From a general point of wiev, a traumatic injury is defined as a physical damage caused by an external factor. Even if we talk about a road traffic accident, a burn or projectile injuries, all of them represents a trauma for the body. Because the first part of this series described the physiologic process of healing and how can wounds be recognized according to the phase in which they are, the second part will highlight how wounds can be addressed.
Initial assessment of the patient
Due to various types of trauma, the patient should be treated according to the requirements. The patient can be unstable after a road traffic accident, after a fighting with another dog or can be bright, alert if superficial lesions are present (patients that develop wounds due to scratching). If the patient is not stable the plan must be focused first on stabilization by checking the major function (A- airway, B- breathing, C-cardiovascular, etc) followed by a good pain control and assess the life-threatening injuries. In an emergency situations is recommended to cover the wounds with sterile gauze or another type of sterile material to provide haemostasis and to protect against another contaminants that are considered already present in the wound.
Evaluation of the wound
When the patient became comfortable, a wound evaluation must be performed. There are some factors that can help the surgeon to take a decision regarding the local management. Therefore, the following should be considered:
- the degree of contamination;
- when the injury took place;
- the degree of tissue ischaemia;
- the amount of tissue loss;
- type of wound (burn, snake bite, etc).
About the length of time between the production of the trauma and the presentation of the patient to the clinic and the degree of contamination, wounds are classified as clean, clean-contaminated, contaminated and infected (see details in part1). Because every injury has as a result blood loss, the tissue exposed may have different aspect and can help with the prognosis. The first aspect of the wound may be misinterpreted due to colour and integrity of the surrounding tissues. Many times the skin is crushed due to a powerfull trauma and just small superficial wounds may be present. If at first presentation the skin looks normal and the small wounds have a clean aspect and the trauma happend in less than 4-6 hours not every time will be a good ideea to do a primary closure. Some wounds may have good viability but because the tissues are crushed can develop necrosis and some wounds may have an ischaemic aspect but if the surrounding tissues are not traumatised the evolution can be favorable. As a conclusion, not every time a primary closure will be a wright decision, sometimes wounds need 2-4 days to “settle” depending of the type of trauma. The amount of tissue loss will guide the surgeon to use specific dressings according to depth and length if second intention healing will be elected. Regarding wound type, some specific considerations must be taken. For example, bite wounds should be explored whereas for an early frostbite wound the patient must be rewarmed first.
Fig1. Basic wound management in six simple steps (Atlas of Small Animal Wound Management and Reconstructive Surgery, 4th Edition Michael M. Pavletic, April 2018
As an approach, wounds can be managed by closure (primary closure, delay primary closure, secondary closure already described in part 1) or can be left for second intention healing.
Second intention healing occurs when a wound is left to heal by contraction and epithelialization. All wounds can be left to heal by second intention but this process may fail at a point or may end without providing a functional outcome. There are some reasons why not every time a complete healing by second intention (especially large wounds and in high motion area-joints, axillary, inguinal) is not recommended: the granulation tissue is very fragile and easly abraded; wound contraction, sometimes excessive, may impede normal function.
Some wounds may fail to completely reepithelialize. Open wound management is indicated in dirty, traumatized, contaminated wounds in which cleansing and debridement is necessary.
Wound preparation – cleansing
To prevent further contamination of the wound in the time of cleaning, all equipement must be sterile. Prior to application of topical treatments, the wound bed must be properly prepared. Initially the wound must be protected with a sterile lubricant (eg. K-Y sterile gel) or sterile gauze soaked in warm saline. After protection, the hair that surrounds the wound must be clipped. The hair represent one of the main foreign body that can imped wound healing in a clean wound. Next, lavage the wound with a proper solution under 7-8 psi to remove the surface contaminants and in the end dry the skin surrounding the wound. This may facilitate the adhesion of the dressing and also will prevent maceration of the skin if the wound is highly exudative.
- Wound lavage: many lavage solutions are availabile. Most popular are
Fig.2 Basic kit for wound lavage composed by seringe, 3 way-stop cock, 18G needle, intravenous tube and 500ml bag of sterile saline.
clorhexidine, betadine, Ringer’s and sterile saline. A study from human medicine compared tap water with sterile saline for wound irrigation and showed no difference in occurance of infection. Clorhexidine is availabile in many concentrations (4%, 2%, 0,5%) but for open wounds 0,05% solution should be used. To obtain this concentration, 25ml of clorhexidine 2% must be mixed with 1liter bag of solution. Betadine may be a good option to use in wounds located on the face, particulary near eyes because clorhexidine have very toxic effect if will get in contact with the eyes. Betadine also must be diluted to a proper concentration (0,1%-1% solution). To obtain this solution, 1-10ml of 10% betadine must be mixed with 1 liter bag of solution. As a comparation, clorhexidine is not activated by anorganic matter while as betadine is inactivated by anorganic matter such as blood or exudate. Also a 0,01% clorhexidine gluconate with tris-EDTA solution was described for wound lavage. This combination help lyse Pseudomonas aeruginosa, Escherichia coli, and Proteus vulgaris. Recently polyhexanide/betaine (Prontosan), a solution or gel containing 0.1% of the antimicrobial agent polyhexanide and 0.1% of the surfactant betaine was described as a lavage solution in wounds with good results.
One of the key of this procedure is not necessarily the type of solution used, but the amount used. A copious lavage of 500-1000ml is recommended. The ideal pressure of 7-8 psi can be provided by different systems. The most cheapest way is to use an 18G needle, a 3 way stop cock, saline bag, 35-60ml seringe and an intravenous tube. Pressure cuff also can be attached to the solution bag and 300mm Hg pressure can be maintained to provide 7-8 psi in the time of lavage. If the pressure is too high, the healthy tissue can break; if the pressure is under 7-8 psi the surface contaminants may not be removed completely.
After cleansing, if the wound is not considered contaminated, primary closure is indicated. Most of traumatic wounds need also debridement.
Fig. 3 Wet to dry bandage applied on a wound located on the ventral aspect of the metatarsal area in a cat as a nonselective form of debridement
Debridement: can be selective or nonselective. Usually chronic wounds needs debridement but also fresh wounds which present devitalized tissue. Surgical and mechanical debridement are considered nonselective forms. For surgical debridement different surgical instruments can be used (scalpel, scissors, etc.) and adherent bandages (wet-to-dry / dry-to-dry) are used for mechanical debridement.
Surgical debridement must be performed in layers, step by step until the necrotic/ devitalized tissue has been removed and blood can be visible from the wound edges or from the bed. An en block surgical debridement can be performed but this can be limited due to location and size. The wound margins should be closed with suture material or towel clamps can be applied for a temporary closure and after the entire wound is excised, including a margin of healthy tissue. Wound irrigation is also considered a nonselective debridement.There is no strong evidence that cleansing wounds increases healing or reduces infection, but it is almost universally recommended.
Three forms of selective debridement are described: enzymatic, autolytic, biosurgical/ biotherapeutic.
- Enzymatic debridement – includes proteolytic enzymes that break down the necrotic
Fig.4 An example of ointment with papain and urea used for enzymatic debridement
tissue. Papain, trypsin, chymotripsin, fibrinolysine, collagenase, urea are the most common enzymes used for enzymatic debridement. Castor oil, balsam of Peru, desoxyribonuclease are also described.
As an advantage, they will not damage healthy tissue. This type of debridement is used less and less nowadays in wound management because is less effective and needs a long period of time to have the proper effect. Surgical debridement may facilitate enzymatic debridement.
- Autolytic debridement – is the most preferate selective debridement. Is less painfull in
compare with the other types. This method involves maintaining a moist environement on the wound so that natural enzymatic “phenomens” can take place. Hydrogels, hydrocolloids and foams are very common used to support autolytic debridement and will be described later as moisture retentive dressings. Due to their high osmolarity, honey and sugar can also be used also for autolytic debridement. They attract the fluid and will keep a moist environement.
- Biosurgical debridement – refers to usage of maggots (Lucilia Sericata, Phaenicia
Sericata) and have and FDA approval since 2004. The maggots produce enzymes that dissolve the necrotic tissue and don’t interact with healthy tissue, that’s why the debridement is selective. They are applied in the wound as larva stage (4-7 days of life) and can be left in place 3-4 days. At the moment of application the larvae have 2-3 mm and in 4 days grow until 10-15mm. The optimal activity of the maggots depends on the wound pH. They don’t survive in an acidic environment. An 8.5 pH in the wound is preffered. Each maggot may consume up to 75mg of necrotic tissue every day. They cannot penetrate dry necrotic tissue or eschar therefore are not indicated for this situation.
Moisture retentive Dressings (MDR’s)
Transepidermal water loss represents the the amount of fluid lost by the normal skin. In humans with intact skin the transepidermal water loss is 4–9 g/m2/h. In partial and full-thickness wounds the water loss increase up to 90 g/m2/h. Dressings that have a low moisture vapor transmission value, less than 35 g/m2/h, are considered moisture retentive. In humans was found that the dressing with a water vapor transmission rate of 2028.3 ± 237.8 g/m2/24h was able to maintain an optimal moisture content for the proliferation and regular function of epidermal cells and fibroblasts in a three-dimensional culture model. The process of wound healing can be accelerated by a moist environment. MDR’s retain water and hydrate the tissue and facilitate natural autolytic debridement. All wounds need to be covered with a specific dressing to maintain a proper moisture until full epithelialization otherwise the granulation tissue will get dry and eschar will occur. MDR’s are availabile on the market in various sizes, shapes, thicknesses, with or without adherent margins. They must be applied on top of the wound as a first layer and after can be covered with the second (absorbent layer) and third layer (protective layer).
Fig.5 Lateral view of a polyurethanic foam. Noticed the convex shape that the foam acquired after beign moistened. Due to this particularity this dressing have a good contact with the wound bed.
Polyurethane foams: is a porous nonadherent dressing that can be used in moderate to high exudative wounds. It absorb several times it’s weight. Is recommended to be used in sterile wounds and regularly must be changed every 3-5 days. With time, the period in which the dressing must be kept in place will change according to the amount of exudate. Some articles described that can be used also over infected wound bed but must be changed every 24 hours.
Can or cannot have adhesive borders and does not transform in gel. It is contraindicated in wounds with low exudate and not recommended in areas with bony proeminence because is very soft and cannot protect the damaged area. In compare with hydrocolloids and alginates, foams are less effective for autolytic debridement.
Alginates (calcium alginate): have high absorbtive properties. It absorbs 20-30 times its weight in fluid. In contact with the exudate, alginates transforms in gel. Is derived from brown seaweed and is recommended in high exudative wounds. It promotes haemostasis and Ca2+ stimulates macrophages and fibroblast activity. Is not recommended to be used in low exudative wounds.
Fig.6 Calcium alginate appearance. Left picture represents calcium alginate sheet applied on dorsal and ventral aspect of metatarsal area in a cat with a degloving injury after surgical debridement; Right picture represents the aspect of calcium alginate 24 hours later in the same patient; Note the transformation from dry fibers in gel and the proximal area in which the dressing was absorbed (yellow arrow).
As a presentation form, alginates are used in flat sheets and can be applied even in narrow cavities. On the market alginates can be found in combination with silver, zinc or honey.
Hydrogels: are indicated in low exudative wounds. They donate fluid to wound but can also absorbe it. Can be found in two presentation forms-sheet and gel. Contains 60-95% water and the cooling effect may decrease pain. Is not indicated in high exudative wounds because maceration can occur. Overgranulation has been reported after usage of hydrogels in excess. In cavitary wounds the gel form is inficated due to better contact. Hydrogels can also be used to soak the dry necrotic tissue.
Fig.7 Left picture describes hydrogel sheet used on the lateral aspect of digit IV in a dog with and abrasion wound. The wound had partial epithelialization and a small area with granulation tissue and the level of exudate was low. In the right picture gel shaped hydrogel is placed on Primapore.
Various forms of hydrogels combinations are availabile: with hyaluronic acid, alginate, collagen, etc. Can be left in place 3-4 days in non-infected wounds. They are permeable to gas and water and have proven to be a less effective bacterial barrier than occlusive dressings.
Hydrocolloids: have in composition may constituents like sodium arboxymethylcellulose,
gelatin, pectin, and polyisobutylene. Gelatin, pectin, elastomers, alginates, silver, and other materials can be added to these substrates. In contact with exudate it transform in gel and maintain a moist environment. Hydrocolloids are indicated in wounds with low to moderate exudate.
Sheets, powder and paste are the form of presentation. In compare with alginates, foams and hydrogels, the contact face of hydrocolloids is adherent but just on the skin, not on the granulation bed. Regarding permeability, hydrocolloids are semi-permeable to water vapour and oxygen but not permeable to bacteria and other contaminants. Is not recommended in infected wounds. May cause overgranulation.
Fig. 8 Different aspects of hydrocolloid dressing. (a) Fresh hydrocolloid applied on a mild exudative wound in a dog; the dressing have is brown and opaque. (b) View of the dressing 5 days after application on the dorsal metacarpal area in cat. Note the brown dark colour that hydrocolloid achieved. (c) Dressing removal in the same patient in the same day. Note the yellow, gelly and bright aspect due to granulation bed contact.
Honey – called also natural dressing, they are composed by glucose, fructose, sucrose, maltose, amino acids, vitamins, minerals and enzimes. Honey is the most popular product used as a topical treatment for wounds; have an antimicrobial effect due to low pH (3-4.5 ), release of small amounts of hydrogen peroxide or the presence of methyglyoxal. Honey promotes autolytic debridement and reduce oedema due to high osmolarity. It was demonstrated that honey have effect against a multitude of bacteria including Pseudomonas spp., MRSA and E. coli. Composition of honey does vary according to the geographical source. Many types of honey are availabile, from raw honey to medical grade. Manuka honey (Leptospermum scoparium) that originates from New Zealand is the most common used in humans and animals for wound care. Medical grade Manuka honey is recommended despite raw honey because raw honey may contain bacteria and fungal contaminants including anaerobic spore‐forming organisms. Recently was developed a new type of honey was developed which is not manuka honey. SurgihoneyRO is an antimicrobial wound gel utilising bioengineered honey to deliver Reactive Oxigen and is superior to Manuka honey. It cames in a variety of form such as gels, sheets, in combination with alginates or simple gauze. Honey is recommended in wounds that needs debridement and is not recommended to be applied over the granulation tissue. Despite the multitude of benefits, the quality of the evidence is variable.
Silver dressings– should be used when infection is suspected. Has been shown that silver ions have an antibacterial effect in contact with the exudate. Because silver ions are activated by a moist environment, is not indicated to be used in wounds with moderate-to-low exudate. There are some evidence that suggest delay healing if silver dressings are used in acute wounds. Is available as gel, sheets, impregned in alginates, foams and hydrocolloids and can be left in contact with the wound up to 7 days. Silver is a broad-spectrum antimicrobial agent that is effective against bacteria, fungi, viruses, and yeast. It has also been proven to be active against MRSA and vancomycin-resistant enterococci (VRE) when used at an appropriate concentration. Silver destroy bacteria due to multiple mechanisms: disrupts bacterial cell walls, inactivates bacterial enzymes, and interferes with bacterial DNA synthesis. Therefore bacterial resistance has yet to be documented, although reports of isolated Escherichia coli and Pseudomonas aeruginosa have shown resistance to silver in vitro. Despite the benefits, some articles concluded that is still a lack of evidence about usage of topical silver and silver dressings for treatment of infected or contaminated chronic wounds.
Collagen dressing: are available in different forms such as granules, powders, sheets, pastes, gels. The collagen from these products derived from bovine, porcine, equine, piscean or avian source. Collagen has been widely used in cosmetic surgery, as a healing aid for burn patients for reconstruction of bone. Is the main structural protein in the extracellular space. Is resistant against bacteria and in this way it helps to keep the wound sterile. Platelets interact with the collagen to make a hemostatic plug. Collagen based dressings need a secondary dressing layer to maintain a moist environment. Products that contain collagen promotes angiogenesis and stimulates fibroplasia. Recently, usage of Tilapia skin fish in veterinary medicine and blue shark skin in human medicine for burns were described with promising results.
Silicone dressings– are used mainly in humans to reduce the hypertrophic scar. The mechanism of action of silicone dressings is not fully understood. It is believed that silicone due to occlusive effect, decrease the oxygen of the tissue until anoxia, environment in which fibroblasts cannot have a normal function and undergo apoptosis. In humans has been shown to help reduce trauma and pain. Silicone dressings were tested in rabbits, rats and horses. Silicone dressings are nontraumatic and the contact surface is adherent but just on the skin surrounding, not to the granulation bed. A comparison between silicone dressing and silicone gel in a controlled trial for treatment of keloids and hypertrophic scar. Compared to the untreated controls, all of the measured parameters including scar size and induration were reduced in both silicone and nonsilicone-treated groups. In 2005, silicone dressing was used with good outcomes in horses with exuberant granulation tissue. In 2017, a review of silicone gel sheeting and silicone gel for the prevention of hypertrophic scars and keloids concluded that was statistical significance in the effectiveness of both of them but most of the trials had poor quality with high or uncertain risk of biases.
Borate glass nanofiber – was developed in 2010 by human engineers and is recognized to have regenerative properties on bones and soft tissues due to stimulation of angiogenesis and osteogenesis. Two borate glasse with (1605) or without (13-93B3) CuO and ZnO were studied along with the silicate-based glass, 45S5 for the potential effect on vascular endothelial growth factor. The study demonstrate that silicate glass is inferior to borate glass. Copper and zinc ions together with calcium, phosphorus, magnesium, etc., stimulate the proliferation of human endothelial and osteoblast-like cells, promote angiogenesis, and stimulate vascular endothelial
growth factor secretion. Osteogenesis is encouraged because the fibers convert to hydroxyapatite.
Fig.9 Borate based glass nanofiber. Macroscopic aspect, “cotton-candy” like (left picture) and electron microscopy (right picture).
In 2017, borate glass nanofiber was evaluated for treatment of full thickness wounds in six dogs. The study had many criteria: wound cause and location, type and duration of previous wound management, time to granulation tissue formation, time to complete wound healing, subsequent procedures if applicable, outcome, and complications associated with treatment. With a “cotton candy” aspect and soft texture, the borate glass can be applied to any defect, even in deep wounds can be packed. Is not expensive and did not require hospitalization. A veterinary product was developed and is available (RediHeal) for cats, dogs and horses. Because promotes bone growth, the product can be packed also in the defect which result after dental extraction. After application, the fibers degrades at a controllable rate and release ions.
Wet-to-dry Vs MDR’s
· Wet to dry bandages: first they overhydrate and after dessicate the wound bed. As
a result, cells involved in the healing process will lose their function. Because is a nonselective debridement form, when wet to dry bandages are removed normal cells (WBCs, macrophages, granulation tissue) are pulled off with the surface contaminants. The environmental bacteria can penetrate the gauze.
Because is adherent, in the time of removal will be not comfortable for the patients due to pain sensation. Small gauze fibers can remain in the wound bed, will act as a foreign body and will extend the inflammatory phase. They are not expensive but if are used as a sole treatment for wounds, the cost may increase semnificatively due to delay healing and daily replacement.
· Moisture retentive dressings: during the inflammatory phase, support selective
Fig.9 Characteritics of an ideal dressing
autolytic debridement and promote healing because will keep a moist environment. They are nonadherent and nonpermeable for bacteria so the infection rate is lower in compare with wet to dry bandages. They also require replacement every 3-6 days (depends on the product and the wound appearance) therefore decrease the costs for total wound care. Because MDRs are occlusive or semioclusive in nature, they decrease the pH and oxygen tension in wound and, as a result, WBCs are attracted, angiogenesis and collagen formation are stimulated and inhibit bacteria. MDRs are comfortable not painfull for the patient when are removed from the wound bed. Also they prevents dessication and necrosis.
There is no dressing that meets all the conditions and cannot be considered that one is better than the other. The aim is to use the correct dressing according to the needs of the wound. Therefore, the physiology of wound healing needs to be understood. As an example, even if gauze (wet-to-dry) have many negative consequences, it can be used for debridement as part of wound management and is very effective but contraindicated in the proliferative phase while calcium alginate (MDRs) is less effective and can dessicate the wound bed when is applied on dry wounds.
Regarding moisture, a simple general rule is considered: exudative wounds need dressing that will absorb the fluid and dry wounds need dressings that will deliver moisture. It is detrimential to assess the volume and the appearance of the exudate each time the bandage is changed. A wound with a favorable evolution will produce less and less exudate with a clear clear aspect.
Wounds have different behavior and the evolution depends on many factors (localization, degree of contamination, size, etc.). In particular situations, wounds may not heal by second intention or they may decrease in size in the time of treatment but in some cases the proliferation may stop. If surgical closure cannot be achieved, alternative therapies may be considered. As an example, vaccum assisted closure (negative pressure therapy), laser therapy or platelet-rich plasma (PRP) should be considered.