Final answer:
The nurse's priority intervention for a patient with bipolar disorder should be monitoring the client's vital signs and medication administration, as it is critical for ensuring the patient's well-being and effective management of their condition.
Step-by-step explanation:
The priority intervention for a nurse planning care for a client with bipolar disorder on an acute mental health unit is D) Monitor the client's vital signs and medication administration. This is essential as it pertains to the client's immediate physical health and safety, which is paramount in the hierarchy of nursing care.
Monitoring vital signs is critical because it can detect early signs of a medical emergency or adverse reactions to medications, which are common in acute settings. Additionally, ensuring the appropriate administration of medication is vital in managing the symptoms of bipolar disorder and preventing complications.