Histological effects of occlusive dressing on healing of incisional skin wounds

Abstract

Occlusive dressing is widely accepted and used to manage skin ulcers. However, with respect to its application to incisional wounds, most studies have been conducted about the clinical effects on incisional healing of surgical sites. Studies of the histological effects of occlusive dressing for incisional wounds have been few. The aim of this study was to clarify the histological effects of occlusive dressings on healing of incisional skin wounds. Rat dorsal skin was incised down to the panniculus and sutured immediately. Dressing types included 2‐octyl cyanoacrylate and hydrocolloid materials as occlusive dressings and no‐dressing as the open therapy. Histological examination and dermoscopic observation were performed 1, 2, 4 and 7 days after surgery. The findings from each dressing type were compared. In the open therapy group, the upper portion of the edge of incision was necrosed minimally and finally healed with wide scar formation. However, in the occlusive dressing groups, micronecrosis of the incision edge seen in the no‐dressing group was not observed, healing was more rapid and the remaining scar was finer. Occlusive dressing can prevent micronecrosis of the incision edge, resulting in rapid and excellent healing. This study shows that the efficacy of and supports the use of occlusive dressing in incisional wound management.

Introduction

The concept underlying occlusive dressing, first reported by Winter 1, 2, 3, is that dehydration of the wound, which causes necrosis and scab formation of the wound surface, is prevented by occlusion, resulting in rapid healing. Since then, many studies have been performed on skin wound healing with occlusive dressing. Currently, occlusive dressing is widely accepted and used to manage skin ulcers. However, with respect to its application to incisional wounds, most studies have been conducted about the clinical effects on incisional healing of surgical sites. Very few studies have been conducted so far on the histological effects of occlusive dressing for incisional wounds.

The aim of this study was to clarify the histological effects of occlusive dressing on the healing of incisional skin wounds. Incisional wounds of rat skin were examined histologically, comparing occlusive dressing to open therapy. This article reports new and interesting findings related to the use of occlusive dressing for incisional skin wounds.

Materials and methods

Male hairless rats (Hairless Wistar Yagi; Japan SLC, Inc., Shizuoka, Japan), aged 8–10 weeks, were used. Under general anaesthesia induced by intraperitoneal injection of medetomidine hydrochloride, a skin incision down to the panniculus was made on the dorsum of the rat using a surgical scalpel. The incision length was about 4 cm. The incisional wound was closed immediately by subdermal sutures using 5‐0 nylon and coaptation sutures using 6‐0 nylon. Subdermal sutures were used to stitch the panniculus and the deep dermal layer by 3 or 4 points per incision. Coaptation suturing was performed by single‐knot sutures at approximately 5‐ to 7‐mm intervals. This technique was used to simulate actual clinical technique.

Three types of dressing were used after wound suture: no‐dressing as the open therapy; 2‐octyl cyanoacrylate (Dermabond, Johnson and Johnson, Inc., NJ) as an occlusive dressing and hydrocolloid materials (Duoactive CGF, ConvaTec, Inc., NJ) as another occlusive dressing. In the no‐dressing group, the sutured incision was left without any dressing materials. In the 2‐octyl cyanoacrylate group, Dermabond was applied to the incision immediately after suture. After Dermabond application, no‐dressing materials were wrapped over the surface. If splitting of Dermabond from the wound was found, it was reapplied. In the hydrocolloid group, the incision was overlaid with Duoactive CGF immediately after suture; Duoactive CGF was fixed by suturing its margin to the skin.

Three rats were prepared in each group. Each rat was placed in an individual cage after surgery. Then, 1, 2, 4 and 7 days after suture, the wound surface was observed using a dermatoscope at six magnifications, and specimens were harvested from each group. The specimens were stained with haematoxylin–eosin for light microscopic examination. There were four observation points for each incision, placed in the middle between adjoining sutures to avoid the effects of the stitches. Three rats were used in each group, so that 12 tissue samples were obtained from each group.

To evaluate the effects of occlusive dressing, necrosis and scab formation of the wound surface and deformities of the healing sites were estimated quantitatively. These were compared statistically between the no‐dressing group and each of the 2‐octyl cyanoacrylate group and the hydrocolloid group. The protocol of this study was approved by the Animal Research Committee, National Defense Medical College.

Statistical analysis

The necrotic area of the histological sections of day 1 and the sectional area of the furrows that developed at the healing sites on day 7 were measured using an area‐calculating software package, and the results of the open therapy group were compared with those of the occlusive dressing groups. The necrotic area was determined as a region with darker staining collagen fibres surrounded by inflammatory cells. Statistical analysis was carried out using the Mann–Whitney U‐test (Stat Mate II, Atms Inc., Tokyo, Japan). Results with a P‐value of <0·01 were considered significant.

Results

No‐dressing group

Day 1

Dermoscopy showed that a scab was formed over the entire length of the incision (Figure 1). Histological examination showed that the upper portion of the incision edge was beginning to necrose. Leucocyte infiltration emerged at the boundary between the normal and the darker staining dead dermis. This necrosed area appeared as ‘a horn’ in a sectional view, measuring about 0·4–0·6 mm in width. The epidermis of this portion decayed completely (Figure 2). In this study, this very small amount of necrosis of the incision edge was described as ‘micronecrosis’ to distinguish it from wound necrosis as an adverse event after surgery. The area of micronecrosis varied from 0·0067 to 0·0900 mm² (mean, 0·0412 mm²) (Figures 3 and 4).

Figure 1.

Day 1 after surgery. Dermoscopy findings. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Figure 2.

Day 1 after surgery. Histological findings. Haematoxylin–eosin stain ×200. Dotted line indicates the incision. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Figure 3.

The area of micronecrosis on day 1. In 10/12 of the 2‐octyl cyanoacrylate group and 11/12 of the hydrocolloid group, no necrosis is observed.

Figure 4.

Quantitative evaluation of the area of micronecrosis on day 1. The area of micronecrosis is significantly larger in the no‐dressing group than in the occlusive dressing groups (P < 0·001*, **). There is no significant difference between the 2‐octyl cyanoacrylate and hydrocolloid groups. NS, not significantly different.

Day 2

Dermoscopic observation demonstrated that scab formation was more obvious (Figure 5). Histologically, demarcation between the dead and living dermis became apparent. Epithelial migration from the surviving part grew downwards to separate the dead part from the living tissue. As a result, the dead tissue forming the scab was preparing to detach (Figure 6).

Figure 5.

Day 2 after surgery. Dermoscopy findings. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Figure 6.

Day 2 after surgery. Histological findings. Haematoxylin–eosin stain. ×100 No dressing after surgery (Left). Arrows indicate the tips of epithelial migration between the dead and living tissue. ×200 2‐Octyl cyanoacrylate (Middle). ×200 Hydrocolloid (Right).

Day 4

On dermoscopic observation, the scab appeared to rise up as if it was peeling from the wound surface (Figure 7). The epithelium had grown downwards from either side of the incision and completely covered the wound. The dead tissue was completely detached from the surface of the wound, resulting in a V‐shaped, inverted surface (Figure 8).

Figure 7.

Day 4 after surgery. Dermoscopy findings. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Figure 8.

Day 4 after surgery. Histological findings. Haematoxylin–eosin stain ×200. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Day 7

The furrow of the healing site was becoming wider and shallower. The fibrous arrangement around the incision was widely disturbed (Figure 9). These findings showed a wide and depressed scar on dermoscopic observation (Figure 10). The sectional area of the furrows varied from 0·0050 to 0·0943 mm² (mean, 0·0356 mm²) (Figure 11).

Figure 9.

Day 7 after surgery. Histological findings. Haematoxylin–eosin stain ×200. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Figure 10.

Day 7 after surgery. Dermoscopy findings. No dressing after surgery (Left). 2‐Octyl cyanoacrylate (Middle). Hydrocolloid (Right).

Figure 11.

Quantitative evaluation of the furrows at the healing sites on day 7. The sectional area of the furrows is significantly larger in the no‐dressing group than in the occlusive dressing groups. (P < 0·001*, P < 0·01**). There is no significant difference between the 2‐octyl cyanoacrylate and hydrocolloid groups. NS, not significantly different.

2‐Octyl cyanoacrylate group and hydrocolloid dressing group

The findings of the 2‐octyl cyanoacrylate group and the hydrocolloid group were almost the same. Side‐effects, such as erythema, caused by the dressing materials were not observed in the occlusive dressing groups.

On dermoscopy, the colour tone of the 2‐octyl cyanoacrylate group may appear different from the other groups because Dermabond has a light purple colour, and when it coagulates it may include exudate from the wound. Dermoscopic observation was performed through the coagulated Dermabond adhered to the skin surface.

Day 1

Dermoscopy showed no scab formation along the incision (Figure 1). On histological examination, the epidermis and dermis were completely alive, although there was slight leucocyte infiltration at the edges. The epidermis of either edge of the incision was already united. Thus, the incision was totally covered by epidermis (Figure 2). The micronecrosis of the incision edge seen in the no‐dressing group was not observed in most specimens. If observed, it remained minimal and already separated from the living dermis by the epithelialisation. The area of micronecrosis varied from 0·0000 to 0·0070 mm² in the 2‐octyl cyanoacrylate group and from 0·0000 to 0·0076 mm² in the hydrocolloid group. The mean was 0·0008 mm² in the 2‐octyl cyanoacrylate group and 0·0006 mm² in the hydrocolloid group (Figures 3 and 4).

The area of micronecrosis on day 1 was significantly larger in the no‐dressing group than in the occlusive dressing groups. There was no significant difference between the 2‐octyl cyanoacrylate and hydrocolloid groups (Figure 4).

Days 2, 4 and 7

Observations on days 2, 4 and 7 showed that the 1‐day findings had continued to progress over time (Figures 5, 6, 7, 8, 9, 10). Healing progressed with no necrotic changes throughout. On day 7, the depression of the healing site and the disturbance of fibrous structure seen on histological examination were less, and the scar observed on dermoscopy was finer than in the no‐dressing group (Figure 10).

The sectional area of the furrows at the healing sites varied from 0·0013 to 0·0279 mm² in the 2‐octyl cyanoacrylate group and from 0·0012 to 0·0157 mm² in the hydrocolloid group. The mean was 0·0133 mm² in the 2‐octyl cyanoacrylate group and 0·0077 mm² in the hydrocolloid group. There was a significant difference between the no‐dressing group and each of the occlusive dressing groups. No significant difference was found between the 2‐octyl cyanoacrylate and hydrocolloid groups (Figure 11).

Discussion

The healing process of incisional skin wounds was studied in considerable detail by Ordman and Gillman.4 They examined histologically the healing of incisions through the skin of the pig. In their study, the phenomenon of necrosis at the incision edge and healing with minor scar was described. Essentially, similar results were obtained in the present experiment in the no‐dressing group. Preventing the phenomenon of micronecrosis is especially important for surgeons who need to achieve excellent healing and a fine scar. However, this phenomenon has not been well understood or even ignored. This study showed that the occlusive dressing successfully prevented micronecrosis of the incision edge. Winter and coworkers 2, 3 reported that, in skin‐defect healing using pig models, the superficial part of the dermis and the wound edge necrosed because of dehydration of the tissue under dry conditions, and this created a thicker scab and delayed epithelial migration. They also proved that occlusive dressing could prevent dehydration of the tissue and scab formation, resulting in rapid epithelialisation. Thus, it is natural that the incision edge necroses under dry conditions, and that this is prevented under the occluded condition due to the same mechanism. Consequently, rapid and excellent healing was achieved.

This experiment was performed using rat skin. Thus, although the scar of the occlusive dressing at 7 days after surgery was found to be finer than that of the open therapy, it is not certain whether this result would also be seen in actual human cases when maturing of the scar is complete. However, most clinical studies have demonstrated that the occlusive dressing was better 5, 6, 7, 8 or there was no difference 9, 10, 11, 12 in the cosmetic outcome compared with the conventional or no‐dressing group. No studies showed that the occlusive dressing resulted in a worse cosmetic result. Kloeters and colleagues 13 histologically examined the effects of semi‐occlusive dressing on incisions using rat models and reported that the use of an occlusive dressing reduced epidermal inflammatory cytokine expression and mitigated dermal proliferation and inflammation in a rat incisional model, resulting in an anti‐scarring effect. However, their observations were made from 3 to 21 days after surgery. Therefore, the micronecrosis occurring within 1 or 2 days after surgery was not noticed and not at all described. In addition to their result, it is possible that the effect of the occlusive dressing histologically demonstrated in this study is one of the causal factors related to the cosmetic outcome.

However, rats are very mobile and tend to twist and move, which increases the amount of scabbing and bleeding immediately after surgery. Thus, splinting the wound by 2‐octyl cyanoacrylate and hydrocolloid dressing might contribute to the observed effects of the occlusive dressing. These observed effects may be exaggerated compared with actual human cases. However, splinting the wound is one of the benefits of the occlusive dressing, as well as preventing desiccation of the wound. Wound splinting can also be effective in humans, especially at mobile sites such as the face or joints of the extremities.

Topical application of ointments such as Vaseline may prevent micronecrosis. However, from clinical experience, a very large amount of ointment would be needed to prevent desiccation of the wound surface along with occlusive therapy. To confirm the effects of ointment therapy, many kinds of ointments, the volume to be applied and the number of dressing changes would have to be examined. This will be the subject of our next study.

It was proven in this study that occlusive dressings accelerated incisional wound healing by preventing necrosis of the incision edge. The results of this study show the efficacy and usefulness of occlusive dressing in incisional wound management.