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Compendium March 2004 (Vol 26, No 3)

Partial-Thickness Skin Grafting for Large Thermal Skin Wounds in Dogs

by Carlos L. Aragon, DVM, Stephanie E. Harvey, DVM, Sheila W. Allen, DVM, MS, DACVS, M. A. McCrackin Stevenson, DVM, PhD , DACVS

    Abstract

    An optimal clinical outcome for large, full-thickness thermal skin wounds in dogs is predicated on aggressive preoperative wound management, assessment and treatment of concurrent medical problems, careful surgical planning and execution, and intensive postoperative care. Skin stretching, expanding and advancing techniques, skin flaps, omental grafts, and full-thickness skin grafts have been described for use alone or in combination for managing large skin wounds. Partial-thickness skin grafting may be a feasible surgical option when these familiar full-thickness techniques are not practical because of the size and location of the wound(s). This article describes the indications, advantages, disadvantages, and technical aspects of partial-thickness skin grafting and provides case-based examples of its application in dogs.

    Large thermal skin wounds involving greater than 15% to 20% of the total body surface area in dogs present multiple medical and surgical treatment challenges. These skin injuries most commonly result from accidental or malicious thermal burns, sometimes involving a chemical accelerant. Dogs with these injuries have a wide variety of clinical presentations, from seemingly unaffected to severe shock. Those severely affected require aggressive stabilization and medical management. Concomitant medical problems that can result from loss of large areas of skin include anemia, neutropenia, hypoproteinemia, dehydration, electrolyte imbalances, pain, and weight loss. Repair of the wound prevents loss of red and white blood cells, blood and tissue proteins, body fluid, and electrolytes through the wound.

    Some large skin wounds may not be amen­able to repair by full-thickness reconstruction techniques. Techniques such as skin stretching, expansion and advancement, tension-relieving primary closure, and skin flaps may not be possible because of insufficient adjacent skin. Free full-thickness skin grafting and microvascular free grafting may not be practical if the size of the defect exceeds what can be covered by the amount of distant donor skin available for full-thickness grafting. The size of the wound may impair wound contraction, and the location may predispose the animal to a function-limiting wound contracture if healing only by second intention is allowed (Figure 1). This article describes the use of partial-thickness skin grafting in dogs with large thermal skin wounds and reviews the advantages, disadvantages, indications, and technical considerations of this surgical treatment option.

    Initial Wound Management and Assessment for Surgical Treatment

    Dogs with large thermal skin wounds should first be treated for life-threatening complications, if present, such as shock, smoke inhalation, and hemorrhage. The initial goal of wound management is to establish a healthy bed of granulation tissue free of necrotic debris and infection.1 Historically, wound debridement involves serial changes of three-layer bandages containing an adherent contact layer to promote granulation tissue.

    Once granulation tissue is present, occlusive or semiocclusive dressings can be used to promote epithelialization, dermal healing, reduction in perceived pain, better cosmetic results, ease of application, and reduction in the number of bandage changes.1 An important factor in the enhancement of healing open wounds is the composition of the bandage material used. A study evaluating the effects of equine amnion, a biosynthetic hydrogel dressing, transparent polyethylene sheeting, and a semiocclusive rayon-polyethylene nonadherent dressing on open-wound healing in dogs concluded that the mean percentage of wound contraction and total wound healed of the amnion-bandaged wounds was greater than that for wounds bandaged with the other dressings.2,3

    Modern advancements in wound management have produced a multitude of medications that stimulate wound healing, dressings that enhance healing, and skin protectants to assist in wound protection. Release of interleukin-1 and tumor necrosis factor by macrophages can be stimulated by products such as acemannan. Together, these cytokines stimulate and enhance fibro­blast proliferation, neovascularization, collagen deposition, and epidermal motility and growth.3,4 Once the wound is sufficiently covered in healthy granulation tissue, definitive surgical therapy can be initiated.

    The location and size of the wound should be considered when selecting an appropriate method of surgical closure. The location of the wound can determine whether healing by second intention will be deleterious to adjacent joints or body orifices, whether neighboring or distant donor tissue for a skin flap is available, or whether recipient vessels are available for a microvascular free-transfer flap. The size of the wound will determine whether secondary closure or full-thickness grafting is feasible. The donor sites for full-thickness grafts must be surgically closed, limiting the size of the recipient site that can be covered. The donor sites for thin and medium partial-thickness grafts are partial-thickness wounds and need not be closed. The partial-thickness defect created can reepithelialize within 3 weeks.1 Therefore, the amount of donor skin available for partial-thickness grafting greatly exceeds that for full-thickness grafting. Both full- and partial-thickness grafts can be meshed to allow expansion for covering large areas.

    The cost of medical and surgical care associated with management of large thermal skin wounds is very high, even without complications. Veterinary clinicians must educate clients thoroughly regarding staged medical and surgical management.

    Indications, Advantages, and Disadvantages

    Partial-thickness skin grafts have a variety of advantages and disadvantages compared with other forms of wound closure. Careful consideration of each is important before managing every case. The primary indication and advantage of partial-thickness skin grafts in dogs is in the reconstruction of large full-thickness wounds without sacrificing full-thickness skin from donor sites. Donor sites heal as partial-thickness wounds and have the advantage of minimal tissue injury because the wound is made under aseptic conditions with minimal trauma.1 Partial-thickness skin grafts have also been shown to survive more readily than full-thickness skin grafts because of the denser capillary network in the more superficial dermal layers, which more readily allows capillary linkup.5,6 This may explain the higher percentage of viability of partial-thickness skin grafts than full-thickness skin grafts in early studies.5,7 Al­though subsequent studies showed that full-thickness grafts had a higher percentage of viability than previously reported, the difference in viability between partial- and full-thickness grafts was not statistically significant.7,8 A previous comparison study by McKeever and Braden9 of meshed, thin partial-thickness grafts (0.063 cm); meshed, medium partial-thickness grafts (0.127 cm); and meshed, full-thickness grafts in dogs suggested that thin partial-thickness grafts had the highest survival rate (89%), with full-thickness grafts (58%) and medium-thickness grafts (47%) having lower success rates.9 Meshing both a partial- and full-thickness skin graft decreases graft contracture by increasing the number of edges from which epithelialization can occur. Additional advantages of meshed skin grafts include the reconstruction of irregular surfaces (concave and convex) and application in a graft bed with exudate (blood or serum). Furthermore, meshed partial-thickness skin grafts possess the characteristics of rapid donor site reepithelialization and multiple harvests of partial-thickness skin from areas of thick skin.10

    Disadvantages of partial-thickness skin grafts include technical difficulty while harvesting, initial low durability of partial-thickness skin that is susceptible to trauma, sparse or absent hair growth on both the grafted and donor sites, and a scaly appearance resulting from the lack of sebaceous glands.6,9,10 Partial-thickness skin grafts also require the use of specialized and expensive equipment and additional training.10 Furthermore, the expense and time associated with intense postoperative care can be expensive and time-consuming. Despite the difficulty of harvesting, it has been reported to become easier with practice.11 Our experience supports the use of partial-thickness skin grafting in dogs with large thermal skin wounds that are irreparable by traditional methods.

    In summary, partial-thickness skin grafting can be useful when applied in managing large thermal skin wounds in dogs. Partial-thickness skin grafting would most likely be performed at a veterinary medical school or a highly equipped surgical specialty practice because of associated intense postoperative care as well as the required expensive equipment and training for its use. This surgical option is chosen based on the size and location of the wound(s), availability of the necessary equipment, experience of the surgeon, and availability of personnel to provide postoperative care. Furthermore, the primary advantage of partial-thickness skin grafting is that the donor sites do not have to be surgically apposed and are allowed to heal by reepithelialization. This advantage enables more versatility in selecting donor site locations when limited donor sites are present, an obvious advantage over full-thickness skin grafting. Partial-thickness skin grafting should be considered when other forms of wound closure are not practical or achievable as a sole means of therapy.

    Surgical Technique for Meshed, Partial-Thickness Skin Grafts

    Allowing a bed of granulation tissue to form over the wound before the surgical application of a partial-thickness skin graft is critical for graft survival.1,5-7,10,12 Granulation tissue fills in wound space, functions as a protective barrier, and provides nourishment to applied skin grafts.12 Healthy granulation tissue does not bleed excessively and is flat, red, and free of a surface film of sloughing collagen.10

    There are multiple methods for harvesting partial-thickness skin grafts.1,5,6,10,13 One method uses various types of freehand skin graft knives and blades. Depth control can be a concern, although several types of knives have depth-control mechanisms.5 Examples of freehand devices include safety razors (although hard to find), scalpel blades, and skin graft knives.5,14 Alternatively, several dermatomes have been used to obtain split-thickness skin grafts in dogs, thereby producing a more consistent result.1,6,14 Examples include the Zimmer Dermatome (Zimmer Manufacturing, Warsaw, IN), the Brown Electric Dermatome (Zimmer Manufacturing), and the disposable Davol/Simon Cordless Dermatome (Davol, Cranston, RI).1,15 Dermatome use has also been described in humans and horses.16-18 Booth reported an 88% graft acceptance rate of split-thickness autogenous skin transplantation in horses.16

    Graft donor sites are relatively flat surfaces such as the lateral thoracic wall.6,10,13 However, the ventral thorax, lateral thigh, back, and neck have been described as split-thickness graft donor sites in dogs.6,9,15 Following aseptic preparation of the donor site, sterile saline may be injected subcutaneously to assist in elevating the skin from the underlying bony structures in very thin dogs.6,10,13 Next, the skin should be lubricated with sterile water-soluble lubricant or sterile mineral oil. The blade of the dermatome should also be lubricated. A lever and an exchangeable base plate on the dermatome determine the thickness and width of the graft, respectively. Thickness of the graft can be selected from 0 to 0.76 mm. A graft 0.38-mm thick is usually selected for use on dogs.6 Graft harvesting requires a team of surgeons. A minimum of three surgeons is needed, with the primary surgeon operating the dermatome and assisting with holding the skin taut. One assistant surgeon holds the skin taut in the opposite direction as does the primary surgeon. The second assistant surgeon elevates the graft as it is being harvested (Figure 2), meshes the graft, and then places it on the recipient site.

    Meshing the graft can expand it by three to nine times its original area.1 Templates for graft meshing are selected based on the amount of expansion necessary. Meshing a graft can be performed either by hand, using a No. 11 or 15 scalpel blade, or using a mesh graft expansion unit1,5,6 (Figure 3). The use of a scalpel blade is generally reserved for full-thickness grafts.1 When using a mesh graft expansion unit, a dermatome-harvested partial-thickness graft is placed dermal side down on the aluminum block with staggered, notched, parallel rows of cutting blades (Padgett Instruments, Kansas City, MO). A Teflon roller is then passed over the graft in the direction of the blades to cut slits in the graft. Repeated application and roller compression may be needed for complete cutting of the graft.1,5,6 Meshing the graft also allows fluid drainage from beneath the graft.6,19

    The grafts should be placed on the wound immediately. If this step must be delayed, the skin grafts should be placed in gauze sponges moistened with sterile saline. Grafts should be placed on the wound so that they overlap the wound edges by 1 to 4 mm.6,10 The graft can then be carefully attached by simple interrupted sutures or staples to the surrounding skin, and tacking sutures can be used to hold meshed grafts to the central regions of the wound and to assist in pulling the graft into concavities.1,5,6,10,14,15,20 Careful attention is required while placing these tacking sutures to address and limit bleeding.1 Affixing the graft to the surrounding skin with tissue adhesives has also been documented in several species.21-23 Fibrin glues are preferred by many human surgeons for their hemostatic and adhesive effects and convenience of application.21 In humans, fibrin glues remain the most versatile and have proven clinical efficacy in improving skin graft survival and in decreasing blood loss when grafting large burn sites.23 In dogs, a recent study evaluated the tensile strength of sutured skin incisions with and without the application of fibrin glue. Results suggested a significant increase in tensile strength in the fibrin glue group.21

    Partial-thickness donor sites do not require primary closure, which is one of the major advantages of this technique. A disadvantage of partial-thickness skin grafting is that donor sites managed as open wounds tend to be more painful than if they were excised and primarily closed.6 After placement of the graft, the wound should be gently irrigated with saline solution or thrombin before applying the dressing.1,6,20 Antibiotic ointment on a finely woven, nonadherent dressing or petrolatum-impregnated gauze commercially purchased or prepared by the surgeon can be applied to the wound followed by absorbent bandage layers. The bandage should be secured with circumferential elastic tape on the limbs or umbilical tape tied through suture loops anchored in the skin for trunk, abdominal, and perineal areas.1,6

    Postoperative Management

    Failure of partial-thickness skin graft survival can be caused by motion of the graft over the wound bed, infection, or hematoma and seroma formation beneath the graft, which prevent adhesion and capillary linkup.1,10,24 The adherence and revascularization process occurs over the first 48 to 72 hours.1,5,6,15,24 This is a staged process that functions as a continuum involving graft adherence, plasmatic imbibition, inosculation, and the penetration and ingrowth of new vessels.1,5,6 Initially, a fibrin network adheres the graft to its bed. Once the cut vessels dilate, the fibrinogen-free, serum-like fluid and cells are absorbed into the graft.1,5,6,14,15,25 This process in which capillary action pulls cells and serum into dilated graft vessels is called plasmatic imbibition. Inosculation is the anastomosis of graft vessels with recipient bed vessels of approximately the same diameter and takes place as early as 22 hours after graft placement.5,6,14,24

    Postoperative immobilization and preventing the dog from molesting the graft are critical components of the initial graft adherence process. Immobilization can be achieved by casts/splints, sedation, or general anesthesia. Immobilization choices should be made through a combined assessment of patient status, size and location of the skin grafted sites, and financial concerns of the owners. If general anesthesia is deemed most appropriate for initial postoperative immobilization, controlling complications associated with long-term anesthesia (e.g., hypotension, hypothermia, aspiration pneumonia, renal compromise) is of utmost concern.

    The first bandage is usually changed 48 hours after surgery.6,10 Because of the risk of contamination or graft movement, the longer the intervals between bandage changes, the better.2,5,6,9 Skin grafts near joints and high-movement areas can pose a significant challenge with immobilization, and grafts over pressure points require pressure relief. Casts and splints may be used in conjunction with wound dressings to aid in graft immobilization,5,20 but improper placement or slippage may put damaging bandage compression on the grafts as well.

    At every bandage change, skin graft viability should be assessed based on color, swelling, and adherence to the wound bed. Colors to note are pink, blue (cyanotic), black, and white. Pink indicates that the graft is undergoing revascularization. Blue suggests that cyanosis is occurring, which indicates congestion of the graft with resultant fluid and erythrocyte embedment. The eryth­rocytes within the graft temporarily lose oxygen and produce a blue color. As the graft revascularizes, the cyanosis subsides as the oxygen content increases. Areas of the graft that appear white immediately after graft placement on the recipient site are due to vasospasm of intradermal vessels. As plasmatic imbibition and revascularization occur, the vasospasm subsides and the graft becomes pink. A graft or part of a graft that remains white indicates that revascularization has not occurred. The wound bed should be checked for discharge and a foul smell. Culture and sensitivity samples should be collected if infection is suspected. After the first bandage change, subsequent bandage changes can be repeated in a similar fashion every 2 to 3 days, depending on graft appearance.1,6 Donor sites can be covered with a light bandage containing a single layer of petrolatum-impregnated gauze or antibiotic-coated nonadherent pads. Donor site bandage changes can coincide with recipient site bandage changes. Special attention should also be directed toward pain control, systemic monitoring for sepsis, and testing for hypoalbuminemia and anemia.

    Conclusion

    Thermal wounds in dogs can range from minor epidermal irritations to extensive full-thickness skin defects. We have had successful surgical reconstructive results with partial-thickness skin grafting of large thermal skin wounds when other forms of full-thickness repair are not usable as a sole or combined means of surgical therapy. This technically challenging surgical treatment modality is not intended to replace full-thickness skin grafting but instead is intended to add to the reconstructive options useful in managing large thermal skin wounds in dogs. Patient individualization and assessment determine adjunctive surgical needs, and consideration of referral to a highly equipped surgical center for partial-thickness skin grafting is an option.

    Acknowledgment

    The authors thank Drs. Christine Egger, Karen Cornell, Clarence Rawlings, and the students and staff of The University of Georgia Small Animal Teaching Hospital for their contributions to intensive patient management.

    See box .

    Downloadable PDF

    1. Pavletic MM: Atlas of Small Animal Reconstructive Surgery, ed 2. Philadelphia, WB Saunders, 1999, pp 11–32, 107–119, 131–296.

    2. Ramsey DT, Pope ER, Wagner-Mann C, et al: Effects of three occlusive dressing materials on healing of full-thickness skin wounds in dogs. Am J Vet Res 56(7):941–949, 1995.

    3. Swaim SF: Advances in wound healing in small animal practice: Current status and lines of development. Vet Derm 8(4):249–257, 1997.

    4. Swaim SF, Gillette RL: An update on wound medications and dressings. Compend Contin Educ Pract Vet 20(10):1133–1144, 1998.

    5. Swaim SF: Surgery of Traumatized Skin: Management and Reconstruction in the Dog and Cat. Philadelphia, WB Saunders, 1980, pp 423–476.

    6. Swaim SF: Skin grafts, in Slatter DH (ed): Textbook of Small Animal Surgery, ed 3. Philadelphia, WB Saunders, 2003, pp 321–338.

    7. Bauer MS, Pope ER: The effects of skin graft thickness on graft viability and change in original graft area in dogs. Vet Surg 15(4):321–324, 1986.

    8. Pope ER: Effect of skin graft preparation and graft viability on the secondary contraction of full-thickness skin grafts in dogs. Am J Vet Res 46(12):2530– 2535, 1985.

    9. McKeever PJ, Braden TD: Comparison of full- and partial-thickness autogenous skin transplantation in dogs: A pilot study. Am J Vet Res 39(10):1706– 1709, 1978.

    10. Probst CW, Peyton LC, Bingham HG, et al: Split-thickness skin grafting in the dog. JAAHA 19:555–568, 1983.

    11. Spreull JSA: The principles of transplanting skin in the dog. JAAHA 4:71–84, 1968.

    12. Lee AH, Swaim SF: Granulation tissue: How to take advantage of it in management of open wounds. Compend Contin Educ Pract Vet 10(2):163–168, 170, 172–173, 1988.

    13. Fox SM, Probst CW: Split-thickness autogenous skin transplantation in a dog. Vet Med Small Anim Clin 77:782–787, 1982.

    14. Hedlund CS: Skin grafts, in Fossum TW (ed): Small Animal Surgery. St. Louis, Mosby, 1997, pp 128–134.

    15. Swaim SF: Skin grafts. Vet Clin of North Am Small Anim Pract 20(1):147–175, 1990.

    16. Booth LC: Split-thickness autogenous skin transplantation in the horse. JAVMA 180(7):754–757, 1982.

    17. Frankland AL: Autologous, split skin transplantation on the lower limbs of horses. Vet Rec 104(26):590–595, 1979.

    18. Sidebottom AJ, Stevens L, Moore M, et al: Repair of the radial free flap donor site with full or partial thickness skin grafts. Int J Oral Maxillofac Surg 29(3):194–197, 2000.

    19. Pope ER: Skin grafting in small animal surgery. Part II: Full-thickness skin grafting techniques. Compend Contin Educ Pract Vet 10(9):1068–1077, 1988.

    20. McGregor AD, McGregor IA: Fundamental Techniques of Plastic Surgery and Their Surgical Applications, ed 10. London, Churchill Livingstone, 2000, pp 1–99.

    21. Park W, Kim WH, Lee CH, et al: Comparison of two fibrin glues in anastomoses and skin closure. J Vet Med 49(7):385–389, 2002.

    22. Schumacher J, Ford TS, Brumbaugh GW, et al: Viability of split-thickness skin grafts attached with fibrin glue. Can J Vet Res 60(2):158–160, 1996.

    23. Gosain AK, Lyon VB: The current status of tissue glues. Part II: For the adhesion of soft tissues. Plastic and Reconstructive Surgery 110(6):1581–1584, 2002.

    24. Pope ER: Skin grafting in small animal surgery. Part I: The normal healing process. Compend Contin Educ Pract Vet 10(8):915–923, 1988.

    25. Converse JM: Plastic surgery and transplantation of skin, in Skin Surgery. Springfield, IL, Charles C. Thomas, 1970, pp 161–182.

    References »

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