Evaluation of a Low Profile Noncontact Normothermic Wound Dressing for Split-Thickness Skin Graft Donor Site Healing

Split-thickness skin graft (STSG) donor sites often can be more painful and uncomfortable for patients than the recipient wound. Ideal donor site dressings facilitate rapid re-epithelization and minimize pain. It is well established that re-epithelization is more rapid in a moist environment.¹ The literature also cites the benefits of warmth on wound healing.^2–7 Noncontact normothermic wound therapy (NNWT) provides a moist wound environment without direct contact between the dressing and wound bed. Additionally, NNWT helps warm the wound toward normothermia and has shown promising results in enhancing the healing of pressure ulcers, venous stasis ulcers, and surgical wounds.^8–16 The authors proposed that NNWT would promote healing of split-thickness donor sites and reduce pain. This study was a pilot trial that used a specifically designed, low-profile NNWT device and compared it to a commonly-used impregnated gauze dressing in healing of STSG donor sites. Time to healing, infection rates, pain, and scar characteristics were assessed.

Materials and Methods

Five healthy volunteers were enrolled in the study after institutional review board approval was received. Each subject served as his or her own control. Split-thickness skin graft donor sites (3 cm x 5 cm intermediate depth, 0.012 in) were created on each subject’s buttocks using sterile technique and an electric dermatome while under local anesthesia. The control group was randomly assigned and covered with petrolatum-impregnated gauze (Xeroform Petrolatum Gauze, The Kendall Company, Mansfield, Mass), a 4 x 4 dry piece of gauze, and transparent film dressing (Op-Site®, Smith & Nephew, Largo, Fla) to maintain moisture. The study group was covered with the low profile, flexible NNWT dressing (Warm-up® Active Wound Therapy, Augustine Medical Inc, Eden Prairie, Minn, Figure 1). A manually activated disposable warming pack was applied (externally) over the noncontact occlusive dressing. This pack provides an operating temperature range of 38ºC to 42ºC for approximately 2 hours.¹⁷ The subjects applied the packs twice daily for 2 hours at a time. Dressings were changed and wound sites were evaluated and photographed every other day for 14 days and then at 4 weeks. Prior to replacing the dressing, each wound was irrigated with 10 cc of sterile normal saline, and saline moistened gauze was used to gently remove nonadherent exudate. Swab cultures were obtained on Days 2, 4, and 8, using the Bornside and Bornside quantitative swab method that utilizes a sterile cotton-tipped swab moistened with 0.1 mL sterile saline solution that is placed in the wound center and rotated clockwise 3 times. Each swab was eluted in 0.9 mL of saline solution. Eluates were then streaked on blood agar and MacConkey’s medium for quantitative bacteriology. Pain was assessed using a visual analog pain scale. After epithelization was complete, as evidenced by lack of drainage, dressing changes were discontinued. Scar quality was assessed subjectively, comparing pliability and color.

Statistical Analysis

Statistical analysis was performed using a student’s t-test. A P value < 0.05 was considered significant for this study.

Results

Time to healing was significantly prolonged in the NNWT group compared to the control group (mean 14 and 10.8 days, respectively; standard deviation [SD] 1.22 and 0.84, respectively; standard error of the mean [SEM] 0.55 and 1.87, respectively; P < 0.03). Figure 2 shows time to healing (in days) for both groups. Sequential comparisons between the wounds consistently showed exudate covering the NNWT treated wound. Although no wounds were grossly cellulitic, the NNWT wound cultures demonstrated significantly more Staphylococcus aureus colonization than control (mean = 8 x 10³ cfu, and 0.6 x 10² cfu, respectively; SEM 1990 and 40; P = 0.012). Figure 3 shows culture results for each group. Generally, study participants rated the NNWT dressing as more painful than control. Scar quality at 4 weeks was comparable in terms of color and pliability. One patient suffered from a reaction to the NNWT dressing adhesive. No other significant untoward events occurred.

Discussion

In 1962, Winter¹ and Chang et al¹⁸ demonstrated that moisture enhances wound re-epithelization. Winter’s study utilized a porcine model to demonstrate that occlusive dressings that maintain moisture and warmth were optimal for healing. More recent studies have looked specifically at the effects of warming on wound healing. Local warming increases local perfusion and oxygen tension, supports enzymatic reactions, and increases the availability of immune cells.^2-4,6,7,19 Other studies have shown that warming of wounds decreases bacterial counts and increases fibroblast activity.^2,3 Noncontact normothermic wound therapy has been shown to be effective in the treatment of chronic wounds—pressure, venous stasis, and diabetic ulcers—but no studies have evaluated the efficacy for healing acute wounds.^{8–16,19–21}
The present study evaluated the efficacy of NNWT for healing STSG donor sites. The study hypothesis was that NNWT should be ideal for healing STSG donor sites because the warm, moist environment would maximize re-epithelization and reduce pain. However, the results suggest that this type of wound dressing is inferior to commonly used impregnated gauze dressings. It appears that the warmth and moisture provided by the NNWT dressing is not enough to achieve optimal healing. Compression, exudate absorption, and antimicrobial activity are important components the NNWT dressing lacks.²² The noncontact or noncompressive nature of the therapy allows exudate to form over the wound surface, which slows healing. An overabundance of exudate rich in matrix metalloproteinases (MMPs) and inflammatory cells may hinder epithelization. In particular, the authors noted that the region under the plastic “bubble” that was in contact with the overlying foam divider healed the fastest (Figure 4D).
A major critique of this study is that the wound bed was disturbed periodically to evaluate wound progress. Impregnated gauze used on donor sites is usually applied and left undisturbed until the wound is healed. For the purposes of the study, the dressings were changed every 2 days. This resulted in disruption of the wound bed, pain during dressing changes, and increased opportunity for bacterial contamination. Dressing changes were performed in the clinic using aseptic technique, and each wound was gently cleansed with sterile saline, which should have decreased bacterial counts. Another potential critique is that petrolatum-impregnated gauze has mild bacteriostatic activity and is not the standard of care for a clean, partial-thickness wound. Dressings that maintain a moist wound interface, including hydrocolloids, have been shown to produce faster healing than conventional fine mesh gauze.^23–25 In selecting a control dressing, the authors thought it was important to utilize the simplest, most commonly used dressing while continuing to maintain a moist wound interface between the skin graft donor site and the dressing. Petrolatum-impregnated gauze continues to be used due to its low cost, ease of application, and availability in most operating rooms. Occlusive film dressings are also used but are difficult to use on large donor sites due to fluid collection that occurs under the dressing. Thus, the authors compromised and used a hybrid dressing that has gained popularity at the authors’ hospital: petrolatum-impregnated gauze covered with dry gauze to absorb exudate, topped with an occlusive film dressing to maintain moisture. In the end, despite these critiques, NNWT resulted in delayed healing and increased pain compared to petrolatum-impregnated gauze with an occlusive secondary dressing despite removing the impregnated gauze every 2 days. The fact that this occurred in healthy volunteers rather than in patients who would be even more susceptible to infection and impaired healing adds concerns regarding the use of NNWT for STSG donor site healing.
The beneficial effects of NNWT better target the obstacles to healing that are commonly seen in chronic wounds (ie, decreased local blood flow, high bacterial counts, and low oxygen tension). In an acute, superficial wound, such as a STSG donor site, there is sufficient, if not increased, local blood flow, a sterile environment, and adequate oxygen tension for normal healing. Therefore, the characteristics of NNWT as evaluated in the present model are not optimal for STSG donor site healing.

Conclusion

This study demonstrates that NNWT does not provide any benefit over moist occlusive dressings for STSG donor site healing. The ideal donor site dressing will provide a moist, warm environment, minimize bacterial colonization, and manage exudate.19,22 The combination of a bacteriostatic impregnated gauze dressing that prevents adherence to the wound, a secondary gauze dressing to manage exudate, and an occlusive dressing to maintain moisture balance remains the authors’ choice for use on large STSG donor sites.