The Effect of a Hydrocolloid Dressing on Second Intention Wound Healing in Cats
ABSTRACT
The objective of the present study was to evaluate the effect of a hydrocolloid dressing on second intention wound healing in cats. Two full-thickness skin wounds, measuring 2 × 2 cm, were created on both sides of the dorsal midline of 10 cats; bilaterally, one randomly selected wound was bandaged with a hydrocolloid dressing and the second one (control) with a semiocclusive pad. Subjective clinical evaluation of granulation tissue formation, of the quantity and nature of wound exudate, and planimetry were performed on the right-side wounds, and histological examination on the left. No significant differences in subjective clinical evaluation or in planimetry were observed between the hydrocolloid-treated wounds and controls. Most wounds had serous or absence of exudate (41.25% and 25%, respectively), whereas purulent exudate was observed in 7.5% of wounds. Edema was significantly increased in the hydrocolloid-treated wounds compared with controls on day 7 but no significant differences in the other histological variables were observed.
Introduction
Open wound management is routinely performed in small animal practice. Protection and moisturization of a wound creates an optimal microenvironment and enhances the healing process.1,2 Hydrocolloids are a type of occlusive dressing consisting of adhesive, absorbent (carboxymethylcellulose), and elastomeric (gelatin, pectin) ingredients that form a gel by interacting with wound fluid.3 Their main properties are the prevention of desiccation or abrasion of the wound, the maintenance of a moist environment, and the advancement of autolytic debridement.4–6 Hydrocolloid dressings enhance epithelialization and granulation tissue formation.7 They are easily applied, and dressing changes are painless and the interval between them prolonged (performed every 2–7 days). Furthermore, because of their occlusive nature, they can be applied even in areas subject to contamination by urine and feces.5 Their disadvantages include predisposition to growth of anaerobic organisms, higher cost, and inability to inspect the wound daily.3,5,7
Hydrocolloid dressings may be applied to acute or chronic, partial- or full-thickness wounds with a low-to-moderate quantity of exudate, where granulation or epithelialization is needed.3,5 However, they are contraindicated in cases of infected and ischemic wounds, especially in anaerobic wound infections because they are impermeable to oxygen. Their use is also contraindicated in cases of wounds producing large amounts of exudate, because of the danger of maceration.3
Studies have evaluated the effects of hydrocolloid dressings on wound healing in horses, pigs, and dogs, but there are no reports on their efficacy in cats.6,8–10 Studies performed on other species cannot be directly adapted to cats, because it is well-established that cutaneous healing is slower in cats, at least when compared with dogs.11 More specifically, the rates of granulation tissue formation, wound contraction, epithelialization, and total healing are all reduced in cats compared with dogs.11 Hydrocolloids promote debridement and stimulate granulation tissue formation, which might accelerate wound healing in cats.5,7 Hydrocolloids adhere to the surrounding skin but not to the wound surface; therefore, when applied in the epithelization phase, bandage changes do not remove the migrating cells from wound surface.6 Furthermore, the changes are painless and the intervals between bandage changes are prolonged. To prevent maceration of the surrounding skin, hydrocolloids should be cut to the shape of the wound.5 This, along with the prolonged intervals between bandage changes, render their use cost-effective in feline wounds. Our hypothesis was that second-intention cutaneous healing in cats might benefit from the use of hydrocolloid-occlusive dressings. The objective of the present study was to evaluate and compare the effectiveness of a hydrocolloid dressing with a semi-occlusive dressing on the healing of full-thickness skin wounds in cats.
Materials and Methods
Animals
The study was performed on purpose-bred laboratory cats. Its protocol had been approved by the National Animal Ethics Committee (license number: 162/2009) as being in accordance with the European Union legislation concerning humane animal treatment and welfare of laboratory animals (Animal Protection Act § 7-9; EU Convention on the protection of animals revised directive [86/609/EEC] included). Τen (five females, five males) neutered healthy domestic shorthaired cats, aged 22–50 mo (median 35 mo) and weighing 2.9–4.1 kg (median 3.3 kg) were included in the study. Before the study physical examination, complete blood count, serum biochemical analysis, and fecal parasitology were performed in all the animals. The cats had been routinely treated for parasites, were fully vaccinated, and received no other drugs for 2 mo prior to the experiment. They were fed a standard commercial dry maintenance diet and water was offered ad libitum. The cats were housed in large enclosures with plenty of rest areas and hiding places, had free outdoor access, and were well socialized to humans. After completion of the study, the cats were given for adoption.
Anesthesia
On the day of wound creation and on biopsy days, following premedication with dexmedetomidinea (40 μg/kg intramuscular [IM]) and butorphanolb (0.4 mg/kg IM), anesthesia was induced with ketaminec (10 mg/kg IM). Lactated Ringer’s solution (10 mL/kg/hr IV) was administered during anesthesia, and a single dose of cefuroximed (20 mg/kg IV) was administered preoperatively.
Dressing changes and cleaning of the wounds were performed with the cats lightly anesthetized by IM injection of dexmedetomidinea (20 μg/kg), butorphanolb (0.4 mg/kg), and ketaminec (4 mg/kg).
Wound Creation, Assignment to Type of Dressing, and Postoperative Care
Animals were positioned in sternal recumbency and, by using a template and a surgical marker, the areas of the experimental wounds were outlined. Two 2 × 2 cm full-thickness skin wounds were created on each side of the trunk, between the caudal border of the scapula and the tuber coxae, at a distance of 4 cm from the dorsal midline and 4 cm apart from each other. The right-sided wounds were used to evaluate second-intention wound healing by subjective clinical evaluation and planimetry, and the left-sided wounds were used for histological evaluation. All wounds were covered with a three-layer padded bandage as follows. Bilaterally, the contact layer of one wound consisted of a hydrocolloid dressinge (treatment protocol C), whereas the second wound was covered with a sterile, low-adherent, semi-occlusive padf and served as control (treatment protocol M). Wounds were randomly assigned to each treatment protocol by using a computer program (Random Number Generator). The second bandage layer consisted of cotton roll gauzeg, applied in multiple layers crossing over the shoulders and between the forelimbs to prevent the bandages from slipping, and the third of a self-adhesive bandageh.
Analgesia was provided until the third postoperative day by administration of butorphanolb (0.4 mg/kg IM q 4 hr). Dressings in treatment protocol Mf were changed daily for 8 days and then every other day until the 21st postoperative day. At the same time, wounds with treatment protocol Ce were checked daily, although these dressings were changed on days 4, 7, 14, and 21, or in case of loss of adhesiveness (Figure 1).
Citation: Journal of the American Animal Hospital Association 54, 3; 10.5326/JAAHA-MS-6604
Evaluation of Wound Healing
Subjective clinical evaluation was performed by the same person throughout the study by observation of the wounds during dressing changes. The period of time until first appearance of granulation tissue in the wound, coverage of the bottom of the wound by granulation tissue, and filling of the entire wound by granulation tissue reaching the level of the surrounding skin was recorded. The quantity and nature of any wound fluid in the bandages, as well as any sign of infection or other abnormalities, were also recorded on days 4, 7, 14, and 21. The quantity of wound fluid was scored as none [0], slight [1], moderate [2], or extreme [3], and its nature was described as absence of fluid [0], serous [1], serosanguineous [2], sanguineous [3], or purulent [4].12
Planimetry was performed on days 0, 7, 14, and 21. Digital photos of the wounds and computer softwarei were used to estimate the area of the initial wound and that covered by the advancing epithelium. The area within the margin of advancing epithelium was the open or unhealed wound area. The percentage of epithelialization, wound contraction, and total wound healing were calculated for each wound according to formulas reported by Bohling et al.11
Histological evaluation was performed on specimens obtained on days 7, 14, and 21; as already mentioned, the animals were under general anesthesia during biopsies. The excised skin on day 0 served as control. A 6-mm biopsy punch was used and the specimens were obtained from the wounds’ corners along with 1–2 mm of surrounding normal skin. The dorsal and cranial corner was used for the first biopsy while the other specimens were collected by rotation in a clockwise fashion. Specimens were placed in 10% neutral-buffered formalin, routinely processed, and stained with hematoxylin and eosin. The pathologist was unaware of the dressing material corresponding to each specimen. Stained sections were microscopically evaluated to assess the degree of inflammatory cell infiltration, edema, acute hemorrhage, necrosis, collagen density, and angiogenesis, in 10 high-power fields (×400) per section. The degree of cellular infiltration was evaluated by scoring the number of infiltrating neutrophils, eosinophils, lymphocytes, plasma cells, macrophages, and mast cells as follows: <3 cells/field was considered normal [0], 3–10 cells/field mild [1], 11–30 cells/field moderate [2], and >31 cells/field substantial increase [3].13 Edema, acute hemorrhage, and necrosis were also scored as normal [0], mild [1], moderate [2], and substantial increase [3]. Absence of separation of cells and collagen by nonstained or poorly stained acellular material was considered normal [0], slight separation was considered mild edema [1], a separation of 30–50 μm moderate edema [2], and a separation of >50 μm substantial edema [3].14 Sparsely scattered extravasated erythrocytes or necrotic cellular debris were considered a mild increase in acute hemorrhage or necrosis, respectively, whereas focal-dense accumulations of each of these components in wound tissue were considered a moderate increase, and massive hemorrhage or extensive necrosis that involved the surrounding tissue were considered a substantial increase for each of these variables, respectively.15 Collagen density was scored as follows: no collagen [0], scant collagen bundles slightly separating fibroblasts [1], dense accumulations of collagen between fibroblasts [2], and extensive separation of fibroblasts by collagen [3].13 Scoring of angiogenesis was as follows: <3 blood vessels, capillary buds, or activated fibroblasts/field [0], 3–10 [1], 11–30 [2], and >30 [3].15 The thickness of epidermis (in μm) was also evaluated on day 21 in 10 random points per sample under a micrometer scale, and the mean was compared with the thickness of normal epidermis of excised skin on day 0 (control) and was assigned to a score of 0 (thickness similar to that of normal epidermis), 1 (slightly increased), 2 (moderately increased), or 3 (substantially increased).16
Statistical Analysis
The normality of data distribution was assessed with the Shapiro-Wilk test. Continuous data following normal distribution are presented as mean ± standard deviation. Qualitative data are presented as frequency and percentage. For comparisons in variables of subjective evaluation between groups, the Mann-Whitney U test was used. The Student t test was used for group comparisons in planimetry and histological variables. The level of statistical significance for all comparisons was set at 5% and all the calculations and tests were performed using commercial softwarej.
Results
The cats always had an uneventful recovery from anesthesia and showed a normal appetite and behavior and no signs of pain. Complications related to surgical or biopsy procedures were not observed.
Subjective Clinical Evaluation
Hydrocolloids were easily applied and in almost all cases remained in place until changing. Hydrocolloid dressings were partially detached in only two wounds. In one occasion, detachment was observed on day 4 on a right-sided wound, whereas in the other occasion, detachment was observed on day 5 on a left-sided wound. Crusts developed on the control wounds. Mean time to first appearance of granulation tissue was 4.4 days for treatment protocol Ce and 4.9 days for treatment protocol Mf. Mean time to coverage of the bottom of the wound by granulation tissue was 6.7 and 7.9 days for treatments C and M, respectively. Mean time to filling of the entire wound by granulation tissue was 10.9 and 12.3 days for treatments C and M, respectively. No significant differences were found in the aforementioned variables between the hydrocolloid-treated wounds and the controls.
Mean values (scores) of the quantity of wound exudates with each treatment on days 4, 7, 14, and 21 are presented in Table 1. No significant differences were found between the hydrocolloid-treated wounds and the controls.
Regarding the nature of wound exudate, in most wounds serous fluid was observed with both treatments (60% and 22.5% for treatments C and M, respectively), although no fluid was noticed in 20% of wounds treated with C and 30% of wounds treated with M. Serosanguineous exudate was observed in 12.5% and 10% of wounds treated with C and M, respectively. Sanguineous exudate was noticed only in the controls (30%). Finally, only 7.5% of wounds treated with C and 7.5% of controls had purulent exudate.
Planimetry
There was no detectable area of epithelialization in any wound 7 days post wounding. The mean % epithelialization, % wound contraction, and % total wound healing with each treatment on days 7, 14, and 21 are presented in Table 2. No significant differences were found in planimetry variables between the hydrocolloid-treated wounds and the controls. In the wounds in which total wound healing was not achieved by day 21, the treatment was continued until total healing, which was attained in 1–10 days.
Histological evaluation
Changes in histological variables during the wound healing process (days 7, 14, and 21) in each group are presented in Table 3. Edema was significantly increased with treatment C compared with treatment M (P = .013) on day 7 but no significant differences were observed in the other histological variables.
Discussion
Moist environment, facilitated by hydrocolloid dressings, accelerates wound healing.3,4,7 There are several reports on the use of hydrocolloid dressings in human wounds3,17 but in dogs the results have not been encouraging10. Full-thickness wounds in dogs covered with hydrocolloids have been reported to have less total wound area healed compared with other dressings.10 On the other hand, hydrocolloids are reported to accelerate healing of partial-thickness and full-thickness wounds, burns, and ulcers in humans.3,7,18 Because cutaneous healing appears to differ among species, more research is required to determine the most suitable product for each animal species.1 In the present study, the adherence of the hydrocolloid to surrounding skin proved effective because almost all dressings stayed in place. Hydrocolloid dressings may be left on the wound for 2–7 days, depending on the wound healing phase, whereas semi-occlusive dressings may need multiple changes per day.5,7 The risk of contamination of wounds during bandage changes is high, thus the prolonged intervals between hydrocolloids’ changes offers an advantage over conventional dressings.5 Hydrocolloid changes in this study were well tolerated by the cats; therefore, they may be performed even by the owner, thus reducing nursing time and hospitalization cost. Hydrocolloids are reported to be more cost effective than wet-to-dry dressings in human studies.7 Hydrocolloid sheets were cut to the appropriate size to cover the wounds in the present study, thus further reducing the cost. Although in the present study right-sided and left-sided wounds were used for different evaluation methods, we don’t believe that there was bias against sides, because it has been reported that in cats, in contrast to humans, there is symmetry in the vasculature between opposite sides of the body.20
Hydrocolloids promote debridement and granulation tissue formation, and enhance epithelialization.17–19,21,22 All these properties are desirable, especially in cats, for whom cutaneous perfusion is lower and wound healing is slower than in dogs.11 Acceleration of granulation tissue formation in hydrocolloid-treated wounds was not supported statistically in the present study. One of the advantages of hydrocolloid dressings is that the firm pressure applied to the floor of the wound by the dressing favors moisture and low oxygen tension, resulting in early production of healthy granulation tissue.1 The mean time to first appearance of granulation tissue (4.4 days for C and 4.9 days for M), coverage of the wound's bottom (6.7 and 7.9 days for treatments C and M, respectively), and filling of the entire wound (10.9 and 12.3 days for treatments C and M, respectively) by granulation tissue in the present study was shorter than that reported by Bohling et al. (a median time of 6 and 20 days, respectively, to the first appearance and total filling of feline wounds with granulation tissue)11. These differences could be attributed to the different wound locations and to individual variations. Furthermore, the percentage of epithelialization (80.4% and 85.5% for treatments C and M, respectively) was higher than that (34.4%) reported by Bohling et al.11 This could be attributed to the faster granulation tissue formation in our study, and it is well recognized that epithelialization begins when an adequate granulation bed has formed.21
Granulation tissue is a source of myofibroblasts that are believed to contribute to early wound contraction.21 However, in the present study, the % contraction of wounds managed with both treatments was not affected by faster granulation tissue formation. Crust formation on wounds with treatment M might have mechanically impeded contraction, whereas in the hydrocolloid treated wounds this could be attributed to the adherence of dressings to the surrounding skin, thus limiting skin’s capability to stretch and opposing the centripetal pull of the myofibroblasts in the granulating wound.7,10,21,23 It is reported that contractile capability of fibroblasts relates to the wound’s anatomic location and to species differences.11,23
It has been reported that in humans and pigs hydrocolloids should be applied in acute wounds within the first 2 hr of their creation in order to promote epithelialization.3,18 However, it has been reported in dogs that occlusive dressings are more beneficial when applied following granulation tissue formation.12 Generally, the use of hydrocolloids in humans is reported to increase epithelialization rates up to 50% and to speed up wound healing two to six times compared with controls.7,17,18 However, in the present study, the use of hydrocolloids immediately after wound creation did not significantly promote granulation tissue formation, epithelialization, contraction, or total wound healing. This could be attributed to species differences regarding anatomy, physiology, and wound-healing mechanisms.
In the present study, significant differences between the two treatments were not noted in planimetry variables, although, on days 7 and 14, mean values in hydrocolloid-treated wounds were increased relative to controls. One possible explanation for this finding is the different local wound environment created by the hydrocolloids, which retains water and stimulates growth factors and enzymes that mediate healing or debridement.7,17,22 However, we did not analyze the wound exudate under the occlusive dressings, and further investigation is required to elucidate its role in feline wound healing.
In our study, the amount of wound exudate did not differ between treatments. Once hydrocolloid dressings make contact with wound exudate, they form a gel, which prevents adherence to the wound and thus protects the newly formed granulation tissue. The moist wound environment produced by hydrocolloids prevents desiccation and eschar formation, and, as a result, improves cosmetic appearance and minimizes scarring and fibrosis.3,5,22 This was also observed in the present study, in which crusts developed only in control wounds. Moisture retention in the wound bed also prevents fluid loss, thus reducing fluid replacement needs in patients with extensive wounds.7
Most of the hydrocolloid-treated wounds in our study had serous exudate, whereas the 7.5% of wounds with purulent exudate were equally likely to be treated with hydrocolloid or control dressings. Serous exudate was clear, thin, and yellow in appearance in the wounds with treatment C. Purulent exudate was thick, opaque, and greyish in color. As hydrocolloid dressings dissolve at the moist wound surface, a yellow fluid is produced, which should not be mistaken for septic exudate. It is reported that wounds treated with occlusive dressings have an increased microbial flora compared with air-exposed wounds.17 However, the lower wound pH under hydrocolloids impairs bacterial proliferation and acts as barrier against exogenous microorganisms.3,7,24,25
In the present study, almost all evaluated histological variables appeared to be the same with both treatments. Young et al. reported a more edematous granulation tissue in hydrocolloid-treated wounds 7 days after wounding and attributed this to the presence of particulate matter.24 Although in the present study increased edema was observed on day 7 in the hydrocolloid-treated wounds, particulate debris was not detected. Similarly, neither benefit nor disadvantage was observed by histological examination between full-thickness skin wounds treated with occlusive and nonocclusive dressings in pigs.22
Limitations of the present study include the small sample size and the low power of the statistical analysis that showed no significant effect of hydrocolloid dressings on acute full-thickness skin wounds in cats. In addition, analysis of the wound exudate under the occlusive dressings and bacterial cultures were not performed.
Conclusion
Hydrocolloid dressings produced equivalent healing to conventional wound treatment in the study reported, but without the need for daily bandage changes, which simplifies feline wound care. Further research is needed to see if various hydrocolloid dressings have different effects on acute feline wounds and whether they could assist in the healing of chronic or indolent wounds that are often encountered in this animal species.
Representative open wounds on days 7 (A, D), 14 (B, E) and 21 (C, F) treated with a hydrocolloid dressing (treatment C) and with a semi-occlusive dressing (treatment M).
Contributor Notes
