ATV Accident

You are caring for a 53 year old female who was involved in a 4-wheeler accident. Patient was semi-concious and combative on-scene. First arriving paramedic unit elected to intubate due to airway protection concerns. Patient has some an obvious closed femur fracture, and bleeding around her left ear. The paramedic states that she was initially hypertensive and tachycardic. After transitoning her into your aircraft and placing her on the vent her blood pressure starts to fall. Can you identify the cause?