A nurse in an emergency department is administering naloxone to a client who is experiencing opioid toxicity. Following administration of the medication, which of the following should the nurse assess first?

The correct answer is D: Breath sounds. When administering naloxone for opioid toxicity, the priority assessment should be the client's breath sounds. Naloxone can cause rapid reversal of opioid effects, potentially leading to respiratory depression or even respiratory arrest. Therefore, assessing the client's breath sounds will help the nurse determine if the client is effectively breathing post-administration. If breath sounds are absent or inadequate, immediate intervention may be necessary to maintain airway patency and oxygenation. Assessing heart rate (A), pain level (B), and blood pressure (C) are important but come after ensuring adequate breathing.