Relationship of burn size to vascular permeability changes in rats

Studies to determine the relationship between increased vascular permeability, water content and protein leakage, and burn size were performed on rats. Partial thickness scald burn covering 10, 20, 30 and 40 per cent of the rats' body surface area were induced in four groups of rats. A fifth group of rats served as the controls. Following the burn, all rats received intravenously fluid resuscitation. Burn edema was maximal at three hours postburn for the 30 and 40 per cent groups. The edema persisted throughout the 24 hour study period. No significant change in water content of unburned skin was demonstrated. Albumin leakage into injuried tissues was maximal at 30 minutes and disappeared by 12 hours postinjury. The size of the burn had no effect on 131Risa leakage into injuried tissues. Albumin leakage into noninjured tissues occurred only in the 30 and 40 per cent burn groups was mild compared with that in burned tissues and also disappeared by 12 hours postburn. Extravasation of albumin in lung, liver, spleen, kidney and muscle was mild and seen only in the 30 and 40 per cent burn groups. Except for a mild increase in water content of lung tissue in the 30 and 40 per cent groups only, no consistent increase in the water content of other organs was observed. While the size of the burn appears to have some influence on capillary permeability, burns up to 40 per cent of the body surface have only a mild and transient effect upon capillaries distant to the site of injury. This observation supports the concept of a humoral mediator for capillary permeability and suggests that more pronounced changes can occur with larger burns. Nonetheless, extravasation of albumin appears to be short-lived.