- 1 - Welcome to the fourth edition of the Dressings Times. In this issue we begin a short series of articles on the selec- tion and use of wound dressings for the treatment of specif- ic types of wound. When complete, it is intended that this series should form a basic introduction to this important but often confusing area. Also in this issue, for the first time, there is a short correspondence section which, it is hoped, will develop into an informal forum for the interchange of information and views on dressings related topics. Selection of Wound Dressings In recent years many new dressings have become available which differ greatly in performance from the simple ab- sorbent products made from cellulose fibre which have been used in the past. The majority of these modern materials are designed to maintain a moist environment at the surface of the wound providing conditions which were shown by Winter and others to facilitate rapid epithelialisation.1, 2 A num- ber also combine with exudate to change their physical and chemical state, forming a gel like covering on the surface of the wound. These so called `interactive' materials pro- duce a micro-environment at the wound interface which can facilitate rapid wound healing. As dressings become more sophisticated, they also tend to become more `wound-specific' and some products have perfor- mance characteristics which make them particularly well suited for application to certain types of wounds but less appropriate for others. As no single dressing is suitable for the management of all types of wounds and few are ideal- ly suited for the treatment of a single wound during all stages of the healing cycle, the choice of the most appro- priate product for use in any given situation can be ex- tremely difficult. A simple wound classification system has therefore been adopted to facilitate the selection process which is based entirely upon the physical appearance and condition of the wound. It should be emphasised however that this classification takes no account of the cause of the wound or any of the other factors which are known to have an important influence on wound healing such as the nu- tritional state of the patient, the presence of underlying disease or the administration of drugs such as corticos- teroids. All of these factors should be considered when de- ciding the overall treatment of the patient but with a few important exceptions, they will probably have little influ- ence upon the selection of the primary dressing. Wound Classification For the purposes of dressing selection, wounds may be clas- sified as shown below. o Black and necrotic - covered with a hard dry layer of dead skin o Sloughy/necrotic - covered or filled with a soft yellow slough o Clean and granulating with significant amount of tissue loss o Epithelialising It will be recognised that this classification not only rep- resents different types of wounds but also the various stages through which a single wound may pass as it heals. It follows therefore, that as the condition of the wound changes, it may be necessary to change the type of dressing which is used. For example, a product which is ideally suit- ed for the management of a granulating wound may be of lit- tle value when applied to a dry necrotic lesion. This issue of The Dressing Times describes those products which may be used in the management of necrotic and sloughy wounds. Dressings which may be of value for the treatment of the other wound types outlined above will be discussed in future issues. Necrotic Wounds If left untreated, wounds such as pressure sores often take on a black leathery appearance as the epidermis dies and be- comes dehydrated. These black areas are particularly common on the heels, buttocks and sacral regions of elderly bedrid- den patients and are often a source of considerable pain or discomfort. Depending upon the severity of the condition, the necrotic layer may be relatively superficial but in more serious cases it can be much thicker. Often, large cavities may develop beneath this layer which are filled with dead or partially liquified tissue. In exceptional cases these cavi- ties can even extend right down to the bone. Sloughy Wounds Wounds such as burns and leg ulcers often develop a gluti- nous yellow covering commonly referred to as slough. This is not dead tissue but a complex mixture of fibrin, deoxyri- bonucleo-protein, serous exudate, leucocytes and bacteria. Slough can build up rapidly on the surface of an otherwise clean wound and its presence is sometimes even accepted as a normal part of the healing process. It has been shown exper- imentally however that slough or devitalised tissue will predispose a wound to infection by acting as a bacteriologi- cal culture medium and inhibiting the action of leucocytes in the wound.3,4 For this reason it is generally agreed that in order to achieve an acceptable rate of healing, a necrot- ic or sloughy wound must first be properly cleaned or de- brided. There is no doubt that surgery is by far the quick- est method of debridement but as this is not always practi- cable, other techniques must be adopted. Traditionally, agents such as sodium hypochlorite and hydrogen peroxide have been used in the form of soaks but these are of limited efficacy and also have other disadvantages which were de- scribed in the last issue of the Dressing Times. More re- cently, it has been recognised that adequate debridement can be achieved without recourse to surgery by the use of dress- ings and other agents and it these alternative methods that will be described here. Removal of Necrotic Tissue Given favourable conditions, the black leathery skin cover- ing a pressure sore will generally separate spontaneously from the healthy tissue beneath. This occurs as a result of autolysis and presumably involves macrophage activity and/or the action of proteolytic enzymes. However if a pressure sore is exposed to the atmosphere, the epidermis is unable to control the loss of moisture vapour and thus becomes de- hydrated. If this process continues and the skin dries out and goes hard, it becomes progressively more difficult for autolysis to take place and the separation of the slough may be delayed indefinitely. It follows therefore that any products which reverse this process of dehydration will help to accelerate the removal of the necrotic tissue. One con- venient method is by the use of hydrocolloid dressings for example, Granuflex, Biofilm or Intrasite. These materials are relatively impermeable to moisture vapour in their in- tact state and if such products are placed on necrotic wounds, they act as a physical barrier, preventing the loss of moisture vapour through the dead tissue. As a result, the black area becomes rehydrated and the autolytic process de- scribed above can take place at an enhanced rate. The speed at which this occurs depends upon the depth of the wound and the blood supply to the area but some change in the condi- tion of the necrotic skin is usually evident within a few days as the hard black layer softens and changes to a brown or olive green colour. On superficial wounds, the autolytic process may be allowed to continue undisturbed apart from an occasional change of dressing and in these situations the necrotic layer will eventually separate to reveal a healthy granulating wound surface beneath.5, 6 On deeper or more ex- tensive injuries however, once the dead tissue starts to loosen, it is usually advisable to remove it as quickly as possible. Once this outer layer has been removed, it is not unusual to find a deep cavity filled with a foul smelling semi-liquid mass of necrotic tissue. At this stage it may be appropriate to consider a change of treatment to complete the cleansing process as described in the management of sloughy wounds below. If for some reason a hydrocolloid dressing cannot be used, similar beneficial results may usually be achieved by the application of one of the amorphous hydrogel dressings such as Scherisorb or Bard Absorption Dressing. Both of these ma- terials contain a significant proportion of water and when they are placed on to the necrotic epidermis, some of this water is taken up by the dead tissue which becomes rehydrat- ed so that autolysis may take place as before. Hydrogels have a tendency to dry out if left exposed to the air and therefore for this particular application, they should be covered with a secondary dressing which will prevent or re- duce the loss of moisture vapour. Perforated plastic film dressings such as Melolin or Telfa have been found to be particularly useful for this purpose but semipermeable films such as Opsite Tegaderm or Bioclusive have also been used. Despite their different modes of action, there is probably little to choose between the hydrocolloid dressings and the hydrogels in terms of their ability to rehydrate necrotic tissue, although for relatively small areas on heels or but- tocks the hydrocolloids are more convenient to use. The gel dressings are to be preferred on more extensive wounds or areas which are hard to dress with the hydrocolloid sheets. It has been suggested that preparations containing prote- olytic enzymes or other agents which can breakdown fibrin and slough may be used to debride necrotic areas which have first been scarified with a scalpel. Alternatively it has been said that these solutions can be injected beneath the eschar with a hypodermic syringe. There is little evidence available to support the use of these materials when applied in this fashion and neither procedure should be undertaken unless specifically requested by the medical officer in charge. These enzyme preparations are probably best reserved for the treatment of wounds containing soft yellow slough or necrotic wounds once the epidermal layer has been removed. Treatment of Sloughy Wounds The treatment of wounds containing significant quantities of yellow slough or soft necrotic tissue will depend largely upon their size and the amount of exudate which they pro- duce. Relatively small moist wounds are sometimes dressed with polysaccharide bead dressings such as Debrisan or Io- dosorb which may be used alone or in the form of a paste made with polyethylene glycol. The beads absorb fluid and progressively move bacteria and cellular debris away from the surface of the wound.7 Iodosorb has the additional ad- vantage that it also liberates iodine which imparts antibac- terial properties to the dressing. Relatively shallow sloughy wounds which produce limited amounts of exudate can be dressed with hydrocolloid dressings which facilitate au- tolysis by the mechanisms described previously. In addition it has recently been shown that one of the ingredients found in certain of the hydrocolloid products may confer addition- al benefits. In laboratory studies it has been shown that Granuflex is able to lyse human fibrin clots in vitro8 and it is possible that this effect may contribute to the wound cleansing process. Hydrocolloid sheets should be applied with caution over the top of deep cavity wounds although the pastes or granules produced by some manufacturers may often be used with advan- tage in these situations since they can be introduced di- rectly into the body of the cavity. Alternatively an amor- phous hydrogel may be used in a similar fashion and covered with a secondary dressing as before. If a wound is producing large volumes of exudate, a moisture retaining dressing will not be required and it may be more appropriate to use a sim- ple absorbent pad as the secondary dressing under these cir- cumstances. With deep flask shaped wounds, it is sometimes necessary to use a packing material in order to prevent the outer surface closing prematurely. In these circumstances, ribbon gauze impregnated with Scherisorb may be used in place of Eusol or proflavine. Large pressure areas on the buttocks and sacrum and certain fungating carcinomas often become infected with anaerobes which can make the wound very offensive. The application of Scherisorb gel containing 0.8% metronidazole has been found to be extremely effective in controlling the infection and thus reducing the odour but this treatment should only be carried out under medical supervision. Odour absorbing dressings containing activated charcoal such as Actisorb Plus or Lyofoam C can also be of value in these situations. Heavily exuding wounds such as leg ulcers or necrotic surgi- cal wounds which also have some sloughy areas can be dressed with alginate dressings as the exudate which is liberated from the wound will interact with the dressing to form a gel. This gel will form a moist covering over the slough preventing it from drying out and becoming hard. In general terms however, alginates should not be applied to dry sloughy wounds or wounds which are covered with hard necrot- ic tissue. Other materials which are sometimes used to debride sloughy wounds include the enzymatic agents referred to previously. Tryptar (Armour Laboratories, and Trypure Novo (Novo Labora- tories) contain stabilised trypsin, a proteolytic enzyme. Varidase (Lederle Laboratories) consists of a mixture of streptodornase and streptokinase. Streptokinase is an ex- tracellular enzyme produced from certain microorganisms which is able to initiate a sequence of biochemical events in vivo leading to the release of plasmin, an active prote- olytic enzyme which is able to breakdown fibrin and other polypeptides. Streptodornase consists of a different group of enzymes which liquify and degrade DNA which forms a sig- nificant component of slough.9 In the last few years there has also been new interest in the use of polysaccharide materials such as honey and su- crose in the treatment of sloughy wounds. Although ordinary granulated or icing sugar has been used successfully in the past,10, 11, most interest is now focused on the use of pastes made from granulated or caster sugar, polyethylene glycol 400 and hydrogen peroxide.12, 13 although modified formulations have also been reported. The value of sugar in wound management was reviewed by Keith and Knodel14 who con- cluded that because of a lack of convincing evidence derived from controlled clinical studies, the use of sugar as the sole treatment of wounds could not be recommended. However the encouraging results referred to previously suggest that the sugar paste treatment may be worthy of further investi- gation. References 1. Winter G.D., Formation of scab and the rate of epitheli- sation of superficial wounds in the skin of the young domes- tic pig, Nature, 1962, 193, 293-294. 2. Hinman C.C. et al., Effect of air exposure and occlusion on experimental human skin wounds, Nature, 1964, 200, 293-294. 3. Haury B. et al., Debridement: An essential component of traumatic wound care, in Wound Healing and Infection, Hunt T.K. (ed.), Appleton-Century-Crofts, New York, 1980. 4. Hohn D.C. Host resistance to infection: established and emerging concepts, ibid. 5. Tudhope M., et al., Management of pressure ulcers with a hydrocolloid occlusive dressing: Results in twenty three pa- tients, J.Enterostom. Ther., 1984, 11 102-105. 6. Johnson A., Towards rapid tissue healing, Nurs. Times, 1984, Nov., 39-43. 7. Jacobsson S. et al., A new principle for the cleansing of infected wounds, Scand. J. plast. reconstr. Surg., 1976, 10, 65-72. 8. Lydon M.J. et al., Fibrinolytic activity of hydrocolloid dressings, in Beyond Occlusion; Wound Care Proceedings, Ryan T.J. (ed.), International Congress and Symposium Series No. 136, Royal Society of Medicine, London, 1988, 9-17. 9. Hellgren L. and Vincent J., Degradation and liquefica- tion effect of streptokinase-streptodornase and stabilised trypsin on tissue necroses, crusts of fibrinoid, purulent exudate and clotted blood from leg ulcers, J. int. med. Res., 1977, 5, 334-337. 10. Sugar sweetens the lot of patients with bedsores, JAMA, 1973, 223, 122. 11. Knutson R.A. et al., Use of sugar and povidone iodine to enhance the wound healing: five years experience, Sth med. J., 1981, 74, 1329-1335. 12. Gordon H et al., Sugar and wound healing, Lancet, 2, 663-664. 13. Middleton K.R. and Seal D., Sugar as an aid to wound healing, Pharm. J., 1985, 235, 757-758. 14. Keith J.K and Knodel L.C., Sugar in wound healing, Drug Intell. clin. Pharm. 1988, 22, 409-410. Editor's note The advice expressed in this article is based upon the expe- riences of the author. However there will doubtless be oth- ers who hold different or contradictory views. Any corre- spondence on this or any other issue related to wound man- agement would be welcomed and reproduced in a subsequent edition of the `Dressings Times' Letters to the Editor Dear Sir, I noted with interest the section headed `Proflavine' in The Dressing Times, 1988, 1, No.3. While it is true that a water in oil cream does not release the Proflavine and therefore has little antibacterial activity, an oil in water cream does release the proflavine and is an effective an- timicrobial agent. Work carried out some time ago by the Mersey Regional Quality Control Department proved the effi- cacy of the oil in water formulation we manufacture at Clat- terbridge. As a result of their work the regional contract for purchasing Proflavine Cream BPC was discontinued and hospitals in the Mersey Region now buy from us or manufac- ture to our formulation. Further, the Clatterbridge formu- lation of proflavine cream has a cetomacrogol base and does not contain wool fat. Miss H.S. Cooke, Staff Pharmacist, Special Products Unit, Clatterbridge Hospital. Merseyside. The Dressings Times is produced by the Welsh Centre for the Quality Control of Surgical Dressings, East Glamorgan Hospi- tal, Church Village, Pontypridd, Mid Glamorgan. Telephone No. (0443) 202641.