ORIGINAL RESEARCH Veterinary Surgery 23:494-502. 1994 zy The Effect of Occlusive and Semi-Occlusive Dressings on the Healing of Acute Full-Thickness Skin Wounds on the Forelimbs of Dogs PAUL W. MORGAN, D V M , D V S c , ALLEN G. BINNINGTON, D V M , MSc, Diplomate ACVS, CRAIG W. MILLER, DVM, MVSc, Diplomate ACVS, DALE A. SMITH, D V M , DVSc, ANNE VALLIANT, a n d JOHN F. PRESCOTT, MA, Vet MB, PhD BSc, zyxwvutsrq zyxwvu zyxwvu zyxwvutsrq zyxwvut zy This project compared the effects of hydrocolloid (HC) and hydrogel (HG) occlusive dressings and a polyethylene (PE) semi-occlusive dressing on the healing of acute full-thickness skin wounds on the forelimbs of 10 dogs. All treatments resulted in a similar degree of healing at postoperative days 4 and 7. No significant differences existed in the number of wounds that were more than 90% healed at postoperative day 28 between the group treated with the HG dressing and the group treated with the PE dressing. There were significantly fewer wounds more than 90% healed at postoperative day 28 in the group treated with the HC dressing. Wounds under the HG dressing had the largest mean percentage of contraction at postoperative days 2 1 and 28. Wounds under the HG dressing also had the largest contraction/re-epithelializationratio (postoperative days 2 I and 28) compared with wounds under the PE and HC dressings. Wounds under the PE dressing had a significantly higher mean percentage of re-epithelialization than wounds under both occlusive dressings on postoperative days 14, 2 I , and 28. Wounds under the two occlusive dressings had exuberant granulation tissue present more often than wounds under the PE dressing. The two occlusive dressings had significantly higher bacterial counts on wounds compared with wounds under the PE dressing; analysis of variance (ANOVA), P = .0008. Wounds under the HC dressing showed the poorest healing in all parameters. @Copyright I994 by The Americun College of C'L.ferinur,vSirrgcwns I NJURIES to the extremities that result in fullthickness skin loss occur commonly in dogs.' Other full-thickness wounds on limbs occur secondary to tumor removal or skin excision caused by penvascular injections of caustic agents. One method of treatment is management as an open wound with second intention healing2 Healing of full-thickness open wounds takes place by wound contraction and epitheliali~ation.~ It has been suggested that healing of an open wound will occur more quickly if it is covered with a bandage.3 Selection of the proper bandage material and method of application may affect the rate of healing. A semiocclusive dressing creates a moist environment that allows excess exudate to be absorbed by the intermediate layer of the bandage. This helps to prevent tissue maceration and infe~tion.~ Occlusive dressings, in contrast, prevent exudate loss from the surface of the wound. They reportedly increase the rate of re-epithelialization in partial-thickness There may be a relationship between the rate of re-epithelialization and the degree of occlusion by the dre~sing.~,~ The effect of occlusive dressings on dermal repair has received less attention.6 Some researchers report From the Department of Clinical Studies. Department of Pathology, Department of Microbiology and Immunology, Ontario Veterinary College, University of Guelph. Guelph, Ontario. Canada. Address reprint requests to Allen G. Binnington. DVM. MSc, Diplomate ACVS, Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N lC 2W 1. OCopyright 1994 by The American College of Veterinary Surgeons 016 1-3499/94/2306-0008$3.00/0 494 MORGAN ET AL more rapid dermal repair in wounds covered by occlusive In contrast, others report a decrease in the healing of wounds under occlusive dressings compared with wounds exposed to the air." There are also conflicting results with respect to the degree of bacterial contamination, tissue maceration, and wound contraction that occur under occlusive dressings.'?-I9 There is a lack of consistency in the literature describing healing of full-thickness wounds treated with occlusive dressings. This study compared the effects of two types of occlusive dressings and a more traditional semi-occlusive dressing on the healing of full-thickness wounds on the forelimbs of dogs. 495 applied to position C, dressing no. 2 was applied to position A, and dressing no. 3 was applied to position B, on the right limb of dog no. 2 and so on. Three dressings were evaluated in this study, two occlusive dressings and one semi-occlusive dressing. The two occlusive dressings were a hydrogel (Curity Conforma Gel. Kendall Canada Inc., Peterborough, Ontario, Canada) (HG) (treatment no. I , high 02,C 0 2 permeability) and a hydrocolloid (Comfeel Systems, Smith & Nephew Inc., Lachine, Quebec, Canada) (HC) (treatment no. 3 , low 02,C 0 2permeability). Neither had been previously evaluated for use in full-thickness wounds in dogs. The semiocclusive dressing (treatment no. 2) consisted of two layers of perforated polyethylene (Melolite, Smith & Nephew lnc) (PE) with a layer of fleece cotton interposed between them. This dressing is commonly used for the treatment of open wounds in dogs. All dressings were covered with a fine mesh gauze, rolled cotton, and stretch porous tape (Easifix Cohesive Bandage, Smith & Nephew Inc) to keep them in place. Elizabethan collars were used to keep the dogs from damaging the bandages. The bandages were inspected on a daily basis by the principal investigator. The occlusive dressings were changed every 4 to 7 days according to the manufacturer's criteria, or sooner if wound fluid was noted penetrating the bandage. Bandage changes also were performed in association with the bacterial culture and wound tracing schedule (postoperative days 4, 7, 14, 21, and 28). The semi-occlusive bandages were changed according to standard wound treatment protocol^,^ every 1 or 2 days when fluid accumulation was high and every 4 to 7 days thereafter as fluid production decreased. Bandage changes followed the outlined protocol with the exception of 10 occasions in which a bandage was soiled, had slipped, or was partially removed by individual dogs. In such cases, the dogs were restrained and the bandages were repaired and the dressings were replaced if necessary. Postsurgical evaluations were done on days 4, 7, 14, 21, and 28. The wounds were evaluated for bacterial growth, quantity and quality of granulation tissue, rate of healing, and microscopic evidence of healing (postoperative day 28). On each evaluation day, the dogs were sedated with oxymorphone and acetylpromazine using the previously noted doses. The dressings were removed and excessive debris was cleaned from each wound with a sterile gauze pad. Bacterial analysis was done by rolling a sterile cotton swab over the entire wound surface, with no wound area being swabbed more than once. The cotton swab from each wound was placed in a sterile container filled with 2 mL of phosphate-buffered saline, stored at 4°C and plated within 4 hours of retrieval. Aliquots ( 1 mL) of the suspension were measured in a I: 10 dilution and a 1: 100 dilution. Each dilution was plated on blood agar and MacConkey's agar using a 0.0 I-mL loop. After 48 hours zyxwvutsr MATERIALS AND METHODS zyxwvut Ten healthy adult mixed breed dogs, weighing between 20 and 25 kg, with forelimbs measuring approximately 17 cm between the elbow joint and carpus, were used in the study. The protocol was approved by the institutional animal care and use committee. The dogs were sedated with oxymorphone (0.10 mg/kg intramuscular [IM]) and acetylpromazine (0.05 mg/kg IM). Anesthesia was induced by intravenous injection of 10.0 mg/kg thiopental and maintained with halothane and oxygen. Both forelimbs were prepared for aseptic surgery; the dogs were alternated from left to right lateral recumbency to allow exposure of each forelimb. Three squares, measuring 2.0 cm along each side, were outlined on each forelimb between the elbow and the carpus using a sterile pen and plastic template. The proximal site was designated as position A, the middle site designated as position B, and the distal site was designated as position C. The proximal square was outlined on the lateral aspect of the antebrachium 3 cm below the elbow joint. The second outline was marked 3 cm distal to and 120" clockwise from the proximal wound. The third outline was similarly marked 3 cm and 120" from the second outline. The outlined areas were excised through the full thickness of the skin, including the entire dermis, using a # 10 scalpel blade. Dressings were designated as treatment no. 1, no. 2, or no. 3 and were applied to the newly created wounds; no. 1 was placed at position A, no. 2 was placed at position B, and no, 3 was placed at position C on the right limb ofthe first dog. Subsequent dressing placements were systematically rotated to ensure each dressing was applied to each site an equal number of times. On the left limb of the first dog, the dressings were moved distally by one position so that dressing no. 1 was applied at position B, dressing no. 2 was applied at position C , and dressing no. 3 was applied at position A. This procedure was performed on each of the remaining dogs' forelimbs for a total of 20 limbs. Dressing no. 1 was zyxwvuts zyxwvutsr zyxwvutsrq 496 zyxwvut EFFECT O F OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS of incubation, the species and number of colonies of bacteria isolated from each wound were identified using standard procedures.*' After bacterial cultures were obtained, the quality of the granulation tissue under each dressing was subjectively assessed as healthy (red and granular) or unhealthy (grey and friable). Exuberant granulation tissue was defined as granulation tissue completely filling the wound bed and protruding above the level of normal skin. Wound surface area analyses were performed by tracing each wound onto clear plastic sheets, outlining the wound edge and the advancing edge of epithelium (Fig I A). The wound edge was defined as the margin between intact skin and either granulation tissue or new epithelium. The tracings were then transferred onto clear acetate sheets: the surface areas were digitized and computed in square millimeters using an Image I morphometrics analysis package (Empix Imagin, Universal Imaging Corp., WestChester, PA). The areas measured for each wound included the remaining unhealed wound area, ie, that not covered by either contracting skin or advancing epithelium, and the area covered by advancing epithelium but not by contracting full-thickness skin. The surface areas of each wound were determined on day 0, immediately after excision. This served as the baseline for obtaining rates of contraction, re-epithelialization, and wound healing for each wound. The percentage of wound contraction, percentage of wound re-epithelialization, unhealed wound area (unepithelialized granulation tissue), and contraction/epithelialization ratio were calculated for each wound (Figs 1A and IB). A healed wound was defined as a wound covered by either fullthickness skin, as the result of contraction, or by advancing epithelium from the wound margins. Uncovered granulation tissue was classified as not healed. Means and standard errors were determined for the three treatment groups and were used for statistical comparisons. On completion of the study (postoperative day 28), the dogs were anesthetized as previously described, and a 5to 6-mm wide longitudinal strip of tissue, including normal skin proximal and distal to the wound, was removed from the central wound area. The tissue samples were fixed in 10% neutral buffered formalin and embedded in paraffin. Each sample was sectioned at 6 pm and was stained with hematoxylin-eosin (HE) to assess the organization of the epithelial and dermal cellular components. The samples also were stained with Masson's trichrome to evaluate dermal connective tissue organization. At the end of the study, the dogs were placed for adoption or returned to the animal care facility. An analysis of variance (ANOVA; general linear model) was applied to the calculated variables (percentage of contraction, percentage of epithelialization, percentage healed, contraction/epithelial ratio, and bacterial counts) to determine the overall significance of treatment, posi- original wound margin (w.M.) contracted skin ~ \ * ** \ margin zyxwvutsrqpo zyx zyxwv advancing epithelial edge 0= / epithelialized (E.A.) area 0 W.A.= area (mm') of original wound (W.M.) on day 0. G.T.= area of granulation tissue (mm'). E.A.= epithelialized area (mm'). C.A.= contracted area (mm'). Percentage contraction (P.C.) = W.A. Percentage of original wound area epithelialized (P.E.) - I G.T W.A. .+ E.A.I x 100 zyxwv =E.A.x 100 W.A. Percentage of wound not healed (P.N.H.) ( = % O f W.A. with G.T.) Percent healed (P.H.) = 100 Contraction/Epithelial - =G.T. x 100 W.A. P.N.H. ratio (C/E) = W.A. - I G.T. + E . A . ~ E.A. Fig 1 . (A) Diagram showing the original wound margin, the contracted skin margin, the advancing epithelial edge, and the unhealed area of granulation tissue. The original wound margin was outlined on day 0. The contracted skin margin, and the advancing epithelial edge were outlined at each time interval and used for area calculation. (B) List of formulas used to calculate the percentage of contraction, epithelialization, total wound healed, and the contraction/epithelialization ratio; see also Fig 1A. zyxwvu zyx zyxwvu tion, and side. When significance was detected, a Duncan's multiple range test was used to identify the significantly different treatment. A significance level of P < .05 was used for all statistical analyses. RESULTS During the first week, both occlusive dressings were changed every 1 to 2 days, because of wound fluid leaking from the confines of the dressing. The PE dressing was changed every 1 to 3 days during the first week. zyxwvu z 497 MORGAN ET AL After 14 days, there was minimal fluid production under the PE dressing; three of 20 wounds at all positions were dry with a scab forming on top. The occlusive bandages had noticeable fluid production at all positions. As the wounds matured under both occlusive dressings the fluid production was less, so bandages were changed every 4 to 7 days as recommended. The exudate underneath the HC dressing was malodorous and tenacious and difficult to remove from the intact skin on all wounds, whereas the exudate underneath the HG dressing was easier to remove from the intact skin and had little odor. None of the dressings adhered to the wounds at any time during the study. On two wounds, use of the HC dressing resulted in maceration of the epithelium, one at postoperative day 21 and one at postoperative day 28. The initial ANOVA of wound area data indicated confounding factors including position, treatment* position, and treatment*side. The wounds at position A were slower to heal than those at positions B and C. When an ANOVA was performed on the wound area data from positions B and C alone, the confounding factors of position and side were absent and comparison of treatment groups was possible. Therefore, data from positions B and C were analyzed separately. This resulted in an analysis of 40 wounds divided into the three treatment groups (HG, n = 13; PE, n = 14; and HC, n = 13). Data from the 20 wounds at position A were analyzed separately (HG, n = 7; PE, n = 6; and HC, n = 7) and exhibited similar trends to positions B and C. However, data from position A had a larger standard error. The following results include data from positions B and C only. There were no statistically significant differences between treatment groups in percentage of contraction, percentage of re-epithelialization, contraction/ epithelialization ratio, or total percentage of wound healed on postoperative days 4 or 7. Initially, all wounds expanded at day 0; by postoperative day 4 contraction had begun and was apparent for the remainder of the study (Fig 2). On postoperative day 28 the mean percentage of contraction f standard error was 78.93 k 2.49 (HG), 61.46 t- 3.65 (PE), and 62.59 k 5.72 (HC); ANOVA, P = .016. At postoperative days 21 and 28, the wounds under the HG dressing were significantly different with a greater mean percentage of contraction than the HC and PE dressings. The wounds loo 8o - Hydrogel - - Polyethylene 11 Hydrocolloid * I 0 4 7 14 TIME (days) 21 zyx zy * 28 Fig 2. Percentage of contraction over time for treatment groups at positions B and C. Mean f standard error. *Hydrogel is significantly different (P< -05). under the HC and PE dressings were not significantly different on both days (Fig 2). Re-epithelialization was not apparent in any of the wounds until postoperative day 14. On postoperative day 14, the mean percentage of re-epithelialization f standard error was 27.59 +- 1.80 (HG), 42.88 k 3.20 (PE), and 33.10 i 2.77 (HC); ANOVA, P = .0006. The percentage of epithelium coverage was highest on postoperative day 14 for all treatments. On postoperative days 14, 21, and 28, wounds under the PE dressing had significantly more new epithelium covering them than wounds under both the HG and HC dressings (Fig 3). The wounds under the HG and HC dressings were not significantly different from each other on postoperative days 14, 2 1, and 28. The ratio of contraction to epithelialization was significantly larger for wounds treated with the HG dressing on postoperative days 21 and 28 (Fig 4). On postoperative day 28 the mean contraction/epithelialization ratio f standard error was 4.86 f 0.64 (HG), 1.86 t- 0.23 (PE), and 2.62 k 0.36 (HC); ANOVA, P = .0001. Wounds under the PE and HC dressings were not significantly different from each other on postoperative days 21 and 28. There was a significant difference in the total percentage of wound healed among treatments at postoperative days 14, 2 1, and 28 (Fig 5). On postop- zyxwvutsrq zyx zy zyxwvuts zyxwv 498 100 Z - - Hydrogel - - Polyethylene ---- Hydrocolloid - =l ! 60 - a a I k W W dressings had significantly higher bacterial counts than wounds under the PE dressing; ANOVA, P = .0008. Bacterial counts under both occlusive dressings were not significantly different from each other (Fig 6). There were no day/treatment interactions. Elevated bacterial counts were associated with a slipped or chewed bandage on four occasions when compared with the previous evaluation time at which the bandages were intact. In three of four wounds, the bacteria count decreased to a lower number on subsequent bandage changes when the bandages remained intact. Granulation tissue was present in all wounds by postoperative day 7. Exuberant granulation tissue (Fig 7) was evident on four of 13 wounds on postoperative day 14, four of I3 wounds on postoperative day 2 1, and six of 13 wounds on postoperative day 28 under the HG dressing. Exuberant granulation tissue was evident on six of 13 wounds on postoperative day 14, six of 13 wounds on postoperative day 2 1, and five of 13 wounds on postoperative day 28 under the HC dressings. Exuberant granulation tissue was evident on only two of 14 wounds on postoperative day 14 under the PE dressing. There zyxwvutsrq zyxwvutsrq 80 2 !I- zyxwvutsrq zyxw zyxwvutsrqpon zyxwvuts EFFECT OF OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS 40 - IY x 20 - 0 - zyxwvutsr zyxwvutsrqpo ~~ 0 ~~ 4 7 14 TIME (days) 21 28 zyxwvuts zyxwvuts Fig 3. Percentage of re-epithelialization over time for treatment groups at positions B and C. Mean _+ standard error. *PE is significantly different ( P < .05). erative day 28 the mean total percentage of wound healed was 98.04 k 0.78 (HG), 100.00 (PE), and 88.94 f 5. I2 (HC); ANOVA, P = .04. On postoperative day 14, wounds under the PE dressing were significantly higher. At postoperative days 2 1 and 28, wounds under the HG and PE dressings were not significantly different in their total percentage of wounds healed. Wounds under the HC dressing had significantly less total wound area healed on postoperative days 21 and 28. By postoperative day 2 1, 1 3 of 14 wounds under the PE dressing were healed, five of 13 wounds were healed under the HC dressing, and two of 13 wounds were healed under the HG dressing. On postoperative day 28, all 14 wounds were healed under the PE dressing, whereas seven of 13 wounds were healed under each of the HG and the HC dressings. Comparing the treated wounds at postoperative day 28, 13 of 13 wounds under the HG dressing were 290% healed, and nine of 13 wounds under the HC dressing were 290% healed. Sraphylococciis aiueiis (50 wounds), beta hemolytic Streptococcus sp. (25 wounds), Staphylococcus epidermidis (2 1 wounds), alpha hemolytic Streptococcus sp. ( 16 wounds), Escherichia coli (nine wounds), and Protetis mirabilis (nine wounds) were cultured most often. A two-factor ANOVA considering day and treatment found wounds under both the H G and HC - Hydrogel -- Polyethylene -__-Hydrocolloid T 5 - 4 - 0 F 3 - d w 0 2- 1 - 07 I I) 0 4 7 14 TIME (days) 21 * 28 Fig 4. The contraction/epithelialization ratio over time for treatment groups at positions B and C. Mean _+ standard error. "HG is significantly different ( P < .05). 499 MORGAN ET A L zyxwvutsrqpon zyxwvutsrqp zyxwvuts zyxwvut zyxwvutsrqp - Hydrogel - - Polyethylene Hydrocolloid 100 0 Y sI 0 Z 3 t- z w 80 60 of exuberant granulation tissue was noted in four of 12 unhealed wounds: one of six under the HG dressing and three of six under the HC dressing. Wounds under the PE dressing had 14 of 14 with mature granulation tissue present throughout the dermis when evaluated using Masson's trichrome stain. Wounds under the HG and HC dressings each had seven of 13 with mature granulation tissue throughout the dermis. DISCUSSION 40 V [L: w a 20 The traditional method of bandaging open wounds in small animals is to use absorbent dressings to draw wound fluid away from the wound surface into the bandage. This may be accomplished with an adherent wet-to-dry contact layer in the initial stages of wound treatment which aids in debridement of superficial debris.*' As re-epithelialization commences the adherent contact layer is replaced by a nonadherent nonocclusive or semi-occlusive contact layer. In either case, the objective is to draw wound fluid away from the wound surface to reduce contamination and allow wound healing to proceed. Occlusive dressings are currently used extensively to treat wounds in humans. These dressings prevent absorption of fluid from the surface of the wound. Wound fluid may contain substances that increase zyxwvutsr zyxwvutsrqponm 0 TIME (days) Fig 5. The percentage of total wound healed over time for treatment groups at positions B and C. Mean -+ standard error. *PE is significantly different; **HC is significantly different ( P < .05). was no exuberant granulation tissue present on postoperative days 2 1 or 28 under the PE dressing. The granulation tissue was healthy and granular underneath all of the dressings up to postoperative day 14. Five of 13 wounds under the HC dressing had unhealthy, grey, and friable granulation tissue from postoperative day 14 throughout the remainder of the study. None of the wounds under the HG or PE dressings had unhealthy, grey, and friable granulation tissue. On histological evaluation using HE stain, the normal epidermis adjacent to the wounds had a mean thickness of 56.68 t- 3.60 pm and was composed of two to four cell layers. Keratinization of the new epithelium was present in all of the wounds regardless of the stage of healing. Mitotic figures were noted in the advancing epithelium in five of 12 unhealed wounds: three of six under the HG dressing and two of six under the HC dressing. Epithelial sliding was present in six of 12 unhealed wounds: four of six under the HG dressing and two of six under the HC dressing. Two of the 12 unhealed wounds, one of six under the HG dressing and one of six under the HC dressing, had epithelial sliding present on one side, while the other side of advancing epithelium was blunted. Blunting of the advancing epithelium on both sides o Hydrocolloid v Hydrogel Polyethylene zyxwvu zyxwvut TNTC- IZ 0 PO V 400- 3 0 V 5 300- [II 0 W IV 4 m 0 200- v0 0 V 0 PO Po 0 f loo roo 0 4 7 0 l o0 PO8 PQO 14 21 28 DAY Fig 6. Scatter plot showing bacterial colony counts over time at positions B and C; PE has significantly lower counts (P< .05). 500 zyxwvutsrq zyxwvutsr EFFECT OF OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS Fig 7. Photograph of a wound (HC occlusive, position B) on postoperative day 14. Exuberant granulation tissue is evident above the level of normal skin. the rate of wound healing and perhaps should not be prematurely removed from the wound surf a ~ e . ~ ’Increased .*~ rates of healing in wounds treated with occlusive dressings have been reported in humans and experimental animal^.^,^.'^.'^,^^ Possible disadvantages of occlusive dressings include increased bacterial growth and increased tissue maceration in the moist e n ~ i r o n m e n t . Much ’~ of the research into occlusive dressings has been performed on partial-thickness wound^.^-^ The few studies that did evaluate occlusive dressings for the treatment of dermal repair reported conflicting results.6.’0,’I No studies have evaluated the use of occlusive dressings for the treatment of acute full-thickness dermal wounds in dogs. Overall, wounds covered with the HC dressing had significantly less total wound area healed than either the HG or the PE dressing. When considering the type of healing that occurred, the wounds treated with the PE dressing had a greater percentage of wound area covered by advancing epithelium than either of the occlusive dressings. Epithelium will migrate across granulation tissue in a layer two or three cells thick if there is no impediment such as an exudate or a scab. In the presence of an impediment, a much thicker layer, or wedge, of migrating epithelium is observed.26This blunting or wedging of migrating epithelium was noted histologically only in the occlusive dressing treatment groups. This may have been caused by the greater amount of exudate or exuberant granulation tissue noted under both occlusive dressings. The wounds treated with the HG dressing had a significantly greater percentage of the wound area healed by contraction. This pattern was confirmed by the contraction to epithelium ratio that was also significantly greater for the wounds treated with the HG dressing. Healing by contraction is superior to healing by epithelialization because contraction provides a durable covering of full-thickness skin. Normal skin is both mechanically and cosmetically superior to scar tissue, thus contraction is preferred as long as it does not impair f ~ n c t i o n . ~ .New ” epithelium provides a covering that may be easily disrupted by minor trauma. Contraction is related to the production and maturation of granulation tissue. The environment under the HG dressing seemed to favor granulation tissue production and rapid wound contraction. Therefore, it appears that the H G dressing was the best treatment evaluated in this study, if contraction is desired. There were only seven of 13 wounds healed under both the HG and HC dressings at the end of the study. In comparison, all 14 wounds were healed when treated with the PE dressing. All of the wounds that were treated with the occlusive dressings and that were not completely healed at the end of the study had exuberant granulation tissue. Exuberant granulation tissue has been associated with delayed wound healing on the extremities of dogs.28 It appears that the environment under both occlusive dressings was conducive to the formation of exuberant granulation tissue, however, the wounds under the HC dressing did not go on to contract as well as the wounds under the HG dressing. The adhesive nature of the HC dressing has been postulated to delay wound contraction by sticking to the wound edges and physically opposing the centripetal pull of the myofibroblasts in the granulating wound.’ The H G dressing is more fluid in nature and did not stick as readily to the wound margins. This may be an explanation for the differences in rates of contraction between the two occlusive dressings. Another explanation may lie in the different microenvironments created by the two occlusive dressings because the granulation tissue observed under the HC dressing was less healthy in appearance than that observed under the HG dressing. It is known that the oxygen permeabilities of the two dressings differ.23.‘9Reports suggest that a minimum of 20 mm Hg of oxygen tension are required for optimal collagen synthesis.30 The HC dressing is not permeable to oxygen and carbon dioxide.29 zyxwvu zyxwvu zyxwvut M O R G A N ET AL 50 1 ror of the results at position A. This variation was Bacterial contamination describes the presence of likely in part caused by the proximity of the wound organisms in a wound that d o not create an overto the elbow joint causing motion and bandage slipwhelming inflammatory response. The physiological page and leading to a difference in healing. It is the state of the tissue, including the host defenses within authors' recommendation that wounds be created the wound are as important as the presence and type 3 cm distal to the elbow joint when further than of bacteria.3' Bacterial contamination did not appear comparing wound healing on the antebrachium of to be a significant factor in wound healing in this dogs. study. Although bacteria were cultured and there were significantly higher bacterial counts under both occlusive dressings compared with the PE dressing, REFERENCES colony counts were generally too small to establish 1. Kolata RJ. Krant NH, Johnston DE: Patterns of trauma in a correlation with wound healing among the three urban dogs and cats-A study of 1000 cases. J Am Vet treatment groups. Med Assoc I64:499-502. 1974 The increased bacterial counts under both occlu2. Lee AH, Swaim SF, Yang ST, et al: The effects ofpetrolatum, polyethylene glycol, nitrofurazone, and a hydroactive sive dressings on postoperative day 28 is likely caused dressing on open wound healing. J Am Anim Hosp Assoc by the progressive increase in bacteria over time due 22:443-45 I , 1986 to the moist environment established. Although oc3. Swaim SF: Wound healing, in: Surgery of Traumatized Skin: clusive dressings have been described as creating an Management and Reconstruction in the Dog and Cat. environment conducive to bacterial g r o ~ t h , ~this '-~~ Philadelphia, PA, Saunders, 1980, pp 70-1 15 4. Swaim SF, Henderson RA: Wound dressing materials and does not necessarily slow healing. Elevated bacterial topical medications, in: Small Animal Wound Managecounts did not appear to inhibit the healing of the ment. Philadelphia. PA, Lea & Febiger, 1990, pp 34-5 1 HG covered wounds when compared with wounds 5. Winter GD: Formation of a scab and the rate of epithelialunder the PE dressing. Wounds under both the HG ization of superficial wounds in the skin of domestic pigs. and PE dressings had healthy, red, and granular Nature 193:293-294, 1962 6. Alvarez OM, Mertz PM, Eaglstein WH: The effect of ocgranulation tissue, which is extremely resistant to clusive dressings on collagen synthesis and re-epithelialinfection and serves as a barrier against systemic inization in supeficial wounds. J Surg Res 35: 142-148, 1983 fe~tion.~.~' 7. Eaglstein WH, Mertz PM: New method for assessing epiAlthough humane considerations prevented the dermal wound healing: The effects of triamcinolone acecomparison of wound dressings to untreated wounds, tonide and polyethylene film occlusion. J Invest Derm 71:382-384, 1978 we chose a dressing (PE semi-occlusive) that is com8. Geronimus RG, Robins P: The effect of two new dressings monly used in dogs as a measurement standard. on epidermal wound healing. J Dermatol Surg Oncol 8: Wounds under the HG dressing and PE dressing had 850-852, 1982 similar total percentage of wound healed. However, 9. Silver IA: Oxygen tension and epithelialization, in Maibach the HG dressing healed primarily by contraction HI, Rovee DT (eds): Epidermal Wound Healing. Chicago, IL, Year Book Medical Publishers, 1972, pp 291-305 leaving a smaller scar and a more cosmetically ac10. Winter GD: Epidermal regeneration studied in the domestic ceptable limb. Therefore, we conclude that the HG pig, in Maibach HL, Rovee D T (eds): Epidermal Wound dressing was preferred over the HC and PE dressings Healing. Chicago, IL, Year Book Medical Publishers, in this study. In dogs, proper management and de1972, pp 71-1 12 bridement of exuberant granulation tissue in wounds I 1. Linsky LB, Rovee DT, Dow T: The effects of dressings in wound inflammation and scar tissue, in Smith A, Dineen treated with occlusive dressings may enhance conH (eds): The Surgical Wound. Philadelphia, PA, Lea & traction and speed wound healing. Further study is Febiger, 198 I , pp 19 1-205 indicated to identify and quantitate the differences 12. Mertz PM, Marshal DA, Eaglstein WH: Occlusive wound in the wound microenvironment by various wound dressings to prevent bacterial invasions and wound infecdressings with the progression of healing. tion. J Am Acad Dermatol 12:662-668, 1985 13. Osment LS: The skin in wound healing, in Menaker L (ed): Finally, the wounds at position A followed the Biologic Basis of Wound Healing. Hagerstown, MD, Harsame trends as wounds at positions B and C. The per & Row, 1975, pp 274-290 results of the percentages of contraction, re-epithe14. Edlich RF, Rodeheaver GT, Thacker JG: Technical factors lialization, the contraction/epithelialization ratio, in the prevention of wound infections, in Simmons RL, and the total wound area healed were similar for all Howard RJ (eds): Surgical Infections and Disease. New York, NY, Appleton-Century-Crofts, 1982, pp 449-472 treatments. However, there was a larger standard er- zyx zyx 502 zyxwvut zyxwvutsrqp EFFECT OF OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS 15. Noe JM, Kalish S: Dressing materials and their selection, in Rudolph R, Noe JM (eds): Chronic Problem Wounds. Boston, MA, Little, Brown and Co, 1983, pp 37-46 16. Swaim S F Bandages and topical agents. Vet Clin North Am 20:47-65, 1990 17. Bennet RG: The debatable benefit of occlusive dressings for wounds. J Dermatol Surg Oncol 8: 166-167, 1982 18. Reuterving C. Agren M, Soderberg IT, et al: The effects of occlusive dressings on inflammation and granulation tissue formation in excised wounds in rats. Scand J Plast Reconstr Surg 23:89-96, I989 19. Aly R: Effect of occlusion on microbial population and physical skin conditions. Semin Dermatol 1: 137- 142, 1982 20. 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