Standardized burn model using a multiparametric histologic analysis of burn depth

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.