Standardized burn model using a multiparametric histologic analysis of burn depth

Objective: Burn depth and extent determine prognosis and therapy. The current classification into first-, second-, and third-degree burns is crude, making comparisons between studies difficult. The authors standardized a reproducible burn model and a precise histopathologic method for describing burn depth in swine. Methods: This was a prospective, cross-sectional interventional animal study. Eighteen paired sets of burns were inflicted on the clipped 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°C, 60°C, 70°C, 80°C, 90°C, or 100°C. The bar was applied for 10, 20, or 30 seconds. Full- thickness skin biopsies were obtained 30 minutes after injury for blinded histopathologic evaluation using hematoxylin and eosin staining. Two dermatopathologists made two sets of measurements and were masked to each other's evaluations. The depth of injury was measured with an ocular microtome for each of five dermal parameters: collagen discoloration, intercollagen basophilic material, endothelial cell necrosis, epithelial cell necrosis, and mesenchymal cell necrosis. The correlation between burn depths of the paired sets of experiments was calculated to assess the reliability of the model. Inter-and intraobserver correlations were calculated to assess the reliability of the scale. Analysis of variance (ANOVA) was used to assess the relation between temperature and exposure times on burn depth. Results: Depth of injury for all five dermal elements was related to temperature and exposure times (ANOVA, p < 0.001 for each). The depth of injury in the paired sets of burns was highly consistent (Pearson correlation, range = 0.88-0.95). Inter- and intraobserver correlations were excellent for all measured elements (range = 0.91-0.97 and 0.95-0.99, respectively). Conclusions: The authors describe a simple and reproducible animal burn model and histopathologic scale for measuring burn depth that they believe will facilitate standardization and comparison within future burn studies.