Final answer:
The priority nursing problem after a client has received an excessive dose of morphine is respiratory depression, which can be life-threatening and requires immediate attention to monitor and possibly counteract the effects of the overdose. The option (D) is correct.
Step-by-step explanation:
The nurse is caring for a client who has received twice the ordered dose of morphine an hour ago and realizes a medication error has occurred. The priority nursing problem at this time is respiratory depression. This is because morphine is a potent opioid analgesic that can depress the respiratory system, especially when taken in excessive amounts, leading to a potentially life-threatening situation.
It is paramount to monitor the client's respiratory status and vital signs, administer oxygen if needed, and consider the use of naloxone, an opioid antagonist if signs of overdose are present. Therefore, option (D) is correct.