A 70-year-old man presents with sudden epigastric pain, guarding, and rebound tenderness. He has a history of H. pylori-associated peptic ulcer disease and long-term NSAID use. An abdominal X-ray shows free air under the diaphragm. His blood pressure is 85/60 mmHg, and heart rate is 120 bpm. What is the next best step in management?