Introduction Cutaneous wound healing of post-burn injuries is a complex interaction between cells and the extracellular matrix.[1,2] While researchers and clinicians may understand the complexity of the intercellular and intracellular signaling, the cellular language is still a mystery. To achieve regeneration of the skin without scarring remains the ultimate goal of burn care researchers and clinicians. Wound healing manipulation to achieve regeneration without scarring is being approached from many angles, with work in the fields of fetal wound healing, cytokine expression, cellular responses, and tissue engineering. Currently, however, wound healing manipulation is not performed in a consistent manner due to lack of adequate research in these areas. The complex wound healing process starts with the initial onset of injury and continues, or evolves, through the fully matured scar response. This understanding and the proper interventions should be combined with accurate assessment of the temporal phase of healing for optimal healing and minimal scarring to occur. Clinicians may attempt to manipulate the scarring process through the following: presurgical wound care that minimizes bacterial contamination and maximizes tissue salvage; surgical preparation of the wound bed; introduction of skin grafting techniques; and postoperative graft care to facilitate incorporation. In addition to these strategies, cellular epithelial autografts (CEAs) may also be used in the treatment of burn wounds and, ultimately, prevention of scarring. Since 1993, CEAs have been used to augment wound healing. The aim of this paper is to describe the clinical implementation of CEA suspension in context with holistic burn patient care. The current clinical management of burn wounds utilizing this technology in combination with other techniques is described and discussed in this article. Clinical Management Assessment. Burn wound assessment is the vital first step in developing an appropriate burn management plan. The key features of assessment should be to determine the depth of the injury, the extent of the injury, and the body sites involved. Figure 1 illustrates the different levels of burn wounds with the appropriate treatments for each level. A burn wound that heals in less than 10 days has a four-percent risk of developing scar hypertrophy. However, a burn wound that takes 21 days or more to heal has a 70-percent or greater risk of developing scar hypertrophy; therefore, time to healing is pivotal in achieving the optimum outcome. A wound that heals in approximately 10 days is treated conservatively with attention to tissue preservation and control of secondary infection and with a dressing system that is comfortable and easy to use. As the burn wound heals, or evolves, the initial assessment of potential healing capacity may need revision. Until recently, clinicians have had to rely on clinical judgment; however, the use of the laser Doppler scanning technology has improved the objectivity of assessment. Surgical intervention. If a burn wound of sufficient depth takes longer than 10 days to heal, then it is appropriate to consider surgical interventions. Prior to surgical intervention, every effort should be made to salvage tissue with accurate resuscitation to preserve the zone of stasis. The surgical intervention required is dictated by the burn defect in terms of size, depth, and site. The skin thickness and vascularity varies over different body sites, e.g., the dorsum of the hand compared to the buttock. Further, the surface characteristics vary at different body sites depnding on function, e.g., the eyelids to the palms of the hands. When planning the optimal surgical intervention, the clinician must consider the anatomy of the defect, function of the area, extent of the injury and general patient condition, cosmetic implications, and donor tissue availability. CEA suspension. The focus of care should be on dermal preservation using debridement, which should combine sharp dissection and dermabrasion. A mid-dermal injury predominantly loses epidermis; therefore, in order to replace “like with like,” a site-matched CEA suspension may be introduced to the debrided and cleaned wound bed. The CEA suspension is a perioperative harvested cell population and may be obtained using the ReCell® kit* (Clinical Cell Culture Ltd., Bentley, Western Australia), a medical device used for harvesting autologous skin cells. Developed as an “off-the-shelf” kit, it enables a thin split-thickness biopsy, taken at the time of procedure, to be processed into an immediate cell population for delivery onto the wound surface. This process facilitates the provision of an epidermal suspension by the combination of enzymatic and physical disintegration. The expansion ratio for this technique is 1:80; therefore, if the area of wound cover is greater than two to four percent of total body surface area, CEA suspension spray, CellSpray®* (Clinical Cell Culture Ltd., Bentley, Western Australia) may be used. The CEA suspension spray is a single-cell suspension of cultured epithelium delivered to a wound in an aerosol spray. The process of laboratory-based expansion of cell number takes five days and the ratio of expansion is at least 1:500. The CEA suspension is predominantly made up of keratinocytes, but melanocytes coexist in the cell population, which are clinically evident by return of appropriate pigmentation.[9,10] When using CEA suspension, the cells are very active across the surface of the wound but they are also very vulnerable to fibrinolysis associated with bacterial contamination. Further, they do not form keratin and, hence, do not develop a waterproof structure until they become confluent. Therefore, the dressing system used should protect the wound surface, allow modest transpiration, be flexible, and avoid sheering in order for the cells to attach, proliferate, migrate across the surface, become confluent, and differentiate. The use of CEA suspension has rapidly been incorporated into routine clinical use in both the adult and pediatric burn units of Western Australia. In addition to the treatment of acute burn injury, CEAs have been used for a variety of clinical indications (Table 1). Since 1997, the authors have used the peri-operative cell harvesting kit for immediate peri-operative use in more than 200 patients (Figures 2A–C, 3A–D, and 4A–C). Dermal grafts. If an injury progresses into the deep layers of the reticular dermis, the epidermal cells are in increasingly unfamiliar territory. Therefore, a papillary dermal element should be introduced into the environment. This may be achieved using a thin split-thickness skin graft or a thin split papillary dermal graft. The grafts can be meshed to increase the area of cover and the CEA suspension may be sprayed over the mesh. The epidermis should be site-matched wherever possible. The rapid disappearance of the mesh pattern is anticipated with rapid evolution of the scar. Skin substitutes. In a full-thickness injury, dermal replacement should be considered. Although this can be achieved in a number of ways, as suggested by research,[11–13] in this article, the authors discuss the use of Integra™ tissue-engineered skin substitute (Johnson & Johnson Medical, Division of Ethicon, Inc., Arlington, Texas). This skin substitute provides a template for autologous cell growth from the wound bed. The fibroblasts and endothelial cells express the phenotype of reticular dermis when they migrate into this architectural environment. The wound may then progress from a full-thickness defect to a deep dermal defect during the period of vascularization and dermal regeneration. After this, the clinicians can then proceed with the epidermal replacement, which involves the use of mesh split-thickness grafts and site-matched CEA suspension sprayed onto the surface. During the postoperative phase of graft incorporation, the focus of the multidisciplinary burn care team should be on protection of the grafted wound. The dressing should protect the surface to prevent sheer, prevent excess moisture losses, and prevent contamination, which may lead to infection. Between four and seven days postsurgery, mobilization should be initiated. Mobilization. Initially, nonweight-bearing mobilization should begin at dressing changes while the clinician visually inspects the graft and wound bed for problems. Once the wound stabilizes, days five through seven, the wound should be covered with a protective dressing, and pressure and mobilization should be initiated that encourage normal patterns of movement by the patient. Pressure. As soon as possible after seven days, pressure should be applied to the grafted area. The area should be protected with a retention dressing. The pressure garments incorporate a lining of hydrophobic fabric to further reduce sheer and wick moisture from the surface, which prevents maceration. Early surveillance for scar hypertrophy should be undertaken, and intervention with contact media, steroids, and secondary surgery should occur when necessary. The philosophy of the author’s unit is that rehabilitation commences at the time of injury and is continuous throughout the healing process. Discussion The focus of the author’s multidisciplinary burn team is scar minimization. Scar formation can be influenced at every stage of wound healing from first aid at the site of injury to secondary reconstructive surgery many years later. Scarring can result from the initial injury as well as from the length of time taken for the injury to heal. Many other factors play roles in scar formation. For example, genetic predisposition to scarring and infection can affect the formation of scars. However, since the length of time to achieve healing is key, use of tissue-engineering technologies that provide wound cover in shorter time frames is important. Ten years ago, CEAs were used in sheet form. Initially, the sheets took three weeks to produce.[15–17] This timeframe was too long to impact scar quality.4 By 1993, this time frame had been reduced to 10 days, which was more acceptable for routine clinical use. However, a major problem with sheet CEAs was their fragility, which led to difficulty in handling in laboratory and clinical settings.[13,14] This problem led to the investigation of the use of CEAs in a suspension. Benefits of CEA suspension are that it can be produced for clinical use in five days and it is relatively easy to use and handle in both the laboratory and clinical settings. More importantly, the performance of the suspension on the wound is superior relative to previous experiences with sheet CEA.[18,19] The cells in CEA suspension are actively attaching, migrating, and proliferating. The surface signaling is in the proliferative phase. Once the cells become confluent, they differentiate to produce keratin. The author’s clinical experience has been that scar quality is improved in terms of color and contour with the use of CEA suspension. On review of scar management techniques, the author has shown in her clinic a decrease in the need for pressure garments from 91 percent in 1992 to 18 percent in 2001 in the pediatric population. The transfer of appropriate pigment is routinely seen clinically.[23,24] The observation that scars are smooth with rapid fading of the mesh pattern in the author’s clinic has led to collaborative studies investigating the speed of healing and quality of epidermis comparing mesh split skin graft (SSG) to mesh SSG with CEA spray. The concept of cell signaling is key in manipulating regeneration not repair. Harvesting cells from a noninjured site that are programmed for regeneration and introducing these harvested cells into a site where the local cells are programmed for repair is of great interest and warrants further research. The balance in the cell population may influence the outcome in terms of regeneration versus repair. There is evidence that scarring is not purely a dermal phenomena. The interaction of all cells within the three-dimensional structure of the extracellular matrix have an influence or are influenced by the wounding and scarring process. Keratinocytes interact with the dermal fibroblasts, which is key. The introduction of CEA suspensions can enhance epithelial repair in a timely fashion to improve the quality of the scar outcome. * ReCell® and CellSpray® are pending clinical trials and regulatory approvals.
Clinical Potential of Autologous Epithelial Suspension
Issue: Volume 15 - Issue 1 - January 2003
Index: WOUNDS. 2003;15(1):16-22.