PRESSURE-VOLUME CHARACTERISTICS OF THE INTACT AND DISRUPTED PELVIC RETROPERITONEUM

Hemorrhage is a major cause of mortality in pelvic fractures. Bleeding can be controlled in hypotensive patients by direct ligation, angiogr aphic embolization, pelvic packing, and acute external fixation. Acute application of an external fixator can reduce pelvic volume and reduc e bleeding fractures to effect tamponade. This therapy assumes that th e pelvis represents a closed space, which clearly is not true anatomic ally. However, the premise may hold functionally. This study explored the relationship between pressure and volume in the intact and disrupt ed pelvic retroperitoneum. In cadaveric specimens, the external iliac vein was dissected, ruptured, and cannulated. This method allowed cont rolled pow of fluid, with simultaneous measurement of pressure, into t he intact retroperitoneum. Open book pelvic fractures were created by applying external rotation to the pelvis through the femoral heads. Th e pressure-volume measurements, without and with external fixation app lied, were repeated after the fracture, as well as after a laparotomy. In the intact retroperitoneum, pressures rapidly rose to an average o f 30 mm Hg after infusion of 5 liters of fluid. After fracture, up to 20 liters of fluid could be infused at pressures not exceeding 35 mm H g. External fixation increased pressures approximately 3 mm Hg at low fluid volumes, and approximately 11 mm Hg at the highest fluid volumes . Laparotomy decreased retroperitoneal pressure from approximately 35 mm Hg to approximately 15 mm Hg. The results of the study suggest that low-pressure venous hemorrhage may be tamponaded by an external fixat or, given that enough fluid volume is present in the pelvic retroperit oneum. However, external fixation may not generate sufficient pressure to stop arterial bleeding. In any case, it seems that a large volume of fluid must be lost into the pelvis before an external fixator can h ave much effect on retroperitoneal pressures.