A 26-year-old woman in her sixth month of pregnancy is brought to the emergency department. She had been punched in the abdomen. She is found to have generalized abdominal pain, tenderness, abdominal distention, ileus, and absent fetal heart sounds. The patient's blood pressure is 80/60 mm Hg; despite administration of 3 L of Ringer's lactate, her blood pressure only comes up to 90/60 mm Hg. What is the next step in management?