Final answer:
The nurse should first start intravenous (IV) fluids to stabilize a patient with signs of shock due to the severity of their vital signs, before considering other interventions such as pain relief or antipyretics.
Step-by-step explanation:
The prescribed intervention that a nurse should implement first for a patient admitted to the emergency department with severe abdominal pain, rebound tenderness, high fever, tachycardia, tachypnea, and hypotension is C) Start intravenous (IV) fluids. The vital signs suggest that the patient may be experiencing shock, potentially due to sepsis or another severe infection. Immediate IV fluid resuscitation is critical to address the hypotension, which can be life-threatening. This takes priority over pain medication, blood cultures, and antipyretics to ensure adequate circulation and perfusion. Administering IV fluids will help stabilize the patient's blood pressure and can improve outcomes in septic shock.