Mechanisms behind increased dermal imbibition pressure in acute burn edema.

We have measured tissue pressures in excised rat skin subjected to in vitro burn injury and investigated the mechanisms behind the increased imbibition (swelling) pressure in burned skin. Skin pieces wrapped in aluminum paper were immersed into boiling hot water for 10, 30, or 60 s. Dermal imbibition pressure was measured with micropipettes and tissue osmometry as interstitial fluid hydrostatic pressure (Pif) and/or interstitial fluid colloid osmotic pressure (COPif). COPif was also measured in interstitial fluid sampled with intradermal wicks. Control values of Pif (micropipettes) and of COPif (wick fluid) averaged -1.5 mmHg and -17.5 mmHg, respectively. An increase in imbibition pressure was seen after thermal injury. After 10 s of heat exposure, the imbibition pressure gain was mainly due to a strongly negative hydrostatic pressure (Pif mean value -33.3 mmHg). Pif became slightly positive and COPif increasingly negative after longer exposure (mean Pif 0.3 and mean COPif -133 mmHg after 60-s exposure). Collagen degradation and water solubility increased with extension of the heat exposure time. Thermal degradation of collagen seems to be the main mechanism responsible for the generation of increased imbibition pressure.