- 1 - Welcome to the second edition of the Dressings Times, a new publication which is intended to provide a forum for the ex- change of information on dressings and related topics. We hope that you will find it of interest as the active support of health care staff associated with wound management is es- sential if the "Times" is to continue and develop. The prod- ucts and topics covered in this issue were selected by the editor but requests for information or suggestions for arti- cles on specific topics for inclusion in future editions would be welcomed. Short articles, case histories or letters on dressings related topics are also invited. In this issue a significant amount of space has been devoted to the sub- ject of bandaging, an often underrated aspect of patient care. There can be little doubt however that the appropriate selection and correct application of a bandage can be a ma- jor factor in determining the outcome of the treatment of leg ulcers and other vascular disorders. BANDAGES AND BANDAGING Bandages have been used for thousands of years to dress wounds and to apply support and compression using simple fabrics such as linen which were often coated with resins and other medicaments. In modern times until the relatively recent development of knitted bandages and other products containing elastomeric yarns, most bandaging needs were met by the use of white open wove bandage (WOW) or one of the Crepe type products. The application of these older materi- als was a skilled task which required considerable practice to perform correctly. In the first half of this century, a number of books and articles were written on the subject of bandaging which formed an important part of a nurse's train- ing. Unfortunately, with the development of tubular ban- dages and lightweight extensible products, much of this skill has been lost and it is now not uncommon to see ban- dages applied incorrectly or used for purposes for which they were never intended. This is particularly true in re- lation to the management of oedema and other conditions where the sustained application of pressure is required. This short review is intended to provide a brief introduc- tion to the theory of bandaging together with some indica- tion of the levels of compression which the various types of products are able to achieve. A method of bandaging a fractured clavicle (circa 1939) Classification of bandages Bandages can be classified in a number of different ways but possibly the most useful method is one based upon their function as follows. o Retention bandages o Support bandages o Pressure/compression bandages The ability of a bandage to perform one or more of these functions is largely determined by its elastic properties, although the thickness, weight and conformability of the fabric is also important. The pressure which may be applied and maintained by a bandage is a function of the tension in- duced in the fabric during application and the radius of curvature of the limb. The pressure beneath the bandage may be calculated using a simple equation derived from Laplace's Law. P=______ where, P = pressure in mm Hg T = bandage tension in kilograms force (Kgf) C = circumference of the limb in centimetres W = bandage width in centimetres It is important to appreciate that the effects of additional layers of bandage are additive and two turns applied at a constant tension will therefore give twice the pressure of a single turn. From the equation shown above, it follows that a bandage ap- plied with constant tension to a limb of increasing circum- ference will produce a pressure gradient with the highest pressure on the narrowest part of the limb. Such a gradient has been shown to be important in the management of circula- tory disorders and a number of papers have been published which discuss the levels of pressure which are required. For recumbent patients it is generally agreed that a gradi- ent of 18 mm Hg at the ankle to 14 mm Hg at the calf is suf- ficient to increase deep venous velocity and hence reduce the likelihood of a thrombosis. For the treatment of venous disorders in ambulant patients, much higher levels of pres- sure may be indicated. Some workers suggest that for phlebitic limbs, ankle pressure of 30-40 mm Hg may be appro- priate and in particularly severe cases even higher levels may be required. Somewhat lower levels of pressure of the order of 20-30 mm Hg may be needed to control mild oedema during pregnancy or following the stripping of varicose veins or sclerotherapy. The ability of a bandage to produce and maintain these lev- els of pressure can be predicted in the laboratory by mea- suring its extensibility and elasticity using an instrument which extends a sample of the material at a constant rate whilst recording the tension which is developed within it. This information may be used to determine the maximum ten- sion which can usefully be applied to a bandage and there- fore, from Laplace's Law, the maximum pressure which it might be expected to apply under normal conditions of use. It should always be remembered however that a product which may be capable of producing a given level of pressure on an average sized leg may be totally unsuitable for use on a large or oedematous limb because in order to maintain a con- stant level of sub-bandage pressure, an unacceptable in- crease in bandage tension may be required to compensate for the increase in circumference. Retention Bandages Retention bandages are used to retain dressings or other wound contact materials in position. They should not be used to apply pressure and are therefore totally unsuited for use in the management of varicose ulcers or for the control of oedema. A number of different types of retention bandages are available. The first products to be developed for this purpose were the Cotton Conforming Bandages, more familiarly known as Kling or Crinx. These lightweight cotton products have very little elasticity but are sufficiently extensible to give them a useful degree of conformability. More recent- ly lightweight woven and knitted bandages have been intro- duced which contain elastomeric yarns. These bandages, some- times called `contour' or `conforming stretch' bandages are often cheaper than the original cotton products and are said to be easier to use. Many different types are available which include Slinky, Stayform, Tensofix, J Form and J Fast. Light pressure/support bandages Used to provide support and low levels of pressure (up to a maximum of about 15mm Hg on an average ankle), they include the familiar `crepe' type products. Although these bandages may be used to prevent the formation of oedema and give sup- port in the treatment of sprains and strains, they are not suitable for controlling or reducing existing oedema or for exerting even low levels of pressure on limbs of larger than average dimensions. For these and other applications where more powerful products are required, two other groups of bandages are available. Moderate to high compression bandages Bandages in this group can be used to apply moderate to high levels of pressure in the range of 18-35mm Hg at the ankle. They are indicated for the treatment of gross varices, post thrombotic venous insufficiency, gross oedema in limbs of average circumference and the management of venous leg ul- cers. They include, Tensopress, Bilastic Medium, Rowden Foote and Veinopress. Products in this category are not nec- essarily able to achieve these levels of pressure on very large limbs which are further enlarged by the presence of oedema. Although all the elasticated bandages tend to be signifi- cantly more expensive than traditional crepe products, nev- ertheless, they can be highly cost effective when used ap- propriately. High performance compression bandages These products are capable of applying the highest levels of pressure which are ever likely to be required clinically, generally in the order of 35-50 mm Hg. The power in these bandages is such that they can be expected to apply and sus- tain these pressure on even the largest and most oedematous limbs for extended periods of time. They include, Elastic Web (Blue Line Webbing) and Bilastic Forte In order to attain the pressures referred to above, it is assumed that the bandages in question are applied in the form of a spiral with a 50% overlap between turns, effec- tively producing a double layer of bandage at any point on the limb. Tubular bandages Tubular bandages like the roll bandages described above are available in a number of different forms each of which is intended to perform a different function. Lightweight non- elastic materials (stockinettes) are used beneath or- thopaedic casts and as coverings for simple dressings whilst lightweight elasticated products such as Tubifast are used for dressing retention. A heavier more elastic fabric is used in the manufacture of Elasticated Tubular Stockinette. More familiarly known as Tubigrip, Tensogrip etc., these ma- terials are quick and easy to apply and are often used to provide pressure and support to swollen limbs. Unfortunate- ly, many medical and nursing staff frequently over estimate the levels of pressure which these bandages are able to gen- erate. For example, two layers of bandage (size D) applied to an average sized leg in accordance with the manufactur- er's instructions would produce a pressure in the order of 9 mm Hg at the ankle and 12 mm Hg on the calf, effectively causing a reversed pressure gradient down the leg. It is obvious from these results that Elasticated Tubular Stock- inette in no substitute for a good quality compression ban- dage and should not be used as the sole means of applying pressure to swollen limb or in situations where significant levels of compression are required. NEW PRODUCTS AND DEVELOPMENTS In recent months a new film dressing has been launched in the United Kingdom. The product called Omiderm was developed in Israel by Omikron Scientific and consists of a thin, flexible, transparent membrane some 40 microns thick. It is manufactured from polyurethane which has been chemically modified by the addition of hydrophilic monomers such as acrylamide and hydroxyethyl methacrylate. In the dry state the film is relatively inelastic but when brought into con- tact with wound exudate or aqueous solutions, it absorbs wa- ter and changes its physical properties, becoming highly conformable and elastic. Unlike traditional semipermeable film dressings such as Opsite, Tegaderm and Bioclusive, Omi- derm is not coated with adhesive but nevertheless will ad- here to a moist wound without the need for additional fixa- tive agents or sutures. The film is easily removed without causing pain or trauma but if left undisturbed it will sepa- rate spontaneously from a healed wound once epithelial cover is achieved. The film itself is highly permeable to moisture vapour, at least 20 times more permeable than the tradition- al film dressings, and is thus able to cope with the exudate produced from all but the most heavily exuding wounds. Omi- derm is also significantly more permeable to oxygen than standard polyurethane film dressings. However the permeabil- ity of the film is not limited to water and oxygen. Antimi- crobial agents such as silver sulphadiazine, povidone iodine and chlorhexidine gluconate can pass through the film onto the wound beneath if applied to the outer surface of the dressing in the form of a cream or as an aqueous solution absorbed on several layers of gauze. It has been suggested that this technique may be used to administer topical an- timicrobial agents to wounds dressed with Omiderm to prevent infection or lower the bacterial count. Omiderm is recommended for the treatment of donor sites, dermabrasions and partial thickness burns and may also be used as a temporary dressing on full thickness wounds at the discretion of the medical officer in charge. It is not cur- rently recommended for use on infected or dirty wounds. Omiderm is available in a range of sizes and marketed by Cambac Instruments Ltd. Cambridge from whom further informa- tion can be obtained. References Golan J. et al., A new temporary synthetic skin substitute, Burns, 1985, 11, 274-280. Behar D. et al., Omiderm, a new synthetic wound covering; Physical properties and drug permeability studies, J. Biomed. Mat. Res., 1986, 20, 731-738. Cristofoli C. et al., The use of Omiderm, a new skin substi- tute, in a burn unit, Burns, 1986, 12, 587-591. PRODUCT PROFILE: ALGINATE DRESSINGS Two major brands of alginate dressings are currently avail- able, Sorbsan from Steriseal and Kaltostat from Britcair Ltd. The 5cm x 5cm size of these dressings have recently been included on the Drug Tariff and are therefore available upon prescription where it is anticipated they may make a significant contribution to primary health care. Although both dressings are manufactured from salts of al- ginic acid, a polysaccharide material derived from certain species of brown seaweed, there are significant differences in their chemical composition. These differences affect both the performance and method of use of the dressings and for this reason the two products should not be considered to be identical or totally interchangeable in use. Alginic acid itself consists of a polymer containing mannuronic and gu- luronic acid residues, the relative proportions of which vary according to the species of seaweed from which they are derived. Alginates rich in mannuronic acid (like Sorbsan) form soft flexible gels whereas those which are rich in gu- luronic acid (like Kaltostat) form firmer gels. The calcium salt of alginic acid is insoluble in water but the sodium salt is soluble forming an absorbent hydrogel. In the pres- ence of sodium ions from serum or saline solution, calcium alginate fibre absorbs liquid and undergoes an ion exchange reaction forming the soluble sodium salt. Sorbsan is sup- plied in the form of a white fibrous fleece composed of pure calcium alginate fibre, Kaltostat is similar in appearance but consists of a mixture of calcium and sodium ions in the ratio of 80:20. Both products may be used in the management of a variety of exuding wounds such as leg ulcers and pres- sure areas etc., but are of limited value in the treatment of dry non-exuding lesions. In use the alginate sheets are placed on the surface of the wound and covered with a suitable absorbent pad. Sorbsan can be allowed to overlap onto the area surrounding the wound but Kaltostat should be trimmed to approximately the size and shape of the defect to prevent exudate being transferred on to the surrounding skin. The method of removal of the two dressings is also different. Sorbsan which is readily soluble in saline, can usually be removed by irrigation with a sterile solution of 0.9% saline but Kaltostat which tends to gel much more slowly may have to be lifted of the surface of the wound with sterile forceps. Both the dressings may be left in place for a number of days on clean, relatively low exudate wounds, but should be changed more frequently on high exudate, infected, or sloughy wounds. Both products are manufactured in a number of different sizes and presentations in addition to the sheet form. Sorb- san is available in the form of a loose rope and ribbon and Kaltostat in the form of a loose ball, all of which may be use for packing cavities and sinuses. An additional preparation of Kaltostat has been developed in which a layer of alginate fibre is combined with a layer of activated charcoal cloth. This dressing called Kaltocarb is recommended for use on infected, malodorous wounds. 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.