Effect of nonprotein colloid on postburn edema formation in soft tissues and lung

We studied the effect of a nonprotein colloid solution - namely low molecular weight dextran (LMWD) - on edema formation in burned and nonburned soft tissue and lung. Adult sheep with lung and bilateral flank lymph fistulas were given a unilateral 25% to 30% full-thickness burn under ketamine anesthesia and followed for 72 hours. Resuscitation (24-hour period) was performed with lactated Ringer solution (LR) (n = 9) or 10% LMWD in saline (n = 8) to restore baseline vascular pressures and cardiac output. Interstitial edema and microvascular protein permeability were monitored by lymph flow (Q(L)) and lymph to plasma protein ratio, respectively. With LR Q(L) values in nonburned skin and lung were increased twofold to threefold in the first 24 hours, while with LMWD, values remained at baseline. The nonburn edema with LR was due to the burn-induced hypoproteinemia state. The prevention of this process with LMWD was due to the generation of a twofold to threefold increase in the plasma to interstitial colloid osmotic pressure (COP) gradient. Burn Q(L) was increased fivefold in both groups despite a higher COP gradient with LMWD. Net fluid requirements for the first 24 hours were 75 and 35 ml/kg for animals treated with LR and LMWD, respectively. After cessation of dextran administration in the second 24 hours, the COP gradients for the two groups were equal but Q(L) in nonburned skin and net fluid requirements now increased significantly in the LMWD group. The development of nonburn edema was believed to be due to the persistent hypoproteinemic state. We conclude that edema formation in nonburned tissues, which is due to hypoproteinemia, acounts for a substantial amount of the net fluid requirements after thermal injury. This process can be prevented by infusion of a nonprotein colloid as long as the COP gradient is increased. Edema in burned tissue appears to be unaffected by changes in COP.