Acute hemodynamic effects of thermal skin injury in the rat

Heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), and cardiac index (CI) were measured in anesthetized rats subjected to thermal injury covering 10 and 40% of the body surface area (BSA). These were compared to corresponding sham controls. No fluid substitution was provided. MAP decreased rapidly from 110 mm Hg preburn and leveled off at 75-80 mm Hg after 60 min postburn in the 40% burn group and at 80-95 mm Hg in the 10% burn group. CVP was not influenced by thermal injury. CI fell from about 270 to 208 and to 173 ml X min-1 X kg-1 during the first 15 min after injury in the 10 and 40% burn groups, respectively. Thereafter, CI continued to fall more slowly in both groups, being lower in the 40% than the 10% burn group for the whole postburn course (P less than .001). HR fell slightly in both burn groups (P greater than .05). Stroke volume index followed the same pattern as CI indicating that the fall in CI was caused by reduction in stroke volume. Total peripheral resistance increased slightly after injury. Previous measurement of hematocrit in thermal injury of the same type and extent suggests a 35% increase in viscosity. Consequently, vascular hindrance was unchanged. Compensatory tachycardia or vasoconstriction could not be demonstrated.