Skin Debris and Micro-organisms on the Periwound Skin of Pressure Ulcers and the Influence of Periwound Cleansing on Microbial Flora
Wound cleansing is important for preparing a topical environment to heal pressure ulcers.1,2
Sterile normal saline is widely recommended as a wound cleansing solution because it is isotonic and does not impede the normal healing process, damage tissue, cause allergic reactions, or change the normal microbial flora on the skin.2-9 Skin cleansers are toxic to wound tissues and should not be used to cleanse wounds.
Therefore, it is generally thought that periwound skin (defined in this study as a 1 cm area of skin surrounding the wound) and the wound bed itself may be cleansed by normal saline solution because the same wound dressing covers both areas. However, skin debris such as water-insoluble proteins and lipids are not efficiently removed by normal saline solution alone. Contamination of the periwound skin by stool, urine, and sweat — creating the potential for critical contamination of the wound — is sometimes observed even though the wound bed was cleansed with normal saline. Therefore, periwound skin should be cleansed in the same manner as non-periwound skin.10
Only one previous study11 sought to ascertain the effect of a skin cleanser on periwound skin. Using a skin cleanser was found to decrease the bacterial count in a pressure ulcer and contributed to the normalization of water content in the skin when applied to the periwound area only. However, because the validity of periwound cleansing using a skin cleanser has not yet been scientifically proven, this practice is not widely established.12
Cleansing to remove skin debris and dirt from the skin surface remains one of the most important methods to maintain a homeostatic skin environment.1,13,14 Skin debris comprises sweat, lipids, and desquamating fragments of keratinized cells on the skin surface (all produced from the skin) and sebum. Sweat consists mainly of water, but also contains a small amount of electrolytes, lactate, urea and ammonia, and other compounds (see Table 1).15 The two main types of lipids are sebaceous gland lipids (eg, triglycerides, wax esters, fatty acids, squalene16; and stratum corneum (the outer layer of skin) lipids (so-called intercellular lipids) such as ceramides, cholesterol, cholesterol esters, and fatty acids (see Table 2 and Table 3).17 In the study discussed here, squalene represented the sebaceous gland lipids and cholesterol represented the stratum corneum lipids. Desquamating fragments of keratinized cells are composed mainly of a water-insoluble fibrous protein called keratin.18 Water-soluble substances in keratinized cells are collectively called the natural moisturizing factor (NMF)19-21 and are composed mainly of amino acids (see Table 4).21
Relevant to this study, the stratum corneum serves two functions — to provide a protective physical barrier to the external environmental and to keep the skin adequately hydrated.18,22 Normal skin holds 10% to 30% water in the stratum corneum, which is primarily associated with NMF19-21 and intercellular lipids.23-25
The ideal skin cleanser should remove only skin debris and dirt while maintaining the skin’s two primary functions of protection and water retention. A suitable skin cleanser should be selected according to the type of skin debris or microbial flora that is present on the periwound of a pressure ulcer.
This descriptive study was undertaken to collect and analyze the skin debris and microbial flora found on the periwound skin of patients with pressure ulcers and to evaluate the effect of periwound cleansing on such microbial flora, both on the periwound and in the wound bed. This study addressed the following questions: 1) Are the skin debris and micro-organisms found on the periwound different than those found on normal skin? 2) How does the use of a skin cleanser for periwound cleansing affect the micro-organisms on the periwound or wound bed?
Recruitment and procedure. Patients with pressure ulcers in an urban long-term care facility were recruited by a Director of Nursing for this study and individual or family consent to participate was obtained. Common practice in this facility includes cleansing pressure ulcers with normal saline solution when the dressing is changed (once a day). Depending on the condition of the pressure ulcer, a medical ointment and gauze covered with polyurethane film or an alginate dressing with polyurethane film is applied. When infection is severe, povidone iodine is used as an antiseptic agent.26,27
Skin debris was collected from the periwound (1 cm away from the wound edge) and normal skin (10 cm away from the wound edge). Before cleansing and/or wound irrigation, micro-organisms were collected from three regions: the wound bed, the periwound, and normal skin.
To obtain the various components of skin debris, lipids were wiped off the skin surface with a cotton ball containing an organic solvent (acetone: diethylether, 1:1, vol/vol). A pasteboard frame was used to make the 2.5 cm x 4 cm opening that was applied to the skin to create the fixed opening from which lipids were taken. Squalene and cholesterol were analyzed from among the lipids obtained using gas chromatography (HP 4890A, Agilent Technologies, Palo Alto, Calif.), using a previously developed method.28
Proteins and water-soluble substances were obtained by tape-stripping a different area from the lipid sampling area on the periwound and normal skin. To standardize this procedure, polyphenylenesulfide tape (PPS, Nichiban, Tokyo, Japan) was cut into 2.5 cm x 4 cm sections for stripping. Water-soluble substances were extracted from the stripped tape using deionized distilled water. The water extract was analyzed for sodium, potassium, nitrogen, and urea. Sodium and potassium were analyzed by an atomic absorption spectrometer (Z-6100, Hitachi, Tokyo, Japan) at 589 nm and 766.5 nm, respectively. Nitrogen was analyzed using a total nitrogen analyzer (TN-05, Mitsubishi, Tokyo, Japan) according to the method developed by the American Society for Testing and Materials.29 Urea was analyzed by a mass spectrometer (API 100, Applied Biosystem, Forster City, Calif.) attached to a liquid chromatography (HP 1100 series, Agilent Technologies, Palo Alto, Calif.) using a mass spectra with an intensity of m/z 61. The insolvent residue was extracted by an aqueous 8 M urea/10% sodium dodecyl sulfate solution. The protein assay reagent (BCA-200, Pierce, Rockford, Ill.)30 was added to the extracted solution before analyzing the proteins by a spectrophotometer (U-2000A, Hitachi, Tokyo, Japan) at 562 nm.
Micro-organisms were obtained, even from dry skin, using a sterile cotton-tipped swab moistened in a sterile normal saline solution. Microbial samples were taken uniformly throughout the wound bed. To obtain microbial samples from the periwound and normal skin, a sterile pasteboard frame with a 1 cm x 1 cm opening was applied in a different area from the previous two skin debris-sampling areas. The collected samples were applied to culture media (brain heart infusion agar, sheep blood agar, mannitol salt agar, MSO agar, candida medium, XM-G agar, NAC agar, and EF agar, Nissui, Tokyo, Japan) in order to isolate the micro-organisms, after which they were incubated at 37° C for 24 to 48 hours. Microbial species were identified by a combination of standard manual and automated techniques. Microbial counts were determined by standard plating techniques.
In five of the 17 patients, the periwound was cleansed with a skin cleanser (SOFTY Medicated Skin Cleanser, Kao, Tokyo, Japan) to collect the micro-organisms from the wound bed and periwound at three times: 1) immediately after cleansing, 2) 6 hours after cleansing, and 3) 24 hours after cleansing. The skin cleanser was applied to wet gauze, fully lathered, and the gauze rubbed gently on the area. The periwound was subsequently rinsed with lukewarm water. After the pasteboard frame was applied, the sampled areas were marked for future sample tests to be taken. Because this is a time-consuming procedure, not all 17 patients were able to participate.
Data analysis. Analysis-of-variance techniques and Students t-test were used to compare the components of skin debris and microbial counts between the periwound and normal skin using Pearson’s test. A value of P <0.05 was considered to be statistically significant. Data are presented as means ± SD.
Seventeen patients (nine men, eight women, ages between 54 and 96 years, mean age 73), each with one pressure ulcer provided consent and participated in this study. Of the 17 pressure ulcers, seven were located at the sacrum, seven at the trochanter, and three at the ischium. All pressure ulcers were in the proliferation phase of Stage III or IV, as defined by the National Pressure Ulcer Advisory Panel (NPUAP).31 The wounds of five participants were cleansed with the skin cleanser; three others received povidone iodine treatment for infection.
Skin debris (see Table 5).
Lipids. The quantity of cholesterol on the periwound was 1.5 µg/cm2 compared to 0.4 µg/cm2 on normal skin — a statistically significant difference (P = 0.0027). The difference in quantity of squalene on the periwound and normal skin was not statistically significant (0.06 µg/cm2 on periwound and 0.12 µg/cm2 on normal skin).
Proteins. No statistically significant difference was found between the amount of proteins present on the periwound and normal skin.
Water-soluble substances. No statistically significant difference was found between the amounts of sodium, potassium, and urea on the periwound and normal skin. However, the quantity of nitrogen-containing substances on the periwound area was 10.6 µg/cm2 compared to 4.2 µg/cm2 on the normal skin (P = 0.0054).
Detected micro-organisms. The 17 wound beds yielded 47 micro-organisms (11 species) and the periwound areas yielded 51 micro-organisms (13 species) (see Table 6). The most common isolated species was Staphylococcus aureus (including MRSA), followed by ß-haemolytic streptococcus. Of the 51 micro-organisms isolated from the periwound area, 39 of the same micro-organisms also were isolated from the wound and 13 from normal skin. Twelve micro-organisms were isolated from all three regions of the wound bed, periwound, and normal skin (see Figure 1).
Microbial counts and skin debris. From the wound bed, periwound, and normal skin, 1.8 x 105 CFU/cm2, 2.9 x 105 CFU/cm2, and 4.2 x 104 CFU/cm2, respectively, were quantified. The microbial counts detected on the periwound were significantly larger than the microbial counts detected on normal skin (P = 0.01) (see Figure 2). Protein showed the highest correlation to the microbial count (r = 0.71, P = 0.0014), followed by nitrogen-containing substances (r=0.59, P = 0.013). Micro-organisms were virtually nonexistent in cultures from patients whose wounds were treated with povidone iodine. With the exception of the skin samples to which povidone iodine was applied, protein (r = 0.76, P = 0.0016) and nitrogen-containing substances (r = 0.70, P = 0.0053), showed a high correlation to the microbial count.
Effect of cleansing on microbial counts. The microbial counts were examined before and after cleansing. Of the five wounds sampled, 16 micro-organisms (seven species) from the wound bed and 15 micro-organisms (seven species) from the periwound area were isolated before cleansing (see Table 7). An additional micro-organism was isolated from the wounds 6 to 24 hours after cleansing. Tables 8 and 9 show the number of isolated micro-organisms and whether their microbial counts decreased or increased after periwound cleansing. For the periwound areas, the microbial counts in all isolates decreased immediately after cleansing. The number of isolates exhibiting increased microbial counts increased over time. For the wound beds, the number of isolates whose microbial counts decreased was greater than the number of isolates whose microbial counts increased after cleansing. However, both numbers were nearly the same after 24 hours.
Wound healing is a multifaceted process, involving the formation of granulation tissue and epithelialization that can be challenged by the presence of debris and bacteria. Cleansing with a saline solution to remove debris is a safe and appropriate cleansing method; skin cleansers are toxic to wound tissue and should not be used.12,32 Furthermore, the connection between the characteristics of skin debris on the periwound skin and the validity of removing it from the periwound skin has not yet been proven; therefore, skin debris on periwounds and the influences of periwound cleansing on microbial flora should be investigated.
Proteins. Proteins were found in larger quantities than any other component of skin debris collected from the skin samples. The amount of protein on the periwound and normal skin were greater than the amount of protein reported to be present on the sacrum of younger (mean age 37 years) healthy persons (31 ± 4 µg/cm2).33 Thus, the results of this study suggest that the skin of patients with pressure ulcers has a larger amount of desquamating fragments of keratinized cells than the skin of healthy persons. It can be generally summarized that a dry stratum corneum layer is easily exfoliated, causing an increase in desquamating fragments of keratinized cells. In this study, the skin surface of elderly nursing home residents was found to be drier than that reported and observed in healthy persons. No statistically significant difference was found in the amount of protein between the periwound and normal skin. One possible explanation is that wound dressing hydrated the periwound skin of some residents.
Lipids. Squalene was present in smaller amounts on the periwound than on normal skin, while cholesterol was present in larger amounts on the periwound than on normal skin. As mentioned previously, squalene was the representative lipid derived from the sebaceous gland and cholesterol was the representative lipid of the stratum corneum. Therefore, it was found that a greater amount of lipids was derived from the stratum corneum than from the sebaceous gland on the periwound. However, the effect of lipids in not evident.
Water-soluble substances. Nitrogen-containing substances were present in greater amounts on the periwound than on normal skin. Regarding the compositions of sweat (see Table 1)15 and NMF (see Table 4),21 the nitrogen-containing substances in this case were amino acids, urea, and ammonia contained mainly in keratinized cells. Therefore, it can be concluded that a large amount of water-soluble components were derived from the stratum corneum (eg, amino acids) on the periwound.
Although no statistically significant difference was found in the amount of protein (the principal constituents of the stratum corneum) present on the periwound and normal skin, lipids and water-soluble substances derived from the stratum corneum were present in greater amounts on the periwound than on normal skin. Therefore, it can be postulated that the stratum corneum, which is not normally keratinized from the epidermis, was exposed to the skin surface on the periwound area where fewer sebaceous glands are found - thus, lipids on the periwound skin facilitated the easy removal of components in the stratum corneum from the skin surface.
Micro-organisms. A number of species such as S. aureus and ß-haemolytic streptococcus were detected on both the periwound area and the wound bed of the 17 patients with pressure ulcers. Because some micro-organisms were found only on the periwound and not in the wound bed, the periwound was not necessarily infected with the micro-organisms in the wound. The microbial count and variety of microbial flora found on the periwound were greater than those found on normal skin. However, 13 of the 51 microbial flora detected on the periwound skin also were present on normal skin. This suggests that, in some patients, microbial contamination occurred over a range as wide as 10 cm away from the wound.
The relationship between the amount of skin debris and microbial count was examined to determine the influence of skin debris on periwound skin micro-organisms. Microbial counts increased proportionately with the amount of protein, which was the most common component of skin debris found. This suggests that protein supports the growth of micro-organisms on the periwound.
Microbial counts of each isolate were examined to determine whether counts increased or decreased after cleansing. On the periwound area, microbial counts in all isolates decreased immediately after cleansing, suggesting that micro-organisms on the periwound were removed together with the skin debris by periwound cleansing. However, the number of isolates with increased microbial counts increased over time; whereas, in the wound bed the majority of isolates showed a decrease in microbial counts. This suggests that the removal of skin debris by periwound cleansing may directly influence wound bed cleansing. The numbers of isolates with both increased and decreased microbial counts returned to nearly the same values after 24 hours. Thus, it can be postulated that the effect of periwound cleansing on the microbial flora in the wound bed lasts for less than 1 day, suggesting that the periwound skin should be cleansed at least once daily.
Skin cleansers are used to remove skin debris and dirt from skin surfaces, keeping it as clean and healthy as possible. However, skin cleansers may strip away beneficial components such as NMF and intercellular lipids that keep water within the skin. A skin cleanser designed for daily use should be mild enough to avoid skin irritation from occurring. In this study, large quantities of components derived from the stratum corneum were present as skin debris on the periwound area; therefore, it is presumed that the stratum corneum of the periwound is not keratinized in a manner similar to that of normal skin.
The results of this study suggest that periwound cleansing caused a decrease in wound and periwound microbial counts. However, the effect of cleansing on wound healing was not studied. Because the sample size was small and pressure ulcers were located at the sacrum, trochanter, and ischium, generalization of these findings to larger populations and other pressure ulcer locations is somewhat far-reaching. Specifically, in the case of leg and heel ulcers, the type and amount of micro-organisms may be very different from that seen on the sacrum, trochanter, and ischium. Another limitation was the age of the study sample and results may be different in a non-elderly population. Further research needs to be conducted to assess the effect of periwound cleansing on microbial flora and wound healing.
Implication for Practice
Prevention and control of wound infection promotes granulation tissue formation and epithelialization and facilitates the wound healing process. Results from this study suggest that periwound cleansing can reduce the microbial count on both the periwound area and wound bed. To avoid critical contamination of the wound bed, cleansing the periwound at least once daily is recommended as an important nursing care practice for elderly patients with pressure ulcers.
Skin debris and micro-organisms on the periwound skin area of patients with pressure ulcers was analyzed and the effect of periwound cleansing on the microbial flora in the wound bed and on the periwound skin was evaluated. Large amounts of skin debris derived from the stratum corneum and micro-organisms were found on the periwound skin. Results suggest that periwound cleansing makes the wound cleaner, even if the wound itself is not directly cleansed. This effect seems to last for less than 24 hours. Therefore, cleansing periwound with a skin cleanser daily may be an effective nursing care practice to promote wound healing. Further research is necessary and warranted.