Annals of Burns and Fire Disasters - vol. XIV - n° 1 - March 2001

EVALUATION OF "MICROMAT" DRESSING (VISCOSE POLYMER VEHICLE FOR CHLORHEXIDINE) IN PARTIAL-THICKNESS BURNS AND SKIN GRAFT DONOR SITES

Bhattacharya S., Ahuja R.B., Topaz M., Tripathi C.D.

Department of Burns and Plastic Surgery, Plastic Surgery Unit, Lok Nayak Hospital & Associated Maulana Azad Medical College, New Delhi, India
Plastic Surgery Unit, Hillel Yaffe Medical Center, Hadera, Israel
Department of Pharmacology, Lok Nayak Hospital & Associated Maulana Azad Medical College

SUMMARY. In this study, "Micromat"® 0.5% (a chlorhexidine-impregnated viscose polymer dressing) was evaluated for treatment of partial-thickness burns and split skin graft donor sites with a dual objective: one, to compare the dressing with traditional methods, and two, to study viscose polymer as a vehicle for delivering chlorhexidine. Only fresh cases of partial-thickness burn injury between 10-25% total body surface area (TBSA) in patients over 12 years of age were included in the study. All consecutive split skin graft donor sites harvested with a Watson's modified Humby's knife were included for the other part of the trial. Thirty patients with partial-thickness burns and 30 split thickness skin graft donor sites were evaluated. In nine patients with 20% TBSA deep dermal injury, mirror-image areas of burns were available for comparison. In these, one side was dressed with 1 % silver sulphadiazine cream, which acted as a control. Burn dressings were changed after 72 h, or as warranted by the state of the wound and the patient's general condition. Additionally, in six patients with 20% TBSA burns, chlorhexidine estimation was performed in blood. In split skin graft donor sites, the proximal half was dressed with Micromat 0.5% and the distal half with ordinary paraffin gauze (Fairlie, Johnson & Johnson). The dressings were allowed to separate by showering after 10-11 days. We observed no difference in the healing rate or pattern between Micromat treated wounds and controls. Amongst the burn patients there was no conversion of partial-thickness injury to full-thickness in either group. Many burn wounds treated with Micromat were found to be dry at the time of dressing change. Also, there were no complications like wound sepsis or septicaemia requiring substitution of the local antimicrobial agent or a need for systemic antibiotic in any of the patients. Chlorhexidine could not be detected in the blood sample of any patient. Thus, for partialrhickness burn injury in up to 25% TBSA, treatment with Micromat compares favourably with 1% silver sulphadiazine cream, and For treatment of skin graft donor sites the results of Micromat and ordinary paraffin gauze are comparable, and the former has the added advantage of delivering an effective antibacterial agent. It was also observed that viscose polymer was an effective vehicle for delivering chlorhexidine. Micromat dressing was easy to handle and relatively non-adherent, and had a capacity to absorb the discharge.

Introduction

Partial-thickness burns and split skin graft donor sites heal by epithelialization from surviving pilosebaceous units. Their healing demands a proper environment for survival of these epidermal units. Dressings are required during this period to provide physical protection, contain exudate, diminish pain, avoid infection, and enhance the healing process, if possible, by providing a moist environment. Thus, partial-thickness burns and skin graft donor sites provide a good model for the evaluation of newer dressing materials.
The first description of a burn wound dressing dates back to Egyptian papyri (1500 BC), which mention the use of gum and goat's milk.' A major breakthrough in dressing materials came in 1880 when Joseph Samson Gamgee used bleaching cotton wool enclosed in a gauzelike material called "Tiffany".2 This gamgee dressing is still widely used, although "Tiffany" has long since been replaced by surgical gauze. From the concept of the occlusive dressings introduced by Winter' in 1962, which provide a moist environment considered optimal for healing, to the concept of "interactive dressings",' where the dressing interacts biochemically within the wound to hasten healing, wound management has been revolutionized. Enormous technological advances in the last century have seen the emergence of numerous dressing materials like films, gel, foam, and polysaccharide materials.
In burn wounds an additional concern is the prevention of wound sepsis, which led to the development of a number of local antimicrobials. Moncrief' introduced mafenide in 1963, followed by Charles Fox,6 who developed silver sulphadiazine in 1969. Silver sulphadiazine continues to be the most widely used topical agent in burn wound management. Other agents like povidone iodine, 0.5% silver nitrate, framycetin, bacitracin, chlorhexidine, and mupirocine are also used in burns. Chlorhexidine is a broadspectrum antimicrobial agent and its antibacterial activity is comparable with that of silver sulphadiazine.' The combination of chlorhexidine with 1 % silver sulphadiazine is more potent in its antibacterial activity! Chlorhexidine is also available as 0.5% solution impregnated on paraffin gauze/tulle gras or as a cream for wound management' The drawback of chlorhexidine has been its toxicity, and an `ideal vehicle' for dispensing it has still not been documented.' The present prospective study was instituted to evaluate the efficacy of a chlorhexidine-impregnated viscose dressing in partial-thickness burns and split skin graft donor sites, with two objectives: one, to compare the new dressing with traditional, time-tested methods for managing partial thickness skin injury, and two, to study viscose polymer as a vehicle for delivering chlorhexidine. We also investigated the toxicity with the use of 0.5% chlorhexidine in burns in up to 25% total body surface area (TBSA). The Micromat material is marketed by Sion Misgav Am, Israel, and samples for the trial were provided by the company.

Material and method

The study consists of two parts: Micromat 0.5% dressing was evaluated in partial-thickness burns and a comparison with 1 % silver sulphadiazine was attempted wherever mirror-image areas of burn were available. Micromat 0.5% dressing was also compared with paraffin gauze dressings (Fairlie, Johnson & Johnson ) in split skin graft donor sites. Protocol criteria included only fresh cases of partialthic:kness burn injury between 10 and 25% TBSA in patients who were over 12 years of age. Even though it was not specified by protocol, all patients had a significant percentage of deep dermal injury as admission logistics excluded others. All consecutive split skin graft donor sites harvested with a Watson's modified Humby's knife were included for the other part of the trial.

Micromat dressing

Micromat dressing is made of knitted viscose polymer impregnated with chlorhexidine gluconate in a concentration ranging from 0.5 to 2%. It is a hydrophilic and nonadherent sheet. The agent is activated by coming in contact with an aqueous environment, such as body fluid, medication, saline, distilled water, etc. The viscose polymer vehicle has good absorption qualities and can imbibe fluid equivalent to its weight. It does not adhere to the wound bed, making removal painless and atraumatic. Chlorhexidine has broad-spectrum antibacterialactivity against both gram-positive and gram-negative bacteria. It is impregnated on the viscose polymer in a sustained release formulation which obviates frequent changes of dressing. The dressing can thus be retained for 72 h unless excessive exudate or patient condition warrants an earlier change. Micromat is available in various sheet sizes: 10 x 10 cm, 10 x 15 cm, and 10 x 20 cm. It is packed singly in sterile sachets. After application the dressing is moistened by saline irrigation and covered with gamgee pads and bandaged much like an ordinary paraffin gauze.

Study of partial-thickness burns

This group consisted of 30 patients allocated by the selection criteria. Burns > 25% TBSA were excluded from this study as, presumably, chlorhexidine alone would not have been sufficient to combat development of wound sepsis in such patients. Patients with inhalation injury and other associated injuries and those with metabolic or systemic disease were also excluded. All patients in this group had a significant component of deep dermal injury, since patients with superficial burns, even of this magnitude, do not get admitted for want of sufficient beds. Patients requiring intravenous resuscitation were given fluid according to the Parkland formula (3 ml/kg/%a TBSA burn). All patients were dressed within 4-5 h of sustaining burns. In nine patients mirror-image areas of identical depth were available for comparison to act as controls. The control areas were treated with 1% silver sulphadiazine cream. The trial areas were dressed with Micromat having 0.5% chlorhexidine. Dressings were changed every 72 h in the trial area unless an earlier inspection was warranted by wound condition. Control areas were generally dressed daily or maximum after 48 h. Preliminary photographs and wound descriptions were recorded and pre-dressing wound swabs sent for culture/sensitivity tests. The progress of healing was observed and a photographic record maintained (Figs. 1, 2).

Fig. 1a - Second-degree superficial burns in rigth shin in adult female Fig. 1b - Wond covered with Micromat dressing after cleaning. Fig. lc - Healed wound after 10 days with only two changes of Micromat.

Fig. 2a - Second-degree deep burns in both legs in adult female. The burn areas in each leg present  mirror-image areas for comparison. Fig. 2b - The right leg was dressed with Micromat and changed every 72 h and the left leg with 1 % silver sulphadiazine cream. The left leg had to be dressed almost every day because of soakage. Fig. 2c - The right leg was dressed with Micromat and changed every 72 h and the left leg with 1 % silver sulphadiazine cream. The left leg had to be dressed almost every day because of soakage.

Pus swabs were sent for culture and sensitivity tests at each dressing change. Additionally, in six randomly selected patients with burn injury of more than 20% TBSA we estimated chlorhexidine levels in blood. Five millilitres of blood were collected from a peripheral vein at 2, 4, and 6 h intervals after the second application of Micromat 0.5%. Serum was separated and stored at -20 °C until analyses were performed. Estimation of chlorhexidine gluconate was carried out by a modified method as described in British Pharmacopeia'2 by HPLC. In this procedure a stainless steel column (20 cm x 4 mm) packed with stationary phase C (IOum) (Nucleosil ODS) was used. The mobile phase of  0.01 m sodium octane sulphonate in a mixture of 73 volumes of methanol, 27 volumes of water, and glacial acetic acid was prepared and a flow rate of 1.5 ml/min was maintained. A detection wavelength of 254 nm was used. The method showed sensitivity of 0.05-0.1 ug/ml.

Study of skin graft donor sites

This group included 30 patients who consecutively underwent skin grafting for various reasons, excluding postburn raw areas. Only thin- to medium-thickness skin grafts were harvested using a Watson's modified Humby's knife. In 20 patients the graft was harvested by the first author and in 10 patients by the third author. On all donor sites the proximal half of the wound was dressed with Micromat (0.5%) and the distal half with paraffin gauze (Fairlie, Johnson & Johnson). This was done with the idea of providing near perfect similarity of wound area and depth for comparison. The dressings were overlain with gamgee pads and bandaged. The inner dressings were left to separate spontaneously by showering on day 10/11 and a photographic record was maintained (Fig. 3).

Fig. 3a - Split thickness skin graft harvested from left thigh by Watson's knife. Fig. 3b - The proximal half of the donor site was dressed with Micromat and the distal portion with `Fairlie' (Johnson & Johnson). Fig. 3c - Both legs healed at the same time after 24 days.

Results

The patients were assessed for rate and quality of healing, evidence of infection, and pain during change of dressings. The patients were asked to assess pain or discomfort at dressing change as none, mild, moderate, or severe, because the visual analogue method for pain assessment" has proved to be impractical." All patients were followed up till complete healing. The efficacy of viscose polymer as a vehicle for delivering chlorhexidine was also assessed.

Partial-thickness burn group

The antimicrobial agent (chlorhexidine gluconate 0.5%) was evaluated in patients with burns in up to 25% TBSA for the incidence of wound sepsis and septicaemia and for the need to substitute the local agent or add systemic antibiotic. In six patients with 20% TBSA deep dermal burns, chlorhexidine gluconate levels were also estimated in blood. The vehicle (viscose polymer) was assessed in terms of ability to absorb exudate, ease of dressing change, and required frequency of dressings. There was no evidence of wound sepsis in any burned area in the trial group or the controls. No patient developed septicaemia, and no patient therefore needed substitution of the local antimicrobial agent or administration of systemic antibiotics.
All the patients were categorical that there was mild discomfort at dressing change where Micromat had been used. On the contrary, in nine patients where a mirror-image area had been dressed with 1 % silver sulphadiazine cream, patients complained of moderate pain in the control area during dressing change. Almost all burn areas dressed with Micromat were found to be dry at the time of dressing change performed every 72 h. In comparison, the nine control areas dressed with 1 % silver sulphadiazine cream had to be dressed daily (or occasionally on alternate days). In these control areas the wound exudate combined with silver sulphadiazine cream to leave a residue on the wound surface which presented a wet look at dressing change.
Qualitative analysis of bacterial flora in pus cultures from the trial and control areas revealed that the same spectrum of organisms was colonizing both areas. All burned areas in both the trial and the control groups healed at the same time (Fig. 2). In six patients with 20% TBSA burns in whom chlorhexidine gluconate estimation was performed in blood, chlorhexidine could not be detected in any of the samples.

Split skin graft donor site group

Although it is difficult to quantify pain objectively, especially when the areas compared are contiguous, all patients reported mild and comparable discomfort during dressing removal in both Micromat and paraffin-gauze-treated donor areas, on post-operative day 10 or 11 day, when the dressings were allowed to separate by showering. In all patients both the areas had completely epithelialized, with the same quality of neo-epithelium, at the time of removal of the dressing (Fig. 3).

Discussion

Micromat, a chlorhexidine-impregnated viscose dressing, was introduced to us as a new, inexpensive dressing material for managing partial-thickness skin injury. We decided to evaluate its place in the dressing armamentarium. Thus, there were two objectives: one, to compare the. new dressing with traditional, time-tested methods for managing partial thickness skin injury, and two, to study viscose polymer as a vehicle for delivering chlorhexidine. Split skin graft donor sites provide an injured area akin to partial-thickness burn. By analogy the dressing material for both kind of wounds could be similar, with less need of topical antibacterial agents for donor sites since the donor site wound, in terms of percentage TBSA, is generally limited. For such donor sites, in Great Britain" and elsewhere, the most widely used dressing has traditionally been tulle gras overlaid with gamgee and crepe bandage.
This form of dressing continues to be costeffective compared with hydrocolloids and alginate dressings, although the latter have their advantages."-'b Polyurethane dressings like opsite are also being used on donor sites and they significantly reduce pain; however, the wound exudate and blood get trapped under it and the dressing has to be changed several times to allow their removal." Thus, the management of skin graft donor site remains individualized to the surgeon's preference. The comparison of Micromat with paraffin gauze on donor sites was more in line to test whether viscose polymer retards healing or how it compares with a traditional and time-tested approach. No attempt was made for an earlier inspection because under paraffin gauze the donor sites are known to heal around day 10 or 11, and here the donor sites under comparison were contiguous. We were not expecting an earlier healing of the donor site with viscose polymer dressing since it does not provide a. moist environment, which is known to hasten epithelialization. Earlier removal of the dressing for wound inspection would have resulted in peeling-off of the neoe pithelium. Similarly, partial-thickness burns can be treated by tulle gras, hydrocolloid gels, polyurethane films and alginates, etc., if the percentage of body surface burns does not warrant a topical antibacterial agent. For burns in more than 10% TBSA a topical antibacterial agent is generally used in dressings to prevent the development of wound infection. Our study reveals that Micromat offers another alternative comparable in efficacy with paraffin gauze, and it also additionally provides an excellent antibacterial topical agent. Since Micromat renders the wound relatively dry, we propose that it should be allowed to separate from donor sites by showering rather than by peeling. Chlorhexidine for burn dressing has been reported by a. number of authors.' 9 It is regarded as a broad-spectrum antimicrobial agent. Monafo et al.' reported that the antibacterial activity of chlorhexidine was comparable with that of silver sulphadiazine, but the combination of silver sulphadiazine and chlorhexidine was more effective than silver sulphadiazine alone.
A similar result was reported toy Snelling et al.' in a comparative study of chlorhexidine and silver sulphadiazine in burns. An in vitro study done by Holder" at the Shriners Burn Institute using the wet disc test reported that chlorhexidine, silver sulphadiazine, and mafenide had comparable efficacy. Our study, although in concurrence with these reports, was not directed towards this aspect. However, the above reports encouraged us to use chlorhexidine in burns as the sole antibacterial agent. We limited the study to burns < 25% TBSA as we were not confident that chlorhexidine alone would be sufficient to prevent burn wound sepsis in extensive burns, when it is established that in such cases quite frequently the topical agent may have to be changed depending on the local bacterial flora. At the same time the eschar penetration of chlorhexidine is not well documented.'' There still exists a doubt about toxicity from chlorhexidine, vis-a-vis its vehicle. Toxicity resulting from chlorhexidine can cause hypersensitivity reaction and ototoxicity." Miller" studied different concentrations of chlorhexidine cream and found that the toxicity is less frequently observed below 0.5% concentration.
He suggested a pharmaceutical improvement in its vehicle system. Most of the formulations of chlorhexidine used till now have been in cream form, although chlorhexidine is also available impregnated on tulle gras/paraffin gauze.' In Micromat, chlorhexidine is impregnated on a viscose polymer, for sustained release, in a concentration ranging from 0.5 to 2%. We used only 0.5% sheets for our study. Han and Maitra' studied chlorhexidine on tulle gras dressing and compared it with povidone iodine rayon dressing, obtaining a comparable result. Antikiszko et al .2° experimented on mice with chlorhexidine-impregnated microdressings of collagen membrane and concluded that such preparations could be useful in treating burns. Viscose polymer offers yet another vehicle for dispensing chlorhexidine. A major thrust of our study was directed towards investigating whether viscose polymer as a vehicle could be more useful and whether any toxicity resulted from the use of 0.5% chlorhexidine in burns of up to 25% TBSA. We observed that viscose polymer was an effective vehicle for chlorhexidine. Chlorhexidine impregnated onto it in a sustained release form renders it free of toxicity, at least in a concentration of 0.5%. Since chlorhexidine levels were undetected in blood at this concentration in burns of up to 25% TBSA, it is quite unlikely that it would be detectable in toxic levels if used in the same concentration in a larger burn area. However, the usefulness of chlorhexidine alone in larger burns would need separate investigation. Viscose polymer has another distinct advantage in that it provides an absorptive capacity to hold the exudate and to render the wound relatively dry, without adhering to the neo-epithelium

RESUME. Dans cette etude, les Auteurs ont evalue le "Micromat"® 0.5% (un pansement polymere visqueux impregne de chlorhexidine) dans le traitement des brulures d'epaisseur partielle et des sites donneurs de greffe de la peau d'epaisseur variable. Les deux buts de 1'etude etaient de confronter le pansement avec les methodes traditionelles et d'evaluer le polymere visqueux corome vehicule pour livrer la chlorhexidine. Seulement les cas nouveaux de bralures d'epaisseur partielle de 10-25% de la surface corporelle dans des patients ages au moins de 12 ans ont ete inclus dans 1'etude. Les Auteurs presentent leurs methodes et leurs resultats et concluent que pour les types de brnlures pris en consideration le traitement avec le Micromat soutient bien la comparison avec la creme sulphadiazine argentee, et aussi dans le traitement des sites donneurs de greffe de la peau les resultats obtenus avec le Micromat et la gaze commune paraffine sont comparables; le Micromat offre Favantage supplementaire de livrer un agent efficace antibacterien. Les Auteurs ont en outre observe que le polym6re visqueux est un vehicule efficace pour livrer la chlorhexidine. Le partsement Micromat est facile a utiliser et relativement non-adhesif et il possede la capacite d'absorber la suppuration.

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