thickness (deep dermal) burn wound is confined to reticular dermis, epidermis is destroyed together with the papillae of corium and the nerve endings. The prick test is negative, blisters appear above mottled burn area, which does not blanch with pressure (capillary refill is negative). Due to prolonged period of spontaneous epithelization from surviving subdermal elements, lasting longer than 21 days, the resulting scars are hypertrophic, frequently with contraction.
The conversion of superficial dermal into deep dermal or even into full thickness skin loss is encountered during the whole course of burn treatment. The causes of conversion are local and systemic.
Among local causes belong:
Among systemic causes belong: shock hypoxia due to vasoconstriction and to systemic edema; metabolic derangements (diabetes mellitus); atherosclerosis and other diseases of peripheral vessels; massive wound sepsis caused by Pseudomonas. This microb initiates thrombosis in the subcutaneous tissue and thus progression of necrosis follows.
Unless additional insults convert the wound in deep dermal (deep partial-thickness) wound, biological cover is the best treatment modality.
Burn wound dressing should fulfil 3 functions: - protective = barrier to infection,
- metabolic = reducing evaporative heat losses,
- comfort = eliminating air currents + acting as a splint.
Conventional dressing made up of gauze + tulle gras does not fulfil any of the functions in comparison with some synthetic and biological dressings that are of different types.
Wound coverage materials include:
I. synthetic dressings:
films: polymer sheets include polyurethane, polyethylen, polycaprolactone, polytetrafluoroethylen, dimethyl aminoethyl methacrylate. Films have no absorbing capacity, they are impermeable to water and gases and provide no barrier to microbes;
foams: copolymers of hydroxy vinyl chlorid acetate, polyvinyl, polyurethane, silastic foam, lyofoam. Foams have absorbing capacity, they provide thermal insulation and are permeable to gases and water;
composite (synthetic dressings): hydrocolloid dressings (Granuflex, Epigard, Biobrane), hydrogel sheets (Vigilon), gels (HEMA = hydroxy ethyl methacrylate), super absorbent (Conva Tee);
II. biological coverage is important:
a) in superficial partial-thickness wounds, where it avoids dessication, limits microbial invasion, minimizes pain, reduces fluid and protein losses;
b) as temporary coverage in excised and granulating wounds;
c) for coverage of widely meshed autografts in the intermingled transplantation to prevent desiccation of the wound bed exposed between the bridges of autografts:
Wound coverage must be distinguished from wound closure!
Wound coverage materials rely upon adhesion into the wound fibrin layer or into the wound coagulum in excised full-thickness wounds. They do not biodegrade, they function only as temporary substitutes and must be replaced with patient's own skin, either by reepithelialization or autografting (isografting) or by skin substitutes (artificial skin, skin equivalents), that would be biologically accepted by the wound bed and become incorporated permanently into the healing area:
• INTEGRA (produced by Lifesciences corporation) consists of porous collagen-glycosaminoglycan layer coated with a silicone membrane, which serves as a temporary substitute for the epidermal layer of skin by providing mechanical protection and moisture retention.
Histological examination showed cellular ingrowth leading to formation of random collagen fibres resembling normal dermis. After removal of silicone membrane (artificial epidermis) ultrathin split-thickness skin graft was transplanted to the dermal template.
• Cellular artificial shin substitute (2) was produced by short period simultaneous culture of fibroblasts on a dermal collagen sponge and keratinocytes on an epidermal collagen sponge placed on the dermal collagen sponge so that the keratinocytes would not enter the pores of the dermal collagen sponge. One week after grafting, kerationocytes formed 6-10 layers consisting of basal, squamous, granular and horney layers. Rete pegs were formed between epidermis and dermis, indicating papillary formation.
The skin equivalents should supplement insufficient autografts in extensive burns with shortage of donor sites!
Burn eschar involving full-thickness skin loss (and thrombosis in subcutaneous tissue) represents an open wound providing no barrier to infection, no barrier to plasma loss nor to heat loss. Although the tissue is dead metabolically, it contains heat-derived products causing distant organs dysfunction. Lipid protein complex stimulates cytokine cascade and development of the systemic inflammatory response syndrome.
Treatment is based on removal of dead tissue using two types of escharectomy:
Deep partial-thickness (deep dermal) burns - falling somewhere between the two - superficial and full-thickness skin loss, heal by delayed epithalization and by hypertrophic scar formation (Fig. 3, 4, 5, 6).
| <% immagine "Fig. 3","gr0000011.jpg","Deep partial-thickness burn of face in an 11-year-old boy.",230 %> | <% immagine "Fig. 4","gr0000012.jpg","Tangential excision 20 days after accident. ",230 %> |
| <% immagine "Fig. 5","gr0000013.jpg","Healed thin split-thickness skin graft. ",230 %> |
<% immagine "Fig. 6","gr0000014.jpg","2 years after accident: upper and lower lip + chin required reconstruction using full-thickness skin",230 %> |
Needless to say that appropriate healing cannot be achieved until the slough of dermis is removed. Re-epithalization is dependent upon the presence of an appropriate substrate on which epidermal cells can migrate. The papillary dermis and basement membrane are vital in this respect and not only provide a structural scaffold for epidermis, but are a source of cytokines and growth factors for the subsequent maturation of the overlying new epidermis (5).
Whereas superficial partial thickness burns generally heal within 3 weeks under conservative treatment (under biological coverage) for deep partial thickness burns various treatment modalities have been tried for removal and after removal of necrotic layer of dermis:
For removal of the necrotic layer of dermis in chemical burns A. Eldad, A. Weinberg et al. (1) compared tangential excision to laser ablation and to enzymatic debridement using Debridase gel or Trypsin. Excimer laser ablation accelerated significantly wound closure. Lesion area of laser ablated burns was reduced by 80 % of its original size within 6 days and closed within 2 days.
Surgical tangential excision did not improve wound healing and it is difficult to control the amount of tissue to be removed and to control the blood loss.
| <% immagine "Fig. 7","gr0000015.jpg","Vertical section of the RHPS. ",230 %> |
<% immagine "Fig. 8","gr0000016.jpg","Petri dish containing RHPS which has skin-like consistency and thus is easy to handle.",230 %> |
| <% immagine "Fig. 9","gr0000017.jpg","Deep dermal (deep partial-thickness) burn on upper extremity.;",230 %> | <% immagine "Fig. 10","gr0000018.jpg","Burn wound after tangential excision and RHPS coverage.",230 %> |
The healing effect of Debridase was highly significant on day 7, resulting in a graftable bed that healed within 10-14 days. A quick and simple technique used for removal of necrotic layer of dermis in chemical burns published by P. Rice et al. (5) that could be carried out even by non-medical personnel in mass injuries is dermabrasion. Dermabrasion of thermal burns was reported already in 1947 by P.C. Iverson who was using Sandpaper, then in 1963 by Lorthior J., later in 1977 by Krant S. M., Arons M. S. and in 1984 J. D. Holmes and CRW. Rayner employed power driven carborundum wheel. The need for skin grafting and complications of hypertrophic scarring or excessive granulations - has limited acceptability of this method.
The studies (5) evaluating dermabrasion in experiments on pigs by means of emery cloth showed the problem of achieving accurate dermabrasion without damaging the surrounding normal epidermis. Therefore, in further studies a hand-held cordless electric drill fitted with either small circular sanding discs or grinding stones was employed. In these experiments burn wounds subjected to dermabrasion started to epithelize in one week and were completely closed by new differentiated epidermis by 4 weeks. Areas left untreated showed no epithelial regeneration before 3 weeks and burn wound closure was not complete by 8 weeks post-exposure. During this prolonged healing phase infection is always a significant problem, as it destroyes epithelium in the remnants of skin appendages and stimulates granulation tissue to proliferate. To avoid this proliferation after removal of the necrotic layer of dermis skin substitutes for coverage have been used o encourage wound closure by spontaneous reepithalization and thus preventing also hypertrophic scarring.
In our experience, an effective way to reach wound closure - not only coverage - is the method of „upside-down" application of recombined human/pig skin, composed of allogeneic human keratinocytes cultured on cell-free pig dermis (3). For removal of dead layers of corium there has been used either tangential excision or deep dermabrasion employing a forceps when the necrotic layer of dermis had been dissolved by antibacterial creams or by means of the apparatus AESCULAP GB 400. After meticulous hemostasis the allogeneic epidermal cells were applied covered by xenodermis (cell-free). There was proved temporary „take" (3).
The final closure of excised or abraded wounds was achieved by replacing the allogeneic donor keratinocytes with the epithelia from adnexa remnants in the wound bed. Allogeneic keratinocytes stimulate healing not only by early coverage of the wound but also by producing growth factors and cytokines.
It should be pointed out that any surgery to burns that would heal spontaneously in a short time, is not only unnecessary, but is unjustifiable and harmful to the patient and doing no harm is one of the principles in medical ethics!
The recombined human/pig skin negates the requirements for additional autografting and additional morbidity from donor sites, and in some cases - especially in children - avoids hypertrophic scarring causing „permanent stigmatization by apparence, which is then reinforced at every stage of education and is the root of the patient's distress" (Mc Growther, 1997).