The nurse observes that a client has become lethargic 30 minutes after receiving an opioid injection for pain. Which vital sign should the nurse obtain first?

A. Pulse rate: While monitoring the pulse rate is important for assessing overall cardiovascular function, it is not the most immediate concern when a client becomes lethargic after receiving an opioid. Opioids are known to potentially cause respiratory depression, which is a more critical issue to address first. B. Blood pressure: Blood pressure changes can occur with opioid use, but in the context of sudden lethargy, the primary concern is to check for respiratory depression. This condition can lead to significant complications and requires immediate attention. C. Temperature: Temperature monitoring is important for identifying infection or other issues, but it is not the most relevant vital sign to assess immediately after noticing lethargy from opioid administration. Respiratory rate is more directly affected by opioids. D. Respiratory rate: Opioids can cause respiratory depression, which can lead to lethargy and other serious complications. Assessing the respiratory rate first is crucial to determine if the client is experiencing slowed or irregular breathing, which may require immediate intervention such as administering naloxone or providing supplemental oxygen.