THE ROLE OF INTERSTITIAL STARLING FORCES IN THE PATHOGENESIS OF BURN EDEMA

The formation and sustainability of burn edema require substantial cha nge in net microvascular forces. We directly measured interstitial hyd rostatic pressure (Pi) and total interstitial absorptive pressure (Pi + Pi i), in dermis of anesthetized sheep, before and after a 70% to 85 % total body surface area scald and during fluid resuscitation. The mo st rapid change occurred in Pi in the burn wound, which rapidly decrea sed from its baseline value of approximately -2 mm Hg to -11 mm Hg in the first 5 minutes, and thereafter increased but remained approximate ly -4 mm Hg through 4 hours of resuscitation. Pi in nonburned skin slo wly increased from its preburn level -2 mm Hg, to become positive +1 m m Hg after 4 hours of resuscitation. The total interstitial absorptive pressure, Pi + Pi i, slowly declined similarly from 15 to 16 mm Hg to approximately 10 to 11 mm Hg over 6 hours of resuscitation in both bu rned and nonburned dermis. Taken together, these data suggest that the rapid formation of burn edema is the result of development of a negat ive Pi in the burn wound, and its sustainability is the result of a la rge increase in interstitial compliance. Edema in nonburned skin did n ot start until after fluid resuscitation was initiated, and then devel oped as the plasma oncotic pressure declined from 21 to 10 mm Hg.