Boarding refers to the practice of holding patients, including those with mental health disorders, in the emergency department (ED) for extended periods due to the unavailability of appropriate psychiatric or mental health treatment facilities. This situation often occurs when there is a lack of inpatient psychiatric beds or insufficient community-based mental health resources.

When the nurse notifies the manager about clients with mental health disorders still present in the ED for over 48 hours, they are likely raising concerns about the practice of boarding. The nurse is highlighting the issue of keeping individuals with mental health disorders in an inappropriate setting for an extended duration, which can have negative implications for both the clients and the ED. 

The other options are not directly related to the phenomenon of clients with mental health disorders staying in the ED for an extended period: 

1. Temporary detaining orders for clients: Temporary detaining orders refer to legal provisions that allow for the involuntary detention of individuals who are at risk to themselves or others due to mental health concerns. While this may be relevant in certain situations, it does not address the broader issue of clients staying in the ED beyond 48 hours. 

2. The revolving door for clients: The revolving door phenomenon refers to individuals repeatedly seeking care in the ED due to ongoing or recurrent health issues. While this may be a concern in the context of mental health, it does not specifically address the issue of clients with mental health disorders staying in the ED for over 48 hours. 

3. The cost of holding clients in the ED for over 48 hours: While the cost of providing care and resources to clients staying in the ED for an extended period is a valid consideration, it does not encompass the broader issue of the appropriateness of this practice for clients with mental health disorders.