- 1 - Welcome to the tenth edition of the Dressings Times which contains the second half of Dr Mary Bliss' article describ- ing her individual approach to the management of `chronic' wounds. Dr Bliss would be the first to admit that some of her views do not always agree with those of other workers involved in wound management so it is hoped that her article in this issue will lead to some interesting correspondance in future issues of the Dressings Times. This edition also contains a facinating article on maggots written by Dr Ian Burgess, Deputy Director of the Medical Entomology Centre at the University of Cambridge in which he describes the various flies that can cause infestation of open wounds. THE MANAGEMENT OF PRESSURE SORES IN ELDERLY PATIENTS In comparison with leg ulcers, pressure sores are usually easy to heal, and therefore a controlled trial of different types of dressing and wound management techniques should be possible. The condition of the patient is less critical for healing a pressure sore than with the much more mixed aeti- ology of the leg ulcer. In this sense, a pressure sore is not dissimilar to an artificial wound in an experimental an- imal. It is caused by local application of pressure which angulates and stretches the capillaries in the surrounding tissue, cutting off the blood supply. If this disruption to the blood supply continues for too long, thrombosis occurs causing permanent ischaemia and death of cells in the af- fected area. Depending on the general condition of the pa- tient and whether the source of pressure was primarily ex- ternal, (e.g., friction on the skin due to damp sheets) or internal (e.g., a bony prominence such as the sacrum press- ing down on adjacent tissues with decreased resilience due to low blood pressure or other causes), the resulting sore will be primarily superficial or deep. In either case the damage is strictly limited to the area affected by the com- pression. With few exceptions (e.g., the feet in patients with peripheral vascular disease) the surrounding tissue is perfectly healthy. Providing pressure is relieved and the blood supply restored, it is fully capable of carrying out the normal processes of repair, including debridement of necrotic tissue, fibrinogenesis, contraction and eventual epithelialisation and remodeling. A pressure sore heals by secondary intention in the same way as any similarly inflicted injury, e.g., due to a cut or a blow. The process is slower in elderly patients1 but not significantly so. The reputation of pressure sores for be- ing `chronic' wounds is almost entirely due to inadequate pressure relief by allowing patients to continue to sit or lie on the site. Once this is understood, and pressure has been alleviated by means of bedrest on an alternating pres- sure mattress or on a low pressure mattress with regular repositioning, local management is simple especially for deep sores. Surgical debridement is rarely necessary. Med- ical debriding or hydrolysing agents such as Varidase or Scherisorb gel are frequently used but are probably unneces- sary as the slough usually breaks down and separates natu- rally in about 2 - 4 weeks, leaving a clean, granulating cavity. Packing or lining the wound with gauze is painful, damaging to granulation tissue and retards the healing pro- cess. Silastic foam is probably less injurious but has to be sterilised with antiseptics which also damage regenerat- ing tissue. Any form of packing is unnecessary as pressure sores never need to be `kept open' to avoid abscess forma- tion as this virtually never occurs, at least in uncompli- cated full thickness sores, i.e., those not involving bones and joints. Elderly patients in whom the slough does not separate natu- rally are invariably dying2 so that treatment other than covering the affected area and providing adequate analgesia (for which opiates are usually necessary) is inappropriate. Antibiotic therapy is rarely helpful so that most pressure sores do not need to be swabbed. The slough is invariably infected, but providing the area has a good blood supply, the infection seldom spreads to the surrounding tissue or causes a significant septicaemia. The foul discharge is liquified necrotic tissue, not pus, and represents the first stage of normal healing. As it separates, the wound appears to get deeper, but in fact is merely revealing the extent of the original ischaemic damage which is nearly always greater in the subcutaneous tissue than in the skin. It is undesir- able, and generally unsuccessful, to try to seal off the wound at this stage as it needs to drain as freely as possi- ble. It may either be dressed with ample pads of gauze bridged across the opening, or the patient may simply be laid on a clean absorbent sheet which is changed frequently. When the wound is clean and the discharge has diminished or stopped, attempts may be made to cover it with an occlusive dressing. However, this may be impracticable for a sacral sore adjacent to the anus, and any adhesive dressing can se- riously damage the surrounding skin. Hydrocolloid dressings have the additional disadvantage that they become hard and crumpled in areas subjected to friction such as the sacrum and heel causing the sore to become uncovered and creating a risk of renewed tissue distortion and pressure damage. In my opinion, they should rarely be used for the treatment of pressure sores. In fact, there is no evidence that leaving a full thickness sacral sore undressed, even in a patient who is doubly incontinent, causes hazard or delay in healing and it is much less likely to cause new problems in the sur- rounding skin. Contamination with urine and faeces is a negligible cause of delayed healing compared with an inade- quate blood supply due to poor pressure relief. Superficial sores in the sacral area are more difficult to dress than deep sores. They are usually caused by a combi- nation of pressure, increased humidity and friction associ- ated with incontinence and superficial skin infections in sick patients. The damp surrounding skin has reduced ten- sile strength so that it is easily torn by dressing materi- als and adhesives. Hydrocolloids are rarely successful in this situation and all occlusive dressings tend to exacer- bate excoriation of the skin. Even semipermeable films which might appear to be least damaging usually become dis- placed and roll up causing ridgeing and pulling on the sur- rounding tissues. Collodian paints or sprays have similar disadvantages. The skin should be as dry as possible prior to application of any dressing and the edges powdered to prevent it from sticking on the sheets. When the dressing is removed, it should be stretched and lifted, not pulled or ripped off the skin. Because of these difficulties, I pre- fer to manage many of my patients with superficial sacral sores with no dressing on a good pressure relieving mattress with a fleece under the pelvis to minimise further skin dam- age. Once the area is dry and any associated skin infection healed, the sore may be covered by a semi-occlusive or oc- clusive dressing, e.g., a semipermeable film such as Tega- derm, in the hope that this will speed epithelialisation. However, to my knowledge no controlled trial of the benefit of dressings versus exposure has ever been carried out in this area. It is amazing how quickly most pelvic sores heal whatever their treatment once the patient's general condi- tion and nutrition improve. Sloughs of heel sores are more tenacious than those of pelvic sores. Resolution may be accelerated by a debriding agent such as Scherisorb gel, Varidase, or Aserbine cream (taking care not to cover the surrounding skin), under an occlusive dressing such as Tegaderm. As soon as the wound is clean, the debriding agent should be discontinued. The leg should be kept elevated preferably on a bed, but walking should be encouraged. A bedcradle at night is essential. Nurses frequently bandage the foot to prevent rumpling and displacement of the primary dressing but this should be avoided if possible for two reasons. Firstly, bandaging hides the site of the sore so that the patient and atten- dants are less likely to appreciate the need to keep the area free of pressure. Secondly, any bandage, however light or loose, can cause pressure sores in susceptible patients, e.g., those with diabetic neuropathy or peripheral vascular disease. A common site for a bandage sore, usually unrecog- nised, is over the instep where bandages, (and even tubular net dressings such as Netelast), are liable to develop mul- tiple tight folds, especially if applied with the foot ex- tended. References 1. Davies I. The mechanisms of ageing. In - Monk B.E., Gra- ham Brown R.A.C. and Sarkany I., Skin disorders in the el- derly, Oxford, Blackwell Scientific Publications, 1988, 3-29. 2. Barton A.S. and Barton M. The management and prevention of pressure sores, London, Faber and Faber, 1978. MYIASIS - THE DEVELOPMENT OF FLY LARVAE IN LIVING ORGANISMS The possibility that a wound may become infected with mi- croorganisms is regarded as something of a fact of life in the field of wound management. However, the invasion of le- sions by larger creatures such as fly maggots is often greeted with surprise, if not horror, and in some circles is considered a sign that the standard of patient care has deteriorated. No doubt such an attitude results in consid- erable under reporting of incidents of myiasis in temperate countries.1,2 Obligate myiasis is rarely encountered in temperate regions and normally requires particular management according to the species of fly involved. This article deals with faculta- tive myiasis and illustrates that in supervised patients it is no more a reflection on the standard of care than the de- velopment of any other infection. Three families of flies are commonly involved: the house- flies (Muscidae), the blowflies (Calli-phoridae) and the fleshflies (Sarcophagidae). All normally breed in excre- ment, decaying organic materials and cadavers as well as op- portunistically infesting wounds with varying degrees of success. In practice the majority of species found in wounds will be feeding on bacteria, macerated tissue and wound exu- date. Normally only the fleshflies and some strains of blowflies attack living tissues. Do maggots have any clinical value? Almost all of the fly species involved in myiasis form the first wave of faunal succession invading a cadaver and ac- celerate the rate of autolysis3. That maggots similarly erode necrotic tissue from wounds was known from the mid- sixteenth century and surgeons in Napoleon's army recorded that maggots in wounds removed putrefying tissues resulting in improved granulation. Deliberate introduction of maggots into wounds was not performed until the American Civil War but use of non-sterile maggots increased the risks of gan- grene and tetanus. The first clinical studies were per- formed following observations that Wohlfahrtia fleshfly mag- gots successfully cleared the wounds of soldiers left lying for hours on First World War battlefields. Paradoxically these men often did not develop infections like osteomyeli- tis whereas those who received prompt treatment did. By sterilising the eggs of blowflies and then rearing the mag- gots aseptically, Baer achieved a 90% success rate in treat- ing osteomyelitis at a time when the mortality resulting from open leg fractures was around 75%4. Subsequent work showed that maggots not only enhance healing by physical ir- ritation they also produce enzymes that help to macerate the tissues and substances like ammonium carbonate that were said to promote healing.5 Since the advent of antibiotics, maggot therapy has become unfashionable, particularly since it holds a degree of aes- thetic unacceptability for patients and carers alike. Never- theless maggots have shown their worth when infestations succeeded where modern therapy failed.6,7,8 Why do flies attack wounds? All myiasis flies can breed in a variety of decomposing ma- terials. They have an acute sense of smell and easily detect suitable breeding sites. Consequently odour produced by suppurating or necrotic wounds will prove highly attractive. However, there are differences. The common housefly, Musca domestica, has only been recorded from humans in insanitary conditions or a state of neglect9 which fits with its normal saprophagous habit and it is not found in wounds receiving regular and adequate treatment. In contrast the blowflies and fleshflies are true opportunists that may attack any wound. The risk of infestation is increased in; 1. elderly or debilitated patients 1,2 2. the presence of a pre-existing circulatory disorder which results in a lowering of the temperature of the extremities1,2 3. wounds containing gangrenous, sloughy or necrotic ma- terial. 4. wounds covered with dressings saturated with serous fluid, macerated tissue or urine.10 Additionally the incidence of myiasis in Britain appears to be closely related to spells of warm weather. Up to 1988, the number of cases reported to our Centre averaged one an- nually, but during two recent warm summers this increased to three cases in 1989 and nine in 1990. Four cases so far re- ported in 1991 each occurred during hot weather. A similar relationship with temperature was found by Lukin1. However, the bluebottle blowflies, Calliphora spp, and the black blowflies, Phormia spp, prefer lower temperatures than the greenbottle blowflies, Lucilia spp, and the fleshflies, Sar- cophaga spp. All species only visit buildings in search of breeding sites and the internal conditions will affect behaviour.3,11 Lu- cilia and Sarcophaga prefer sunny areas whereas Calliphora and Phormia choose shade and will even lay eggs at night. However, just to confuse things recent studies have shown that under some circumstances Lucilia will also oviposit at night11. Can myiasis be avoided? In practice, like other infections, myiasis cannot be to- tally prevented. Unless wards are sealed and air- conditioned or thoroughly fly-screened, flies will always enter during warm weather when windows are opened to allow free flow of air. Fleshflies such as Sarcophaga do not lay eggs, instead they deposit small batches of about fifteen active larvae which burrow into tissues and are lost to sight in under an hour. The eggs laid by blowflies hatch in anything from a few minutes to about twelve hours, depending on the time the female has spent seeking an oviposition site. In some cases desperate females may lay active lar- vae. As a result the chances of larvae being detected are small unless they are caught in the act of migrating to the wound at a dressing change. In most cases maggots are not detected until they have developed to the second or third larval stage. At body temperatures the feeding period of the larvae may be as little as five days following which they leave the wound in search of a place to pupate. In some cases they are only detectable at this stage, especial- ly if the wound is deep and full of slough or partially oc- cluded due to a small aperture. Treating myiasis After the initial shock of finding maggots in a wound has subsided a clinical decision is required to evaluate whether the patient has actually benefited from the infestation.6-8 If it is decided that the maggots should be removed, rather than allowed to run their course, then the aim should be to extract them with minimum trauma. Any maggots lying exposed can be lifted out with forceps followed by flushing the wound with saline. In some cases, where maggots have invaded living tissues, addition of up to 10% chloroform to the saline relaxes the maggots. In some cases under anaesthetic neat chloroform or ether have been used12. Surgical debridement may be necessary for some species of Sarcophaga, which can burrow deeply into tissue sinuses, but in any case where mechanical means are used care should be taken to avoid bursting maggots since some patients may respond anaphylactically to the larval protein. Since such a variety of flies may be involved, of varying degrees of pathogenicity, it is probably advisable to have all maggots identified at the earliest opportunity. What of the future? Concern has been expressed recently that certain dressings, such as hydrocolloids and calcium alginate gels, may attract flies with their noticeable odour. The impermeable nature of some of these dressings would tend to preclude this pos- sibility. However, in one reported case a wound covered with an alginate dressing that was seen to be intact one day was found to be perforated on the next day with young maggots in the wound. The state of development of these larvae sug- gested that they were around 20 hours old and they had ap- parently burrowed through the dressing to the ulcer beneath. Another aspect of facultative myiasis is that only one prop- erly designed prospective study, on the types of flies and risk factors involved, has been performed in recent years1. Consequently our knowledge of the condition is extremely limited and contributes to a general unwillingness to reveal quite how frequently myiasis occurs in patients. References 1. Lukin L.G., Human cutaneous myiasis in Brisbane: a prospective study. Med. J. Aust., 1989, 150, 237. 2. Erzinclioglu Y.Z. and Davies S.W., The blue-bottle fly Calliphora vicina R-D as a parasite (primary myiasis agent), particularly in small mammals, Naturalist, 1984, 109, 31. 3. Smith K.G.V., A manual of forensic entomology. British Museum (Natural History), London and Cornell U.P., 1986, 205. 4. Baer W.S., The treatment of chronic osteomyelitis with the maggot (larva of the blowfly), J.Bone Joint Surg., 1931, 13, 438. 5. Robinson W., Ammonium bicarbonate secreted by surgical maggots stimulates healing in prurulent wounds, Am. J. Surg., 1940, 47, 111. 6. Horn K.L. et al., Maggot therapy for sub-acute mastoidi- tis. Arch. Otolaryngol, 1976, 102, 377. 7. Bunkins J. et al., Maggot therapy revisited. West. Med. J., 1985, 142, 554. 8. Reames M.K. et al., The use of maggots in wound debride- ment. Ann. Plastic Surg., 1988, 21, 388. 9. Burgess I. and Davies E.A., Cutaneous myiasis caused by the housefly, Musca domestica, Br. J. Dermatol., (in press). 10. Roche S. et al., Cutaneous myiasis in an elderly debil- itated patient. Postgrad.Med.J., 1990, 66, 776. 11. Greenberg B., Nocturnal oviposition behaviour of blowflies (Diptera: Calliphoridae), J. Med. Ent., 1990, 27, 807. 12. Alexander J O'D., Arthropods and human skin, Springer- Verlag, New York, 1984, p93. The Dressings Times is produced by the Surgical Materials Testing Laboratory, (SMTL) Bridgend General Hospital, Quarella Road, Bridgend, Mid Glamorgan. Telephone No. (0656) 752820.