Abstract
Heavy bacterial colonization results in exit-site infection. Antiseptic and non antiseptic agents have both been used for exit-site cleansing. An ideal cleansing agent should not only reduce the number of microorganisms, but should also be harmless to the body's defenses and should not interfere with wound healing. In vitro studies using animal cells have demonstrated that some antiseptic agents have adverse effects on wound healing. Strong cytotoxic antiseptics should be discouraged in exit-site cleansing.
In choosing an appropriate cleansing agent for exit-site care, the phase of wound healing, the condition of the exit site, and the goal of cleansing should be taken into consideration. Antimicrobial soap is recommended for cleansing a healed exit site, but biocompatible solution is preferred for the postoperative, infected, or traumatized exit site. In vivo studies on the effectiveness of some cleansing agents are still lacking, and clinical study of exit-site cleansing is needed to determine the most effective agents for the task.
Opinions on the use of wound antiseptics have shifted as background scientific knowledge and experience have increased (2). Recommendations on exit-site cleansing from experts in the field have been issued since the international survey on cleansing agents was conducted. Currently available information helps our understanding concerning the use of cleansing agents for exit-site care and the appropriate and effective application of various cleansing agents according to the condition of the exit site.
Cleansing Agents
Wound cleansers include antiseptic agents that have been in use since the First World War as well as newly discovered non antiseptic cleansers. Scientific, evidence-based knowledge concerning wound cleansing agents has been enriched with the passage of time. Such information enhances our understanding of the properties and effects of cleansing agents, enabling us to make appropriate decisions about their use.
Povidone Iodine
Povidone iodine is a water-soluble complex of the polymer polyvinylpyrrolidone and iodine, which is a broad-spectrum antiseptic. Povidone iodine is supplied as a 10% solution that contains 1% available iodine. Studies have revealed that 1% povidone iodine is cytotoxic in open wounds and that it delays wound healing (3,4). The compound is therefore contraindicated as an antimicrobial agent in the care of open wounds. The 10% solution can be diluted to 1:1000 to avoid cytotoxicity (3), but then the bactericidal effect drops to an equivocal level (5).
The use of povidone iodine in wound management is controversial, and the use of iodine fell from favor at the beginning of 1990 (6). However, povidone iodine retains an important role as a prophylactic antiseptic, reducing surgical wound infection by disinfecting the skin before surgery (7).
Hydrogen Peroxide
Hydrogen peroxide releases molecular oxygen when in contact with tissues. The oxidizing effect destroys anaerobic bacteria and removes slough from wounds. Hydrogen peroxide loses its effect when it comes into contact with organic material (6). Studies have revealed that 3% hydrogen peroxide is cytotoxic to fibroblasts unless diluted to 0.003%, but then the bactericidal effect also drops to a level that is controversial (3,5).
Hydrogen peroxide should not be used on cavity wounds. If hydrogen peroxide has to be used on a wound, the wound should be irrigated with normal saline afterward (6).
Acetic Acid
Acetic acid (vinegar) has been used as a wound antiseptic because microorganisms do not proliferate at low pH. All acids are bacteriostatic at low concentrations and bactericidal at higher concentrations (8). Acetic acid has been recommended for treatment of wounds infected with Pseudomonas aeruginosa (8,9). In vitro study revealed that 0.25% acetic acid is cytotoxic to fibroblasts (wound-healing cells) and retards epithelialization (3).
Sodium Hypochlorite
Sodium hypochlorite was introduced for wound irrigation in the First World War, but is now known to be injurious to tissue. However, this agent is considered an excellent disinfectant for inanimate surfaces (10). It has germicidal, deodorizing, and bleaching properties. The postulated mechanism is inhibition by free chlorine of enzymatic reactions within cells, protein denaturation, and inactivation of nucleic acids (8). At 0.5%, sodium hypochlorite is toxic to fibroblasts and interferes with wound healing. At 0.005%, it may be effective against microorganisms without the cytotoxic effects (3). Eusol, a common form of sodium hypochlorite, has been banned in many places (6).
Alcohol
Alcohols have excellent antibacterial activity against both gram-positive and gram-negative organisms. They are superlative skin antiseptics. The most effective alcohol concentrations are those between 70% and 92% (11). However, alcohol preparations should be used only on intact skin, because they are cytotoxic to open wounds (12). Alcohol also leads to dehydration of the skin (11).
Chlorhexidine
Chlorhexidine is a broad-spectrum antiseptic, but it is more effective against gram-positive than gram-negative organisms. When used as a skin antiseptic, chlorhexidine has extremely low toxicity, even for newborn infants (13). As a wound antiseptic, it is toxic to human fibroblasts, but it is a less cytotoxic agent than hydrogen peroxide or sodium hypochlorite (14). Chlorhexidine is not recommended for use in full-thickness wounds (8).
Soap
Pure soaps remove microorganisms by physical means. Soap emulsifies the lipid coating of the skin and removes that coating along with resident and transient bacteria. One advantage of soap is the profuse rinsing with tap water that occurs during cleansing. However, excessive use of soap may interfere with the water-holding capacity of the skin and may impair bacterial resistance (11). Soap is alkaline in nature, but the skin surface is slightly acidic—a state that plays an important role in preventing bacterial penetration (15). Use of alkaline soaps may increase skin pH and thus change bacterial resistance (11). Some soaps contain low concentrations of antimicrobial agents that serve more as preservatives than as antiseptics (10).
Antimicrobial soaps can both physically remove bacteria and inhibit and destroy microorganisms (16). Concerns have been raised about the use of antimicrobial soap: it may eradicate from the skin surface the resident bacteria that provide protection against pathogenic microorganisms, possibly enhancing the survival of S. aureus and the subsequent development of infection (17). But that phenomenon was not observed in a study that compared the use of pure soap and chlorhexidine soap in exit-site care (18).
Surfactants
Nonionic surfactants—for example, Pluronic F-68 (JRH Biosciences, Lenexa, KS, U.S.A.) and Shur-Clens (ConvaTec, Princeton, NJ, U.S.A.)—have no antimicrobial effect, do not interfere with tissue resistance to infection, and are nontoxic (10). This group of chemical polymers are known as “nonionics” because they carry no molecular charge. Polymer molecules that contain 80% oxyethylene are totally biocompatible. Tests have indicated that charged materials interact with the cell membrane and perturb it, and are therefore toxic to tissue defense and inhibit wound healing (19). Surfactants reduce surface tension and tissue damage during the cleansing process. They have been recommended as substitutes for antiseptics and for use when enhanced cleansing capacity is necessary because they facilitate removal of contaminants without breaking down local defenses (10,20).
Factors Affecting the Choice of a Cleansing Agent
Given the variety of wound cleansers available (antiseptic or non antiseptic in nature), current opinion suggests that a suitable cleansing agent should not only reduce the number of microorganisms, it should also be harmless to the body's defenses and should not interfere with wound healing (10). Some antiseptic agents have been demonstrated to have adverse effects on wound healing, because their primary mechanism of action is to destroy cell walls regardless of the identity of the cells. Those antiseptics are therefore also toxic to wound-healing cells (3). That toxicity directly interferes with wound healing at a cellular level and places the patient at greater risk of wound infection (4,15). Use of such antiseptics on wounds should be avoided (21).
Antimicrobial Agents
In addition to cleansing agents, the antimicrobial agent mupirocin has also been used in daily exit-site care for controlling exit-site infection. Mupirocin is available as an ointment for topical application. It is active against gram-positive cocci, and its use is directed against S. aureus, including the methicillin-resistant strains (22). Some studies report that daily application of mupirocin ointment at the exit site reduces the incidence of S. aureus exit-site infection (23-25). However, concern has arisen with regard to the use of mupirocin for prophylaxis, because repeated application has resulted in the emergence of mupirocin-resistant S. aureus (26,27), actually increasing the risk of S. aureus exit-site infection (27). Another potential problem with mupirocin is its role in the development of structural alterations in polyurethane peritoneal dialysis catheters (28).
Clinical Findings concerning Exit-Site Cleansing
In a study conducted to compare the effect on healed exit sites of three different methods of cleansing (soap and water; povidone iodine; and hydrogen peroxide followed by application of povidone iodine ointment), patients using povidone iodine and hydrogen peroxide experienced a higher infection rate. It was hypothesized that those results were attributable to the toxic effects of chronic exposure to the antiseptics (29). The use of povidone iodine or hydrogen peroxide as daily exit-site care has also been reported to lead to dry and erythematous exit sites, and thence to excoriation and subsequent infection (30).
Another study that compared three different methods of exit-site care (chlorhexidine gluconate, 0.005% sodium hypochlorite, and 10% povidone iodine swabsticks) came to the conclusion that none of the methods was superior in preventing exit-site infection. However, a high percentage of the patients using chlorhexidine and sodium hypochlorite developed a dry crust, which was felt to be a localized noninfectious tissue reaction to the antiseptic used (31).
A recent study compared rates of exit-site infection with the use of pure soap and chlorhexidine soap during daily exit-site cleansing. The results showed a lower infection rate in patients using chlorhexidine soap—in particular, fewer exit-site infections with gram-positive organisms. Exit-site infections with gram-negative organisms showed no difference (18).
Cleansing the Exit Site
Selection of the appropriate cleansing agent requires an understanding of the properties and effects of the various agents. It also requires consideration of the exit-site status, including the phase of healing and the condition of the exit site. The goal of exit-site cleansing should also be considered: Is the emphasis on prevention of infection, or creation of an optimal environment for wound healing? Other considerations include the immune status of the individual patient (which may predispose the patient to infection) and the possibility of an allergic reaction to certain kinds of cleansing agents. Under different conditions, exit sites present with specific characteristics, and different cleansing agents may be required under those different circumstances.
Cleansing a Postoperative Exit Site
After the peritoneal catheter is implanted, the newly created exit wound immediately sets off a healing process, with a series of physiologic responses. The presence of the peritoneal catheter causes the exit wound to heal more slowly, because the edges of the surgical incision are not approximated (32). The healing time has been estimated to range from 2 weeks to 6 weeks (33).
A sterile and undisturbed condition at the exit site supports sinus epithelialization (20); heavy bacterial colonization can affect the repair process (32). “Colonization” is the presence of replicating microorganisms in the wound in the absence of injury to the host (2). Because of the lack of an epidermal barrier to microorganisms during the lengthy healing process, the exit wound is more subject to infection (32). The risk of surgical wound infection is related to the number and virulence of the microorganisms present. Therefore, in this case, the goal of wound cleansing is to prevent wound infection by reducing the amount and type of microbial contamination (34).
To delay bacterial colonization, it is important to maintain sterility during the healing period. The solution used in wound cleansing must be carefully selected to provide antibacterial activity without interrupting the wound healing process or causing chemical trauma (9). Chemical trauma occurs when a physiologically incompatible agent is added to a wound (19). In exit-site cleansing, chemical trauma may occur when the chemical enters the sinus, possibly damaging granulation tissue and delaying healing.
The focus of postoperative cleansing of the exit wound is to minimize microorganisms and to create an optimal environment for wound healing. A non irritating or biocompatible solution such as a nonionic surfactant is preferable to a strong antiseptic in cleansing a postoperative exit wound (33).
Cleansing a Healed Exit Site
The exit site comprises the most external part (0.5 – 1 cm) of the sinus tract and the skin surrounding the exit of the tunnel. A study on the morphology of the peritoneal catheter tunnel showed that epithelium covers only part of the sinus tract in most tunnels. The epithelium may cover the entire sinus and reach the cuff only if the cuff is located less than 1.5 cm from the exit (35).
The sinus tract close to the exit site is covered with epithelium. The rest of the sinus tract is typically covered with granulation tissue, which does not attach to the peritoneal catheter. The granulation tissue reaches the cuff, which is surrounded by a dense, fibrous capsule (20). It has been discovered that almost all exits and sinus tracts are colonized by bacteria and that bacterial penetration into deeper parts of the sinus tract is contained by the granulation tissue barrier (35). The tissue defenses protect the body against bacterial invasion, and the wound has an exquisite capability to protect itself against bacterial challenges if natural defenses are not inhibited (36). However, as the number of virulent bacteria deeper in the sinus increases, an infection may result if the opposing forces of the colonizing bacteria and the bodily defense mechanisms cannot be balanced (36,37). The tissue defenses are overwhelmed, and the incidence of wound infection increases when the bacterial count exceeds 105 cfu (19).
Prevention of exit-site infection is the prime objective in chronic care of a healed exit site. Daily exit-site cleansing is recommended to prevent infection by reducing the number of microorganisms. For a healed exit site, cleansing with either an antimicrobial liquid soap during a shower or with a medical antiseptic has been recommended (38,39). When a large crust is present at the exit site, a nonionic surfactant can be used to remove the crust (20).
Cleansing an Infected Exit Site
In an infected exit site, the epithelium in the sinus has usually regressed, and the remainder of the visible sinus is covered with granulation tissue (37). The purpose of cleansing an infected exit site is to remove wound exudates and microorganisms, and to prompt wound healing. It is therefore important that cytotoxic agents not be allowed to enter the sinus. Preferably, such agents should be avoided in cleansing an infected exit site. Mild, non irritating wound cleanser is preferred (20,38).
Cleansing an Equivocal Exit Site
An equivocal exit-site infection is a low-grade infection in which discharge is present only in the sinus, accompanied by regression of the epithelium and occurrence of slightly exuberant granulation tissue in the sinus. An equivocal exit site may improve spontaneously, but most will progress to overt infection if untreated (39). Exit-site cleansing is required to remove exudates, to minimize the microorganism count, and to maintain an optimal environment for healing to take place. Mild, non irritating wound cleanser is preferred for cleansing an equivocal exit site.
Cleansing a Traumatized Exit Site
Accidental trauma to the exit site from a hard pull may result in bleeding. Blood in the exit site should be removed, because blood is a good culture medium, and colonizing bacteria will multiply rapidly and infect the disrupted tissue in a trauma wound (20). Non irritating wound cleanser can be used to clean a trauma wound.
Conclusion
The selection of a cleansing agent requires an understanding of the properties and effects of various agents on microorganisms and wound-healing cells alike. In selecting an appropriate cleansing agent for exit-site care, the phase of wound healing and the condition of the exit site should also be taken into consideration, as should the goal of the cleansing (to prevent infection or to create an optimal environment for wound healing).
Antimicrobial soap is recommended for cleansing a healed exit site. Biocompatible solution is preferred for postoperative, infected, and traumatized exit sites. In situations in which an antiseptic is justified, the use of strong cytotoxic antiseptics is discouraged. A desirable antiseptic will be effective in reducing the number of microorganisms while minimizing tissue irritation and interference with wound healing. Despite the fact that cleansing recommendations are currently available, data from clinical research on the effectiveness of some cleansing agents are still lacking. We need scientific evidence and new findings from clinical research to determine which agents are most effective for exit-site cleansing.