Final answer:
The primary action for a nurse caring for a client with bipolar disorder during a manic episode is to ensure the client's safety due to the potential for overactivity and impaired judgment.
Step-by-step explanation:
The priority action by the nurse for a client with bipolar disorder who is experiencing mania should be to ensure the client's safety. When mania occurs, clients may have impaired judgment, be overactive, and show risk-taking behaviors that can threaten their own well-being. Therefore, maintaining a safe environment should always be the top consideration, as it directly addresses the immediate risk to the client.