Final answer:
The elderly patient with blood per rectum and signs of shock requires immediate stabilization with fluid resuscitation and blood transfusion, followed by diagnostic procedures tailored to her hemodynamic status.
Step-by-step explanation:
A 70-year-old woman presenting with large amounts of blood per rectum (BRR) and signs of hemodynamic instability (tachycardia and hypotension) requires immediate assessment and management. In the emergency department (ED), initial studies should include a complete blood count (CBC) to assess for anemia, coagulation studies, blood type and crossmatch, and basic metabolic panel to evaluate electrolytes and kidney function. A hemodynamic support with intravenous fluids, and potentially blood transfusions, is essential. If the patient is stable, a colonoscopy may be performed to identify the source of bleeding. In unstable patients, angiography or a radionuclide bleeding scan may be utilized. More broadly, management should follow the principles of resuscitation, including airway protection if necessary, fluid resuscitation, and close monitoring.