ORIGINAL RESEARCH
Veterinary Surgery
23:494-502. 1994
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The Effect of Occlusive and Semi-Occlusive Dressings on the
Healing of Acute Full-Thickness Skin Wounds on the
Forelimbs of Dogs
PAUL W. MORGAN, D V M , D V S c , ALLEN G. BINNINGTON, D V M , MSc, Diplomate ACVS,
CRAIG W. MILLER, DVM, MVSc, Diplomate ACVS, DALE A. SMITH, D V M , DVSc, ANNE VALLIANT,
a n d JOHN F. PRESCOTT, MA, Vet MB, PhD
BSc,
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This project compared the effects of hydrocolloid (HC) and hydrogel (HG) occlusive dressings
and a polyethylene (PE) semi-occlusive dressing on the healing of acute full-thickness skin wounds
on the forelimbs of 10 dogs. All treatments resulted in a similar degree of healing at postoperative
days 4 and 7. No significant differences existed in the number of wounds that were more than
90% healed at postoperative day 28 between the group treated with the HG dressing and the
group treated with the PE dressing. There were significantly fewer wounds more than 90% healed
at postoperative day 28 in the group treated with the HC dressing. Wounds under the HG
dressing had the largest mean percentage of contraction at postoperative days 2 1 and 28. Wounds
under the HG dressing also had the largest contraction/re-epithelializationratio (postoperative
days 2 I and 28) compared with wounds under the PE and HC dressings. Wounds under the PE
dressing had a significantly higher mean percentage of re-epithelialization than wounds under
both occlusive dressings on postoperative days 14, 2 I , and 28. Wounds under the two occlusive
dressings had exuberant granulation tissue present more often than wounds under the PE dressing.
The two occlusive dressings had significantly higher bacterial counts on wounds compared with
wounds under the PE dressing; analysis of variance (ANOVA), P = .0008. Wounds under the
HC dressing showed the poorest healing in all parameters.
@Copyright I994 by The Americun College of C'L.ferinur,vSirrgcwns
I
NJURIES to the extremities that result in fullthickness skin loss occur commonly in dogs.'
Other full-thickness wounds on limbs occur secondary to tumor removal or skin excision caused by
penvascular injections of caustic agents. One method
of treatment is management as an open wound with
second intention healing2
Healing of full-thickness open wounds takes place
by wound contraction and epitheliali~ation.~
It has
been suggested that healing of an open wound will
occur more quickly if it is covered with a bandage.3
Selection of the proper bandage material and method
of application may affect the rate of healing. A semiocclusive dressing creates a moist environment that
allows excess exudate to be absorbed by the intermediate layer of the bandage. This helps to prevent tissue
maceration and infe~tion.~
Occlusive dressings, in
contrast, prevent exudate loss from the surface of the
wound. They reportedly increase the rate of re-epithelialization in partial-thickness
There may
be a relationship between the rate of re-epithelialization
and the degree of occlusion by the dre~sing.~,~
The effect of occlusive dressings on dermal repair
has received less attention.6 Some researchers report
From the Department of Clinical Studies. Department of Pathology, Department of Microbiology and Immunology, Ontario
Veterinary College, University of Guelph. Guelph, Ontario. Canada.
Address reprint requests to Allen G. Binnington. DVM. MSc, Diplomate ACVS, Department of Clinical Studies, Ontario Veterinary
College, University of Guelph, Guelph, Ontario, Canada N lC 2W 1.
OCopyright 1994 by The American College of Veterinary Surgeons
016 1-3499/94/2306-0008$3.00/0
494
MORGAN ET AL
more rapid dermal repair in wounds covered by occlusive
In contrast, others report a decrease in the healing of wounds under occlusive
dressings compared with wounds exposed to the
air." There are also conflicting results with respect
to the degree of bacterial contamination, tissue maceration, and wound contraction that occur under
occlusive dressings.'?-I9
There is a lack of consistency in the literature describing healing of full-thickness wounds treated with
occlusive dressings. This study compared the effects
of two types of occlusive dressings and a more traditional semi-occlusive dressing on the healing of
full-thickness wounds on the forelimbs of dogs.
495
applied to position C, dressing no. 2 was applied to position A, and dressing no. 3 was applied to position B, on
the right limb of dog no. 2 and so on.
Three dressings were evaluated in this study, two occlusive dressings and one semi-occlusive dressing. The two
occlusive dressings were a hydrogel (Curity Conforma Gel.
Kendall Canada Inc., Peterborough, Ontario, Canada)
(HG) (treatment no. I , high 02,C 0 2 permeability) and
a hydrocolloid (Comfeel Systems, Smith & Nephew Inc.,
Lachine, Quebec, Canada) (HC) (treatment no. 3 , low
02,C 0 2permeability). Neither had been previously evaluated for use in full-thickness wounds in dogs. The semiocclusive dressing (treatment no. 2) consisted of two layers
of perforated polyethylene (Melolite, Smith & Nephew
lnc) (PE) with a layer of fleece cotton interposed between
them. This dressing is commonly used for the treatment
of open wounds in dogs. All dressings were covered with
a fine mesh gauze, rolled cotton, and stretch porous tape
(Easifix Cohesive Bandage, Smith & Nephew Inc) to keep
them in place. Elizabethan collars were used to keep the
dogs from damaging the bandages.
The bandages were inspected on a daily basis by the
principal investigator. The occlusive dressings were
changed every 4 to 7 days according to the manufacturer's
criteria, or sooner if wound fluid was noted penetrating
the bandage. Bandage changes also were performed in
association with the bacterial culture and wound tracing
schedule (postoperative days 4, 7, 14, 21, and 28). The
semi-occlusive bandages were changed according to standard wound treatment protocol^,^ every 1 or 2 days when
fluid accumulation was high and every 4 to 7 days thereafter as fluid production decreased. Bandage changes followed the outlined protocol with the exception of 10 occasions in which a bandage was soiled, had slipped, or
was partially removed by individual dogs. In such cases,
the dogs were restrained and the bandages were repaired
and the dressings were replaced if necessary.
Postsurgical evaluations were done on days 4, 7, 14,
21, and 28. The wounds were evaluated for bacterial
growth, quantity and quality of granulation tissue, rate of
healing, and microscopic evidence of healing (postoperative day 28). On each evaluation day, the dogs were sedated with oxymorphone and acetylpromazine using the
previously noted doses. The dressings were removed and
excessive debris was cleaned from each wound with a
sterile gauze pad.
Bacterial analysis was done by rolling a sterile cotton
swab over the entire wound surface, with no wound area
being swabbed more than once. The cotton swab from
each wound was placed in a sterile container filled with
2 mL of phosphate-buffered saline, stored at 4°C and
plated within 4 hours of retrieval. Aliquots ( 1 mL) of the
suspension were measured in a I: 10 dilution and a 1: 100
dilution. Each dilution was plated on blood agar and
MacConkey's agar using a 0.0 I-mL loop. After 48 hours
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MATERIALS AND METHODS
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Ten healthy adult mixed breed dogs, weighing between
20 and 25 kg, with forelimbs measuring approximately
17 cm between the elbow joint and carpus, were used in
the study. The protocol was approved by the institutional
animal care and use committee. The dogs were sedated
with oxymorphone (0.10 mg/kg intramuscular [IM]) and
acetylpromazine (0.05 mg/kg IM). Anesthesia was induced
by intravenous injection of 10.0 mg/kg thiopental and
maintained with halothane and oxygen. Both forelimbs
were prepared for aseptic surgery; the dogs were alternated
from left to right lateral recumbency to allow exposure
of each forelimb. Three squares, measuring 2.0 cm along
each side, were outlined on each forelimb between the
elbow and the carpus using a sterile pen and plastic template.
The proximal site was designated as position A, the
middle site designated as position B, and the distal site
was designated as position C. The proximal square was
outlined on the lateral aspect of the antebrachium 3 cm
below the elbow joint. The second outline was marked 3
cm distal to and 120" clockwise from the proximal wound.
The third outline was similarly marked 3 cm and 120"
from the second outline. The outlined areas were excised
through the full thickness of the skin, including the entire
dermis, using a # 10 scalpel blade. Dressings were designated as treatment no. 1, no. 2, or no. 3 and were applied
to the newly created wounds; no. 1 was placed at position
A, no. 2 was placed at position B, and no, 3 was placed
at position C on the right limb ofthe first dog. Subsequent
dressing placements were systematically rotated to ensure
each dressing was applied to each site an equal number
of times. On the left limb of the first dog, the dressings
were moved distally by one position so that dressing no.
1 was applied at position B, dressing no. 2 was applied at
position C , and dressing no. 3 was applied at position A.
This procedure was performed on each of the remaining
dogs' forelimbs for a total of 20 limbs. Dressing no. 1 was
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496
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EFFECT O F OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS
of incubation, the species and number of colonies of bacteria isolated from each wound were identified using standard procedures.*'
After bacterial cultures were obtained, the quality of
the granulation tissue under each dressing was subjectively
assessed as healthy (red and granular) or unhealthy (grey
and friable). Exuberant granulation tissue was defined as
granulation tissue completely filling the wound bed and
protruding above the level of normal skin.
Wound surface area analyses were performed by tracing
each wound onto clear plastic sheets, outlining the wound
edge and the advancing edge of epithelium (Fig I A). The
wound edge was defined as the margin between intact
skin and either granulation tissue or new epithelium. The
tracings were then transferred onto clear acetate sheets:
the surface areas were digitized and computed in square
millimeters using an Image I morphometrics analysis
package (Empix Imagin, Universal Imaging Corp., WestChester, PA). The areas measured for each wound included
the remaining unhealed wound area, ie, that not covered
by either contracting skin or advancing epithelium, and
the area covered by advancing epithelium but not by contracting full-thickness skin.
The surface areas of each wound were determined on
day 0, immediately after excision. This served as the baseline for obtaining rates of contraction, re-epithelialization,
and wound healing for each wound. The percentage of
wound contraction, percentage of wound re-epithelialization, unhealed wound area (unepithelialized granulation tissue), and contraction/epithelialization ratio were
calculated for each wound (Figs 1A and IB). A healed
wound was defined as a wound covered by either fullthickness skin, as the result of contraction, or by advancing
epithelium from the wound margins. Uncovered granulation tissue was classified as not healed. Means and standard errors were determined for the three treatment groups
and were used for statistical comparisons.
On completion of the study (postoperative day 28), the
dogs were anesthetized as previously described, and a 5to 6-mm wide longitudinal strip of tissue, including normal skin proximal and distal to the wound, was removed
from the central wound area. The tissue samples were
fixed in 10% neutral buffered formalin and embedded in
paraffin. Each sample was sectioned at 6 pm and was
stained with hematoxylin-eosin (HE) to assess the organization of the epithelial and dermal cellular components.
The samples also were stained with Masson's trichrome
to evaluate dermal connective tissue organization. At the
end of the study, the dogs were placed for adoption or
returned to the animal care facility.
An analysis of variance (ANOVA; general linear model)
was applied to the calculated variables (percentage of
contraction, percentage of epithelialization, percentage
healed, contraction/epithelial ratio, and bacterial counts)
to determine the overall significance of treatment, posi-
original wound
margin
(w.M.)
contracted
skin
~ \ * **
\ margin
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advancing
epithelial
edge
0=
/
epithelialized
(E.A.)
area
0
W.A.=
area (mm')
of original wound (W.M.) on day 0.
G.T.= area of granulation tissue (mm').
E.A.= epithelialized area (mm').
C.A.=
contracted area (mm').
Percentage contraction (P.C.) = W.A.
Percentage of original wound
area epithelialized (P.E.)
-
I G.T
W.A.
.+
E.A.I
x 100
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=E.A.x
100
W.A.
Percentage of wound not healed (P.N.H.)
( = % O f W.A. with G.T.)
Percent healed (P.H.) = 100
Contraction/Epithelial
-
=G.T. x 100
W.A.
P.N.H.
ratio (C/E) = W.A.
-
I G.T. + E . A . ~
E.A.
Fig 1 . (A) Diagram showing the original wound margin, the
contracted skin margin, the advancing epithelial edge, and the
unhealed area of granulation tissue. The original wound margin
was outlined on day 0. The contracted skin margin, and the advancing epithelial edge were outlined at each time interval and
used for area calculation. (B) List of formulas used to calculate
the percentage of contraction, epithelialization, total wound
healed, and the contraction/epithelialization ratio; see also
Fig 1A.
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tion, and side. When significance was detected, a Duncan's
multiple range test was used to identify the significantly
different treatment. A significance level of P < .05 was
used for all statistical analyses.
RESULTS
During the first week, both occlusive dressings
were changed every 1 to 2 days, because of wound
fluid leaking from the confines of the dressing. The
PE dressing was changed every 1 to 3 days during
the first week.
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497
MORGAN ET AL
After 14 days, there was minimal fluid production
under the PE dressing; three of 20 wounds at all
positions were dry with a scab forming on top. The
occlusive bandages had noticeable fluid production
at all positions. As the wounds matured under both
occlusive dressings the fluid production was less, so
bandages were changed every 4 to 7 days as recommended. The exudate underneath the HC dressing was malodorous and tenacious and difficult to
remove from the intact skin on all wounds, whereas
the exudate underneath the HG dressing was easier
to remove from the intact skin and had little odor.
None of the dressings adhered to the wounds at any
time during the study. On two wounds, use of the
HC dressing resulted in maceration of the epithelium, one at postoperative day 21 and one at postoperative day 28.
The initial ANOVA of wound area data indicated
confounding factors including position, treatment*
position, and treatment*side. The wounds at position A were slower to heal than those at positions B
and C. When an ANOVA was performed on the
wound area data from positions B and C alone, the
confounding factors of position and side were absent
and comparison of treatment groups was possible.
Therefore, data from positions B and C were analyzed separately. This resulted in an analysis of 40
wounds divided into the three treatment groups
(HG, n = 13; PE, n = 14; and HC, n = 13). Data
from the 20 wounds at position A were analyzed
separately (HG, n = 7; PE, n = 6; and HC, n = 7)
and exhibited similar trends to positions B and C.
However, data from position A had a larger standard
error. The following results include data from positions B and C only.
There were no statistically significant differences
between treatment groups in percentage of contraction, percentage of re-epithelialization, contraction/
epithelialization ratio, or total percentage of wound
healed on postoperative days 4 or 7.
Initially, all wounds expanded at day 0; by postoperative day 4 contraction had begun and was apparent for the remainder of the study (Fig 2). On
postoperative day 28 the mean percentage of contraction f standard error was 78.93 k 2.49 (HG),
61.46 t- 3.65 (PE), and 62.59 k 5.72 (HC); ANOVA,
P = .016. At postoperative days 21 and 28, the
wounds under the HG dressing were significantly
different with a greater mean percentage of contraction than the HC and PE dressings. The wounds
loo
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- Hydrogel
- - Polyethylene
11
Hydrocolloid
*
I
0
4
7
14
TIME (days)
21
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*
28
Fig 2. Percentage of contraction over time for treatment groups
at positions B and C. Mean f standard error. *Hydrogel is significantly different (P< -05).
under the HC and PE dressings were not significantly
different on both days (Fig 2).
Re-epithelialization was not apparent in any of
the wounds until postoperative day 14. On postoperative day 14, the mean percentage of re-epithelialization f standard error was 27.59 +- 1.80 (HG),
42.88 k 3.20 (PE), and 33.10 i 2.77 (HC); ANOVA,
P = .0006. The percentage of epithelium coverage
was highest on postoperative day 14 for all treatments. On postoperative days 14, 21, and 28,
wounds under the PE dressing had significantly more
new epithelium covering them than wounds under
both the HG and HC dressings (Fig 3). The wounds
under the HG and HC dressings were not significantly different from each other on postoperative
days 14, 2 1, and 28.
The ratio of contraction to epithelialization was
significantly larger for wounds treated with the HG
dressing on postoperative days 21 and 28 (Fig 4).
On postoperative day 28 the mean contraction/epithelialization ratio f standard error was 4.86 f 0.64
(HG), 1.86 t- 0.23 (PE), and 2.62 k 0.36 (HC); ANOVA, P = .0001. Wounds under the PE and HC
dressings were not significantly different from each
other on postoperative days 21 and 28.
There was a significant difference in the total percentage of wound healed among treatments at postoperative days 14, 2 1, and 28 (Fig 5). On postop-
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100
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-
- Hydrogel
- - Polyethylene
---- Hydrocolloid
-
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a
a
I
k
W
W
dressings had significantly higher bacterial counts
than wounds under the PE dressing; ANOVA, P
= .0008. Bacterial counts under both occlusive
dressings were not significantly different from each
other (Fig 6). There were no day/treatment interactions.
Elevated bacterial counts were associated with a
slipped or chewed bandage on four occasions when
compared with the previous evaluation time at which
the bandages were intact. In three of four wounds,
the bacteria count decreased to a lower number on
subsequent bandage changes when the bandages remained intact.
Granulation tissue was present in all wounds by
postoperative day 7. Exuberant granulation tissue
(Fig 7) was evident on four of 13 wounds on postoperative day 14, four of I3 wounds on postoperative
day 2 1, and six of 13 wounds on postoperative day
28 under the HG dressing. Exuberant granulation
tissue was evident on six of 13 wounds on postoperative day 14, six of 13 wounds on postoperative
day 2 1, and five of 13 wounds on postoperative day
28 under the HC dressings. Exuberant granulation
tissue was evident on only two of 14 wounds on
postoperative day 14 under the PE dressing. There
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2
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EFFECT OF OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS
40
-
IY
x
20 -
0 -
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0
~~
4
7
14
TIME (days)
21
28
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Fig 3. Percentage of re-epithelialization over time for treatment
groups at positions B and C. Mean _+ standard error. *PE is
significantly different ( P < .05).
erative day 28 the mean total percentage of wound
healed was 98.04 k 0.78 (HG), 100.00 (PE), and
88.94 f 5. I2 (HC); ANOVA, P = .04. On postoperative day 14, wounds under the PE dressing were
significantly higher. At postoperative days 2 1 and
28, wounds under the HG and PE dressings were
not significantly different in their total percentage of
wounds healed. Wounds under the HC dressing had
significantly less total wound area healed on postoperative days 21 and 28.
By postoperative day 2 1, 1 3 of 14 wounds under
the PE dressing were healed, five of 13 wounds were
healed under the HC dressing, and two of 13 wounds
were healed under the HG dressing. On postoperative day 28, all 14 wounds were healed under the
PE dressing, whereas seven of 13 wounds were healed
under each of the HG and the HC dressings.
Comparing the treated wounds at postoperative
day 28, 13 of 13 wounds under the HG dressing
were 290% healed, and nine of 13 wounds under
the HC dressing were 290% healed.
Sraphylococciis aiueiis (50 wounds), beta hemolytic Streptococcus sp. (25 wounds), Staphylococcus
epidermidis (2 1 wounds), alpha hemolytic Streptococcus sp. ( 16 wounds), Escherichia coli (nine
wounds), and Protetis mirabilis (nine wounds) were
cultured most often.
A two-factor ANOVA considering day and treatment found wounds under both the H G and HC
- Hydrogel
--
Polyethylene
-__-Hydrocolloid
T
5 -
4 -
0
F
3 -
d
w
0
2-
1 -
07
I
I)
0
4
7
14
TIME (days)
21
*
28
Fig 4. The contraction/epithelialization ratio over time for
treatment groups at positions B and C. Mean _+ standard error.
"HG is significantly different ( P < .05).
499
MORGAN ET A L
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- Hydrogel
- - Polyethylene
Hydrocolloid
100
0
Y
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0
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3
t-
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w
80
60
of exuberant granulation tissue was noted in four of
12 unhealed wounds: one of six under the HG dressing and three of six under the HC dressing.
Wounds under the PE dressing had 14 of 14 with
mature granulation tissue present throughout the
dermis when evaluated using Masson's trichrome
stain. Wounds under the HG and HC dressings each
had seven of 13 with mature granulation tissue
throughout the dermis.
DISCUSSION
40
V
[L:
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a
20
The traditional method of bandaging open wounds
in small animals is to use absorbent dressings to draw
wound fluid away from the wound surface into the
bandage. This may be accomplished with an adherent wet-to-dry contact layer in the initial stages of
wound treatment which aids in debridement of superficial debris.*' As re-epithelialization commences
the adherent contact layer is replaced by a nonadherent nonocclusive or semi-occlusive contact layer.
In either case, the objective is to draw wound fluid
away from the wound surface to reduce contamination and allow wound healing to proceed.
Occlusive dressings are currently used extensively
to treat wounds in humans. These dressings prevent
absorption of fluid from the surface of the wound.
Wound fluid may contain substances that increase
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0
TIME (days)
Fig 5. The percentage of total wound healed over time for
treatment groups at positions B and C. Mean -+ standard error.
*PE is significantly different; **HC is significantly different ( P
< .05).
was no exuberant granulation tissue present on
postoperative days 2 1 or 28 under the PE dressing.
The granulation tissue was healthy and granular
underneath all of the dressings up to postoperative
day 14. Five of 13 wounds under the HC dressing
had unhealthy, grey, and friable granulation tissue
from postoperative day 14 throughout the remainder
of the study. None of the wounds under the HG or
PE dressings had unhealthy, grey, and friable granulation tissue.
On histological evaluation using HE stain, the
normal epidermis adjacent to the wounds had a
mean thickness of 56.68 t- 3.60 pm and was composed of two to four cell layers. Keratinization of
the new epithelium was present in all of the wounds
regardless of the stage of healing. Mitotic figures were
noted in the advancing epithelium in five of 12 unhealed wounds: three of six under the HG dressing
and two of six under the HC dressing. Epithelial
sliding was present in six of 12 unhealed wounds:
four of six under the HG dressing and two of six
under the HC dressing.
Two of the 12 unhealed wounds, one of six under
the HG dressing and one of six under the HC dressing, had epithelial sliding present on one side, while
the other side of advancing epithelium was blunted.
Blunting of the advancing epithelium on both sides
o Hydrocolloid
v Hydrogel
Polyethylene
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TNTC-
IZ
0
PO
V
400-
3
0
V
5
300-
[II
0
W
IV
4
m
0
200-
v0
0
V
0
PO
Po
0 f loo roo
0
4
7
0
l o0
PO8
PQO
14
21
28
DAY
Fig 6. Scatter plot showing bacterial colony counts over time
at positions B and C; PE has significantly lower counts (P< .05).
500
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EFFECT OF OCCLUSIVE AND SEMI-OCCLUSIVE DRESSINGS
Fig 7. Photograph of a wound (HC occlusive, position B) on
postoperative day 14. Exuberant granulation tissue is evident
above the level of normal skin.
the rate of wound healing and perhaps should not
be prematurely removed from the wound surf a ~ e . ~ ’Increased
.*~
rates of healing in wounds treated
with occlusive dressings have been reported in humans and experimental animal^.^,^.'^.'^,^^ Possible
disadvantages of occlusive dressings include increased bacterial growth and increased tissue maceration in the moist e n ~ i r o n m e n t . Much
’~
of the
research into occlusive dressings has been performed
on partial-thickness wound^.^-^ The few studies that
did evaluate occlusive dressings for the treatment of
dermal repair reported conflicting results.6.’0,’I No
studies have evaluated the use of occlusive dressings
for the treatment of acute full-thickness dermal
wounds in dogs.
Overall, wounds covered with the HC dressing had
significantly less total wound area healed than either
the HG or the PE dressing. When considering the
type of healing that occurred, the wounds treated
with the PE dressing had a greater percentage of
wound area covered by advancing epithelium than
either of the occlusive dressings. Epithelium will migrate across granulation tissue in a layer two or three
cells thick if there is no impediment such as an exudate or a scab. In the presence of an impediment,
a much thicker layer, or wedge, of migrating epithelium is observed.26This blunting or wedging of migrating epithelium was noted histologically only in
the occlusive dressing treatment groups. This may
have been caused by the greater amount of exudate
or exuberant granulation tissue noted under both
occlusive dressings.
The wounds treated with the HG dressing had a
significantly greater percentage of the wound area
healed by contraction. This pattern was confirmed
by the contraction to epithelium ratio that was also
significantly greater for the wounds treated with the
HG dressing. Healing by contraction is superior to
healing by epithelialization because contraction
provides a durable covering of full-thickness skin.
Normal skin is both mechanically and cosmetically
superior to scar tissue, thus contraction is preferred
as long as it does not impair f ~ n c t i o n . ~ .New
” epithelium provides a covering that may be easily disrupted by minor trauma.
Contraction is related to the production and maturation of granulation tissue. The environment under the HG dressing seemed to favor granulation
tissue production and rapid wound contraction.
Therefore, it appears that the H G dressing was the
best treatment evaluated in this study, if contraction
is desired.
There were only seven of 13 wounds healed under
both the HG and HC dressings at the end of the
study. In comparison, all 14 wounds were healed
when treated with the PE dressing. All of the wounds
that were treated with the occlusive dressings and
that were not completely healed at the end of the
study had exuberant granulation tissue. Exuberant
granulation tissue has been associated with delayed
wound healing on the extremities of dogs.28 It appears that the environment under both occlusive
dressings was conducive to the formation of exuberant granulation tissue, however, the wounds under the HC dressing did not go on to contract as well
as the wounds under the HG dressing. The adhesive
nature of the HC dressing has been postulated to
delay wound contraction by sticking to the wound
edges and physically opposing the centripetal pull of
the myofibroblasts in the granulating wound.’ The
H G dressing is more fluid in nature and did not stick
as readily to the wound margins. This may be an
explanation for the differences in rates of contraction
between the two occlusive dressings. Another explanation may lie in the different microenvironments
created by the two occlusive dressings because the
granulation tissue observed under the HC dressing
was less healthy in appearance than that observed
under the HG dressing. It is known that the oxygen
permeabilities of the two dressings differ.23.‘9Reports
suggest that a minimum of 20 mm Hg of oxygen
tension are required for optimal collagen synthesis.30
The HC dressing is not permeable to oxygen and
carbon dioxide.29
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M O R G A N ET AL
50 1
ror of the results at position A. This variation was
Bacterial contamination describes the presence of
likely in part caused by the proximity of the wound
organisms in a wound that d o not create an overto the elbow joint causing motion and bandage slipwhelming inflammatory response. The physiological
page and leading to a difference in healing. It is the
state of the tissue, including the host defenses within
authors'
recommendation that wounds be created
the wound are as important as the presence and type
3 cm distal to the elbow joint when
further
than
of bacteria.3' Bacterial contamination did not appear
comparing wound healing on the antebrachium of
to be a significant factor in wound healing in this
dogs.
study. Although bacteria were cultured and there
were significantly higher bacterial counts under both
occlusive dressings compared with the PE dressing,
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