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To determine the acute circulatory effects of an open fracture and the circulatory effects of different fluid resuscitation strategies after such a fracture.Randomized controlled laboratory study.Medical Research Council laboratory, university medical school.Four groups of ten immature female Large-White pigs (16.5–27.0 kg): those receiving limited resuscitation, moderate resuscitation, and normal resuscitation, as well as surgical controls.After induction and intubation with 3% halothane, anesthesia was maintained with intravenous Saffan. Cannulae were placed in the left external jugular vein and both axillary arteries. A pulmonary artery flotation catheter was introduced through the jugular cannula. The left femur was exposed for fracture with a captive bolt. Resuscitation was with 0.9% saline; the moderate resuscitation group received less than the normal resuscitation group (840 ± 67 mL vs. 1873 ± 96 mL), whereas the surgical control and limited resuscitation groups received the lowest volumes (466 ± 10 mL and 452 ± 19 mL, respectively).Measurements/calculations of global hemodynamics (intravascular pressures, e.g., mean arterial pressure, heart rate, stroke volume index, cardiac output/index, left ventricular stroke work index, and systemic vascular resistance index), metabolism (oxygen delivery index and consumption index, oxygen extraction ratio, plasma lactate, hemoglobin), blood gases, pH, and hematocrit were made before fracture, immediately and 30 mins after fracture, and at 30-min intervals for the next 4 hrs. Hind-limb muscle water content was determined by dessication. Femur fracture led to acute reductions in cardiac output/index, stroke volume index, and oxygen delivery index and increases in systemic vascular resistance index and oxygen extraction ratio. In the absence of fluid resuscitation, these changes persisted and were accompanied by hypotension. Normal resuscitation attenuated the fracture-induced changes such that the only differences during resuscitation between limited resuscitation and normal resuscitation were a reduction in hematocrit in the latter and an increase in oxygen extraction ratio in the former. Water content increased in both injured and uninjured muscle.The cardiovascular and metabolic changes associated with femur fracture in the anesthetized pig can be reversed or prevented by crystalloids given in a volume equivalent to Advanced Trauma Life Support guidelines.