1. Discuss and clarify the utility of intraosseous blood transfusions for treating hypovolemic battlefield injuries in military out-of-hospital settings 2. Compare the advantages and complications of humeral versus sternal intraosseous access for resuscitation of hemorrhagic shock. 3. Identify flow rates, degree of intravascular hemolysis, and occurrence of coagulopathy in single versus double site intraosseous blood transfusion. The American College of Surgeons Advance Trauma Life Support (ATLS) endorses the use of intraosseous devices for the adult trauma patient in extremis. Intraosseous access is frequently used by military physicians administering fluids, blood, and medications for victims of severe battlefield trauma. The optimal intraosseous blood transfusion strategy appears to involve pressure bag transfusion through either the sternum or proximal humerus. Double anatomic site IO catheter placement has the potential to augment resuscitation in cases where vascular access is challenging. We sought to compare flow rates and complications among 4 single and double anatomic site transfusion strategies in a swine model of hemorrhagic shock. 48 Yorkshire swine were placed under general anesthesia during the study protocol. Data from 12 animals completed to date is presented below. Following intra-arterial catheter placement, 30-40% of the animal’s estimated blood volume was removed using the flow of gravity. Subsequently, 15-20% of the animals estimated blood volume was autologously infused via pressure bag through 1 of 4 randomly assigned treatment arms: 1) Proximal Humerus (n=12), 2) Sternum (n=12), 3) Proximal Humerus + Sternum (n=12), 4) Double Proximal Humerus (n=12). Flow rates, intravascular hemolysis, and coagulopathy were recorded. Presence of pulmonary arterial fat embolism was evaluated for by a pathologist blinded to treatment arm. The average weight of swine was 77.8 kg. Average bone density on DEXA scan of the proximal humerus and sternum was 1.001 cm/gm2 and 0.242 cm/gm2, respectively. Average transfusion pressures were 360 mmHg. Infusion rates were as follows: Single Humerus 58.8 ml/min; Sternum 54 ml/min; Sternum + Single Humerus 126 ml/min and Double Humerus 120.3 ml/min. Plasma free hemoglobin levels (baseline, post transfusion) were: Single Humerus 9, 13.2 μg/ml; Sternum 10.5, 18.4 μg/ml; Double Humerus 11.4, 17.8 μg/ml and Sternum + Single Humerus 8.8, 13.9 μg/ml. No significant differences in post transfusion coagulopathy were observed. Blinded pathologist review of pulmonary tissue for edema, inflammation and presence of pulmonary fat emboli between treatment arms is underway. In an animal model of hemorrhagic shock, double site IO transfusion under a pressure bag appears to confer a significant advantage in flow rates. Proximal humerus and sternal IO transfusions achieved similar flow rates in a model that closely resembles the bone density of an adult male. No significant differences between strategies were noted in regard to intravascular hemolysis or coagulopathy. In cases of severe trauma with challenging vascular access, double site access in either bilateral proximal humerus or sternum and proximal humerus may confer a clinical advantage in speed of transfusion without significant complications.