Final answer:
The nurse should first notify the doctor immediately due to the risk of acute compartment syndrome; elevation and ice are supportive but subsequent actions.
Step-by-step explanation:
In pediatric patients presenting with post-reduction unrelenting pain that narcotics aren't relieving, it's essential to consider the possibility of acute compartment syndrome, a surgical emergency. Therefore, the nurse's first action should be to notify the doctor immediately due to the potential severity of the situation. Swelling within the rigid cast can increase pressure in the forearm compartments, compromising circulation and potentially leading to irreversible tissue damage if not addressed rapidly. Although elevation of the limb and application of ice can be supportive measures, they shouldn't delay the notification of the doctor for urgent evaluation.