Wound Infection: Contributing Factors and Selected Techniques for

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IN-DEPTH:
CURRENT CONCEPTS IN WOUND MANAGEMENT
Wound Infection: Contributing Factors and
Selected Techniques for Prevention
Ted S. Stashak, DVM, MS, Diplomate ACVS
Infection is a major factor in delayed wound healing and an important cause of dehiscence after
wound closure. Knowledge of the contributing factors to development of wound infections will
provide the clinician with an improved ability to prevent its occurrence. Author’s address: 965 Los
Alamos Road, Santa Rosa, CA 95409; e-mail: tstashak@sbcglobal.net. © 2006 AAEP.
1.
Introduction
Wound infection is defined as the presence of replicating microorganisms within a wound with subsequent
host injury.1 Infection must be distinguished from
wound contamination (microorganisms are not replicating) and wound colonization (replicating microorganisms are present but do not cause host injury).
Interestingly, some recent studies of dogs suggest that
the organisms that infect a wound may be a subset of
those organisms that colonize the wound site.2,3
Wound infection is considered a major factor in
delayed wound healing, reduced tissue-tensile
strength gain, and dehiscence after wound closure.4 –7 Potential pathogenic bacteria adhere
and/or bind to extracellular matrix proteins (e.g.,
fibronectin and laminin) of exposed tissue, which
may have a direct effect on wound healing. By
binding fibronectin, this protein is not available for
promoting tissue adherence.8 Additionally, bacteria that produce cytotoxic exotoxins (e.g., Clostridium spp, Strep. pyogenes, and Staph. aureus) cause
more tissue damage, creating a microenvironment
conducive to their survival. Those with thick
capsules (e.g., Strep. pyogenes, Staph. aureus,
and Klebsiella pneumoniae) are more resistant to
NOTES
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2006 Ⲑ Vol. 52 Ⲑ AAEP PROCEEDINGS
phagocytosis by leukocytes. During the process
of bacterial degradation, liberated endotoxins can
activate coagulation pathways; this may cause
thrombosis of the microvasculature, systemic organ
or immune dysfunction, and macrophage activation
that releases more inflammatory mediators.9
Circulatory alterations decrease the efficiency of glucose and oxygen delivery; this creates an environment
where the host’s main non-specific defense, the polymorphonuclear leukocyte, is deprived of the materials
necessary for optimum bacterial killing.10,11
Whether infection develops depends on many factors: (1) The dose of microorganisms (we have the
most influence over this); (2) Wound microenvironment/degree of contamination; (3) The virulence and
pathogenicity of the microorganism; (4) Functional
capacity of the host; and (5) Mechanism of
injury.9,12,13
Generally, when bacterial numbers exceed 106 organisms per gram of tissue or per milliliter of exudate in an open wound, the wound becomes
infected.14 A significant increase in failure of delayed wound closure because of infection is seen
when the wound bed contains ⬎105 organisms/g tissue.15 Contaminated wounds with lesser concen-
IN-DEPTH:
CURRENT CONCEPTS IN WOUND MANAGEMENT
trations of bacteria may become infected when
foreign bodies are present (e.g., sutures, glove powder, etc.), necrotic tissue is left in the wound, a
hematoma develops, local tissue defenses are impaired (e.g., burn patients or immune-suppressed
patients), and the vascular supply is altered.9,16,17
Dirty wounds have a 25-fold greater infection rate
than clean wounds.7 Wounds contaminated with
dirt have a higher risk of infection because of specific
infection potentiating fractions (IPFs) found in the
organic components and inorganic fraction. These
IPFs decrease the effects of white blood cells and
humoral factors, and they neutralize antibodies.
As few as 100 organisms can cause infection.17
Wounds contaminated with feces are very susceptible to infection. Feces may contain up to 1011
organisms/g.16
Hemoglobin liberated from hemorrhage in a
wound suppresses local wound defenses. The ferric
ion from hemoglobin also inhibits the natural bacteriostatic properties of serum and the intraphagocytic⫺killing capabilities of bacteria by the
granulocyte.7 The ferric ion also can increase the
virulence and replication of infecting bacteria. Hematoma formation is believed to be a leading factor
in decreasing local wound resistance to infection.18
The use of drains is somewhat controversial, because they represent a foreign body within the
wound; however, if drainage of a hematoma from
“dead space” is needed, the consequences of not using a drain are considerably more serious than the
complications from the drain.18
What caused the injury influences the wound’s
susceptibility to infection. Lacerations caused by
sharp objects such as metal, glass, and knives are
generally resistant to infection. Shear wounds
from barbed wire, sticks, nails, and bites are more
susceptible to infection because of the degree of softtissue damage. Wounds caused by entanglement/
entrapment, impact with a solid object, and/or a kick
are more susceptible to infection because of the degree of the soft-tissue injury and resultant reduction
in blood supply.16 The greater the magnitude of
the energy on impact, the more severe the soft-tissue
damage and the greater the alteration in blood supply. Wounds created by impact injury are reported
to be 100 times more susceptible to infection compared with wounds caused by shearing forces.19
Susceptibility to infection rises in multiple trauma
patients even when the injury/injuries occur at a site
other than the surgical site; reduced tissue perfusion is believed to be the cause.20
Bacterial infection delays healing by mechanically
separating the wound edges from the accumulation
of exudate, reducing the vascular supply (a result of
mechanical pressure and a tendency to form microthrombi in small vessels adjacent to the wound),
increasing cellular responses with prolongation of
the inflammatory phase of wound healing, producing proteolytic enzymes that digest collagen, adhering/binding to extracellular matrix proteins, and
releasing endotoxins that inhibit growth factors and
collagen production.4,8,9 Bacterial injury from infection results in a cellular and vascular response
typical of inflammation.
Wound infection develops in ⬃5–5.9% of our
small-animal surgical patients overall.21–23 In
small animals undergoing clean, elective procedures, ⬃2.5– 4.7% of the patients develop infection.21,22,24 In clean, contaminated wounds, postoperative wound infections develop in ⬃5.9% of
patients. 23 These rates are comparable with
those reported in humans.18 In a study done on
451 horses that evaluated the occurrence of surgical wound infection after orthopedic surgery, it
was found that infection developed in 10% of the
patients overall and 8.1% of the patients undergoing clean surgical procedures.25 The reason for
the increased infection rate in this study compared with studies done in humans and small
animals was believed to be caused by the exclusive
use of orthopedic patients.
2.
Selected Techniques for Prevention
The following section will review selected techniques
in the management of wounds that will help reduce
the incidence of infection.
General Anesthesia and Duration of Surgery
The depth and duration of anesthesia and the duration of surgery have been shown to be significant
risk factors for the development of post-operative
infection.21,23,26 Excessive depth of anesthesia reduces tissue perfusion and oxygenation, which can
cause acidosis and impaired resistance to infection.
Prolonged anesthesia impairs the alveolar macrophage function and depresses systemic leukocyte
migration and function.27–29 Wound-infection
rates have been shown to increase by 0.5% for each
1 min after 60 min of anesthesia.26 This translates
to a 30% greater risk of post-operative infection for
each additional 1 h. Logical recommendations include reducing the depth and duration of anesthesia
and making sure that the patient is well hydrated.
The use of propofol should be avoided, because it has
been shown to increase infection rates by 3.8 times
in clean wounds.30 Mixing thiopentone and propofol at a ratio ⬍1:1 does not improve the bacteriacidal
properties.31
Reducing the surgery time is also logical; wound
infection rates doubled after 90 min of surgery and
nearly tripled when surgery was ⬎120 min.21,32
The use of electrocautery should be limited. Excessive use of electrocautery has been shown to double
infection rates.33 However, if bleeding vessels are
grasped with fine non-serrated tissue forceps and
electrocautery is used, the infection rate is not increased over that of other methods of hemostasis.18
Wound and Skin Preparation
Proper wound and skin preparation includes hair
removal adjacent to the wound, wound cleansing,
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lavage/irrigation, antiseptic preparation of the skin
adjacent to the wound, preparation of the wound for
exploration, and wound debridement.16
1. Hair Removal
If possible, do not clip the hair before the induction
of anesthesia. Clipping the hair with a No. 40 clipper blade before induction of anesthesia has been
shown to significantly increase infection rates in two
large studies done in small animals.21,26 In attempt to answer the reason why clipping was a risk
factor for infection, Hamilton et al.34 used a scanning electron microscope to exam human skin prepared with electric clippers and found that the
clipper “nipped” the skin at the creases. This produced gross cuts in which bacteria could colonize.
Before beginning hair removal, protect the wound
with a sterile, moist gauze sponge. Dampen the
hair with water or coat it lightly with K-Y watersoluble jelly before clipping to prevent hair from
falling into the wound. Clip a wide area of hair
around the wound, and shave only the wound edges
using a recessed-head razor. Using a razor with a
recessed head will minimize damage to the infundibulum of the hair follicle, which reduces skin contamination from bacteria located in the hair follicle
and sebaceous glands.35 Sponges used to pack the
wound are discarded and replaced by new ones.
Scrub the clipped area of skin at least three times
with antiseptic soap and rinse between scrubs with
sterile 0.9% saline solution.
2. Wound Cleansing
Wound cleansing is one of the most important components of effective wound management. In the
strictest sense, wound cleansing is the use of fluids
to gently remove loosely adhered contaminants and
devitalized tissue from the wound surface. If contaminants cannot be removed with gentle wound
cleansing, then more specific cleansing and debridement techniques can be used.
In clean, acute (⬍3 h duration) wounds, water or
saline may be all that is needed for adequate wound
cleansing. For field use, an acceptable saline solution can be made by adding 2 teaspoons of salt to 1 l
of boiling water (8 teaspoons to 1 gallon).36
When enhanced wound cleansing is needed, a
commercial wound cleanser may be used. Unfortunately, most ionic and many non-ionic surfactants in
wound cleansers have been shown to be toxic to
cells, which can delay wound healing and inhibit the
wound’s defenses against infection.37,38 An in vitro
study evaluating the effects of several wound cleansers on human fibroblasts, red and white blood cells
found; Constant Clensa was the most biocompatible,
and Shur Clensb was the least biocompatible.39
In contrast, another in vitro study ranking the relative toxicity of several commercial wound cleansers
found that Shur Clens had a lower toxicity index
than Constant Clens.40 Antiseptics should not be
added to wound cleansers, because their addition
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results in a higher cytotoxic index.36 In a heavily
contaminated wound, the wound bed can be gently
cleansed with a wound cleanser and sterile gauze
sponges. This should be followed by thorough lavage with a sterile salt solution. The coarseness of
the scrubbing device should be as low as possible
while still providing a cleansing action. Wounds
scrubbed with coarse sponges have been shown to be
significantly more susceptible to infection.36 An
advantage to using a commercial wound cleanser is
that the surfactant properties significantly reduce
the coefficient of friction between the scrubbing device and wound tissue.36
Antimicrobial cleansers that are formulated to remove fecal contamination from intact skin (Dermal
wound cleanserc and MicroKlenzd) are more cytotoxic than wound cleansers and therefore, should
not be used in a wound.37 Antiseptic soaps, detergents, and alcohol should not be allowed to contact
raw tissue.41
3. Wound Lavage/Irrigation
Lavage cleans the wound of debris and reduces the
bacterial numbers and IPFs in the acute wound.
Because bacteria and contaminants initially adhere
to the wound surface by an electrostatic charge,
adequate fluid pressure must be used to dislodge
them from the wound. Lavage solutions are most
effective when delivered at an oblique angle by a
fluid jet at a pressure of at least 7 lbs per square inch
(PSI). Pressure ⱖ7 PSI cannot be achieved by
gravity flow or lavage with a bulb syringe.42,43
Pulsatile pressures of 10 –15 PSI have been shown
to be 80% effective in removing adherent bacteria
from a wound.43 Increasing the lavage pressure to
20 –25 PSI does not significantly improve the result.37 However, 70 PSI was found to be more effective in removing wound-tissue fragments and
debris than 25–50 PSI.44 The use of this pressure
is not recommended, because it results in fluid dispersion into wound tissue.45 Thirty PSI delivered
from a single orifice has been shown to penetrate
and damage tissue.46 In a study comparing the
effects of irrigation with saline at 15 PSI to irrigation at 20 PSI on penetrating partial-thickness
wounds, it was found that 20 PSI penetrated the
entire wound thickness. In contrast, irrigation
with 15 PSI resulted in superficial (10 –15%) penetration of the wound tissue.47 Results of this study
suggest that wounds should not be irrigated with
fluids delivered at a pressure ⬎15 PSI.37
As for the methods of delivery, the superiority of a
pulsatile-fluid stream over a continuous stream has
not been established.42 Pulsatile pressures (7–15
PSI) can be achieved by (1) forcefully expressing
lavage solutions from a 35-ml or 60-ml syringe
through a 19-gauge needle, (2) using a spray bottle,
(3) using a “Water Pik,” (4) using a Stryker interpulse irrigation system,e or (5) using a Hydro-T message nozzle.f The “Water Pik” at a low or
intermediate setting delivers 40 –50 ml/min at
IN-DEPTH:
CURRENT CONCEPTS IN WOUND MANAGEMENT
10 –15 PSI.35 The “Water Pik” seems to be most
effective for cleaning heavily contaminated avulsion
dental wounds. The spray bottle or the Stryker
inter-pulse irrigation system are preferred for lavage of most other wounds. The Hydro-T can deliver tap water to the wound surface at a pressure of
⬃15 PSI. Lavage with tap water should be discontinued after a bed of granulation tissue develops.
If continued, it will delay wound healing.48 When
using pressure lavage, care must be taken not to
drive contaminants deeper within the wound and
not to inadvertently separate loose fascial planes.
The clinical benefits of wound lavage have been
established in several studies. In an experimental
study comparing irrigation with a bulb syringe to
fluid delivered at low pressure (8 PSI using a 35-ml
syringe and 19-gauge needle), it was found that
there was a significant reduction in bacteria and a
reduced incidence in infection.49 In a clinical study
done on 335 humans presenting with a traumatic
wound ⬍24 h duration, it was found that wounds
irrigated at 13 PSI using a 12-ml syringe and 22gauge needle had a significant decrease in wound
inflammation and wound infection compared with
wounds irrigated with a standard-bulb syringe.50
The efficacy of low-pressure irrigation (15 PSI) in
removing bacteria is decreased as the wound ages.37
In an acute wound, the majority of the bacteria
reside on the wound’s surface. As time passes, the
bacteria invade the wound tissues; therefore, they
are not removed with irrigation alone, and debridement is required. The exact time period for bacteria to begin to invade the tissue is unknown, but 3– 6
h has been suggested as a reasonable time.35,51
4. Antiseptics Used for Lavage/Irrigation
Hydrogen peroxide (HP) is still commonly used for
wound irrigation. HP has a narrow antimicrobial
spectrum; it is an effective sporocide but has little
value as a wound antiseptic. It is, however, very
effective in dissolving blood clots.37 A 3% solution
of HP damages tissues, is cytotoxic to fibroblasts,
and causes thrombosis in the microvasculature adjacent to wound margins. HP is not recommended
for wound lavage.
Povidone iodine solution (PI) is commonly used as
an antiseptic for wound lavage. A 10% solution of
PI has a broad antimicrobial spectrum against
Gram ⫹/- bacteria, fungi, and candida; bacterial resistance has not been identified.52,53 The iodine in
PI is complexed with polyvinyl-pyrrolidone to increase its stability and reduce its irritation and
staining. Diluting PI uncouples the complexed
bond, which makes more free iodine available for
antimicrobial activity. PI solutions diluted to 0.1
and 0.2% (10 –20 ml/1000 ml) concentrations are
best for wound lavage. These dilutions have also
been shown to be effective in reducing bacterial
numbers in dog wounds.52,54 Diluted solutions
have been shown to kill many bacteria within 15 s.55
PI (5%) inhibits white blood-cell migration, which
results in increased wound infections compared with
wounds irrigated with 1% PI or saline. A 1% PI
solution used for wound lavage of abdominal incisions after closure of the peritoneum was shown to
be significantly superior to saline in reducing postsurgical wound infection.56 PI (0.5%) powder
sprayed in contaminated incision wound beds after
gastrointestinal surgery significantly reduced infection rates to 9.9% compared with 24.4% for
non-sprayed controls. Bacterial contamination
(established by cultures) at the time of surgery
was associated with a 52% infection rate in control
groups; the infection rate was reduced to 11% in
the PI-treated group.57 Irrigation with (1%) PI
does not seem to effect tensile strength gain in
healing wounds.58
There are disadvantages to using PI. It is inactivated by organic material, serum, and blood.
Less than 0.1% concentrations are inactivated by a
large number of neutrophils. Concentrations of
⬎1% are required to kill Staph. aureus. PI can
cause contact dermatitis, metabolic acidosis, thyroid
dysfunction, and ototoxicity. Thyroid dysfunction
may be seen in humans that use PI exclusively for
rinsing and scrubbing their hand and arms. The
disadvantages cited do not diminish the benefits
seen with dilute PI irrigation of wounds.
Chlorhexidine diacetate solution (CHD) is commonly used for antiseptic purposes and wound lavage. CHD has a wide antimicrobial spectrum
against Gram ⫹/- bacteria and viruses. Unfortunately, Proteus spp. and Pseudomonas spp. have
developed or have an inherent resistance to this
product, and it has no effect against fungi or Candida.59 When applied to the intact skin, its antimicrobial effect is immediate and has a lasting residual
effect because of binding to proteins in the stratum
corneum.52 CHD 0.05% has more bactericidal activity than PI.60 Faster wound contraction was reported in wounds treated with dilute CHD or PI
compared with saline controls; however, the differences were only statistically significant for CHD.54
Currently, 0.05% CHD (1:40 ⫽ 25 ml to 975 ml
dilution of the 2% concentrate) solution is recommended for wound lavage. Greater concentrations
are deleterious to wound healing.61 The precipitate that forms when CHD is diluted in salt solutions does not affect its antiseptic quality or delay
wound healing.60 CHD (0.05%) seems to be the
superior lavage solution in dogs and humans; however, the applicability of these results to the treatment of equine wounds is unknown.
Advantages of CD over PI include residual antibacterial capacity and continued activity in the presence
of blood, pus, and organic debris with less systemic
absorption. Disadvantages of CHD are ⬍0.05% solutions result in significant survival of Staph. aureus,
but ⬎0.5% solutions inhibit epithelialization and granulation-tissue formation.61 Additionally, contact
with the eyes causes ocular toxicity.35
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Sodium hypocholorite (SH) 0.5%, also referred to
as Dakin’s solution, releases chlorine and oxygen to
kill bacteria. SH is more effective in killing Staph.
aureus than PI or CHD. Unfortunately, SH is cytotoxic to fibroblasts. The clinical benefit of
Dakin’s solution is probably caused by its ability to
dissolve necrotic tissue.62 Removal of the necrotic
tissue decreases the bacterial load, which results in
improved wound healing. In this situation, it is
being used as a chemical debriding agent, and as
such, its use should be discontinued when the necrotic tissue is gone. SH should not be used routinely as a topical disinfectant. If it is used for
debridement, it is suggested that it be diluted to
one-quarter strength (0.125%).41 In a pinch, it is
suggested that an acceptable approach is to dilute
5% SH with tap water to achieve a 0.025% solution.
In a study evaluating field water from five different
sources used to dilute SH, no bacterial growth was
found in 99 of 100 samples.63 The conclusion was
that this field-expedient modification of Dakin’s solution could substitute for sterile irrigation fluid
when it is neither available nor logistically feasible.
In conclusion, several studies have shown that
dilute PI or CHD are superior to saline alone in
removing bacteria from the surface of the bone and
in soft tissues.54,56 –58 An in vitro study comparing
sterile saline to diluted solutions of PI and CHG that
were delivered at 14 PSI to the surface of bone
contaminated with a fixed number of bacteria found
that the antiseptic solutions reduced the bacteria
numbers 19-fold compared with saline controls.64
Antiseptics seem to be most effective in reducing
bacterial numbers in acutely contaminated wounds
but not in chronic wounds or wounds with established infection.37 The latter should be treated
with topical antibiotics.37
5. Antibiotics for Wound Lavage
The addition of antibiotics to the lavage solution
markedly reduces the number of bacteria in a
wound.65 Experimentally, 1% Neomycin solution
was found to be very effective in preventing infection
in wounds contaminated with feces.66 In a doubleblind study done on 260 sutured lacerations; penicillin sprayed on the wound before closure prevented
3 of 4 infections.67
6. Amount of Fluid Needed for Wound Lavage
In general, the amount of fluid needed for wound
lavage depends on the size of the wound and the
degree of contamination. Minimally, the gross
contaminants should be removed, and lavage
should be discontinued before the tissue becomes
water-logged.35
7. Antiseptic Skin Preparation
The two most commonly used surgical scrubs for
skin preparation are PI (Betadine) and chlorhexidine (Hibiclens). Rinsing with saline or 70% isopropol alcohol after scrubbing does not seem to alter
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the antimicrobial effect of PI; however, rinsing with
70% alcohol reduces the residual effect and antiseptic quality of chlorhexidine.68 Therefore, using a
saline rinse is recommended.
A disadvantage to PI is skin reactions, particularly in small animals. Occasionally, an acute skin
reaction to PI occurs in horses, but it is rare.16
The reaction is most commonly seen in the horse
after clipping, scrubbing, and rinsing with 70% alcohol, spraying with a PI solution, and bandaging.
Skin reactions include SC edema and skin-wheal
formation.
A disadvantage to the use of chlorhexdine scrub is
that short exposure to the eye, even in weak concentrations, results in corneal opacification and ocular
toxicity.35
Although the mechanical effects of scrubbing the
wound with these antiseptic soaps can be helpful in
removing wound debris, they are very cytotoxic and
therefore, should not be used for cleansing
wounds.37 Also, PI surgical scrub was shown to be
ineffective in reducing bacterial levels in wounds.69
Even with the high bacteriocidal effects of these
antiseptics, 20% of the bacterial population in the
skin resides in protected hair follicles, sebaceous
glands, and crevices of the lipid coat of the superficial epithelium.70
8. Surgeon Hand and Arm Preparation
Hand cultures immediately after standard surgical
hand preparation and 4 h in surgical gloves found
that alcohol (70% ethyl) and chlorhexidine (4%) were
effective surgical scrubs with good residual effect.
PI was found to have little residual effect. The
article concluded that (1) chlorhexidine preparations
are superior, (2) PI has poor prolonged effect, (3)
triclosan is not effective, and (4) 70% ethanol (V/V)
has low antibacterial effectiveness. Seventy percent ethyl alcohol is superior.71,72
A waterless skin preparationg seems to have
many desirable qualities. Avagard contains 1%
chlorhexidine gluconate and 61% ethyl alcohol in an
emollient. A blinded study comparing Avagard to
4% CHG or PI for hand and arm preparation over 5
days and under surgical gloves for 6 h found that
Avagard was superior in antiseptic quality and was
less irritating than the PI or CHG.71 Besides being
an effective antiseptic prep for hospital use, it seems
to be very useful in ambulatory practice.
9. Wound Exploration
Wound exploration is done to document the extent of
the wound, identify if a bone or a joint is exposed,
and determine if a foreign body is present. After
the wound is cleaned and free of debris, the wound
can be explored digitally using sterile gloves; make
sure that the talcum powder is rinsed from the outer
surface of the gloves before this is done. If the
wound has a small opening precluding the use of the
digit, then a sterile probe can be used to identify the
depth of the wound, determine if a foreign body is
IN-DEPTH:
CURRENT CONCEPTS IN WOUND MANAGEMENT
Fig. 1. An example of a sterile needle placed in the distal interphalangeal (coffin) joint in a site remote to the wound.
present, or determine if bone is contacted. After
the depth of the wound is reached, a radiograph can
be taken to identify its location in relationship to
bone or synovial cavities. Synovial fluid can be
identified by stringing it between the thumb and
forefinger, and if questions remain, a sample of the
fluid should be submitted for cytology and culture/
sensitivity. If synovial penetration is suspected, a
needle is placed in the synovial cavity at a site
remote to the wound. If synovial fluid can be retrieved, it is submitted for cytology and culture/
sensitivity. After this, sterile saline solution is
injected into the synovial structure; if the synovial
capsule has been penetrated, fluid will flow from the
wound site (Fig. 1). If a synovial structure is involved, it is lavaged with 3–5 l of sterile saline or
crystalloid solution followed by lavage with 1 l of a
10% dimethyl fulfoxide (DMSO) solution. Intrasynovial instillation of antibiotics is also recommended.35
Radiographs (plain and contrast) can be useful in
identifying fractures, joint subluxations and luxation, and some foreign bodies. Ultrasound is most
useful in identifying damaged soft-tissue support
structures, gas accumulation, muscle separation,
and radiographically unapparent foreign bodies
(Fig. 2, A and B).35
Arthroscopy or tenoscopy can be invaluable tools
to identify radiographic occult lesions, particularly
those involving cartilage, and to identify foreign
Fig. 2. This figure shows the value of ultrasound in identifying
a piece of wood that was not found using contrast radiography. (A) Transverse ultrasound image in the mid-metacarpal
region that identifies a hyperechoic density (cursor) located at the
distal extent of carpal-canal sheath between the carpal-check
ligament and deep digital flexor tendon. (B) Longitudinal ultrasound image of the same; note the hyperechoic density (cursor).
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Fig. 3. An arthroscopic view of the distal interphalangeal (coffin) joint that had sustained a penetrating wound 24 h earlier.
Note the pieces of hair and debris in the joint. Without the use
of arthroscopic visualization, these foreign bodies would not have
been identified and probably would not have been removed with
flushing alone.
bodies with the joint or tendon sheath (e.g., hair,
dirt, or other foreign bodies; Fig. 3).
10. Wound Debridement
Wound debridement can either be done with a scalpel, CO2 laser with enzymes, debridement dressings, or chemically with Dakin’s solution. Its
purpose is to reduce the bacterial load, remove
wound contaminants (dead tissue and foreign bodies), and improve the vascular supply. The standard approach is sharp debridement to convert a
contaminated wound into a clean wound. The
types of sharp debridement include (1) excisional
(layered), (2) en block, (3) simple or piecemeal, and
(4) staged. Bone devoid of periostium should also
be debrided.
Layered debridement begins with the removal of
the most superficial tissues and continues deeper in
the wound bed until its depths are reached. En
block debridement is used primarily for small animals and therefore, will not be addressed in this
presentation. Piecemeal debridement is used for
large wounds, usually involving the body. Beginning at one wound margin and then moving toward
the other margin, all devitalized tissue is removed in
a piecemeal fashion (Fig. 4). Staged debridement is
used over a number of days. The advantage of the
staged approach is that it avoids inadvertent removal of viable tissue. Governing criteria are color
and attachment. White, tan, black, or green tissue
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2006 Ⲑ Vol. 52 Ⲑ AAEP PROCEEDINGS
Fig. 4. An example of piecemeal debridement of a large wound
on the lateral thoracic region.
that is poorly attached is debrided. Pink to dark
purple tissue that is well attached is left in place and
debrided later if needed.73 Exposed cortical bone
devoid of periostium should be debrided to promote
the formation of granulation tissue on its surface
and reduce the chances of a sequestrum developing.
If the exposed bone is debrided to reach bleeding/
oozing bone, granulation tissue will proliferate from
the surface. Bone debridement can be accomplished
with a hip arthroplasty rasp (Fig. 5), bone rasp, bone
chisel, or osteotome. Hydrogel dressings containing
acemannanh,i can be used to accelerate the migration
of granulation tissue over exposed bone.74
A CO2 laser can be used instead of a cold-steel
scalpel. The advantages to the laser is that it sanitizes the wound, causes contracture of the collagen
fibers, photoablates exuberant granulation tissue,
reduces post-operative pain, and causes minimal
hemorrhage.
Proteolytic enzymes (PEs) can be used to debride the wound-surface coagulum and bacterial
bio-film that encompasses contaminants and bacteria, which prevents access of topical antibiotics/
antiseptics and systemic antibiotic. PEs are
indicated when surgical debridement is contraindicated, because it could result in damage to or
removal of tissue needed for reconstruction of a
IN-DEPTH:
CURRENT CONCEPTS IN WOUND MANAGEMENT
Fig. 5. (A) An example of a hip arthroplasty rasp that is very effective for debriding the surface of bone stripped of its periostium.
(B) Side view; note the curved head that facilitates bone contact.
wound; they are also indicated for wounds that
approximate nerves and vessels. Products include pancreatic trypsinj, streptodornase or streptokinasek, collagenases, proteases, fibrinolysin,
and deoxyribonucleasel. Recently, collagenase
has been shown to have the highest proteolytic
activity and the greatest likelihood of achieving a
clean wound.75
There are several debridement dressings available: (1) an adherent open-mesh gauze (e.g., 4 ⫻
4 gauze sponges), (2) a wet to dry bandage using 4
x ⫻ 4 mesh gauze or sheet cotton, (3) an antimicrobial dressingm; this is an excellent choice, because it contains a broad-spectrum antiseptic that
has been shown to kill bacteria on the surface of
the wound and prevent strike through), (4) a hypertonic saline dressingn that is best used for necrotic, heavily infected exuding wounds, and (5) an
occulsive dressing that can be used for clean
wounds (this dressing promotes moist-wound healing and “autolytic debridement”).76
Antibiotics
The ultimate aim of antibiotic treatment is to inflict
an insult on infecting bacteria that is sufficient to
kill the organism or render it susceptible to inactivation by natural host defenses.
AAEP PROCEEDINGS Ⲑ Vol. 52 Ⲑ 2006
277
IN-DEPTH:
CURRENT CONCEPTS IN WOUND MANAGEMENT
Topical Antibiotic Application
Topical antibiotics (TAs) can be effective in preventing the development of infection, particularly
against sensitive organisms.37,67 TAs are most effective when they are applied within 3 h after
wounding.16 However, if a wound older than 3 ho
or a chronicly infected wound is debrided, a new
wound is created, which makes TA use appropriate.35 In the latter, systemic antibiotics are also
recommended.1 Although some TA can retard
wound healing (e.g., gentamicin cream, Furacin,
etc.), others have been shown to accelerate wound
healing (e.g., triple antibiotics).48,77–79 TA solutions are best used in wounds that are to be sutured,
and ointments or creams are best used for bandaged
or open wounds.
Because the development of multiple antibioticresistant strains of bacteria continues to be a major
health concern, new emphasis is being placed on the
development and use of alternative wound-care antimicrobial products, particularly those with no
known development of bacterial resistance. Dressings containing antisepticsm and silver ionso,p have
shown great promise and are experiencing a resurgence.1,76,80 Dressings that absorb exudates and
reduce bacterial numbersq,r,s are now available.76
Additionally, the antimicrobial properties of alternative products such as honey and melaleuca alternifolia oil (tea tree oil) are being investigated.81– 86
Extracellular matrices and topical oxygen also seem
to have antimicrobial effects.87,88
3.
Conclusion
There are myriad contributing factors that influence
infection rates in our equine patients. We can influence many of these factors and reduce the chances
of infection occurring under most circumstances.
Continued work needs to be done to further clarify
the role of topical agents and dressings that will
improve the chances of preventing infection.
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a
Constant Clens, Tyco Healthcare Kendall, Mansfield, MA
02048.
b
Shur Clens, ConvaTec, Princeton, NJ 08543.
c
Dermal wound cleanser, Smith & Nephew, Largo, FL 33779.
280
2006 Ⲑ Vol. 52 Ⲑ AAEP PROCEEDINGS
d
MicroKlenz, Carrington Laboratories, Inc, Irving, TX 75038.
Stryker inter-pulse irrigation system, Stryker Instruments,
Kalamazoo, MI 49009.
f
Equine Hydro-T massage nozzle. Innovative Products International, LLC, Bozeman, MT 59718.
g
Avagard, 3M Animal Care Products, St. Paul, MN 55144.
h
Carra Vet, Veterinary Products Laboratories, Phoenix, AZ
85013.
i
Carrasorb, Carrington Laboratories, Irving, TX 75038.
j
Granulex, Bertek Pharmaceuticals, Research Triangle Park,
NC 27709.
k
Varidase, Lederle Lab, Wayne, NJ 07470.
l
Elase, Fujisawa Health Care, Deerfield, IL 60014.
m
Kerlix AMD, Tyco Healthcare Kendall, Mansfield, MA 02048.
n
Cursalt, Tyco Healthcare Kendall, Mansfield, MA 02048.
o
Silverlon Argentum, Lakemont, GA 30552.
p
Actisorb Silver 220, Johnson & Johnson Products Inc., New
Brunswick, NJ 08933.
q
Debrisan, Johnson & Johnson Products Inc., New Brunswick,
NJ 08933.
r
Intracell, Macleod Pharmaceuticals Inc., Fort Collins, CO
80525.
s
Activate, 3M Animal Care Products, St. Paul, MN 55144.
e
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