Wound healing:‘Improving’ on Mother Nature

Doctors believe they need to assist the body’s natural repair mechanisms when treating wounds. But evidence shows that many antiseptics and dressings may do more harm than good.

Cuts, grazes, wounds, and lacerations – to varying degrees, we have all had to deal with them at one time or another. If you are admitted into hospital for surgery – even the minimally invasive variety – you also have the problem of how best to help a wound heal.

Your skin is your body’s biggest organ and plays a large role in keeping you healthy, regulating body temperature and acting as a barrier to keep body fluids in and bacteria out.

Given the optimal conditions, the human body is remarkably efficient at repairing injuries to this barrier. When the skin is cut, complex biochemical reactions are instigated. These include the activation and/or destruction of cellular and molecular elements such as white blood cells, red blood cells, endothelial cells and blood platelets – all part of the initial inflammatory process.

Inflammation, far from being undesirable, is what protects the site from further injury while it begins the process of tissue repair. Yet, for years, as with so many areas of medicine, we have tried to beat Nature at her own game by applying sutures, harsh antiseptics and lots of dry, absorbent bandages to ‘help’ wounds heal better. Many of these practices in wound management have been put to the scientific test in recent years – and many of them have proven to be more destructive than helpful. Doctors from a wide range of specialities now admit that the process of wound care is based largely on habit and anecdote rather than science.

For instance, even though the body is well equipped to fight off invading bacteria, wounds have been swabbed with alcohol, antibiotics, iodine, Mercurochrome (merbromin), merthiolate, hydrogen peroxide and other medications to keep them ‘clean’. Today, antiseptics such as hydrogen peroxide, povidone iodine, acetic acid, chlorhexadine, cetrimide and Dakin’s solution (sodium hypochlorite) are all part of the physician’s antimicrobial arsenal.

Unfortunately, many of these strong antiseptics can also interfere with the body’s own healing mechanisms. In fact, cleaning a wound is often the first hurdle at which doctors fail their patients, since antiseptic solutions can interfere with the process of wound healing in several important ways.

All wounds need to be cleaned before they can be assessed and treated. Serious wounds – for instance, those resulting from a car crash – may be dirty and potentially more liable to infection and, thus, require careful cleaning.

Such wounds may occasionally justify the use of antiseptic washes. The problem is that antiseptics don’t just kill germs; they also kill beneficial leucocytes – the body’s own bacteria-killing cells – as well as fibroblasts, the cells that eventually form new skin (Drug Ther Bull, 1991; 29: 97-100; J Burn Care Rehabil, 1991; 12: 420-4).

The current thinking is that all but the worst types of wounds can be safely and effectively washed with a simple saline solution that is not cytotoxic (deadly to cells). In addition, very dirty wounds can be cleaned with water pressure. In hospital, staff may have access to special equipment but, at home, running water or using a showerhead may be just as effective.

Benefits of moisture
The next question is how best to bandage and maintain the wound during the healing process. For years, the standard advice has been to keep the wound site clean and dry. While no one would argue over the benefits of keeping a wound clean, keeping it dry, usually with a gauze bandage that allows air to get to the site, and allowing a scab to form can actually slow the healing process and is more likely to produce a scar.

Thinking on wound healing began to change in the 1960s when George Winter, PhD, then a student at the University of London, performed a series of experiments in wound healing on animals.

Winter was asking some basic questions – like whether allowing a wound to dry out was the best way to achieve optimal healing. On comparing wounds that were either kept moist with a polymer film or left to dry out, Winter found that, on examination with a microscope, the wounds that were kept moist healed twice as quickly as those allowed to dry out (Nature, 1962; 193: 293).

Not long after Winter had reported on his findings, a human study also found that keeping wounds moist was much more effective than allowing them to dry out (Nature, 1963; 200: 377). Subsequent studies also found that wounds – both superficial and surgical – that are kept moist with, for instance, one of the newer hydrocolloidal dressings, healed faster (J Surg Res, 1983; 35: 142-8; J Invest Dermatol, 1988; 91: 434-9; J Enterostom Nurs, 1993; 20: 68-72).

Gradually, the idea of moist healing evolved and gauze-based bandages have, in some hospitals, been replaced by a range of natural and synthetic materials that effectively maintain the moisture balance at the wound site.

Although often referred to as ‘occlusive’ dressings, this description is not quite accurate since occlusive implies that they prevent the exchange of gases or liquids. Such bandages are really ‘semi-occlusive’ inasmuch as they seal off the wound site, but also allow the transmission of oxygen, nitrogen and water vapour.

Many factors make moist dressings the optimal way to heal wounds. Perhaps most important of all, they provide an ideal environment for cells to stay alive and replicate. The natural environment of the cell is moist. Dry cells, such as hair and nails, are dead cells that are incapable of reproducing at their point of origin. The body, too, is largely an aqueous organism. However, the outer layer of the skin, the stratum corneum, is less watery. Its cells are filled with keratin, which provides a barrier to water loss through the skin.

A wound is a break in this protective barrier that allows moisture to escape from the underlying moist tissue and causes the death of the superficial cells, a process that results in the familiar scab, composed largely of dried blood and other fluids.

While traditional thinking is that the scab is Nature’s own barrier to moisture loss, newer thinking views the scab as inefficient.

Scabs also prevent new cells from colonising the wound area. When a scab is allowed to form, epidermal cells have to penetrate deeper into the dermis, where the environment is moist, before they can proliferate. This means that the wound will only heal from the bottom up whereas, in a moist environment, the wound will heal from the sides and bottom simultaneously.

Newer-type dressings such as polymer films and foams, hydrocolloids, hydrogels and calcium alginates allow much less moisture evaporation, allowing the cells responsible for the filling in and resurfacing of the wound to remain in an environment in which they can live and replicate.

Moist dressings may also act as insulation, helping to maintain the optimal temperature of the skin. Left open to the air, the evaporating moisture has the effect of cooling the wound area. This tissue cooling is thought to be one of the factors that leads to an increased risk of infection. The cooler temperature at the wound site reduces the amount of oxygen available to infection-fighting cells such as neutrophils – which use the chemical byproducts of oxygen metabolism to kill invading bacteria. The process of cell replication may also slow down at lower temperatures.

Less infection
Perhaps the most important aspect of moist dressings is that they are many times more effective than dry dressings in preventing infections. This is as important an aspect of healing to the child in the playground as it is to the patient in hospital, where opportunistic antibiotic-resistant bacteria can so easily enter a wound site.

In this respect, moist healing is something of a paradox. Indeed, one of the concerns voiced in response to George Winter’s earlier conclusions was that a moist environment would be a breeding ground for germs.

This point of view, however, failed to acknowledge how efficient the body is at fighting infection on its own when it is properly supported. This attitude also didn’t recognise that a wound colonised by bacteria is not necessarily at risk of infection. All wounds, no matter how carefully cleaned, are colonised by bacteria.

The problem arises when bacteria are given the opportunity to multiply. In a properly nourished and supported body, natural infection-fighting mechanisms can easily keep bacteria in check.

The copious amount of data that has been amassed on this subject concludes that moist healing does not increase infection rates but, instead, appears to decrease them (Wounds, 1989; 1: 123-33; Hutchinson JJ, A prospective clinical trial of wound dressings to investigate the rate of infection under occlusion, in Proceedings: Advances in Wound Management, London: Macmillan, 1993: 93-6).

This appears to be in part because the newer-style dressings present an effective physical barrier to bacteria that cannot be achieved with traditional gauze bandages while, at the same time, ensuring the optimal function of the body’s infection-fighting cells (Am J Surg, 1994; 167 [Suppl]: 21S-4S; J Am Acad Dermatol, 1985; 12: 662-8).

This was evidenced by the fact that, in one study, the infection rate of wounds treated with a conventional method was 7 per cent compared with 2 per cent using a moist, hydrocolloidal dressing (Am J Infect Control, 1990; 18: 257-68). In another study, bacteria were found to be capable of penetrating 64 layers of gauze, but were incapable of penetrating a single layer of polymer film (Am J Surg, 1994; 167: 21S-4S).

Other theories include the idea that a moist dressing helps maintain the slightly acidic pH of the skin (Am J Surg, 1994; 167: 2S-6S). This, too, may inhibit certain types of bacteria, such as Staphylococcus aureus and Pseudomonas aeruginosa.

Patients also report less pain when wounds are kept moist. Newer-style dressings are thought to protect nerve endings from the environment and keep them moist, thus reducing the perception of pain. With gauze dressings, nerve endings may become damaged during dressing changes. Numerous studies involving people from all walks of life and all occupations, including football players and industrial workers, attest to the fact that patients treated with hydrocolloidal dressings experience less pain (Arch Dermatol, 1991; 127: 679-83; Athl Train JNATA, 1988; 23: 341-6; Military Med, 1988; 153: 188-90; Int J Sports Med, 1991; 12: 581-4).

Another intriguing possibility as regards the effectiveness of moist dressings is that they help to maintain the electrical integrity of the wound site. By keeping the site moist, it allows the body’s own electrical current to flow more or less uninterrupted. It has been demonstrated that the electrical charge of wound tissue is positive in relation to the surrounding intact skin (Clin Dermatol, 1984; 2: 34-44). This positive current is thought to orchestrate the migration of healing cells to the site, but this current cannot flow if the skin is dry. Such information provides a context for studies into electroacupuncture and the successful healing of a variety of wounds, even those that had failed to heal with prior conventional therapy (Am J Acupunct, 1999; 27: 5-14; Minerva Med, 1980; 71: 3709-13).

For this and other reasons, moist dressings may also have aesthetic benefits for patients. Studies show that they can help lessen the appearance of scars (Arch Dermatol, 1991; 127: 1679-83).

When wounds won’t heal
Clean cuts can heal remarkably quickly and well with a minimum of intervention. But some kinds of wounds simply don’t heal. The reasons are manifold. The patient may have an underlying health problem, such as diabetes or venous insufficiency, that interferes with the healing process.

Burns, crush injuries and other extreme traumas may also prove difficult to heal over the longer term. In such individuals, wounds can become chronic and suppurating, and prone to infection. Doctors may treat these with systemic antibiotics – even though these are unlikely to be effective at the local level (Austr Prescr, 1996; 19: 11-2).

Steroids, too, impede the proliferation of fibroblasts and collagen synthesis, and the application of antiseptics, as has already been explained, is unlikely to help chronic wounds, since it only serves to kill the very cells that are necessary for repairing the damage.

In searching for a reason that these particular types of wounds refuse to heal, researchers have developed a theory involving the oxygen supply to the wound that may prove helpful.

Oxygen has a significant role in the process of wound healing inasmuch as it supplies an additional energy source for the repair process (Am J Surg, 1969; 1: 521-5; Townsend Lett Docs, 1998; 180: 66-70). During this process, fibroblasts begin to migrate, divide and produce collagen – which provides the scaffolding for wound repair. But in order for this to take place, sufficient oxygen must be present (Acta Chir Scand, 1972; 138: 109-10). In addition, oxygen is important for killing anaerobic bacteria that can lurk in wounds (Proc Natl Acad Sci USA, 1971; 68: 1024-7).

The amount of oxygen needed to repair wounds is delicately balanced. Too much can interfere with the healing process, especially early on (Exp Cell Res, 1991; 25: 101-13; Acta Physiol Scand, 1969; 334: 1-72). Nevertheless, wounds – especially chronic wounds – have been shown to have lower levels of available oxygen (Hyperbaric Oxygen Rev, 1985; 6: 18-46). Supplemental oxygen – simply breathing in pure oxygen from a mask or in a oxygen chamber, or using a topical hyperbaric oxygen treatment – can all bring about considerable benefits (Arch Surg, 1986; 121: 191-5).

But questions remain
While there is no doubt that moist dressings are currently the best way to heal wounds and reduce the risks of infection, scarring and pain, there are still questions that remain regarding some of the materials from which the current dressings are made.

Some researchers, using laboratory tests, have found that many types of synthetic dressings can be toxic to developing cells (J Biomed Mater Res, 1990; 24: 363-77; Biomaterials, 1992; 13: 267- 75) – a problem similar to that observed when such materials are used for prosthetic devices. As yet, this area is poorly researched and few have actively questioned the use of such potentially carcinogenic materials as polyvinyl pyrrolidone as ‘healing’ dressings.

This is an area of medicine that continues to evolve and the search is still on for dressings – physical barriers made from either safe synthetics or from natural materials that have a beneficial effect on wound healing.

For the best results, patients need to encourage their practitioners to opt for the least interventional approach to wound management – and remember to do the same for themselves when self-treating (see p 6 for more alternatives).

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Written by What Doctors Don't Tell You

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