A 52-year-old man with bipolar disorder on lithium 900 mg daily for 3 years presents to the emergency department with tremor, confusion, and ataxia. His wife reports he has had diarrhea and vomiting for 2 days following gastroenteritis. Serum lithium level is 2.8 mEq/L (normal therapeutic range 0.6–1.2 mEq/L). Serum creatinine is 1.4 mg/dL (baseline 1.0 mg/dL), and eGFR is 52 mL/min/1.73 m². What is the most appropriate immediate next step in management?

Explanation

## Clinical Context This patient presents with **severe lithium toxicity** (serum level 2.8 mEq/L, which is >2.0 mEq/L) with neurological manifestations (tremor, confusion, ataxia) and evidence of acute kidney injury (elevated creatinine, reduced eGFR). ## Management of Severe Lithium Toxicity **Key Point:** Severe lithium toxicity with neurological symptoms and renal impairment requires aggressive intervention — IV hydration, lithium discontinuation, and hemodialysis. ### Rationale for Correct Answer 1. **IV Normal Saline**: Lithium is filtered by the glomerulus and reabsorbed in the proximal tubule (competing with Na⁺). Volume depletion (from diarrhea/vomiting) increases lithium reabsorption. IV saline restores intravascular volume, reduces proximal tubule reabsorption, and increases urinary lithium clearance. 2. **Stop Lithium Immediately**: Continued dosing will worsen toxicity; the drug must be withdrawn. 3. **Hemodialysis Indication**: With serum lithium >2.0 mEq/L AND neurological symptoms (confusion, ataxia) AND renal impairment (eGFR 52), hemodialysis is indicated. Lithium is water-soluble and small (MW 7), making it dialyzable. Rebound increase in serum lithium can occur 6–8 hours post-dialysis, so repeated dialysis or continuous monitoring is needed. ### Severity Classification | Serum Lithium Level | Clinical Features | Management | |---|---|---| | 1.5–2.0 mEq/L | Mild toxicity (nausea, tremor, polyuria) | Hydration, stop lithium, monitor | | 2.0–3.5 mEq/L | Moderate toxicity (confusion, ataxia, diarrhea) | IV hydration, hemodialysis if renal impairment | | >3.5 mEq/L | Severe toxicity (seizures, coma, cardiac arrhythmias) | Hemodialysis mandatory | **Clinical Pearl:** In this case, the combination of level 2.8 + neurological signs + reduced eGFR mandates dialysis; IV hydration alone is insufficient. **High-Yield:** Acute kidney injury in lithium toxicity is a **bidirectional problem**: volume depletion increases lithium reabsorption (worsening toxicity), and lithium toxicity damages the kidney (nephrogenic DI, acute tubular necrosis). Breaking this cycle requires both hydration and removal of the drug. ## Why This Approach Works ```mermaid flowchart TD A[Severe Lithium Toxicity<br/>Level 2.8 + Neuro Sx + AKI]:::urgent --> B[Stop Lithium]:::action A --> C[IV Normal Saline Bolus]:::action A --> D{Indication for Dialysis?}:::decision D -->|Level >2.0 + Neuro Sx<br/>or AKI| E[Hemodialysis]:::action D -->|Mild, no renal impairment| F[Hydration + Monitoring]:::action E --> G[Monitor for Rebound<br/>6-8 hrs post-dialysis]:::action G --> H[Repeat dialysis if needed]:::action C --> I[Restore Volume Status]:::outcome I --> J[Reduce Lithium Reabsorption]:::outcome ``` [cite:Kaplan & Sadock's Synopsis of Psychiatry 12e Ch 31]