The nurse is caring for a patient with ulcerative colitis who reports a sudden increase in abdominal pain and nausea. The nurses' assessment findings include a temperature of 101.4 F, a heart rate of 115 bpm, a blood pressure of 96/40 mmHg, and a rigid, board-like abdomen on palpation. What is the nurse's first action?

A. Administer antibiotics: While antibiotics may be indicated if infection or perforation is suspected, immediate stabilization of circulation takes priority. Administering antibiotics first does not address the acute risk of hypovolemic or septic shock indicated by hypotension and tachycardia. B. Administer ondansetron: Ondansetron can relieve nausea, but treating symptoms does not address the underlying life-threatening complication. Focusing on antiemetics first would delay urgent intervention for hemodynamic instability and potential bowel perforation. C. Administer IV fluids: Hypotension (BP 96/40 mmHg) and tachycardia (HR 115 bpm) indicate circulatory compromise, likely secondary to sepsis or fluid loss from a perforated colon. Rapid IV fluid resuscitation is the priority to restore perfusion, prevent shock, and stabilize the patient before other interventions. D. Administer acetaminophen: Fever can be managed with antipyretics, but lowering temperature does not correct hypotension, tachycardia, or the emergent abdominal findings. Treating pain or fever is secondary to immediate cardiovascular stabilization in a patient with suspected toxic megacolon or perforation.