Development of a long-term ovine model of cutaneous burnand smoke inhalation injury and the effects of early excisionand skin autografting

Yusuke Yamamoto a,c, Perenlei Enkhbaatar a, Hiroyuki Sakurai a, Sebastian Rehberg a,Sven Asmussen a, Hiroshi Ito a, Linda E. Sousse a, Robert A. Cox a, Donald J. Deyo a,Lillian D. Traber a, Maret G. Traber b, David N. Herndon a, Daniel L. Traber a,*aDepartment of Anesthesiology, Investigational Intensive Care Unit, The University of Texas Medical Branch, Shriners Burns Hospital for

Children, 601 Harborside Drive, Galveston, TX 77555-1102, USAb Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USAcDepartment of Plastic and Reconstructive Surgery, Tokyo Women’s Medical University, 8-1 Kawata-cho, Shinjuku-ku, Tokyo 162-8666, Japan

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6

a r t i c l e i n f o

Article history:

Accepted 6 January 2012

Keywords:

Wound healing

Wet-to-dry weight ratio

Net fluid balance

Plasma protein

Oncotic pressure

Hematocrit

Neutrophils

a b s t r a c t

Smoke inhalation injury frequently increases the risk of pneumonia and mortality in burn

patients. The pathophysiology of acute lung injury secondary to burn and smoke inhalation

is well studied, but long-term pulmonary function, especially the process of lung tissue

healing following burn and smoke inhalation, has not been fully investigated. By contrast,

early burn excision has become the standard of care in the management of major burn

injury. While many clinical studies and small-animal experiments support the concept of

early burn wound excision, and show improved survival and infectious outcomes, we have

developed a new chronic ovine model of burn and smoke inhalation injury with early

excision and skin grafting that can be used to investigate lung pathophysiology over a period

of 3 weeks.

Materials and methods: Eighteen female sheep were surgically prepared for this study under

isoflurane anesthesia. The animals were divided into three groups: an Early Excision group

(20% TBSA, third-degree cutaneous burn and 36 breaths of cotton smoke followed by early

excision and skin autografting at 24 h after injury, n = 6), a Control group (20% TBSA, third-

degree cutaneous burn and 36 breaths of cotton smoke without early excision, n = 6) and a

Sham group (no injury, no early excision, n = 6). After induced injury, all sheep were placed

on a ventilator and fluid-resuscitated with Lactated Ringers solution (4 mL/% TBS/kg). At

24 h post-injury, early excision was carried out to fascia, and skin grafting with meshed

autografts (20/1000 in., 1:4 ratio) was performed under isoflurane anesthesia. At 48 h post-

injury, weaning from ventilator was begun if PaO2/FiO2 was above 250 and sheep were

monitored for 3 weeks.

Results: At 96 h post-injury, all animals were weaned from ventilator. There are no signifi-

cant differences in PaO2/FiO2 between Early Excision and Control groups at any points. All

animals were survived for 3 weeks without infectious complication in Early Excision and

Sham groups, whereas two out of six animals in the Control group had abscess in lung. The

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percentage of the woun

post-surgery in the Earl

* Corresponding author. Tel.: +1 409 772 6405; fax: +1 409 772 6409.E-mail address: dltraber@utmb.edu (D.L. Traber).

0305-4179/$36.00. Published by Elsevier Ltd and ISBIdoi:10.1016/j.burns.2012.01.003

d healed surviving area (mean � SD) was 74.7 � 7.8% on 17 days

y Excision group. Lung wet-to-dry weight ratio (mean � SD) was

significantly increased in the Early Excision group vs. Sham group ( p < 0.05). The calculated

net fluid balance significantly increased in the early excision compared to those seen in the

Sham and Control groups. Plasma protein, oncotic pressure, hematocrit of % baseline,

hemoglobin of % baseline, white blood cell and neutrophil were significantly decreased in

the Early Excision group vs. Control group.

Conclusions: The early excision model closely resembles practice in a clinical setting and

allows long-term observations of pulmonary function following burn and smoke inhala-

tion injury. Further studies are warranted to assess lung tissue scarring and measuring

collagen deposition, lung compliance and diffusion capacity.

Published by Elsevier Ltd and ISBI

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6 909

1. Introduction

The short-term pathophysiology of acute lung injury second-

ary to burn and smoke inhalation has been studied extensively

[1–4] but there are few studies of long-term pulmonary

pathophysiology following burn and smoke inhalation [5].

The purpose of present study was to develop an animal model

of smoke inhalation injury and cutaneous burn to document

the long-term effect on the pulmonary parenchyma. In order

to study the long-term effect of injury, the animals need to

survive over 2 weeks with appropriate treatment. Early burn

excision and skin grafting have become the standard of care in

the management of major burns [6]. Many clinical studies and

small-animal experiments support the concept of early burn

wound excision and show decreased operative blood loss,

length of hospitalization, and incidence of infection compared

with late excision [7–12]. The effects of early excision and skin

grafting have not, to our knowledge, been studied well in a

large-animal model. We hypothesized that long-term model

of smoke inhalation injury and cutaneous burn could be

produced if early burn excision and autografting were utilized.

In the present study, we have developed a new ovine model

of smoke inhalation injury and cutaneous burn with early

excision and skin autografting to investigate chronically in

lung tissue. We also demonstrated the effects of the early

excision and skin autografting in our model with inhalation

injury.

2. Materials and methods

This study was approved by the Animal Care and Use

Committee of the University of Texas Medical Branch

(Galveston, TX, USA) and conducted in compliance with the

guidelines of the National Institutes of Health and the

American Physiological Society for the care and use of

laboratory animals.

2.1. Surgical preparation

Eighteen female sheep were surgically prepared for this study

under isoflurane anesthesia. The mean animal weight

(mean � SD) was 34 � 4.6 kg. The right femoral artery was

canulated with Silastic catheter (Intracath; 16 gauge, 24 in.;

Becton Dickinson Vascular Access, Sandy, UT, USA). A

thermodilution catheter (Swan–Ganz model 131F7, Baxter,

Edwards Critical-Care Division, Irvine, CA, USA) was intro-

duced through the right external jugular vein into the

pulmonary artery. Through the left fifth intercostal space, a

catheter (Durastic silicone tubing DT08, 0.062-in. ID, 0.125-in.

OD; Allied Biomedical, Paso Robles, CA, USA) was positioned in

the left atrium. The animals were given 5–7 days to recover

from the surgical procedure, with free access to food and

water.

2.2. Experimental protocol

Before the experiment, the vascular catheters were connected

to the monitoring devices, and maintenance fluid (Ringer

lactate, 2 mL/kg) was started. After baseline measurements

and sample collections were completed, the animals were

randomized into three groups: Early Excision group (20% TBSA,

third-degree cutaneous burn and 36 breaths of cotton smoke

followed by early excision and skin autografting at 24 h after

injury, n = 6), Control group (20% TBSA, third-degree cutane-

ous burn and 36 breaths of cotton smoke without early

excision, n = 6) and Sham group (no injury, no early excision,

n = 6).

Immediately after injury, anesthesia was discontinued.

The animals were allowed to awaken but were maintained on

mechanical ventilation (Servo Ventilator 900C, Siemens-

Elema AB, Sweden) for at least a 48 h experimental period.

This was continued until the weaning process was completed.

Ventilation was performed with a positive end-expiratory

pressure of 5 cmH2O and a tidal volume of 15 mg/kg. During

the first 3 h after injury, the inspiratory O2 concentration was

maintained at 100% to induce rapid clearance of carboxyhe-

moglobin after smoke inhalation. The ventilation was then

adjusted according to blood gas analysis to maintain arterial

O2 saturation >90% and PCO2 between 25 and 30 mmHg. At

48 h post-injury, weaning from ventilator was begun if PaO2/

FiO2 was above 250. Animals were then monitored for 3 weeks.

Fluid resuscitation was given during the first 48 h experimen-

tal period with Ringer’s lactate solution following the Parkland

formula (4 mL/% burned surface area/kg body weight for first

24 h and 2 mL/% burned surface area/kg body weight/day for

the next 24 h). One-half of the volume for the first day was

infused in the initial 8 h, and the remainder was infused in the

next 16 h. From 48 h to 432 h, the animals received Ringer’s

lactate (2 mL/% burned surface area/kg body weight/day). For

96 h post-injury, animals were allowed free access to food but

not to water, to accurately measure fluid intake. Free access to

water was permitted after this period. A Foley catheter was

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inserted to measure urine output until 96 h post-injury. At 24 h

post-injury, early excision was carried out to 20% TBSA and

skin autografting was performed at the time of excision under

isoflurane anesthesia in the Early Excision group. Antibiotics

(Cefazolin, 2 g/day, IV; Marsam Pharmaceuticals Inc., Cherry

Hill, NJ and Tobramycin, 0.24 g/day, IV; Abraxis Pharmaceuti-

cal Products, Schaumburg, IL, USA) were given for 432 h to

prevent possible infection. The animals were monitored for 3

weeks and were euthanized to assess lung tissue after an

injection of ketamine (Ketaset, Fort Dodge Animal Health, Fort

Dodge, IA, USA) followed by saturated KCl.

2.3. Burn and smoke inhalation injury

A tracheostomy was performed on each animal under

ketamine anesthesia and a cuffed tracheostomy tube (10-

mm diameter; Shiley, Irvine, CA, USA) was inserted. The

anesthesia was continued with isoflurane, and the wool on

both sides of the flank was shaved with electric clippers

(Fig. 1A). The hair on one side of flank was removed using a

depilatant (Nair1, Church & Dwight Co., Inc., Princeton, NJ,

USA) to harvest skin. A 20% TBSA third-degree burn was

inflicted on one side of the flank with a Bunsen burner until the

skin was thoroughly contracted (Fig. 1B). Smoke inhalation

was induced with a modified bee smoker. The bee smoker was

filled with 40 g of burning cotton toweling and then attached to

the tracheostomy tube via a modified endotracheal tube

containing an indwelling thermistor from a Swan–Ganz

catheter [13]. Three sets of 12 breaths of smoke (total 36

breaths) were delivered, and the carboxyhemoglobin level was

determined immediately after each set. The temperature of

the smoke was not allowed to exceed 40 8C during the smoking

procedure.

2.4. Early excision and skin autografting

At 24 h post-injury, early excision was carried out to muscular

fascia in the burn area (Fig. 1C) under isoflurane anesthesia in

the Early Excision group. Skin autografting was performed at

the time of excision (Fig. 1D). Split-thickness skin sections (20/

1000 in., 0.5 mm) were harvested from the flank of the other

side using an electric dermatome (Padgett Electro-Derma-

Fig. 1 – Photographs of excision and skin autografting in sheep.

post-escharectomy; and (D) post-grafting.

tome, Padgett Instruments Inc., KC, USA) and meshed in 4:1

ratio using a mesh dermatome (Padgett Mesh-Dermatome,

Padgett Instruments Inc., KC, USA). The graft area was covered

using non-adhering dressing (ADAPTIC1, Johnson & Johnson,

Skipton, UK). The tie-over dressing was performed using

rubber band and removed 4–6 days after placement. After

removing the dressing, the wound was treated using vaseline

without dressing. In order for the animal to maintain body

temperature the operating time was limited to a maximum of

2 h. The ambient temperature in the operating room was

maintained at 30 8C to prevent hypothermia. The Control and

Sham groups were exposed to anesthesia with isoflurane for

100 min in the same operation room. Seventeen days after

surgery, the wound was evaluated and photographed by the

same person (for consistency) each time the site was

evaluated. Each photograph was transferred in digital format

and measured for the size of raw surface (RS; in cm2) and total

graft area (TGA; in cm2) using computer software (ImageJ

1.40g, National Institutes of Health, USA) [14,15]. The percent-

age of the wound healed area (WHA) was calculated using the

following equation:

WHA% ¼ 100 � TGA � RSTGA

:

2.5. Measured variables

Mean arterial (MAP; in mmHg), mean pulmonary arterial

(MPAP; in mmHg), left atrium (LAP; in mmHg), and central

venous (CVP; in mmHg) pressure were measured with

pressure transducers (model PX-1800, Baxter, Edwards Criti-

cal-Care Division) that were adapted with a continuous

flushing device. The transducers were connected to a

hemodynamic monitor (model 78304A, Hewlett-Packard,

Santa Clara, CA, USA). The pressures were measured with

the animal in the standing position. Zero calibrations were

taken at the level of the olecranon joints on the front leg of the

animal. Cardiac output was measured with the thermodilu-

tion technique with a cardiac output computer (COM-1,

Baxter, Edwards Critical-Care Division). A 5% dextrose solu-

tion was used as the indicator. For evaluation of cardiac

function, cardiac index (CI; in L min�1 m�2) was calculated

(A) Design of 20% TBSA burn; (B) third-degree flame burn; (C)

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6 911

with standard equations. Blood gases were measured with a

blood gas analyzer (IL GEM Premier 3000 Blood Gas Analyzer;

GMI, MN, USA). The blood gas results were corrected for the

body temperature of the animal. Oxyhemoglobin saturation

and hemoglobin concentration were analyzed with a CO-

Oximeter (model IL 482, Instrumentation Laboratory, USA).

White blood cells (WBC; in cells/mL); neutrophil (in cells/mL)

were counted (HEMAVET1 HV950FS; Drew Scientific, Inc., TX,

USA). Blood samples for determination of total protein

concentration and oncotics pressure were collected in all

groups. Hematocrit (Hct; in %) was measured in heparinized

microhematocrit capillary tubes (Fisherbrand, Pittsburgh, PA,

USA). Infused fluid volume and urine output were recorded

every 6 h and net fluid balance was calculated by subtracting

urine output from fluid intake. After sheep were euthanized,

the entire right lung was harvested for measurement of wet-

to-dry weight ratios (an index of pulmonary edema) as

described by Pearce et al. [16] and aliquots of lung tissue

were taken for various assays.

2.6. Statistical analysis

Significance was determined using a two-factor analysis of

variance with repeated measures. The two factors were

treatment and time. The differences in the wet-to-dry weight

were evaluated by means of Student’s unpaired t-test. p-

Value < 0.05 was considered to be significant.

3. Result

3.1. Injuries and survival

The arterial carboxyhemoglobin levels (mean � SD), as mea-

sured immediately after smoke exposure, amounted to

58.6 � 10.1% in the Early Excision group and 61.5 � 9.6% in

the Control group. There were no significant differences

between two groups. The Sham group had a significantly lower

mean carboxyhemoglobin level of 6.5 � 0.4%. All animals were

survived for 3 weeks without infectious complication in Early

Excision and Sham groups, whereas two out of six animals had

abscess in lung in the Control group.

Fig. 2 – Photographs of a wound series showing wound closure

PO day 13; and (C) PO day 17.

3.2. Early excision and skin autografting

Early excision and skin autografting were performed in safety

in the Early Excision group. The operative blood loss

(mean � SD) was 82.8 � 44.2 g, operation time (mean � SD)

was 86.7 � 18.6 min and the weight of excised eschar

(mean � SD) was 1127 � 139 g. There was no bleeding

(Fig. 2A) or wound infection (Fig. 2B) after operation. In the

donor site, the wound was closed 2 weeks after surgery. The

percentage of the wound healed area (mean � SD) was

74.7 � 7.8% on 17 days post-surgery (Fig. 2C).

3.3. Cardiopulmonary hemodynamics

No significant differences were noted in CI, MAP, LAP and CVP

between the groups at any time point. MPAP and pulmonary

vascular resistance index (PVRI) in the Early Excision group

were lower compared to the Control group (Fig. 3C and D).

However, there were no significant differences between Early

Excision and Control groups.

3.4. Pulmonary gas exchange

In the Early Excision and Control groups, the average of the

PaO2/FiO2 ratio decreased from 12 h post-injury and demon-

strated significantly lower level vs. Sham group from 48 h to

96 h post-injury (Fig. 3A). The average of worst level in the

PaO2/FiO2 ratio was 246 � 85 in the Early Excision group,

281 � 71 in the Control groups and 489 � 16 in the Sham group

throughout the experimental time period. In the PaO2/FiO2

ratio, no statistical difference was found between the Early

Excision and the Control group. All animals gradually

recovered in the PaO2/FiO2 ratio and were successfully weaned

from the ventilator. All animals recovered to baseline level in

the PaO2/FiO2 at 2 weeks post-injury. No animals showed a

progressive fall in the early postoperative period. The

pulmonary shunt fraction (Qs/Qt) increased from 12 h to

96 h post-injury in the Early Excision and the Control groups

(Fig. 3B). However, these values could not be shown to be

statistically different from baseline. There were no significant

differences between Early Excision and Control groups in the

PaO2/FiO2 and Qs/Qt at any time point.

in the Early Excision group. (A) Postoperative (PO) day 4; (B)

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6912

3.5. Fluid balance

The urine output decreased at 30 h post-injury and was

maintained in the range of 0.5–1 mL/kg/h in the Early Excision

group (Fig. 4B). Despite the same amount of fluid resuscitation

(Fig.4A), significantly higherurine output wasnotedat54 h post-

injury inthe Control group comparedtothe Early Excision group.

The calculated net fluid balance significantly increased in the

Early Excision compared to those seen in the Sham and Control

groups (Fig. 4C). Accumulated positive fluid balance in the Early

Excision groupsignificantly increased vs.Shamgroup during the

first 48 h and Control group during the second 48 h (Fig. 4D).

3.6. Plasma protein and colloid oncotics pressure inplasma

In the Early Excision group, plasma protein and colloid oncotic

were significantly decreased during the first 96 h and

increased up to 432 h post-injury, whereas in the Control

group, these were increased from 48 h post-injury (Fig. 5A and

B). Statistical differences were shown in the plasma protein

and the oncotic pressure vs. Control and Sham groups.

Fig. 3 – The effect of burn wound excision and skin autografting

pulmonary arterial pressure; and (D) pulmonary vascular resistanc

difference ( p < 0.05) vs. Sham group. There are no statistical diffe

3.7. Hematocrit and hemoglobin

Hct of % baseline in the Early Excision group decreased after

injury up to 432 h post-injury and was significantly lower

than the Control group at 408 and 432 h post-injury (Fig. 6A).

Hemoglobin also decreased and showed statistical differ-

ence from 360 h to 432 h post-injury vs. Control group

(Fig. 6B).

3.8. White blood cell counts

The WBC and neutrophil counts were significantly decreased

after burn wound excision and autografting (Fig. 7A and B).

Statistical differences were found at 48, 60 and 72 h post-injury

in the neutrophil vs. Control group and at 60 h post-injury vs.

Sham group.

3.9. Lung bloodless wet-to-dry weight ratio

Lung wet-to-dry weight ratio, an indicator of lung water

content, was significantly increased in the Early Excision

group compared to the Sham group (Fig. 8).

on (A) PaO2/FiO2; (B) pulmonary shunt fraction; (C) mean

e index. Values are expressed as mean W SEM. (*) Significant

rences between Early Excision and Control groups.

Fig. 4 – Fluid balance after injury. All groups received identical amounts of fluid during the whole experimental period.

Values are expressed as mean W SE. (*) Significant difference ( p < 0.05) vs. Sham group; (#) significant difference ( p < 0.05)

vs. Control group. (A) Fluid intake; (B) urine output; (C) net fluid balance; (D) 48 h accumulation of net fluid balance.

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6 913

4. Discussion

Several authors have described long-term clinical effects of

smoke inhalation injury [17,18]. Fogarty et al. showed ventila-

tory defect and small airway obstruction were present in 11

survivors of the King’s Cross underground station fire after 6

months [19]. Desai et al. reported that 64% of pediatric patients

(mean burn size of 44% total body surface) with inhalation

injury had abnormal spirometry and lung volumes at rest 2

years post-injury [20]. Park et al. demonstrated the long-term

effects of smoke inhalation, by examining airway responsive-

ness, airway inflammation, and systemic effects, and conclud-

ed that inflammatory reaction in the airways and peripheral

blood continues for at least 6 months after smoke inhalation

[21]. However, there are no studies using the same criteria that

grade simultaneously the degree of smoke inhalation and the

same methodology to evaluate lung function. Palmieri suggests

the first step in determining the effects of smoke on long-term

pulmonary function is to evaluate it in an animal model [22].

Many animal models with smoke inhalation and cutaneous

burn have been described in the literature involving rodents

without early excision [1–5,23,24], but there have been no

clinically relevant large-animal models which could monitor

pulmonary function and hemodynamics for over and extended

period of 2 weeks or more.

Darling et al. demonstrated the high mortality from

inhalation injuries is most significant in burns >15% TBSA

[25]. Suzuki et al. also reported that the mean full thickness

burn size of 1690 patients with inhalation injury was 20.4%

TBSA in Tokyo [26]. In our model, the size of cutaneous burn

was determined in consideration of the effects on pulmonary

function. It is well established that inhalation injury increases

the mortality in burn patients, but there are few studies to

determine whether early excision at 24 h post-injury would

aggravate pulmonary function in inhalation injury [6].

The present study suggests that early excision and skin

autografting do not aggravate pulmonary function in PaO2/

FiO2 ratio, Qs/Qt, PAP and PVRI compared with no excision

group. At 3 weeks post-injury, these indices showed

recovery from lung injury. Excision therapy and autografting

were safely performed in sheep with impaired lung function

and long-term model of smoke inhalation injury and

cutaneous burn without wound infection. In the present

model, a cotton smoke insufflation injury (36 breaths)

combined with a 20% TBSA third-degree cutaneous flame

burn produces a predictable (PaO2/FiO2 < 300) model of acute

lung injury (ALI). One of the long-term effects of smoke

inhalation injury was demonstrated in lung wet-to-dry

weight ratio, an index of pulmonary edema, in the Early

Excision group (Fig. 8). To show the long-term effects clearly,

further studies are needed using the measurement of

Fig. 5 – The effect of burn wound excision and skin

autografting on plasma protein and colloid oncotics

pressure in plasma. Values are expressed as mean W SE. (*)

Significant difference ( p < 0.05) vs. Sham group; (#)

significant difference ( p < 0.05) vs. Control group. (A)

Plasma protein; (B) colloid oncotic pressure in plasma.

Fig. 6 – (A) The effect of early excision and skin autografting

on hematocrit (Hct) of % baseline and (B) hemoglobin (Hb)

of % baseline. Early excision and skin autografting

significantly decreased Hct and Hb after 2 weeks post-

operation. Values are expressed as mean W SEM. (*)

Significant difference ( p < 0.05) vs. Sham group; (#)

significant difference ( p < 0.05) vs. Control group. (A) Hct of

% baseline value; (B) Hb.

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6914

collagen deposits, lung compliance and diffusion capacity

tests.

There are several wound models in swine for burn

treatment [14,29–31]. Unfortunately, it is difficult to maintain

tight dressing within the first 4–6 days and keep wound clean

without dressing after first dressing change on an awake pig

[14]. In contrast, in the ovine model it is easy not only to

measure pulmonary and hemodynamic function, but also to

treat and observe the wound as the animals can be maintained

in an upright position. In the present model, burn wound of

approximately 1900 cm2 could be monitored for 3 weeks

without infection. Porcine skin is more similar to human skin

than that of sheep [32], as both porcine and human have

sparse body hair and hair follicles play an important role in

reepithelialization. However, we speculate that the differ-

ences in skin do not have effects on wound healing in our

model because wound excision was carried out to muscular

fascia and split-thickness skin (20/1000 in. or 0.5 mm) was

harvested for grafting. The present burn and smoke inhalation

model with early excision is clinically relevant and, to our

knowledge, is the first in the world to be used for long-term

studies.

Many clinical studies have reported that early excision of

the burn wound decreased operative blood loss, reduced the

length of hospitalization and incidence of infection [7,9,12]. In

the present study, hemoglobin of % baseline and hematocrit of

% baseline did not decrease to a statistically significant degree

in the early postoperative period, and the average of WHA

(mean � SD) was over 70% at 18 days post-injury. In the Early

Excision group, the animals demonstrated no incidence of

infection and could have been discharged from hospital had

they been patients. In the Control group, two out of six animals

(33%) had abscess in lung at 3 weeks post-injury.

At the same time, some differences were exposed between

Early Excision and Control groups. In the net fluid balance,

early excision and skin grafting statistically increased fluid

requirements compared to the Control and the Sham groups

(Fig. 4C). In the Control group, the urine volume was

statistically increased in the refilling period (Fig. 4B), and less

fluid volume was required compared to the Early Excision in

Fig. 7 – (A) The effect of early excision and skin autografting

on white blood cell (WBC) counts and (B) neutrophil

counts. Early excision and skin autografting significantly

decreased WBC and neutrophil counts. Values are

expressed as mean W SEM. (*) Significant difference

( p < 0.05) vs. Sham group; (#) significant difference

( p < 0.05) vs. Control group.

Fig. 8 – Lung wet-to-dry weight ratio represents water

content of lung tissue. Values are expressed as

mean W SEM. Early Excision group showed significantly

higher wet-to-dry weight ratio compared to Sham group.

(*) Significant difference ( p < 0.05) vs. Sham group.

b u r n s 3 8 ( 2 0 1 2 ) 9 0 8 – 9 1 6 915

the second 48 h post-injury (Fig. 4D). Hypoproteinemia and

statistical lower oncotic pressure were found after operation

and recovered from 1 week post-injury in the Early Excision

group (Fig. 5A and B). These results showed that we have to

know the differences between burn/inhalation injury with

early excision and burn/inhalation injury alone to determine

the fluid resuscitation volume. Progressive anemia, which was

measured as Hb and Hct, had appeared in the Early Excision

group throughout the experiments though frank bleeding was

not observed after surgery (Fig. 6A and B). In a clinical setting,

hospitalized burn patients often become anemic because of

hemodilution, relative bone marrow suppression, and fre-

quent laboratory draws [33]. Early eschar excision traditionally

has been associated with significant operative blood loss [34].

Our current findings suggest that supplement of albumin and

late blood transfusion should be considered in extensive burn

patients after early excision and grafting. Early wound

excision had been shown in small-animal study to increase

pulmonary leukosequestration compared with the burn injury

alone [35]. In the present model, neutrophil counts statistically

significantly decreased compared to Control group and

baseline value after burn wound excision. We speculate that

neutrophil counts were decreased because of leukosequestra-

tion. Xiao-Wu et al. showed that some patients have

postoperative pulmonary complications that may counter

any benefits from immediate excision such that the 2 effects

cancel each other [6].

5. Conclusions

Early excision and skin autografting were performed in sheep

with 20% burn and moderate smoke inhalation injury without

changes of hemodynamics and pulmonary dysfunction. This

model closely resembles clinical setting, exposes the effects of

early excision and autografting and allows to chronically

monitor pulmonary function following burn and smoke

inhalation injury. Further studies are warranted to assess

lung tissue scaring measuring collagen deposition, lung

compliance and diffusion capacity.

Conflict of interest

The authors declare that there is no conflict of interest.

Acknowledgments

National Institute supported this work for General Medical

Sciences Grant GM66312-01 and Grants 8450, 8630, 8520 and

8954 from the Shriners of North America.

r e f e r e n c e s

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