Key Points
- Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
- Use system-specific risk tools to guide testing and disposition.
- Order high-yield tests first; escalate imaging when indicated.
- Start evidence-based initial therapy and reassess frequently.
Algorithm
- Primary survey and vitals; IV access and monitors.
- Focused history/physical; identify red flags and likely etiologies.
- Order system-appropriate labs and imaging (see Investigations).
- Initiate guideline-based empiric therapy (see Pharmacology).
- Reassess response; arrange consultation and definitive management.
Clinical Synopsis & Reasoning
Hyponatremia requires stepwise classification by tonicity and volume status, then determination of chronicity. Check serum/urine osmolality and urine sodium, review medications (thiazides, SSRIs), and screen for endocrine mimics. Rapid symptom onset and severe neurologic signs signify risk for cerebral edema and guide hypertonic saline use.
Treatment Strategy & Disposition
Treat acute symptomatic cases with controlled 3% saline boluses, then slow correction within safe daily limits to prevent osmotic demyelination. For chronic euvolemic hyponatremia (e.g., SIADH), address triggers, implement fluid restriction, and consider salt tablets, urea, or vaptans when appropriate. Hypervolemic cases benefit from diuretics and sodium restriction; hypovolemic cases need isotonic fluids. Hospitalize when severe, symptomatic, or when frequent monitoring is required.
Epidemiology / Risk Factors
- CKD/AKI, nephrotoxins; obstruction
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|---|---|---|
| BMP | Renal/electrolytes | AKI/lyte changes | |
| UA ± culture | Hematuria/proteinuria/infection | Findings vary | |
| Renal ultrasound (selected) | Obstruction | Hydronephrosis |
Safe Correction Targets
| Population | 24 h Max | 48 h Max |
|---|---|---|
| General | 8–10 mEq/L | ≤18 mEq/L |
| High ODS risk | ≤6 mEq/L | ≤14 mEq/L |
Pharmacology
| Medication | Mechanism | Onset | Role in Therapy | Limitations |
|---|---|---|---|---|
| Hypertonic saline (3%) | Raises serum Na⁺ | Minutes | Severe symptomatic | Risk of osmotic demyelination; slow correction |
| Isotonic saline | Volume expansion | Hours | Hypovolemic hyponatremia | Overcorrection |
| Vaptans | V2 antagonists | Hours | SIADH (selected) | Hepatotoxicity |
| Fluid restriction | N/A | Days | Euvolemic hyponatremia | Non-adherence |
Prognosis / Complications
- Reversibility by cause; electrolyte/volume complications
Patient Education / Counseling
- Explain red flags and when to seek emergent care.
- Reinforce medication adherence and follow-up plan.
Notes
High ODS risk: malnutrition, alcoholism, liver disease, hypokalemia. Consider vaptans in selected SIADH or hypervolemic cases under specialist guidance.