A 72-year-old White man with a 55-pack-year smoking history is brought to the emergency department after collapsing at home. He reports sudden, severe lower back and abdominal pain that began 20 minutes ago. On arrival, he is pale and diaphoretic. Temperature is 36.4°C (97.5°F), blood pressure is 72/38 mm Hg, pulse is 132/min, and respirations are 24/min. His abdomen is diffusely tender; a pulsatile midline mass is palpated. Peripheral pulses are diminished. His ankle-brachial index is 0.75 bilaterally. What is the most appropriate next step in management?