Wound management:
A new protocol for companion animals.
Research Project Faculty of Veterinary Medicine,
Utrecht University
Drs. T. van Hengel
Student number 0461148
Supervisor:
Prof. Dr. J. Kirpensteijn
October 2008
Contents
Preface
p.3
Acknowledgements
p.4
1. Introduction
p.5
2. Wound healing
2.1. Inflammatory phase
2.2. Debridement phase
2.3. Proliferation phase
2.4. Maturation phase
2.5. Differences between acute and chronic wounds
2.6. Differences in wound healing between dogs and cats
p.6
p.6
p.6
p.7
p.9
p.9
p.10
3. Wound management
3.1. Debridement
3.2. Wound irrigation
3.3. Wound closure
3.4. Wound dressings
3.6. Wound reconstruction and transplantation
3.7. Omental flaps
3.8. Advanced techniques
3.9. Wound management in burns
p.11
p.11
p.13
p.14
p.16
p.18
p.21
p.21
p.23
p.24
p.24
p.25
p.25
p.25
p.25
p.26
p.28
4. Protocol for wound management in companion animals
4.1. Protocol
4.2. Cost-effectiveness
4.3. Patient and owner benefit
p.29
p.29
p.33
p.35
5. Conclusion / summary
p.36
6. References
p.36
7. Addendum
An in vitro study into the susceptibility of methicillin-resistant
Staphylococcus intermedius to several antiseptics.
p.41
3.4.1. Moisture-retentive dressings
3.5. Topical medication
3.5.1. Topical antibiotics and antiseptics
3.5.2. Honey
3.5.3. Sugar
3.5.4. Tripeptide Copper-Complex
3.5.5. Acemannan
3.5.6. Growth factors
Wound management: A new protocol for companion animals.
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Preface
During the training of Veterinary Medicine at the Utrecht University, all students perform
a research project on a subject of their interest. This report on wound management in
companion animals is the result of the research project of Drs. T. van Hengel under
supervision of Prof. Dr. J. Kirpensteijn.
The aim of this research project was to compose a protocol for wound management in
companion animals which can function as a guideline for the veterinary practitioner.
Therefore scientific as well as economic aspects were of interest. The protocol is based
on numerous scientific studies, the experience of the veterinary surgeons of the Utrecht
University and experience gained during a short training period in the burn centre in
Beverwijk and the Academical Medical Centre (AMC) of the Amsterdam University.
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Acknowledgements
In the first place I would like to thank Prof. Dr. J. Kirpensteijn for the opportunity to
perform this research under his supervision. I appreciate your help and useful advice as
well as the freedom you gave me during the research project. It has been a valuable
experience to me.
Not only Prof. Dr. J. Kirpensteijn, but also the other members of the staff of the
department of companion animals of the Faculty of Veterinary Medicines, Utrecht
University made this time very instructive and pleasant to me. I would like to thank you
all for your help and enthusiasm.
I would also like to thank Dr. J. Wilmink for sharing her experience with wound
management in horses and for her good advices and remarks.
I am thankful to I.R. Hoogendoorn and S.G. Schipper of the AMC and J. Vloemans of the
burn centre in Beverwijk for their time and the sharing of their experience with the
treatment of wounds in human patients.
Dr. E. van Duijkeren and Prof. Dr. J. Wagenaar I would like to thank for their supervision
during the research project into the susceptibility of MRSI to several topical antiseptics.
This research gave me an extra chance to see and learn about bacteriological science.
Last but not least, the staff of the VMDC needs to be named here. Without them I
probably would not have succeeded in performing the bacteriological tests. Thank you!
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1. Introduction
Wounds can be defined as injuries to the body that result in disruption of the continuity of
the body structure.31 They are very common in veterinary practice and therefore a
veterinarian should be familiar with the process of wound healing and the options for
wound management. Although there are great differences in types of wounds including
incisions, abrasions, burns, bite wounds, avulsions, punctures, contusions, lacerations and
shot wounds, the main principles of wound healing are the same for all these wounds.
Wound classification
Wounds can be classified as open or closed, whereas with open wounds there is a
disruption of the skin or mucous membrane. With closed wounds the superficial layer is
still intact and protects the wound against contamination. Further classification for open
wounds can be done by degree of contamination, which partly depends on the duration of
the injury14,56:
- Class 1 Clean: wounds with no visible contamination, within 0 to 6 hours after surgery.
- Class 2 Clean-contaminated: wounds within 0 to 6 hours after a surgery with a risk for
minimal contamination; for example after operations of contaminated organ
systems.
- Class 3 Contaminated: wounds with minimal contamination that exists for more than 6
hours.
- Class 4 Infected: wounds with obvious contamination or signs of infection, for example
old traumatic wounds. An infected wound contains more than 105 bacteria per
gram tissue.
Another way by which wounds can be classified is acute or chronic. For wound
management it is important to know how long the wound already exists. With chronic
wounds there are often underlying factors which prevent the wound from healing and
which have to be removed first before standard treatment can become a success.
A third way of wound classification is by the thickness of the skin surface that is lost.
With full-thickness skin loss the complete dermis and epidermis are lost, but with partialthickness skin loss, the dermis is still partly intact. Adnexal structures in the partly intact
dermis can serve as source for epithelial cells which are needed for wound healing.56
Abbreviations
ATA = Atmospheres Absolute
HBOT = Hyperbaric Oxygen Therapy
IGF-1 = Insulin-like Growth Factor-1
IL-1 = Interleukin-1
LLLT = Low-Level Laser Therapy
MMP = Matrix Metalloproteinase
NO = Nitrogen Oxide
NSAID = Non-Steroidal Anti-Inflammatory Drug
PDGF = Platelet-Derived Growth Factor
PMN = Polymorphonuclear cell
SSD = Silver Sulphadiazine
TCC = Tripeptide-Copper Complex
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TGF-α = Transforming Growth Factor Alfa
TGF-β = Transforming Growth Factor Beta
TNF-α = Tumor Necrosis Factor Alfa
TNP = Topical Negative Pressure
2. Wound healing
Wound healing can be divided into four main phases which are the inflammatory,
debridement, proliferation and maturation phases. Every wound will follow this path and
to make the right decisions in wound management, a clinician has to be familiar with the
process of wound healing. A wound can be in more than one phase at the same time.
Although the phases of wound healing are the same in dogs and cats, there are some
important differences, which the clinician will have to take into consideration. These will
be discussed at the end of this paragraph.
2.1. Inflammatory phase
After wounding the first thing that happens in the injured area is a short period of 5 to 10
minutes with vasoconstriction, as a protective mechanism of the body to stop bleeding,
together with blood clotting.32,33,56,57,66 This is followed by vasodilatation, which allows
fluid with cells like lymphocytes, polymorphonuclear cells (PMNs) and macrophages and
with chemotactic factors like cytokines and growth factors to reach the injured area.32,33,56
The movement of fluid to the wound area is not only important because of the delivery of
cells and growth factors to the wound bed, but also to dilute toxic substances and provide
nutrients.33,66
Activated platelets release growth factors important for wound healing. The migration of
PMNs, lymphocytes and macrophages is stimulated by chemotactic factors like
complement, platelet-derived growth factor (PDGF), transforming growth factor beta
(TGF-β), interleukin-1 (IL-1), insulin-like growth factor-1 (IGF-1) and tumor necrosis
factor alfa (TNF-α).27,32,56,66
In the early inflammatory phase PMNs dominate in the wound, but from about day 5 the
macrophage is more common caused by the shorter lifespan of PMNs.32,56 PMNs can also
be present in sterile wounds.32 Research showed, however, that PMNs are not essential in
uncomplicated wound healing while macrophages are.32,56,66 Macrophages are an
important source of growth factors.32
The inflammatory phase is being characterized by the classical signs of inflammation
which are redness, pain, heat, swelling and loss of function, also known as rubor, dolor,
calor, tumor and functio laesa, respectively.
2.2. Debridement phase
Necrotic or dead tissue impedes wound healing and thus the removal of it is an essential
phase in wound healing. This necrotic tissue is a stimulus for inflammation and provides
good circumstances for bacteria to proliferate. PMNs and macrophages have an important
function in removing the debris and cleaning the wound. The inflammatory exudate
formed in the previous phase contains these phagocytic cells and proteolytic enzymes,
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which take care of the demarcation. This phase ends with the rejection of non-vital
tissue.57 (Figure 1)
Figure 1: A wound with a lot of necrotic tissue. Debridement will
be necessary before wound healing can continue.
2.3. Proliferation phase
About 3 to 5 days after injury the signs of inflammation will become less, the wound will
become cleaner because of the debridement and the repair of the wound can start. The
proliferation phase can be divided into three processes, namely granulation, contraction
and epithelialization. It is being characterized by proliferation of fibroblasts, endothelial
and epithelial cells. The period before these phases is sometimes called the lag phase
because the wound does not gain strength in the first few days after wounding.32
Granulation
The main components of granulation tissue or fibroangioblast tissue are fibroblasts and
capillaries. The fibroblasts migrate from the surrounding tissues and the new endothelial
cells are formed by the process of angiogenesis from adjacent vessels. For the formation
of granulation tissue, fibrin and fibronectin in the wound are important because they
serve as a scaffold to lead inwardly growing cells.32,56,57,66 The fibroblasts produce
collagen and by depositing it, fibrin is slowly replaced.33,56,57,66,69 The deposition of
collagen is controlled by epithelial cells and fibroblasts themselves which both have
collagenase activity.56 That is why the net collagen synthesis only increases up to 4 to 5
weeks after injury.57 The collagen fibers undergo continuous remodeling by breakdown
and rebuilding of fibers.57
Granulation tissue is characterized by a red, irregular surface because of the newly
formed capillary buds. (See photo 2) It is a very fragile tissue, but important for its
function as a barrier to infection.32,33,66 Main factors for this part of the proliferation
phase are the supply of nutrients, removal of metabolites and presence of oxygen.56 But
on the other hand, slight hypoxia can stimulate the formation of new capillaries.33 An
important nutrient is vitamin C, which is essential to the production of collagen.56 The
formation of a healthy bed of granulation tissue serves as a barrier against environmental
contamination and as a scaffold for migrating epithelial cells.
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Wound contraction
Wound contraction involves the process that pulls the borders of the skin adjacent to the
wound towards the centre of the wound. This centripetal movement is especially striking
in areas of the body with loose skin, e.g. the trunk. The quantity and elasticity of the skin
differ among breeds. Wound contraction is a very important part in the reduction of the
wound area. Normally it is visible from 5 to 9 days after wounding.32
Specialized fibroblasts, called myofibroblasts, are the main contributors, but also normal
fibroblasts are capable of wound contraction.56,57,66,69 These myofibroblasts attach
themselves to the dermis under the skin border and to the underlying fascia or panniculus
muscle layer.56 After attaching they contract, pulling the adjacent skin to the centre of the
wound.56
Wound contraction stops when the tension of the surrounding skin becomes too high or
when the edges of the wound reach each other. If wound contraction is excessive wound
contracture can occur, which is a pathologic process, resulting in limited motion of the
underlying structures.27 Excessive granulation tissue can impede contraction by
preventing the skin from gliding over the wound surface. This is a well-known problem
in horses. Also a normal amount of granulation tissue can impede wound healing when it
is of poor quality.69 Another factor that can inhibit wound contraction is pressure on the
wound, because wound edges are pushed away from each other.69 When applying a
bandage, it is recommended to try to keep the pressure off of the wound by distributing it
around the wound.69
After wound contraction the surrounding skin has been thinned. This will be restored by
proliferation of epithelial cells and connective tissue, called intussusceptive growth.33,56,69
Epithelialization
Epithelialization includes the proliferation of basal epithelial cells from the adjacent skin
border and their moving over and adhesion to the surface of the wound. (Figure 2) They
fill in the rest of the area of the wound that is left after wound contraction, upon the
condition that the area is not too large.
The requirement for good epithelialization is a healthy bed of granulation tissue. The
activity of the epithelial cells leads to the inhibition of the formation of granulation tissue
to prevent excessive amounts of this tissue.57 An exception are closed wounds, because
then epithelial cells migrate over the exposed dermis and through the fibrin clot.33,66 The
movement of new epithelium stops due to contact inhibition. The total duration of
epithelialization can differ from days to weeks, depending on wound size and condition
of granulation tissue.66
The surface of the wound that has become epithelialized is known as the epithelial scar
and is thin and fragile.56 Therefore be careful when applying bandages to wounds in this
phase because migrating cells are easily removed from the surface when changing the
bandage.57 Wound contraction is preferred in areas of the body where it does not impede
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normal function of the skin and movement of the body. A typical scar consists of
granulation tissue with overlying epithelium.
Figure 2: Granulation (red) and epithelialization
(pink).
2.4. Maturation phase
After the proliferation phase it seems that wound healing has been completed, but one
phase is still to be completed. In the maturation phase the strength of the wound increases
by the remodeling of collagen. Collagen III is being replaced by the stronger collagen I,
the collagen bundles become thicker and the number of cross-linkages between collagen
fibers is increased.27,32,33,56,57,66 The newly-formed collagen arranges parallel to the
tension lines of the skin.56,66 This can take several weeks up to 1 or 2 years. The newly
formed skin will never get the same strength as the original, uninjured skin.
Approximately about 80% of its strength will be regained.32,56,66
2.5. Differences between acute and chronic wounds
As mentioned in the introduction of this chapter, wounds can be divided into acute and
chronic wounds. The understanding of the differences between these two types of
wounds is important for proper wound management. In chronic wounds there is a lack of
orderly progression through the four phases of wound healing. The sequence of wound
healing, described above, is disturbed.
The wound fluid in chronic and acute wounds differs biochemically. In chronic wounds,
the levels of inflammatory cytokines are raised for a prolonged period and there seems to
be an excess of matrix metalloproteinases (MMPs) and serine proteinases.62 They lead to
breakdown of the matrix which is needed for epithelialization and to breakdown of
growth factors and cytokines important to wound healing.62
An important cause of chronic wounds is infection which causes a sustained
inflammatory phase. Persisting inflammation results in further trauma to wound tissue
and prevents healing.3 Many other factors that influence wound healing can be found in
literature, like for example malnutrition, radiation, use of corticosteroids and underlying
metabolic diseases. To resume the normal repair process, these limiting factors need to be
addressed.
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2.6. Differences in wound healing between dogs and cats
For many centuries it was thought that wound healing was the same for all mammals. In
the last decades researchers discovered that, although they all follow the same phases of
wound healing mentioned above, this was not true. Differences between horses and
ponies and between rabbits and humans were found, and there seems to be differences
between cutaneous wound healing in dogs and cats too. Much research concerning
wound management was performed in dogs and lately the question arises if these results
can be extrapolated to cats. This fact leads to a more important question for the
veterinarian if wound management should be changed for cats.
Only limited research has been performed to investigate the differences between wound
healing in dogs and cats, but resulted in the discovery of several differences. One of these
differences is the vascular supply of the skin. One study showed that the dog appeared to
have a higher density of tertiary and higher order vessels than the cat, which was in
accordance with a laser Doppler perfusion study.5,71 This laser Doppler perfusion study
concluded that the intact skin of cats was less perfused than the intact skin of dogs.
Additionally, the breaking strength of a wound in cats seemed less (about 50%) than in
dogs 7 days after primary closure.5
There is also a difference in the rate and pattern of production of granulation tissue. The
formation of granulation tissue takes longer in cats compared to dogs. In cats, granulation
tissue first appeared at the edges in contrast to dogs where it appeared simultaneously
from the entire exposed surface.7 The color of the granulation tissue is paler in cats.7
Rates of wound contraction, epithelialization and total healing appeared all to be reduced
in cats.7
In contrast to the previous study, the role of subcutaneous tissue in wound healing in the
dog and the cat seems similar.6 The subcutis was important to wound healing as a source
of precursors for wound healing in both. There were no significant differences between
dogs and cats.
Complications
Complications in wound healing differ between dogs and cats. Pseudohealing and
indolent pockets are much more common in cats.7 Pseudohealing refers to a sutured
wound that appears well healed, but after removal of the sutures dehiscence occurs under
normal stresses.7 Pseudohealing is often observed with bite wounds. Indolent pockets,
also called indolent ulcers, are chronic pockets in the subcutis lined with mature collagen
and containing a thin, serous, modified transudate.7 Wound contraction does not occur in
these wounds.69
Impacts on wound management in practice
Because of the lower breaking strength of sutured wounds in cats as compared to dogs, it
may be reasonable to leave sutures for a few days longer in cats after surgery compared
to dogs. This is especially important when larger parts of the subcutis have been removed
in surgery. More research will be needed to better understand the differences and to
translate them into practice.
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3. Wound management
Many of the wounds that the veterinarian is confronted with will heal naturally. But there
are wounds that may need intervention, like large wounds or wounds with a lot of
necrotic tissue and infected wounds. Besides the wounds that really need an intervention,
certain wounds may heal better with some kind of stimulation. This wound stimulation
may result in a decrease in total healing time, a decrease in risk of complications or a
better cosmetic outcome.
If patients are presented with acute wounds that are still bleeding, the first step is to stop
this bleeding. With major bleedings this can be performed by compression of the
wounded area or the supplying vessels.57 For minor bleedings the use of specialized
dressings with haemostatic properties is also a possibility, like for example alginates with
calcium, adrenaline-soaked gauzes or gelatin sponges.57
The primary goal of the veterinarian is to try to diminish the level of contamination and
to prevent further contamination. Contaminated wounds can best be cleaned within the
‘golden period’. This period of 4 to 6 hours after wounding is the period in which a
contaminated wound can turn into an infected wound because of proliferation of bacteria
to more than 105 per gram of tissue.56,57 Tissue will also be invaded by the bacteria after
this period which makes it much harder to remove the bacteria by irrigation.56,57
3.1. Debridement
There are several ways to accomplish debridement of wounds: mechanical, surgical,
autolytic, enzymatic, chemical and biosurgical. The objective is to convert the open
contaminated wound into a surgically clean wound which can be closed34 or treated as an
open wound if closure is not possible. The choice which method to use, is dependent on
the wound and the patient. Factors which play a role are for example the amount of
necrotic tissue, the laxity and elasticity of the surrounding, if there is a clear demarcation
line and if the patient’s condition is well enough to endure an anesthetic procedure. The
patient’s condition decides if an operation is possible or has to be delayed. In many
instances, more than one debridement procedure may be necessary to result in a healthy
wound.
Mechanical
Mechanical debridement is performed with the use of wet-to-dry or dry-to-dry dressings.
Wet-to-dry dressings are wet when they are placed on the wound and adhere to the
wound surface while drying. When removing the dressing, the adhering tissue is removed
at the same time. Dry-to-dry dressings work by means of the same principle but there is
no solution added to the dressing.
It is an easy method of debridement, but non-selective and painful for the patient when
the dressing is changed. Anesthesia or sedation may possibly be needed for the removal
of the dressings. The costs of the dressings are low, but anesthesia or sedation and the
number of consults of the veterinarian will contribute to higher costs.
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Surgical
Surgical debridement means that the dead or necrotic tissue in the wound is removed
surgically (Figure 3). It is especially important before closure of the wound by sutures.
During the first period after wounding, it is often difficult to distinguish dead from
healthy tissue, caused by insufficient tissue demarcation. The assessment of tissue
viability, often based on color and attachment, is subjective and there is a risk of
removing healthy tissue.14
An approach that is often used for surgical debridement is the layered approach.14 This
means that first superficial devitalized tissue is removed, followed by the deeper tissues.
When depending on active bleeding from the cut surface in making the decision if tissue
is still viable, consider possible present factors like vasoconstriction or –dilatation and
tissue temperature.14
Figure 3 : Surgical debridement.
Autolytic
Autolytic debridement is the most selective method of debridement and is painless for the
patient. Wound exudate is kept on the wound and components like enzymes and
leukocytes remove necrotic tissue. A requirement to perform this method is the presence
of some amount of exudate which contains the needed components. Autolytic
debridement can be performed with interactive dressings like hydrogels, hydrocolloids,
hydrofibers and foam dressings.
Another example of autolytic debridement is the use of honey or sugar. Honey or sugar
can be used as a topical medication and because of its high osmolarity it attracts fluids
and provides a moist environment.24,45,46 Within this moist environment autolytic
debridement can take place.
Enzymatic
With enzymatic debridement proteolytic enzymes are placed on the wound to breakdown
the necrotic tissue. It is a strong selective method of debridement and is painless for the
patient. The enzymes are processed in powders or creams which can be placed on a
wound. The most commonly used enzymes are trypsin, fibrinolysin, chymotrypsin,
desoxyribonuclease and collagenase.34
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Advantages are the selectiveness and the fact that no anesthesia or sedation will be
needed. Unfortunately there are also some disadvantages. The effectiveness of enzymatic
debridement is often minimal and a long time is required to remove the dead tissue.14,34
There is often little advantage over the other methods.14
Chemical
Chemical debridement can be performed with antiseptics like Dakin’s solution,
chlorhexidine, iodine and hydrogen peroxide.38 It is a non-selective manner of
debridement and cells important for wound healing too will be damaged. Because of this
reason, the use of chemical debridement is not generally preferred, except in wounds with
obvious infection.
Biosurgical
Biosurgical debridement includes maggots from Lucillia sericata which produce
enzymes to dissolve the necrotic tissue. They are not harmful to healthy tissue and
therefore selective. The maggots used for this purpose are specially bred and because of
this they are expensive. Proper indications for the use of maggots in wound management
are deep wounds which are difficult to reach by means of other methods of debridement.
3.2. Wound irrigation
Dirty or contaminated wounds can be cleaned by means of irrigation. This means that dirt
and bacteria will be washed away by fluid under pressure. During the irrigation the
pressure should not be too high because it will damage tissue and push contamination
further into the wound. There is specialized equipment for irrigation which produce a
pulsating stream of water with a pressure of about 0,6 kg/cm2 (8 psi).57 This pressure can
also be achieved by using a 19G needle and a large syringe of at least 30 ml.57 (Figure 4)
Figure 4: Wound irrigation.
Many fluids have been used for this purpose, but also many of them appeared to be toxic
to cells important to wound healing. Often used fluids are tap water, the physiological
solutions like saline and Ringer’s solution or antiseptic solutions including povidone
iodine, chlorhexidine diacetate and sodium hypochlorite.
Because of the toxicity of many of these antiseptic solutions, some aspects have to be
considered before using them. Important aspects are the bacterial status of the wound, the
immune function of the patient, the phase of wound healing and the effects of the
antiseptic solution on bacteria and cells needed for wound healing.15 The potential
benefits have to be weighed against the impacts of toxicity. Not only many of the
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antiseptic solutions, but also tap water is cytotoxic to fibroblasts.14 The use of tap water is
indicated in cases of severe contamination.14 In this paragraph the characteristics of saline
and lactated Ringer’s solution will be discussed, while those of the antiseptic solutions
will be discussed in paragraph 3.5.
Saline or lactated Ringer’s solution
A physiologic saline or lactated Ringer’s solution can remove bacteria and foreign
matters mechanically. Both of them are isotonic to blood and should be used in a sterile
form. They are not cytotoxic to cells responsible for wound healing, but neither
bacteriostatic. They are used widely with good results in wounds which are not highly
contaminated. Dealing with this kind of wounds, it is therefore recommended to use one
of these physiologic solutions. When wounds are highly contaminated or infected it can
be advisable to use an antiseptic solution. Even if it impairs wound healing, wound
infection may be prevented.
3.3. Wound closure
A decision which has to be made during wound management is if and when a wound has
to be closed. For wound closure there are four basic options: primary closure, delayed
primary closure, secondary closure and second intention healing.
Primary closure
With primary closure a wound is directly closed after wounding. Another name for
primary closure is healing by first intention. This way of wound closure is appropriate for
clean wounds, like surgical wounds, but also earlier contaminated wounds which have
been cleaned with debridement.56 The wound healing process is in principal the same as
with open wounds described earlier, but all phases are much shorter and many of them
are not visible. Beside the reduction in time, there will be anatomical as well as
functional recovery. (Figure 5)
Primary closure is preferable, if possible.57 After the golden period of 4 to 6 hours,
primary closure will become less desirable because of the increased chance of an infected
wound.56 If the level of contamination, tissue viability, depth of tissue damage or vascular
supply can be questioned, the other options should be considered.14 After closure of a
wound with no disturbances in wound healing, the sutures can generally be removed in 7
to 10 days.57
Figure 5: Well-healed wound after primary closure.
Delayed primary closure
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Delayed primary closure refers to a wound that is not closed directly after wounding, but
before the formation of granulation tissue. This is usually within 3 to 5 days after
wounding. It allows drainage of the wound, a decrease in contamination and the
development of a clear demarcation line to distinguish the dead tissue which should be
debrided.
Secondary closure
With secondary closure the wound is closed after the formation of granulation tissue. It is
often used for contaminated or infected wounds. There are two methods for secondary
closure14,56,57:
1. Leaving the granulation tissue intact and restrict to separating the edge of the skin
from the granulation tissue and advancing the skin over de granulation bed for
closure.
2. Excision of the granulation tissue and thereafter perform primary closure.
The second method is often preferred by veterinary surgeons because the wound edges
are more mobile for closure, there are better cosmetic results and a lower incidence of
infection.56 Factors important in making a choice are the thickness and health of the
granulation tissue and the mobility of the skin edges.14 The total healing time is still
reduced when compared with healing by second intention.
Healing by second intention
Healing by second intention means that the wound is allowed to heal by granulation,
contraction and epithelialization. This process is described in the paragraph above. It is
often used for infected wounds and wounds that are too large to be sutured. It can be
accompanied by other forms of wound care like dressings and topical medication. This
way of closure is chosen a lot in veterinary practices and most times it is effective.
Especially on areas of the body with high motion, excessive contraction and scar tissue
can lead to wound contracture.
Drainage
When suturing a wound, dead space can be formed. Fluid accumulation in these spaces is
a good growth medium for bacteria and to prevent accumulation of fluids, drains can be
placed. For low- contaminated wounds it is most times enough to surgically debride,
lavage and close the wound primarily, but the risk for infection is less when using
delayed primary closure.56 Drainage is often not necessary in these situation. Delayed
primary closure is recommended for grossly contaminated and infected wounds.56
The two most common types of drains are passive and active drains. Passive drains are
easier to apply and cost less than active drains. The most commonly used passive drain is
the Penrose drain, a soft latex tube. Passive drains have to be placed on the lowest points
of the wound so that fluid can leave the wound using gravity. The drain commonly is
secured with two sutures to the skin.
One of the disadvantages of passive drains is the risk of ascending infections, especially
when the drain is left in place for several days. It is recommended to cover the drain with
a sterile dressing. This minimizes the risk of ascending infections, prevents leakage of the
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fluid into the environment and allows assessment of the quantity of fluid that has been
produced. Another disadvantage of passive drains is that it is not possible to place the
drain on every area of the body, because of its dependency on gravity.56
Active drains work by creating a vacuum through the drain. This vacuum will suction the
fluid away from the wound, thus there is no need to work with gravity and the drain can
be placed anywhere on the body. Another advantage is working with a closed system,
which reduces the chance of infection. The placement of active drains is more
complicated because the surgeon has to create an airtight seal, otherwise there a vacuum
cannot be made. Active drains are more appropriate for large areas than passive drains.
A special group of drains are the combination drains.14 They allow ingress of fluid as
well as egress and can be used for wounds with dead space which need drainage and
wound lavage.14 The ingress and egress tubes can be placed with one within the other or
on two separated places in the wound.14
To prevent the patient from removing the drain, use an Elizabethan collar.
3.4. Wound dressings
In human medicine, it has been known for decades that wounds should be kept in a moist
environment because total healing time will then be reduced. In veterinary medicine,
moist wound healing is still not very widely used. During the proliferation phase of
wound healing, the voltage gradient which is preserved with a moist environment will
stimulate the formation of granulation tissue and epithelialization. Growth factors are
kept on the wound, leukocytes are not trapped in a scab and can still function, and the
mildly acidic pH and warm temperature are optimal for wound healing. The moist
environment also prevents trauma due to adherence of dressings. Beside the effects on the
proliferation phase, debridement too can be decreased in time. Autolytic debridement
occurs by keeping exudate with enzymes at the wound surface.
Providing a moist environment is not the only function of a wound dressing. The general
functions of wound dressings are written down in Table 1.
General functions of wound dressings:
1. Providing a moist environment
2. Providing a warm environment
3. Protection from trauma
4. Protection from external contamination
5. Application of topical medication
6. Immobilization of the wound area
7. Supporting the wound edges
8. Absorbing exudate
9. Preventing or reducing oedema
10. Providing an aesthetic appearance
Table 1: General functions of wound dressings
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Dressings which provide a moist environment are the modern moisture-retentive
dressings, also called interactive dressings. Dressings belonging to this group are for
example hydrocolloids, hydrogels, hydrofibers, alginates, foams and polyethylene
dressings. On the other hand there are passive dressings like the traditional gauzes. These
can be made wet to provide a moist environment. Besides these two groups there also are
biologic dressings. Table 2 gives an overview of a possible classification of wound
dressings.
Interactive dressings
- Hydrocolloid
- Hydrogel
- Hydrofiber
- Foam
- Alginate
- Polyurethane film
Passive dressings
- Gauzes:
*Adherent
*Non-adherent
Biologic dressings
- Bovine collagen
- Equine amnion
- Porcine small intestinal submucosa
Table 2: Overview of wound dressings.
The most important thing to remember is that there is no single dressing which is perfect
for all wounds in all phases of wound healing. Every wound needs an individual
assessment and follow-up of wound healing is important because it provides the
opportunity to replace the dressing for a dressing creating a better environment.
Gauzes
Gauzes are non-occlusive dressings and are available in adherent and non-adherent form
as well as sterile and non-sterile form. Because they can dry easily while they are placed
on the wound, it is important to keep them wet to provide a moist wound healing
environment. This requires frequent dressing changes, often more than three times a day.
Another disadvantage of gauzes is that bacteria from the environment can migrate to the
wound through the pores of the dressing.
The use of gauze is recommended when a wound is in an acute phase and has to be
inspected and irrigated regularly, because gauzes are inexpensive and when placed on the
wound for a short period, they will not dry. The modern dressings are only more costeffective when the dressings can stay on the wound for a longer period.8 The modern
dressings are therefore not recommended when there is still a considerable chance of
infection in for example traumatic wounds, because this requires regular inspection and
cleaning.
Gauzes can be impregnated with different kind of fluids and topical medication.
Hypertonic saline dressings for example can be used in the early phases of wound healing
because of its bactericidal mechanism and debridement properties by attracting fluid and
debris from the wound. In contaminated or infected wounds gauzes can be impregnated
with antimicrobials.
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Non-adherent gauzes
Non-adherent gauzes are for example petrolatum-impregnated gauzes.8 The absorptive
capacity is low and fluid can move through pores in the dressing.8 Therefore they should
be covered with a secondary and tertiary bandage layer.8 Unfortunately not only water
can move through the pores, but also bacteria from the environment.8
3.4.1. Moisture-retentive dressings
Moisture-retentive dressings can be divided into occlusive and semi-occlusive dressings.
The difference is that occlusive dressings are impermeable to water as well as to water
vapor and semi-occlusive dressings are impermeable to water only; with the semiocclusive dressings a certain amount of moisture can be lost as vapor. Both types of
dressings protect the wound against external contamination and excessive drying,
whereas semi-occlusive dressings also prevent wetting and maceration up to a certain
point.
Even in one and the same type of dressing (See table 2) great differences occur. A
comparative study of the properties of hydrocolloids made this clear.74 In literature the
‘same’ dressing is sometimes called occlusive and at other times semi-occlusive. It
depends on the moisture vapor transmission rates, which is also dependable on the
different outer layers.
When using an occlusive dressing, extra attention has to be paid to the skin surrounding
the wound. Because of the created moist environment, the risk of maceration of the skin
is greater. Preventive measures can be to cut the dressing to the size of the wound and / or
to protect the wound edges with zinc oxide. Another issue to pay attention to is the
amount of granulation tissue that is formed. Research has proven that with occlusive
dressings the chance of hypergranulation is greater.51 Therefore it is generally
recommended to switch to a semi-occlusive dressing when hypergranulation is observed
or expected.64
An advantage of occlusive dressings over semi-occlusive dressings is that reepithelialization is better stimulated. A disadvantage of occlusive dressings is that no
oxygen from the environment can reach the wound, which is important for collagen
synthesis.22 But on the other hand the low oxygen tension stimulates angiogenesis.43
Many veterinarians are afraid of infections with the use of occlusive dressings, but with
occlusive dressings natural substances that inhibit bacterial growth accumulate in the
wound fluid and wounds are protected against environmental contamination, which are
great advantages.8 The incidence of infection seemed not to be increased with the use of
moisture-retentive dressings.8 But if dealing with an already infected wound, the use of
moisture-retentive dressings is generally not recommended. When removing a (semi-)
occlusive dressing, it can have a purulent appearance and foul odor.8,38 This should not be
mistaken for infection.
Hydrocolloids
Hydrocolloids are modern dressings which stimulate wound healing by providing a moist
environment. They are interactive dressings which change into a gel when absorbing
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fluid and then maintain an environment with optimal conditions, moist and warm, for
wound healing. The amount of exudate which can be absorbed by the dressing depends
strongly on the individual product composition, but is often low to moderate.8,74 To
prevent maceration of the surrounding skin the dressing should be cut according to the
shape of the wound. They are non-adherent to the wound surface, but most have an
adhesive border to attach the dressing to healthy skin. Many of the hydrocolloid dressings
are impermeable to water as well as to water vapor and thus occlusive.8 This protects the
wound against external contamination and excessive drying.
Most research with hydrocolloid dressings is performed on humans, but recently a study
has been performed on dogs.1 Also in dogs the dressings appeared to be easy in use, well
adhesive and wounds healed better than the untreated wounds. The granulation tissue was
more regularly organized and the number of inflammatory cells had decreased. This
research also concluded that the adhesive power makes it suitable for animal use. A
disadvantage of the strong adhesiveness is not only that they are difficult to remove, but
also that wound contraction is inhibited because the force needed to bring the wound
edges together increased.69
Hydrocolloids are indicated especially in the proliferation phase of wound healing, but
care must be taken that hypergranulation does not occur.38,51 They can also be used in the
debridement phase by creating an environment for autolytic debridement.38 The costs and
benefits should also be considered, because many bandage changes are often necessary.
Hydrogels
Hydrogels work by means of the same principle as hydrocolloids, they are occlusive and
provide a moist environment. They are placed on the wound as a gel or as a composite
sheet consisting of the gel adhered to the sheet. The sheets have to be cut to the shape of
the wound to prevent maceration of the surrounding skin. The amount of exudate which
can be absorbed by the dressing depends strongly on the individual product composition,
but is often very low.8,38 They are non-adherent to the wound surface.
Hydrogels are especially indicated in the very acute phase after wounding when the
wound is still very dry and in the proliferation phase of wound healing. During the
proliferation phase, hydrogels may cause formation of exuberant granulation tissue.51
They can well be used to rehydrate a wound by applying the hydrogel together with fluid
onto the wound. It is possible to use them in the debridement phase by creating an
environment for autylotic debridement, but then consider the costs and benefits, because
in that phase many bandage changes are often required.
Hydrofibers
Hydrofibers are composed of sodium carboxy-methylcellulose. When there is contact
with wound exudate a gel is formed and a moist wound environment is created. They can
absorb large amounts of wound fluid and are therefore indicated in moderate to heavily
exudating wounds.
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There are two different applications of hydrofibers, namely dry and wet. When used wet,
they are placed on the wound together with fluid and are replaced before the dressing
dries. If used dry, the dressing is allowed to form a sort of scab on the wound surface
which will come loose when the wound surface heals.
Alginates
Alginate dressings are derived from seaweed and as a special property they contain
calcium ions. Calcium ions are important for hemostasis and therefore these dressings
can be used in mildly bleeding wounds to arrest bleeding. They form a moist gel by
exchanging sodium from wound fluid and calcium ions from the alginate dressing.38
Alginates generally have good absorptive properties. They be used for highly exudative
and infected wounds, thus in the early stages of wound healing. Bacteria will become
trapped in the alginate gel, thereby decreasing the risk of infection.8 They are not
indicated in minimally exudating wounds because there is a chance this will result in
dehydration of the wound.
Foam dressings
Most foam dressings are polyurethane foams and they are available as sheets and as
cavity dressings. The absorptive capacity and water vapor permeability differ between
foams, but is generally good. The in situ foams can be used for the treatment of large
cavity wounds, which then prevent premature closure of the wound.75 Foams keep the
wound environment moist, thereby promoting wound healing and are indicated in the
inflammatory as well as in the proliferative phase of healing.32 They also can be used to
deliver fluid for rehydration or medications.
Polyurethane films
A polyurethane film is a thin film which can be used as a semi-occlusive layer to create a
moist environment. Water and bacteria cannot permeate the film, but water vapor can
escape. Under a polyurethane film autolytic debridement is possible. The possibility to
absorb exudate is none to minimal and therefore they should be used for dry to minimally
exudative wounds. These films can also be used as an occlusive layer over other
dressings.8
Biologic dressings
Biologic dressings are dressings derived from a natural source, for example sheets from
porcine small intestinal submucosa (PSIS), equine amnion dressings or bovine collagen
sheets.22,32 These dressings provide an exogenous source of collagen, growth factors,
hyaluronic acid, heparin, heparin sulfate, chrondroitin sulfate A and fibronectin.22,32
Besides this, they can act as a scaffold for fibroplasia.32 A primary, non-adherent dressing
can be used to cover these biologic dressings.8 These primary dressings can then be
changed more often than the biologic dressing, because the price of biologic dressings is
high.8
Other dressings
The effects of dressings impregnated with topical medications like honey, topical
antibiotics and antiseptics are discussed in the next paragraph.
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3.5. Topical medication
3.5.1. Topical antibiotics and antiseptics
The use of both topical antibiotics and antiseptics is controversial. They are used to
prevent or treat wound infections and to increase the rate of healing, but research,
especially in vitro, has shown that the use of medications on wound healing may have an
adverse effect. General advantages of antiseptics over topical antibiotics are the broader
spectrum of activity against bacteria and other micro-organisms and there are fewer
problems with bacterial resistance. But they are often less powerful when a specific
infection has to be treated or prevented.
When dealing with infected wounds and considering to give an antibiotic, it is preferred
to give the antibiotics systemically to prevent toxic effects on cells important to wound
healing. But for a systemically given antibiotic to reach the wound area, a good blood
supply is needed. The use of antibiotics should be minimized to prevent the development
of bacterial resistance. Usually broadspectrum antibiotics are given for 5-7 days. When it
is decided to use antibiotics, it is recommended to first perform a bacteriological culture
and antibiogram. (Figure 6) The initial antimicrobial therapy can be guided by a Gram
stain.14
Figure 6: Taking a swab to perform a
bacteriological culture.
Commonly used topical antibiotics are silver sulfadiazine (SSD), gentamicin sulfate,
nitrofurazone and triple antibiotic ointment (bacitracin zinc, neomycin sulfate and
polymyxin B sulfate).38 Gentamicin sulfate is effective against gram-negative bacteria
and Staphylococcus spp. Nitrofurazone works against a broad gram-positive spectrum
and triple antibiotic ointment against many bacteria, but usually not against Pseudomonas
spp., where SSD provides good activity against.38
Iodine compounds
Two kinds of iodine formulations are available, namely povidone iodine and cadexomer
iodine. The active component against micro-organisms of both of these products is free
iodine, which has a broad antimicrobial spectrum against gram-positive and gramnegative bacteria, viruses, fungi and protozoa.11,15 A disadvantage of the use of iodine is
that it is inactivated by organic matter and this is always present in open wounds.
The use of povidone iodine for wound irrigation and as a topical medication is also
controversial. Some in vitro studies showed impairment and others improvement of
wound healing when povidone iodine was used, but the relevance of these data for in vivo
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conditions is questionable.39 The concentration of povidone iodine is very important; a
1/1000 dilution of 1% povidone iodine can be made that is still bactericidal, but not
cytotoxic to cells responsible for wound healing.42 Povidone iodine is available as a
solution, cream, ointment and scrub. The scrub should be used on intact skin only.16
The cadexomer iodine products are newer and less toxic to cells responsible for wound
healing. It is even found to be beneficial to wound healing.16 They release iodine at a
non-toxic level and require fewer dressing changes. Cadexomer iodine is available as a
dressing and as an ointment.11 The dressing has good absorptive properties.16
Chlorhexidine solution
Chlorhexidine digluconate is frequently used for wound treatment; other solutions are
chlorhexidine diacetate and dihydrochloride. Chlorhexidine digluconate has a wide
spectrum of activity against gram-positive and gram-negative bacteria and has a low
toxicity.61 In vivo research even showed beneficial effects on wound healing.60 Besides its
broad antibacterial effect, it also has a residual effect for a few hours.60,65 The bactericidal
activity of chlorhexidine seemed to be significantly more than the activity of povidone
iodine in vivo.22
For wound irrigation a 0,02% solution is recommended, a less diluted solution can
probably be used in dressings.61 Chlorhexidine is a good cleansing agent for dirty
wounds, but it is better not to use it in clean healing wounds to prevent causing possible
adverse effects on healing while the risk of infection is low.
Dakin’s solution
Dakin’s solution is a solution of sodium hypochlorite which is bactericidal to the
organisms commonly present in open wounds. To prevent cytotoxic effects on cells
responsible for wound healing, dilution to a 0,005% solution is needed.15 Because of its
toxicity to tissues and negative effect on wound healing, it was often not recommended to
use Dakin’s solution in open wounds.61 But nowadays it is used more often again because
of its aggressive approach and its broad spectrum against micro-organisms. It is indicated
for contaminated or infected wounds in the first phases of wound healing and it is
recommended to use it for a limited period only.
Glycerol
As a topical agent, glycerol can be used to promote wound healing. It has diverse
influences on the skin. Glycerol among other things promotes the normalization of the
epidermal barrier function and improves skin hydration.23 Both are important to wound
healing. It also has an antimicrobial property which is more effective against Gramnegative than Gram-positive species.59 Besides this, glycerol is often used as a
preservative in skin transplantation.
Silver compounds
A well known silver compound is silver sulfadiazine (SSD). SSD is a combination of
silver and the antibiotic sulfadiazine. It is very often used in burns of human patients to
prevent infection. It has good, broad antimicrobial activity in vivo (e.g. against
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Pseudomonas spp.) and it appears that it does not have major negative effects on wound
healing.16,36,38 Silver is also used as an anti-microbiological component of modern wound
dressings.
3.5.2. Honey
Honey has been used in wound management for centuries, but was partly replaced by
more modern medication in the last century. Because of the rising interest in the use of
more natural products and the problems with bacterial resistance, a renewed interest has
taken place in the therapeutic use of honey in wound management in both human and
veterinary medicine. Honey works on the wound by many mechanisms. Its different
functions are summarized in Table 3. The use of honey reduces the total healing time
significantly.44,50
Functions of honey
1. Antimicrobial activity
2. Anti-inflammatory activity
3. Decrease edema
4. Neutralize odors
5. Stimulate granulation
6. Stimulate epithelialization
7. Nutrition source
Table 3 Functions of honey12,44,46,48,54
The antimicrobial activity of honey can partly be explained by the presence of hydrogen
peroxide that is formed by an enzymatic reaction between glucose-oxidase and glucose.54
This reaction takes place when honey is diluted with wound exudate.54 Hydrogen
peroxide can be toxic to cells, but it is not toxic in the low concentrations that are formed
when using honey. A second contributor to the antimicrobial activity is the high
osmolarity of honey which reduces the fluid amount available for micro-organisms,
leading to harder circumstances to survive and grow for them.54 Besides these two main
components also the low pH, phytochemical factors and the presence of inhibin and other
enzymes play a role.2,46,54
Because of the antimicrobial activity of honey, the number of micro-organisms together
with their waste products will decrease, which will lead to diminishing of odors from the
wound.54 The stimulation of granulation and epithelialization is possible because of the
improved nutrition of cells important to wound healing, the creation of a moist
environment and because hydrogen peroxide promotes angiogenesis, growth of
fibroblasts and the mobilization and activation of epithelial cells.46,48,54 Debridement is
also stimulated by the osmotic effect and the moist environment. When necrotic tissue is
present, surgical debridement is preferred before application of honey.
When deciding to use honey as treatment for wounds, two facts can influence the choice
of a product. The first is the sterility of the product. Many products on the market are not
sterile and non-sterile honey can contain Clostridium botulinum spores which can cause
botulism. The sterilization of honey has to be done with gamma-irradiation because heat
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will destroy the enzymes and consequently the antimicrobial activity of honey. The other
issue is the type of honey because their effectiveness differs greatly, dependent on the
bees and flowers used.49 Honeys derived form particular areas in Australia and New
Zealand are probably the most effective, among which Manuka honey.44
Honey is one of the only topical medications for wound management that does not seem
to be toxic for cells needed for wound healing. It is also non-adherent to the wound
surface which increases patient comfort. An occlusive or absorbent secondary dressing is
needed to prevent leakage of the honey. Most manufacturers and researchers advise a
daily change of dressings until the amount of exudate decreases as a result of the antiinflammatory action, from then on dressing changes two times a week will be enough.
The use of honey is indicated for many wounds because of its numerous functions, but
especially in infected wounds with bacteria resistant to antibiotics and in chronic nonhealing wounds.13,49 A known disadvantage of the use of honey in humans is that its
application on open wounds can be very painful. The veterinarian will have to take this
into account and always assure the use of proper pain management.
3.5.3. Sugar
Sugar can be used in wound management because of its functioning by a few different
mechanisms. At first it gives an antimicrobial effect by the same mechanism of
hyperosmolarity as honey. Fluids will be distracted by the sugar and the fluid amount
available for the micro-organisms will reduce, which makes the circumstances to survive
and grow harder for them.46 A disadvantage of sugar is that this effect will be lost when
dilution of the sugar takes place because of distracted fluids.46 The consequence of this
includes more regular dressing changes. Therefore honey is preferred, because even when
diluted the antimicrobial effect of hydrogen peroxide is still present. The attraction of
fluids away from the wound also decreases local edema.45
Sugar also provides nutrients, has a deodorizing action and stimulates granulation and
epithelialization.45 There are no known adverse affects of sugar on wound healing, but
from human medicine it is known that the application of sugar on a wound can be
painful.45 Sugar treatment should be replaced by a treatment with a (semi-)occlusive
dressing like hydrogel or hydrocolloid after the formation of a healthy granulation
bed.38,45
3.5.4. Tripeptide-copper complex
Tripeptide-copper complex (TCC) is a hydrogel which delivers copper to the wound.38
TCC works as a chemoattractant for mast cells, monocytes and macrophages.68 It
influences the inflammation, debridement and proliferation phase of healing and can be
applicated during all these phases.68 The gel can be applied to the wound daily when
covering it with a non-adherent dressing or four times a day when the wound is not
covered.38
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3.5.5. Acemannan
Acemannan is a component of aloe vera and is available as a hydrogel or a foam.38 As
topical wound medication it acts as a growth factor to stimulate macrophages.38,68
Application is indicated from the inflammatory phase until the end of the proliferation
phase, but it is most effective during the inflammatory phase.38,68 It can be used in many
types of wounds, inlcluding in chronic, non-healing wounds.
3.5.6. Growth factors (PDGF)
The interest in the use of growth factors for wound healing has grown during the last few
years, especially for the treatment of chronic non-healing wounds. Because of the great
number of identified growth factors, their complicated relations and the fact that every
phase of wound healing has its own growth factors, it is difficult to decide which factor is
needed at a certain time in wound healing.
Platelets seem to play an important role in wound healing by releasing growth factors like
TGF-α, TGF-β, platelet-derived growth factor (PDGF), epidermal growth factor,
fibroblast growth factor and insulin-like growth factor. Especially PDGF seems to be
important because of its influence on attracting macrophages and PMNs.56 PDGF also
stimulates wound contraction.66 Other important cells which produce growth factors as
well as cytokines important to wound healing are macrophages and lymphocytes.56
PDGF is commercially available now under the name becaplermin gel (Regranex gel,
Johnson & Johnson, New Brunswick, New Jersey).27 In human medicine a treatment with
autologous platelet-rich plasma is also being used in wounds that do not respond to
standard wound management.26 During this treatment activated platelets release growth
factors needed for wound healing.26
3.6. Wound reconstruction and transplantation
Wound reconstruction or transplantations like skin grafts or flaps can be considered as
method of wound closure when dealing with large wounds or wounds in areas where
normal and uncomplicated wound healing is not expected. The use of these techniques
will be explained in the other chapters of this book and will not be discussed further in
this paragraph. The only things important to mention in this chapter are the dressings
which are preferred to use after transplantation. These dressings should be non-adherent
to the transplant and absorbent and should be applied in a way to immobilize the
transplant area as much as possible.57
3.7. Omental flaps
In non-healing wounds in areas with high-motion, the use of omentum is an option for
treatment. The places on the body where these wounds frequently occur are the axillary
and inguinal regions. Omentum has a rich blood supply and helps to reduce wound
edema by lymphatic drainage, stimulates angiogenesis and functions as a source of
monocytes and macrophages to deliver growth factors.38
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3.8. Advanced techniques
In human medicine, new dressings, new topical agents as well as new techniques have
been developed in the last few decades and some of them are used frequently these days.
Their use is often especially important in the treatment of chronic wounds, which do not
heal with the current dressings and topical agents. Good results with these techniques in
human practice will possibly lead to the veterinary use of them in the future and some of
them have already been used in a few veterinary clinical cases. In this paragraph only a
few techniques will be discussed like TNP, LLLT, HBOT and ultrasound. Other, not
further mentioned techniques are for example hydrotherapy and electrostimulation.
Topical negative pressure
Topical negative pressure (TNP) is a therapy which uses sub-atmospheric pressure to
promote or assist wound healing. It is mainly used in chronic wounds that are difficult to
heal with the purpose to drain excess fluid. Other names for TNP are sub-atmospheric
pressure therapy and vacuum-assisted therapy. Besides the common use in human
medicine, TNP is already being used in some veterinary clinics, among others in the
USA.
A foam or gauze dressing is placed on the wound and connected by a tube to the vacuum
pump. This is covered by an adhesive film sheet to provide an airtight seal. The negative
pressure can be applied constantly or intermittently; it is recommended to use a negative
pressure about -125 mmHg because that gave the best results in scientific research.52
TNP has multiple proposed mechanisms of action. The negative pressure will lead to the
removal of excess fluid, including bacteria.76,77 By this action it reduces the chance of
infection and the distance for intercellular diffusion will be diminished, which improves
wound oxygenation.29,76,77 On top of these actions there are mechanical forces to the
surrounding tissues and it is proposed to stimulate the local blood flow in the wound bed
and the formulation of granulation tissue and epithelialization.21,25,76,77
Although a great body of articles have been published about TNP in human literature, the
general conclusion in systematic reviews is that there is a lack of high-level evidence to
support the use of TNP in the treatment of wounds.21,25,76,77 There are some signs though
that TNP has advantages over the moist gauze dressings and more research is needed.21,25
Low-level laser therapy
Low-level laser therapy (LLLT) is a part of phototherapy, which uses light for therapeutic
purposes. One of these therapeutic purposes is wound healing. LLLT is also known under
the name cold lasers. The mechanism by which LLLT stimulates wound healing is not
exactly known. Some authors propose that it works by increasing the local amount of
circulating nitrogen oxide which leads to vasodilatation, but further research on this
subject is needed.30
Laser light stimulates wound healing through many ways like stimulation of fibroblast
development, acceleration of angiogenesis, causing vasodilatation and possibly
improving lymphatic drainage.47 This leads to an increase in granulation tissue formation,
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an increase in the formation of new capillaries and possibly a decrease in swelling.47
Statistical meta-analysis have been performed to determine the treatment effects of LLLT
and it has been concluded that the overall effect was highly significant.20,82 Besides the
stimulation of collagen formation, there also are improvements in the time needed for
wound closure, the strength of the wound, the rate of healing, number and rate of
degranulation of mast cells and flap survival.20,82 Because of these numerous effects of
LLLT it stimulates wound healing in the inflammatory, proliferation and maturation
phase.20,82 The authors of one meta-analysis also concluded from human research projects
that the use of LLLT led to a reduction in pain.20
Nowadays phototherapy is not only used in humans, but also in horses.78 Researches into
LLLT are performed on humans as well as on animals. The outcomes seem to be more
effective in animals.82 A possible explanation for this is that much of the research is
performed on rodents and their skin is looser than the human skin.82 The literature on this
subject is sometimes hard to compare because of differences in for example type of laser,
energy density, wavelength and duration of irradiation.
Hyperbaric oxygen therapy
To enhance healing of chronic wounds, hyperbaric oxygen therapy (HBOT) is being used
in human medicine. This technique is used because hypoxia is a common cause for nonhealing, chronic wounds.38 Patients are placed in a compression chamber and breathe
100% oxygen.40 The pressure is typically between 2.0 and 2.5 atmospheres absolute
(ATA) for periods between 1 and 2 hours once or twice daily.40 It is a therapy that should
be used as an adjunctive to standard wound management and should not replace it.35
HBOT has been suggested to improve wound healing by increasing the oxygen supply to
the wound. By breathing 100% oxygen under a pressure of 2.0-2.5 ATA the hemoglobin
molecules in the bloodstream become saturated and more oxygen can be dissolved into
the blood. To achieve local results at the wound, the blood supply to the wound has to be
intact, at least in part.35 The higher oxygen tension in blood plasma results in
upregulation of growth factors, down regulation of inflammatory cytokines, increased
fibroblast activation, angiogenesis, antibacterial affects by stimulation of leukocytes and
enhanced antimicrobial action.35,58 Beside the delivery of oxygen, the delivery of
nutrients will also be improved.
Research into HBOT in human medicine is still limited and the main conclusion is that
the application can be justified when chronic wounds do not respond to other therapies.
There are not many complications reported, but you have to be careful when delivering
oxygen in high doses because of its toxicity to normally perfused tissues, especially the
lungs and brain.40,58
Ultrasound
Ultrasound is a very common diagnostic tool nowadays, but it is also used for therapeutic
purposes of which wound healing is one. The main difference is that the frequency for
therapeutic purposes varies between 1 and 3,3 MHz, whereas the frequency for diagnostic
purposes lies between 5-10 MHz.27,78 The effects of ultrasound for therapeutic purposes
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can be divided into thermal and non-thermal, but the overall main effects are reduction of
the inflammatory phase and promotion of (mainly the first part) of the proliferative
phase.18,29,70,73,84
Much in vitro research have been performed under laboratory settings and ultrasound
seems to stimulate cellular recruitment, collagen synthesis, angiogenesis, wound
contraction, fibroblasts and macrophages, and fibrinolysis.18,29,84 Beside these effects, the
tensile strength of the collagen increased after ultrasound treatment.29,70 The clinical
evidence is unfortunately not completely convincing and further research needs to be
performed.29
3.9. Wound management in burns
Burns are a special type of wound and need special consideration in order to choose the
right treatment. At first it is important to assess the wound and determine the degree of
the burn72:
- First degree: epidermal burn. There is only redness and slight edema, it is not a
real wound.
- Second degree: dermal burn. Second degree burns can be divided into superficial
and deep wounds, depending on the amount of dermis that is damaged.
- Third degree: subdermal burn. The dermis is fully lost up to the subcutis and with
this the potential for regeneration is also lost.
- Fourth degree and deeper burns: not only the skin is damaged, but also underlying
structures.
Because first degree burns are not seen as wounds, the treatment will not be discussed
here. Second degree burns can be treated with an occlusive dressing like hydrocolloids,
foams, hydrofibers, polyurethane films and/or with an ointment.80 Ointments often used
in the treatment of burns are silver sulphadiazine (SSD), povidone iodine, fucidin and
nitrofurazone.80
Burns in human patients are often treated with topical SSD because of the major risk of
infection. Dealing with methicillin resistant Staphylococcus aureus (MRSA), the
infection can often well be treated with fucidin or nitrofurazone if resistance against SSD
had been determined.80 The benefits of preventing or treating infection then certainly
weigh out against the possible negative effects of these topical medications on wound
healing. Decreasing the amount of bacteria in the wound is not only needed for
undisturbed wound healing, but is also important to prevent systemic infection which can
cause the death of the patient.
With third degree burns the skin has lost its regenerative potential and skin
transplantation will be needed.80 Also with wounds of fourth degree or deeper, surgical
intervention is necessary.80
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4. Protocol for wound management in companion animals
In the previous paragraphs, the different options for wound management were described.
When making a choice between the numerous methods and products, many aspects
contribute to the final decision like effectiveness, costs and patient benefit. To use all
these possibilities in a good way and treat a wound with the best option, always use a
systemic approach. One approach is to follow the protocol written down in Table 4.
4.1. Protocol
Protocol for wound management
1. Use a clean room and aseptic technique.
2. Obtain a complete medical history of the patient.
3. Obtain information about the cause of wounding and the time the wound exists.
4. Make a complete assessment of the wound.
5. Debride necrotic tissue.
6. Remove contamination.
7. Choose the appropriate method of closure.
8. Choose the appropriate dressing.
9. Make regular assessments of wound healing to monitor the progression of wound healing.
Extra step for chronic or difficult to heal wounds:
10. When dealing with chronic wounds not responding to normal wound management,
consider using an advanced technique.
Table 4. Protocol for wound management in companion animals.
Step 1: Use a clean room and aseptic technique.
When treating a wound, you want to prevent further contamination and infection.
Therefore always start with a clean room and table. If multiple patients have to be treated,
begin with the patients with the cleanest wounds and disinfect the room after each
patient. This helps to keep the level of contamination of a room as low as possible.
Other preventive measures are to wear (sterile) gloves, hair nets, face masks and clean
coats. The instruments should be sterilized and the wound covered with sterile gauzes
while clipping the surrounding hair and debriding necrotic tissue.
Step 2: Obtain a complete medical history of the patient.
The medical situation of the patient can be important in selecting a treatment. Some
examples of conditions that influence wound healing negatively are protein deficiency,
anemia, inadequate blood supply to the wound area, uremia and vitamin A or C
deficiency.33 Also the use of corticosteroids or non-steroidal anti-inflammatory drugs
(NSAIDs) and the presence of corpora aliena can delay wound healing.33 This step is
even more important when dealing with chronic wounds, because one of these or other
factors can be the underlying factor preventing wound healing.
Step 3: Obtain information about the cause wounding and the time the wound exists.
The information about the cause of wounding and the time the wound exists, can be
important to assess the level of contamination and the chance of infection as
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complication. The information influences the choice of a treatment. If a traumatic wound
for example exists longer than 4 to 6 hours, the ‘golden’ period, a contaminated wound
has become an infected wound.
Step 4: Make a complete assessment of the wound.
The assessment of a wound provides information about the characteristics of a wound.
This step is important because a wound cannot be treated properly when the main
characteristics of the wound are unknown.
The following characteristics have to be assessed:
- Type of the wound
- Size and depth of the wound
- Tension of the surrounding skin
- Phase of wound healing
- Level of contamination
- Signs of inflammation: calor, rubor, dolor, tumor and functio laesa.
- Level of exudation
- Presence of necrotic tissue
Step 5: Debride necrotic tissue.
Debridement of necrotic tissue has multiple goals. By debriding necrotic tissue the
second phase of wound healing will be accelerated and total healing time decreased. On
top of this the chance of infection will diminish as well as the chance of bad odors. The
different methods for debridement are discussed in Paragraph 3.1. of this Chapter. The
surgical or autolytic method is for many wounds an appropriate way of debridement.
Autolytic debridement is very useful when the patient’s condition is too bad for
anesthesia or when there is no clear demarcation line, because it is a very selective
method for debridement. Another option when there is no clear demarcation line is daily
surgical debridement in different stages.
Step 6: Remove contamination.
The removal of contamination will reduce the chance of infection and creates better
circumstances for wound healing. With minimal contamination it is recommended to use
physiologic solution like sterilized saline or Ringers lactate for pressured lavage. Mild
antiseptics like glycerol, chlorhexidine, Dakin’s or povidone iodine solutions are
recommended for heavier contaminated wounds, but consider their mildly toxic effects.
While irrigating, prevent the spreading of bacteria under the wound edges or into the
wound area.
Step 7: Choose the appropriate method of closure.
The different ways of wound closure are described in Paragraph 3.2. of this Chapter. The
first question is whether a wound should be closed. If a wound can be closed
appropriately by means of primary closure, this is preferable; but in case of infections or
if there still is necrotic tissue present, it is recommended to postpone closing the wound
and choose for delayed primary or secondary closure or healing by second intention.
When the wound area is too large to be closed by suturing and also is not expected to heal
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completely by second intention or when there is a risk of wound contracture, consider the
use of skin grafts or flaps.
Step 8: Choose the appropriate dressing.
In Paragraph 3.3. and 3.4. of this Chapter, the different dressings and topical medications
have been discussed. The number of products is quite variable and will probably only
grow in the next few years.
From human as well as veterinary research, it became clear that many of the topical
agents do more harm than good to wound healing. This is because many of these topical
agents are stimulating one phase of the wound healing, but impede other phases. This
means that they can only be used in a very limited period of wound healing. Probably the
only topical agent with no known harmful effects on wound healing at this moment is
honey. That explains the great interest in honey during the last few years.
To help making the right decision, Table 5 on the following page can be used to select an
appropriate dressing. In this scheme many of the modern products are advised to be used
because of their positive cost-effectiveness and patient benefits, explained in the next
Paragraphs 4.2. and 4.3.
Step 9: Make regular assessments of wound healing to monitor the progression of wound
healing.
Regular assessments of the wound after initial treatment are important to monitor the
progression of wound healing. If offers the opportunity to change the treatment by
progression through the four phases of wound healing or when a wound doesn’t respond
well to the initiated treatment.
Assessments of wounds are preferably made with a non-invasive and objective method.
A B-scan using high frequency ultrasound can be used, but also digital photography can
be very useful.17,19 A B-scan also gives information on the internal structures of the
wound.17 Another option is laser Doppler image scanning (LDIS), which gives
information about the tissue perfusion of the healing wound and planimetry, which
determines the percentage of epithelialization, contraction and total wound healing.67
Extra step for chronic or difficult to heal wounds:
Step 10: When dealing with chronic wounds not responding to normal wound
management, consider using an advanced technique.
The advanced techniques discussed in Paragraph 3.6. of this Chapter are not (yet)
commonly used in veterinary practice. Because some of them result in good responses in
human medicine, they are worth considering in the treatment of chronic wounds. Besides
the fact of improved wound healing, it also will reduce the costs associated with
treatment. The long-term treatment of chronic wounds involves numerous visits to the
veterinarian and a large amount of material and is associated with progressive expenses.
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Wound
color
Black
Wound type
Necrotic wound
Purpose of
treatment
Remove necrotic
tissue
Exudate
++
+
-
Yellow
Exudating wound
Wound cleaning and
removing debris
++
+
Green
Infected wound
Wound cleaning and
clear infection
++
+
-
Red or
pink
Granulating or
epithelializating
wound
Wound protection
and providing a moist
environment to
stimulate healing
++
+
-
Recommended dressing
materials
- Saline gauze†
- Alginate
- Honey dressing*
- Silver dressing*
- Alginate
- Saline gauze†
- Hydrogel
- Hydrocolloïd
- Honey dressing
- Silver dressing
In absence of sings of infection,
the wound can heal under the
scab.
- Alginate
- Hydrofiber
- Foam
- Saline gauze†
- Alginate
- Hydrofiber
- Foam
- Hydrogel*
- Hydrocolloïd
- Saline gauze†
- Antimicrobial gauze dressing†
- Silver dressing†
- Honey dressing†
- Antimicrobial gauze dressing†
- Silver dressing†
- Honey dressing†
- Antimicrobial gauze dressing
- Silver dressing
- Honey dressing
- Hydrofiber
- Foam
- Hydrogel*
- Hydrocolloïd*
- Hydrofiber
- Foam
- Hydrogel#
Table 5. ++ = wet, + = moist, - = dry; * select one with good absorptive properties or use an absorptive
secondary dressing to reduce the number of dressing changes;# rehydration of the wound; † cover with a
secondary absorptive dressing.
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Because of limited research in man and the lack of knowledge of the use of these
techniques in veterinary patients, it is not possible to make recommendations concerning
these techniques at this moment. The use will depend on the patient, the wound and the
presence of equipment.
4.2. Cost-effectiveness
Because wounds are very common in veterinary practice, many costs are associated with
treatment of these wounds. Large wounds as well as chronic wounds often require special
attention and this may lead to increased costs. Costs can be minimized when using the
right wound management protocol.
Dressing materials
When considering the costs of wound management and dividing them into different
groups, the main costs are associated with dressing materials and personnel. To reduce
the costs it is most advantageous to reduce the costs in both of these groups. Reducing the
costs for dressing materials does not mean that the cheapest dressings have to be chosen
because more factors play a role of which the most important ones are:
- Duration of total treatment
- Number and duration of consults
- Time between changing dressing
- Number of dressing changes
- Costs of the dressings
- Additional material costs (gloves, lavage fluid, tape etc.)
The duration of the total treatment can be reduced by stimulating wound healing with
particular dressings, topical medications or advanced techniques, so that the wound will
heal more quickly. Reducing the number of consults can be achieved by choosing
dressings which need less frequent changes and by reducing the duration of the total
treatment.
Factors contributing to the total costs of the dressings are the manufacturer’s price and
the number of dressings used during the whole period of wound healing. That is one of
the reasons why a dressing which seems to be more expensive because of a higher
manufacturer’s price, can reduce the total costs of wound healing. It can diminish the
number of dressings needed, because they can stay on the wound longer and because they
reduce the total time of wound healing. On top of this the costs of personnel can often be
reduced at the same time. Figure 7 will show how the choice of the dressing and its
effectiveness will influence the total costs of wound treatment.
Most factors are related to each other, making the decision of what therapy will be most
cost-effective, at the start of treating a wound, difficult. In human medicine, limited
research has been performed to study the cost-effectiveness relationship between some
different dressings, considering many of the factors mentioned above.
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Total costs of wound
treatment
Cost dressing
Costs additional
materials
Personnel costs
Number of dressing
changes
Time between
dressing changes
Figure 7. Explanation costeffectiveness relationship in
wound
management.
Selection of a particular
type of dressing influences
the time between dressing
changes and the total
duration of treatment. That
will further determine the
number of dressing changes
and thus the total costs of
the treatment.
Total duration
treatment
Type of dressing
Human research
Many of the human research projects compared the traditional saline-gauzes with more
modern, moisture-retentive dressings
like
hydrogels,
hydrocolloids
and
4,9,28,37,53,55,63,71,79,83
foams.
The overall conclusion was that the moisture-retentive
dressings have a better cost-effectiveness relationship and that the total costs will be
lower. One study comparing different hydrocolloid dressings with traditional gauze
dressings also observed relevant differences in costs between treatments with two
hydrocolloid dressings.28
Additionally to the conclusion that the overall costs were lower when moisture-retentive
dressings were used, the researchers described that the total dressing costs were the same
or higher for the moisture-retentive dressings. But the main difference, however, was
caused by personnel costs, which were much higher for the traditional saline-gauze
dressing.4,28,53,83 This was caused by the higher number of dressing changes and the
longer period it took for the wounds to heal.
Some of these research projects also took in consideration the time of total wound
healing.9,53,63,83 Overall this time was shorter for the modern moisture-retentive dressings
compared to the traditional saline gauzes, but this was often not significant.
Conclusion
It is clear that when we consider the cost-effectiveness of a particular dressing, we should
not just look at the cost of the dressing itself, but we will also have to consider the other
factors mentioned earlier.
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Because data about the cost-effectiveness of particular dressings used in companion
animals are very limited, it is hard to extrapolate the human results to the veterinary
medicine. Studies in man are difficult to translate to animals because of differences in
anatomy, physiology and behaviour between the two species. Time between bandage
changes can be influenced by the fact that animals are more eager to remove bandages by
themselves than people and it is harder to keep the bandages clean. A clear anatomical
difference between humans and loose skinned animals is the presence of subcutaneous
panniculus carnosus muscle, which contributes to wound healing. Another point that has
to be considered is the personnel costs and thus the difference in wages between human
nurses and veterinarians. Most veterinarians will do the bandage changes themselves
instead of their assistants.
A publication describing the potential of the human moisture-retentive dressings for the
veterinary practice described good applicability for many of these dressings in animals.75
One research project concluded that veterinary surgeons who used the interactive,
moisture-retentive dressings determined them to be cost-effective.10
Complications in wound healing are more common in horses than in companion animals.
These modern dressings are therefore also used in horses with upcoming interest. The
conclusion from an equine expert on wound healing is that these modern moistureretentive dressings certainly are cost-effective on that species.81 The number of dressing
changes and total healing time are reduced and there is a better cosmetic outcome.
It is also expected that there will be differences in total costs between treatments with
traditional saline-gauze dressings and modern moisture-retentive dressings in companion
animals. The results in equine medicine and the difference in human patients between
these two groups of dressings lead to this conclusion.9,28,53,83 Veterinary research on the
effect of these dressings on wound healing in companion animals is mandatory.
4.3. Patient and owner benefit
When treating patients with wounds, not only the costs and effectiveness are important,
but also animal and owner comfort play an important role. For the animal one should
consider the discomfort accompanying dressing changes, for the owner one should
consider the smell of the wound, leakage of exudate and the total time of treatment with
the number of visits to the veterinarian should be taken in consideration.
The pain accompanying dressing changes can be reduced by dressings that create and
keep a moist environment and that have the property to be not-adherent to the wound
surface, like hydrocolloids and hydrogels. These dressings are less painful in human
research and the expectation is that this will be also the case for animals.79
To reduce the smell of a wound, which can be very unpleasant for the owner, dressings
with activated charcoal and / or silver can be used. Leakage of exudate is not only an
unpleasant sight, it can also contaminate the surroundings. Occlusive and / or absorbent
dressings together with regular dressing changes will avoid leakage. Because of busy
schedules, people, besides the cost, prefer to spend as little time as possible visiting the
Wound management: A new protocol for companion animals.
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veterinarian. To meet their wishes a dressing can be chosen that can stay on the wound
for a few days and which stimulates wound healing optimally to reduce total healing
time. The increased costs of the bandage material are so compensated by fewer visits.
Many of the above summarized benefits for the patient and owner can be achieved by
applying modern dressings for moist wound healing. Because these dressings are
probably also more cost-effective, they will offer in many situations an appropriate
treatment for the healing of wounds in our companion animals.
5. Conclusion / summary
The options for wound management are so numerous that it is possible to choose an
individual treatment for every wound and every phase of wound healing. If optimal
wound management is desired, every wound should be assessed individually and the
treatment should be adapted regularly to the information that is gained from the wound
evaluation.
In conclusion, the modern moisture-retentive dressings have many benefits compared to
the traditional saline-gauzes. They stimulate wound healing more effectively, are more
cost-effective in many situations and also have many benefits for the patient. But this
does not mean that they should be used on every wound. After following the ten-step
protocol a well-informed choice can be made between the available dressings.
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53. Ohlsson P., Larsson K., Lindholm C., Möller M. A cost-effectiveness study of leg ulcer
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7. Addendum
An in vitro study into the susceptibility of methicillin-resistant
Staphylococcus intermedius to several topical antiseptics.
Summary
Because of the problems with resistance of MRSI against many antibiotics, infections
with MRSI can be difficult to treat. When dealing with infections, antibiotics are not the
only way of treatment, antiseptics can be used too. In this research the susceptibility of
MRSI to chlorhexidine digluconate 0,1%, glycerol 65%, natriumhypochlorite 0,1%,
natriumhypochlorite 0,1% in glycerol 65%, a commercial honey product (Dermiel®,
AST Farma) and vinegar (Albert Heijn own brand) was tested in vitro. Chlorhexidine
digluconate 0,1% and vinegar seemed to be most effective against MRSI in vitro.
Introduction
There is a rising interest in methicillin-resistant Staphylococcus intermedius (MRSI) as
the number of wound infections in companion animals with this pathogen is increasing.
S. intermedius belongs to the commensal microflora of the skin of dogs, but can be a
pathogen too. S. intermedius can cause skin and wound infections. Amongst
staphylococci, the emergence and dissemination of antimicrobial resistance is an
important problem in veterinary and human medicine.5 Wound healing is disturbed when
there is a wound infection and should therefore be treated properly.
Because of the resistance of MRSI against many antibiotics, the use of antiseptics can be
an alternative to antimicrobial therapy in wound infections. Resistance against antiseptics
has also been noted, but in a much smaller degree than against antibiotics. In
staphylococci, isolated from Dutch animals, resistance to ampicillin, tetracycline,
erythromycin and lincomycin is common, whereas resistance to gentamicin, enrofloxacin,
trimethoprim-sulfamethoxazole, cephalexine and amoxicillin with clavulanic acid is still
very uncommon.4 Another research project also found frequent resistance of
Staphylococcus intermedius against ampicillin, penicillin G and tetracycline.3 The
prevalence of methicillin resistance among Staphylococcus intermedius shows a large
variation in different research projects, from 0% up to 41%.1
This study is being performed to investigate the susceptibility of MRSI to the antiseptics
glycerol 65%, chlorhexidine digluconate 0,1%, sodium hypochlorite 0,1%, sodium
hypochlorite 0,1% in glycerol 65% and a commercial honey product (Dermiel®, AST
Farma) in vitro in order to provide guidance to the best treatment options in wound
infections caused by MRSI. The susceptibility of MRSI to vinegar (Albert Heijn own
brand) was tested in vitro in order to provide guidance to treat otitis externa caused by a
double infection with Pseudomonas spp. and MRSI.
Materials and methods
The agar dilution method was used to determine the susceptibility of MRSI to the
antiseptics in vitro.
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* Antiseptics
Six antiseptics are used:
1. Chlorhexidine digluconate 0,1% (CHD)
2. Glycerol 65% (GLY)
3. Sodium hypochlorite 0,1% (NaOCL)
4. Sodium hypochlorite 0,1% solution in glycerol 65% (NaOCL-GLY)
5. Commercial honey product (Dermiel®, AST Farma) (HON)
6. Vinegar (Albert Heijn) (VIN)
* Dilution range
Of every antiseptic, a dilution range with four dilutions of 1:2 was made in sterile
physiologic saline. After adding the antiseptic dilutions to the agar, the antiseptic was
diluted 1:2 again. With the exception of the glycerol 65% and the commercial honey
product (Dermiel®, AST Farma), the plates with the highest concentrations of the
antiseptics were therefore 1:2 diluted compared to the original solution. Because of the
viscosity of the glycerol 65% and the commercial honey product (Dermiel®, AST Farma)
these products had to be diluted further and the highest concentrations of these antiseptics
were 1:4 diluted compared to the original product.
* Blood agar plates
60 gram Difco Heart Infusion Agar was mixed with 750 ml sterile water. To dilute the
entire quantity of agar in water, this mixture was warmed to 100 °C. After this the
solution was cooled down again to 55-60 °C in a water bath and 75 ml defibrinated sheep
blood (Biotrading) was added. 10 ml agar including water and sheep blood and 10 ml
antiseptic or dilution of the antiseptic were mixed and poured into a plate. The medium
did solidify under room temperatures. Every concentration was made in duplo.
* Inoculation of bacteria
A culture of MRSI was suspended in a sterile physiologic saline solution till a density of
OD600nm=0.886 was reached. 10µl of this suspension was inoculated on every plate.
* Incubation period
The incubation period for MRSI was 24h at 37°C. After this period the plates were
assessed.
* Assessment of the bacterial cultures
The growth of bacteria was assessed as complete, partly or no inhibition of growth. The
Minimal Inhibitory Concentration (MIC) is the lowest concentration where no growth is
visible.
Results
The results of the bacterial cultures are presented in Table 1. Chlorhexidine digluconate
0,1% is the only antiseptic which inhibited bacterial growth completely with every
dilution used in this study. The MIC-value for chlorhexidine digluconate 0,1% therefore
is less than 0,003%.
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Glycerol 65% and the commercial honey product (Dermiel®, AST Farma) could not be
added to the agar in their original concentration in which they are used as topical
medications on wounds. None of the dilutions of these two antiseptics inhibited bacterial
growth of MRSI, except the first dilution of glycerol (1:4) which partly inhibited the
bacterial growth. Sodium hypochlorite 0,1% did not inhibit bacterial growth of MRSI in
any of the concentrations. Only the first dilution of sodium hypochlorite 0,1% in 65%
glycerol prevented bacterial growth of MRSI and the second dilution partly inhibited
bacterial growth of MRSI. After further dilution, the growth of MRSI was no longer
inhibited.
Dilution
CHD
GLY
NaOCL
NaOCLGLY
-
1:2
-
Not
performed
+
1:4
1:8
1:16
1:32
1:64
-
±
+
+
+
+
+
+
+
+
±
+
+
+
Not
performed
Not
performed
Not
performed
HON
VIN
Not
performed
-
+
+
+
+
+
±
Not
performed
Table 1: Bacterial growth on the blood agar plates with different antiseptics in several dilutions.
The results are divided into undisturbed growth (+), partly inhibited growth (±) or fully inhibited
growth (-).
Discussion
Chlorhexidine digluconate 0,1% seems to be very effective against MRSI, which offers
good opportunities for its use against wound infections caused by this pathogen. In 1992
a research project was performed to investigate the antibacterial activity of different
chlorhexidine preparations against Staphylococcus intermedius.2 The results from this
research project were also very positive; all 0.05% chlorhexidine preparations provided
100% bacterial kill.2 An advantage of the use of chlorhexidine in vivo is its persistent
antibacterial effect, which lasts for a few hours.
In this research project, sodium hypochlorite 0,1% did not show any activity against the
bacterial growth of MRSI. An explanation for this result is that the chlorine could have
been lost partly or completely before inoculation of the MRSI. This antiseptic has to be
stored in an environment with low temperatures of 4 to 7 °C to keep its effectiveness. At
room temperatures, the chlorine will not be kept in the solution and, therefore, the
antiseptic loses its antimicrobial activity. Because the antiseptic had to be mixed with the
agar at 55 to 60 °C and after this had to be kept at room temperatures for about 16 hours
till solidification of the agar occurred, much of the chlorine may have disappeared out of
the solution. An other explanation is that S. intermedius isolates resistant to methicillin
are also resistant to antiseptics as chlorine. Sodium hypochlorite 0,1% is possibly more
effective in vivo.
Wound management: A new protocol for companion animals.
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The combination product of sodium hypochlorite 0,1% in glycerol 65% did not show
much more activity against MRSI. Only the first dilution of this antiseptic provided
antibacterial activity against MRSI. This is probably due to the concentration of glycerol,
because the sodium hypochlorite 0,1% solution did not show any antimicrobial activity at
the same concentration.
The antimicrobial activity of the commercial honey product is possibly less in this in
vitro research project than in an in vivo situation. One part of the antimicrobial activity of
honey depends on the high osmolarity. The osmolarity is lowered when making the
dilutions. Another part of the antimicrobial activity depends on the formation of
hydrogen peroxide. When honey is diluted, the enzyme glucose-oxidase is activated and
hydrogen peroxide is formed. Thus, the hydrogen peroxide had formed already while
making the dilution range and was possibly no longer effective when the bacteria were
inoculated.
The commercial honey product (Dermiel®, AST Farma) appeared not to be very
appropriate to process into the blood agar plates. No proper dilutions in physiologic
saline could be made because of the presence of ethereal oils. These oils did not mix well
with the agar and stayed on top of the plate (Photo 1).
Photo 1. Blood agar plate with honey. The irregular
surface is due to the oils which did not mix with the agar.
Vinegar seems to be very effective against MRSI. For complete inhibition of growth of
MRSI, it should not be diluted further than 1:16. When dealing with otitis externa caused
by a double infection with Pseudomonas spp. and MRSI, the vinegar should also be
effective against Pseudomonas spp. to treat this condition. The susceptibility of
Pseudomonas spp. to vinegar is not investigated during this study.
Conclusion
The results from this in vitro study showed chlorhexidine digluconate 0,1% to be most
effective against MRSI. Vinegar was very effective too, but this is only for use in specific
applications. With the exception of the first dilution of sodium hypochlorite 0,1% in
glycerol 65%; glycerol 65%, sodium hypochlorite 0,1%, sodium hypochlorite 0,1% in
glycerol 65% and the commercial honey product appeared to be not very effective under
these conditions.
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