ELUCIDATING THE VASCULAR-RESPONSE TO BURNS WITH A NEW RAT MODEL

Burn injury causes acute thrombosis and occlusion of vessels in the dermis directly killed by thermal energy. A vascular response also occurs in the uninjured dermis bordering the site of injury. Diminished blood flow leads to progressive ischemia and necrosis in the dermis beneath and surrounding the burn. If blood flow is maintained or restored in this area, the tissue survives. A noninvasive technique for studying dynamic changes in blood flow in this transitional dermis in rats is presented. A rectangular brass bar 19 mm wide with 5-mm transverse notches was heated in boiling water and applied to the skin surface for 20 seconds, making a "comb" burn composed of a row of four rectangular 10 x 19-mm full-thickness burns. Between the burns were 5 x 19-mm bands of uninjured skin, called "interspaces." After burning, blood flow near the surface of both the burn sites and the interspaces was monitored with a laser Doppler perfusion monitor for 24 hours. The vascular patency of blood vessels was directly visualized by latex vascular casts made 24 hours after burn. The possible prevention of progressive ischemia by injecting systemic ibuprofen was examined in this new model. Normal skin has a surface blood flow reading of 80 +/- 16 mV, burn sites have a reading of 11 +/- 4 mV, and interspaces have a reading of 21 +/- 4 mV at 24 hours postburn in untreated rats. Systemic ibuprofen given IM immediately postburn at 12.5 mg/kg increased blood flow to 80 +/- 28 mV within the interspaces, to 17 +/- 12 mV in the burn site, and to 80 +/- 9 mV in normal skin. The vascular casts showed an absence of patent vessels within both the burn sites and interspaces in untreated rats. The four individual burn sites had generated into a larger single full-thickness injury. In treated rats patent vessels were present in the interspaces but not in the burn sites. Four individual wounds were evident at 24 hours. Histologic preparations of vascular casts showed the absence of latex-filled vessels and thrombus-filled vessels in the burn sites and the interspaces of untreated rats. With ibuprofen therapy, latex-filled vessels were evident within the interspaces and dermis as were thrombus-filled vessels within the burn sites.