IMPACT OF ANESTHESIA, ANALGESIA, AND EUTHANASIA TECHNIQUE ON THE INFLAMMATORY CYTOKINE PROFILE IN A RODENT MODEL OF SEVERE BURN INJURY

Anesthetics used in burn and trauma animal models may be influencing results by modulating inflammatory and acute-phase responses. Accordingly, we determined the effects of various anesthetics, analgesia, and euthanasia techniques in a rodent burn model. Isoflurane (ISO), ketamine-xylazine (KX), or pentobarbital (PEN) with or without buprenorphine were administered before scald-burn in 72 rats that were euthanized without anesthesia by decapitation after 24 h and compared with unburned shams. In a second experiment, 120 rats underwent the same scald-burn injury using KX, and 24 h later were euthanized under anesthesia or carbon dioxide (CO2). In addition, we compared euthanasia by exsanguination with that of decapitation. Serum cytokine levels were determined by an enzyme-linked immunosorbent assay. In the first experiment, ISO was associated with elevation of cytokine-induced neutrophil chemoattractant 2 (CINC-2) and monocyte chemotactic protein 1 (MCP-1), and KX and PEN was associated with elevation of CINC-1, CINC-2, IL-6, and MCP-1. Pentobarbital also decreased IL-1 beta. IL-6 increased significantly when ISO or PEN were combined with buprenorphine. In the second experiment, euthanasia performed by exsanguination under ISO was associated with reduced levels of IL-1 beta, CINC-1, CINC-2, and MCP-1, whereas KX reduced CINC-2 and increased IL-6 levels. Meanwhile, PEN reduced levels of IL-1 beta and MCP-1, and CO2 reduced CINC-2 and MCP-1. In addition, decapitation after KX, PEN, or CO2 decreased IL-1 beta and MCP-1, although we found no significant difference between ISO and controls. Euthanasia by exsanguination compared with decapitation using the same agent also led to modulation of several cytokines. Differential expression of inflammatory markers with the use of anesthetics and analgesics should be considered when designing animal studies and interpreting results because these seem to have a significant modulating impact. Our findings indicate that brief anesthesia with ISO immediately before euthanasia by decapitation exerted the least dampening effect on the cytokines measured. Conversely, KX with buprenorphine may offer a better balance during longer procedures to avoid significant modulation. Standardization across all experiments that are compared and awareness of these findings are essential for those investigating the pathophysiology of inflammation in animal models.