Wound Management - The Quest for Optimal Healing
Author: Jim Garland
There are more than 3,000 wound care products worldwide that strive to alter the wound environment and promote healing. So how do today’s leading products encourage wound healing and prevent infection? There is an old maxim about how to heal a rash, “If it is dry, wet it, and if it is wet, dry it.” This recognizes that the skin needs an ideal balance for optimal healing. The industry continues to develop novel wound dressings that provide optimal moisture, pressure, gas exchange and temperature. These products aim to protect the wound from further trauma or contamination without striping off the healing surface during redressing, combining comfort with cost effectiveness.
Optimal Moisture
Optimal moisture provides nutrients and growth factors for granulation, encourages epithelial cells to slide over the wound surface. The right level of moisture allows autolysis that removes obstructing debris that might inhibit gas exchange.
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Excessively wet wounds become macerated at the edges so healing accelerates if the exudate is drawn away from the wound base. More than 2,000 absorptive wound products exist. They act to limit odour and bacterial proliferation. Alginates, like the seaweed from which they are made, can absorb twenty times their weight in moisture forming a gel, and some encourage the clotting cascade. Hydropolymer dressings have a non- adherent wound contact layer with a foam that swells to the wound shape as it absorbs exudate that can evaporate from a protective outer layer. Vapour permeable film permits gas exchange so that water vapour may escape but it protects fragile skin from water or bacteria.
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Foam dressings may be either hydrophilic or hydrophobic and are semi- permeable providing thermal insulation with a bacterial barrier, but because they are non-adherent they can be removed with minimal trauma. Pulsatile lavage with suction removes debris and may stimulate development of granulation tissue.
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Over 50 manufacturers produce more than 350 brands of moisture-retentive wound dressings that encourage new blood vessels and autolysis but are contraindicated in the presence of established infection.
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Hydrocolloids are occlusive hydroactive wafers, beads, pastes, or granules that protect fragile skin from contamination and frictional forces. Hydrogels have a high water content that provides a cooling action and may reduce pain. So the aim is to allow ideal relative humidity without creating a nutrient broth for bacterial growth.
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Optimal Covering
The speediest possible wound covering will protect from incoming infection. Allogeneic living skin equivalents are produced from neonatal fibroblasts and keratinocytes using tissue-engineering technology and can be used in outpatient clinics without the usual problems associated with skin grafting. APLIGRAF® (Graftskin – Novartis) has an outer layer of allogeneic human keratinocytes on an inner dermal layer of human fibroblasts on type 1 collagen dispersed in a protein matrix, but it only has a 5 day shelf life. Dermagraft (Smith and Nephew) is made from human cells placed on a dissolvable mesh material that is gradually absorbed so that the human cells grow and replace the damaged skin.
Recent advances in skin healing seek to combine new technology with physiological healing promoters. The neuropathic wounds of diabetes have high levels of matrix metalloproteinases that increase proteolysis and inactivate growth factors. They can be treated with products such as REGRANEX (Ethicon Inc/Ortho-McNeil Pharmaceutical) a recombinant human platelet-derived growth factor-BB in becaplermin gel that increases wound vascularization and speeds healing by stimulating endothelial cell proliferation.
Experimentally, accelerated re-epithelialization occurs using a gene delivery system of thermosensitive hydrogel containing plasmid TGF-beta 1. Another advance is that stem cells from marrow applied to non-healing chronic wounds can lead to dermal rebuilding and closure.
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Optimal Pressure
Tissue viability is compromised where pressure on skin is inappropriate. For instance, pressure ulcers are localized areas of necrosis that develop in 9% of hospitalized patients and 20% of people in residential homes in the U.K. They may be prevented by air-fluidized beds or low-air-loss mattresses. Offloading devices reduce pressure loading at diabetic foot ulcers allowing them to heal.
Venous ulceration requires multilayer compression bandaging to control oedema and to modulate the microcirculation by either improving lymphatic or venous return. Percutaneous angioplasty with stenting can treat critical ischemia, but patients who are unsuitable for this may benefit from external pneumatic compression devices. Negative pressure wound therapy such as KCI’s V.A.C.® Therapy™ applies computer-controlled sub- atmospheric pressure through an open-cell foam sponge placed in the wound and secured with an adhesive drape permeable to oxygen. This stresses tissues, stimulates mitoses and new vessel formation and draws the wound closed.
Minimal Sepsis
Host immunity and nutrition as well as the type of operation affect the incidence of surgical sepsis but three quarters of the deaths of surgical patients are due to surgical wound infection. Limiting the morbidity, suffering and cost of sepsis requires products that inhibit the growth of microorganisms but are not cytotoxic to the healing wound. Antiseptics include alcohols, anilides, biguanides, bisphenols, chlorine compounds, iodine compounds, silver compounds, peroxygens, and quaternary ammonium compounds. For venous ulcers the topical agents that work better than placebo are allopurinol powder, dimethyl sulfoxide powder, silver impregnated charcoal dressing and silver sulfadiazine, whilst oxyquinolone ointment helps heal pressure sores.
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Newer formulations like cadexomer iodine, which speeds healing, and novel silver delivery systems are safe for human wounds yet prevent infection. Acticoat, by Smith & Nephew, a nanocrystalline silver-coated dressing seems superior to a gauze dressing impregnated with polyhexamethylene biguanide because its antimicrobial effect diffuses further and it causes less bleeding at the wound site. Hydrofera Blue by Hydrofera, LLC, made of a polyvinyl alcohol sponge complexed with Methylene Blue and Gentian Violet effective against MRSA, is useful for orthopaedic wounds.
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New biotechnology bacterostatics include a wound dressing and stitches containing waterborne bacteriophages, which kill the three most common strains of MRSA. Antimicrobial peptides are generally short chain polypeptides anywhere from 8-20 amino acids long that are capable of disrupting the membrane and metabolism of bacteria. Mycoton, a fungal chitin, decreases bleeding and pain and inhibits growth of antibiotic- resistant bacteria. Myticins, isolated from the edible Mediterranean mussel show toxicity against Gram-negative and Gram-positive bacteria, fungus and protozoa.
Given the problems associated with antibiotic resistance, the need for novel approaches such as these to wound healing and sepsis will become increasingly pressing, and will continue to provide a growing market for both wound care companies as well as medical device and biotechnology companies which are progressively more active in this sector.
N.B. Product tables show only a selection of the products that are currently marketed.