Final answer:
In caring for a client with delirium, the highest priority nursing intervention is maintaining physiological safety.
Step-by-step explanation:
The highest priority nursing intervention when caring for a client with delirium is maintaining physiological safety.
Delirium is a state of acute confusion characterized by poor attention, disorganized thinking, and fluctuating mental status. Clients with delirium are at increased risk for falls, injury, and harm due to their altered mental state.
While the other nursing interventions mentioned (maintaining consistency in routine, promoting optimal level of functioning, and promoting orientation to person, place, and time) are important in the care of clients with delirium, ensuring the client's physiological safety takes precedence to prevent any immediate harm.