The nurse administers hydromorphone IV to the postoperative client as prescribed. What is the best method for the nurse to evaluate the client's response to the medication?

A. Observe the client's behavior without the client's awareness, 30 minutes after administration: Observation is subjective and may not accurately reflect the client's pain level. It is less reliable than using a standardized assessment method. B. Use a pain assessment tool before and 30 minutes after administration: Using a standardized pain scale, such as the Numeric Rating Scale (0–10), is the most effective and objective method to evaluate the client’s response to pain medication. It allows consistent comparison and documentation of pain relief over time. C. Assess the client's vital signs before and after drug administration: Vital signs can indicate physiologic responses to pain and medication, such as changes in respiratory rate or blood pressure, but they do not directly measure pain relief. D. Ask the client if the medication has been effective: While useful, simply asking is not sufficient without using a validated tool. Pain assessment tools offer a clearer, quantifiable way to measure changes in pain levels for clinical decision-making.