Microvascular fluid exchange following thermal skin injury in the rat: changes in extravascular colloid osmotic pressure, albumin mass, and water content.

Microvascular fluid exchange was studied in rats subjected to 0, 10, and 40% body surface area (BSA) full-thickness cutaneous burns without providing fluid substitution. The total amounts of water and of albumin entering the entire burned skin area following 10% BSA burns were similar to that in 40% BSA burns. Colloid osmotic pressure in interstitial fluid (COPi) was around 10 mmHg and did not change in the control group or in burned skin from the 40% BSA burn group. COPi after 10% burns increased to 15 mmHg in injured skin, while plasma COP fell from 16 to 12.5 mmHg. Preburn, the interstitial albumin mass (Qalb) was 14.9 mg/g dry tissue weight (DW) and increased to 42 and 20 mg/g DW in injured skin after 10 and 40% burns, respectively. Extravasation of radiolabeled albumin (Ealb) estimated as plasma equivalents per 30 min increased from 6.0 to 321 microliters/g DW at 30-60 min postburn (PB) in injured skin following 10% BSA burns. At 90-120 and 150-180 min PB Ealb in this group was reduced to approximately 120 microliters/g DW. These levels of Ealb were roughly 6 times higher than those after 40% BSA burns. Total tissue water (TTW) was 1.78 ml/g DW preburn and increased to 3.0 and 2.0 ml X g-1 DW PB in the 10 and 40% burn groups, respectively. TTW and Qalb did not change beyond 60 min PB.