In vivo visualization of cerebral microcirculation in systemic thermal injury

We present a model used to describe the effects of systemic thermal injury in cerebral permeability with the use of an open, acute pial window technique. Sprague-Dawley rats were anesthetized, and an open pial window was constructed. The area was then bathed with artificial cerebrospinal fluid with a pH adjusted to 7.4 that was heated to a constant temperature of 37 degrees C, which was allowed to circulate into a reservoir at a rate of 2 cc/min. The fluid was infused with a gas mixture of 5% carbon dioxide and 95% nitrogen. A warming blanket was placed under the animal's ventral surface, and the animal's temperature was maintained at 37 degrees C and monitored with a rectal thermal probe. Experimental animals were submerged to the xiphoid process in 100 degrees C water bath for a total of 6 seconds, which produced a 70% total body surface area third degree burn. Control animals were submerged in 37 degrees C water for 6 seconds. The animals were then injected with a constant infusion of bovine albumin coupled with fluorescein isothiocyanate. Recordings were taken every 15 minutes for 6 hours. The vascular albumin leakage was determined from the ratio of interstitium to vascular fluorescence and expressed as a percentage. The percent albumin leakage in the control group was found to be significantly different from that in the experimental group at all periods measured. The mean increase in permeability ranged from 20% at 15 minutes to 104% at 6 hours. These changes were found to be statistically significant with the use of unpaired t test at a P value of .0001. The model presented is the first to demonstrate changes in cerebral permeability after acute severe systemic thermal injury.