A 35-year-old woman is brought to the trauma centre 45 minutes after a stab wound to the right upper quadrant. She is haemodynamically unstable with blood pressure 88/54 mmHg, heart rate 128 bpm, and respiratory rate 24/min. Physical examination reveals right upper quadrant tenderness with guarding and rebound. FAST scan shows free fluid in the right paracolic gutter and Morrison's pouch. The patient has received 2 units of O-negative blood and 1 litre of crystalloid, but remains hypotensive. What is the most appropriate next step in management?