What immediate action should the nurse take for a client with anorexia nervosa?

In managing a client with anorexia nervosa, the immediate action of initiating intravenous fluids is critical due to the potential for severe dehydration and electrolyte imbalances that can accompany this condition. Clients with anorexia may have significantly restricted food and fluid intake, which can lead to life-threatening complications such as cardiac arrhythmias, diminished renal function, and overall metabolic instability.

By administering intravenous fluids, the nurse can effectively address hydration needs and help stabilize the client, which is essential for their health and safety. This intervention also prepares the client for any further treatment, such as nutritional rehabilitation or psychological support, by ensuring they are physically capable of handling these approaches.

The other options, while relevant in the broader context of the client's care, do not address immediate life-threatening concerns. Discharge planning, medication administration, or testing for lithium levels are not urgent priorities when the risk of dehydration and its complications is present. Thus, initiating intravenous fluids takes precedence as an immediate and necessary intervention.