Objective: Burn depth and extent determine prognosis and therapy. The curre
nt classification into first-, second-, and third-degree burns is crude, ma
king comparisons between studies difficult. The authors standardized a repr
oducible burn model and a precise histopathologic method for describing bur
n depth in swine. Methods: This was a prospective, cross-sectional interven
tional animal study. Eighteen paired sets of burns were inflicted on the cl
ipped flank skin of two anesthetized domestic pigs with a 2.5 cm by 2.5 cm
by 7.5 cm aluminum bar preheated in water to 50 degrees C, 60 degrees C, 70
degrees C, 80 degrees C, 90 degrees C, or 100 degrees C. The bar was appli
ed for 10, 20, or 30 seconds. Full-thickness skin biopsies were obtained 30
minutes after injury for blinded histopathologic evaluation using hematoxy
lin and eosin staining. Two dermatopathologists made two sets of measuremen
ts and were masked to each other's evaluations. The depth of injury was mea
sured with an ocular microtome for each of five dermal parameters: collagen
discoloration, intercollagen basophilic material, endothelial cell necrosi
s, epithelial cell necrosis, and mesenchymal cell necrosis. The correlation
between burn depths of the paired sets of experiments was calculated to as
sess the reliability of the model. Inter- and intraobserver correlations we
re calculated to assess the reliability of the scale. Analysis of variance
(ANOVA) was used to assess the relation between temperature and exposure ti
mes on burn depth. Results: Depth of injury for all five dermal elements wa
s related to temperature and exposure times (ANOVA, p < 0.001 for each). Th
e depth of injury in the paired sets of burns was highly consistent (Pearso
n correlation, range = 0.88-0.95). Inter- and intraobserver correlations we
re excellent for all measured elements (range = 0.91-0.97 and 0.95-0.99, re
spectively). Conclusions: The authors describe a simple and reproducible an
imal burn model and histopathologic scale for measuring burn depth that the
y believe will facilitate standardization and comparison within future burn
studies.