A 58-year-old client with bipolar disorder who takes lithium carbonate 900 mg/day and no other psychiatric medications presents with 3 days of vomiting, diarrhea, and poor oral intake. The client reports increased thirst and urination. Vital signs: BP 98/60 mm Hg, HR 110/min, RR 20/min, temperature 37.2°C (99°F). Neurologic examination shows coarse tremor, ataxia, and new confusion; there is no clonus or muscle rigidity. Laboratory results: lithium 2.4 mEq/L (therapeutic 0.6-1.2), sodium 148 mEq/L (135-145), creatinine 1.8 mg/dL (baseline 0.9), BUN 32 mg/dL (7-20). The next scheduled lithium dose is due now. Complete the diagram by selecting the condition the client is most likely experiencing, 2 actions the nurse should take to address that condition, and 2 parameters the nurse should monitor to assess the client's progress.

Quick answer
Lithium toxicity with volume depletion and kidney injury; hold lithium and start IV 0.9% sodium chloride as prescribed; monitor serial serum lithium levels and serum creatinine/BUN.

Why this is correct
Lithium is cleared almost entirely by the kidneys and is reabsorbed along with sodium. Vomiting and diarrhea caused sodium and volume loss, reducing lithium clearance and raising the level to 2.4 mEq/L, which now causes neurotoxicity. Isotonic saline restores volume and sodium delivery so the kidneys can excrete lithium, while the next dose is withheld. Falling lithium levels and improving creatinine indicate response; rising levels or worsening renal function prompt consideration of hemodialysis.

Easy analogy or mental picture
Lithium rides the same bus as sodium out through the kidneys. When the body is dry and sodium-starved, the bus stops running and lithium piles up at the station; IV saline restarts the route.

Memory hook
"Dry and salt-poor = lithium soars."

NCLEX decision rule
When a client on lithium has neurologic signs and a high level after fluid loss, withhold the drug, restore volume with isotonic fluid, and trend lithium and renal function.

Why the other choices are wrong
Activated charcoal does not bind lithium. Cyproheptadine treats serotonin syndrome, which is unlikely without a serotonergic drug, hyperthermia, or clonus. Oral fluids are inadequate for a hypotensive, vomiting client with kidney injury. Nephrogenic diabetes insipidus explains the thirst and sodium but not a level of 2.4 mEq/L with cerebellar signs, and gastroenteritis alone does not explain the neurotoxicity. Temperature and creatine kinase track serotonin syndrome or neuroleptic malignant syndrome, and urine osmolality tracks diabetes insipidus rather than lithium clearance.