Stage 3 — Prioritize hypotheses. The 46-year-old client with bipolar I disorder takes lithium carbonate 600 mg twice daily and hydrochlorothiazide. For 3 days the client has had vomiting and diarrhea, kept taking lithium, and used ibuprofen every 6 hours. The client last drank alcohol at a wedding 10 days ago. Current findings: coarse tremor of both hands (fine tremor for years), slurred speech, wide-based lurching gait, and disorientation to month and place; the client denies racing thoughts, reduced sleep, or self-harm thoughts. BP 98/62 mm Hg, HR 54/min and irregular with PVCs, temperature 37.6 C, dry mucous membranes, no clonus. Serum lithium 2.3 mEq/L, creatinine 1.8 mg/dL (0.9 mg/dL last year). 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. Take action: hold lithium, hydrochlorothiazide, and ibuprofen, and infuse isotonic sodium chloride. Monitor: serum lithium level and cardiac rhythm.

Why this is correct
Lithium is cleared almost entirely by the kidney and reabsorbed with sodium. Vomiting and diarrhea, a thiazide, and an NSAID all reduce clearance, and the creatinine doubled, so lithium accumulated to 2.3 mEq/L. Neurologic signs and conduction changes show clinically significant toxicity. Stopping all three drugs and giving isotonic saline restores volume and lithium excretion; nephrology decides on dialysis based on the level trend and symptoms. Repeat levels (including checks for rebound) and telemetry show whether the toxicity and its dangerous cardiac effects are receding.

Easy analogy or mental picture
Lithium rides out of the body on the same kidney bus as sodium. Dehydration, the thiazide, and ibuprofen took the bus off the road, so lithium piled up at the station. Fluids and stopping the blockers reopen the route.

Memory hook
Dry + diuretic + NSAID = lithium LOCKED IN: STOP, SALINE; watch LEVEL and RHYTHM.

NCLEX decision rule
For drug toxicity, remove the drug and anything slowing its elimination, support the elimination route, and monitor the drug level plus the organ it endangers most.

Why the other choices are wrong
Wernicke encephalopathy shares confusion and ataxia, but a single drink 10 days ago is not chronic alcohol use and it does not explain a lithium of 2.3 or ventricular ectopy; thiamine is harmless but does not treat this. Serotonin syndrome needs a serotonergic drug and causes clonus and hyperthermia, both absent, so cyproheptadine and core temperature track the wrong problem. Mania is excluded by the absence of racing thoughts or reduced sleep, so a mood scale is not the priority. Activated charcoal does not bind lithium. TSH reflects long-term lithium effects rather than acute toxicity.