Thermal skin injury: effect of fluid therapy on the transcapillary colloid osmotic gradient

The effects of fluid therapy on interstitial colloid osmotic and hydrostatic pressures in thermally injured skin were investigated in anesthetized rats subjected to full-thickness scald burns to 40% of the body surface area and resuscitation for 3 hr by either lactated Ringer's or plasma. Interstitial fluid hydrostatic pressure (Pif) was reduced from -2 mm Hg to -20 to -40 mm Hg after injury, which will profoundly increase transcapillary filtration. Following the onset of fluid therapy, Pif increased to slightly positive values. In control, colloid osmotic pressure in plasma (COPp) was 20.6 +/- 0.4 mm Hg and in interstitial fluid (COPif) 13.7 +/- 0.3 mm Hg (means +/- SEM). The transcapillary oncotic pressure gradient (COPgrad = COPp-COPif) was 6.9 +/- 0.4 mm Hg. Following nonresuscitated thermal injury, COPp declined to 18-19 mm Hg (P less than 0.05) and COPif was reduced to 10.4 +/- 0.5 mm Hg (P less than 0.05). Fluid therapy by lactated Ringer's markedly reduced COPp (12.3 +/- 0.3 mm Hg; P less than 0.05), and COPgrad was almost abolished (2.6 +/- 0.7 mm Hg; P less than 0.05). In contrast, plasma infusion maintained COPp, whereas COPgrad increased significantly (11.1 +/- 1.2 mm Hg; P less than 0.05). Noncolloid saline solutions have been preferred for the initial fluid therapy for burns. The present study provides evidence that this will reduce both COPp and COPgrad, a situation in which edema formation will be favored.