Hyponatremia Treatment Algorithm
Initial Assessment and Classification
Assess symptom severity immediately, as this determines the urgency and aggressiveness of treatment. 1
Symptom Severity Categories
- Severe symptoms (seizures, coma, altered mental status, respiratory distress): Medical emergency requiring immediate hypertonic saline 1, 2
- Mild symptoms (nausea, vomiting, headache, weakness): Less urgent, allows time for diagnostic workup 1, 3
- Asymptomatic: Treatment based on severity of sodium level and underlying cause 1, 3
Sodium Level Classification
- Mild: 130-135 mEq/L 3
- Moderate: 125-129 mEq/L (or 120-125 mEq/L per some guidelines) 1, 3
- Severe: <125 mEq/L (or <120 mEq/L) 1, 3
Volume Status Assessment
Determine if the patient is hypovolemic, euvolemic, or hypervolemic through physical examination 1:
- Hypovolemic signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Euvolemic: No edema, normal blood pressure, normal skin turgor, moist mucous membranes 1
- Hypervolemic signs: Peripheral edema, ascites, jugular venous distention 1
Essential Laboratory Workup
- Serum osmolality, urine osmolality, urine sodium, urine electrolytes 1
- Serum uric acid (<4 mg/dL suggests SIADH with 73-100% positive predictive value) 1
- Thyroid function (TSH) and cortisol to rule out hypothyroidism and adrenal insufficiency 1
- Urine sodium <30 mmol/L predicts 71-100% response to saline in hypovolemic hyponatremia 1
Treatment Based on Symptom Severity
SEVERE SYMPTOMATIC HYPONATREMIA (Seizures, Coma, Altered Mental Status)
Administer 3% hypertonic saline immediately—this is a medical emergency. 1, 2, 3
Dosing Protocol
- Give 100 mL bolus of 3% saline over 10 minutes 1
- Can repeat up to 3 times at 10-minute intervals until symptoms improve 1
- Target: Increase sodium by 6 mEq/L over first 6 hours or until symptoms resolve 1, 2
Critical Safety Limits
- Never exceed 8 mEq/L correction in 24 hours 1, 2, 3
- Monitor serum sodium every 2 hours during initial correction 1
- Transfer to ICU for close monitoring 2
High-Risk Patients (Require Even Slower Correction at 4-6 mEq/L per day)
- Advanced liver disease, cirrhosis 1
- Alcoholism or malnutrition 1
- Prior encephalopathy 1
- Severe hyponatremia <120 mEq/L 1
MILD SYMPTOMS OR ASYMPTOMATIC HYPONATREMIA
Treatment is determined by volume status and underlying etiology 1, 3:
Treatment Based on Volume Status
HYPOVOLEMIC HYPONATREMIA
Administer isotonic (0.9%) normal saline for volume repletion. 1, 3
- Discontinue diuretics immediately 1
- Urine sodium <30 mmol/L confirms hypovolemic state and predicts good response to saline 1
- Correct at rate not exceeding 8 mEq/L in 24 hours 1
Common causes: Diuretics, GI losses (vomiting, diarrhea), burns, dehydration 1
EUVOLEMIC HYPONATREMIA (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment. 1, 2, 3
First-Line Treatment
Second-Line Options (if fluid restriction fails)
- Oral sodium chloride tablets: 100 mEq three times daily 4, 2
- High protein diet to augment solute intake 4
- Urea 0.25-0.50 g/kg/day (highly effective, induces osmotic diuresis) 2
- Demeclocycline (induces nephrogenic diabetes insipidus) 2
Third-Line: Vaptans (Vasopressin Receptor Antagonists)
- Tolvaptan starting dose: 15 mg once daily 1, 5
- Can titrate to 30 mg, then 60 mg daily based on response 5
- Avoid fluid restriction in first 24 hours when starting tolvaptan to prevent overly rapid correction 5
- Monitor closely—risk of overcorrection 1
- Caution in cirrhosis: 10% risk of GI bleeding vs 2% with placebo 1
SIADH diagnostic criteria: Euvolemic state, urine sodium >20-40 mEq/L, urine osmolality >300-500 mOsm/kg, normal thyroid/adrenal function 1, 2
HYPERVOLEMIC HYPONATREMIA (Heart Failure, Cirrhosis)
Fluid restriction to 1-1.5 L/day for sodium <125 mEq/L. 1, 3
Management Steps
- Implement fluid restriction to 1000-1500 mL/day 1
- Discontinue diuretics temporarily if sodium <125 mEq/L 1
- For cirrhosis: Consider albumin infusion alongside fluid restriction 1
- Avoid hypertonic saline unless life-threatening symptoms present—it worsens ascites and edema 1
Pharmacological Options
- Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction 1, 5
- Use with extreme caution in cirrhosis due to bleeding risk 1
Key principle: In cirrhosis, sodium restriction (not fluid restriction) causes weight loss, as fluid follows sodium 1
Special Populations and Considerations
NEUROSURGICAL PATIENTS: Cerebral Salt Wasting (CSW) vs SIADH
Critical distinction: CSW requires volume and sodium replacement, NOT fluid restriction 1
CSW Diagnostic Features
- True hypovolemia with CVP <6 cm H₂O 1
- Urine sodium >20 mEq/L despite volume depletion 1
- Evidence of extracellular volume depletion (hypotension, tachycardia, dry mucous membranes) 1
CSW Treatment
- Volume repletion with normal saline or hypertonic saline 1
- For severe symptoms: 3% hypertonic saline + fludrocortisone 0.1-0.2 mg daily in ICU 1
- Hydrocortisone may prevent natriuresis in subarachnoid hemorrhage patients 1
- Never use fluid restriction in CSW—it worsens outcomes 1
- Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
Critical Correction Rate Guidelines
Standard Correction Limits
Maximum correction: 8 mEq/L in 24 hours for all patients 1, 2, 3
- For severe symptoms: Correct 6 mEq/L over first 6 hours, then limit remaining correction to 2 mEq/L over next 18 hours 1
- High-risk patients: 4-6 mEq/L per day maximum 1
Calculating Sodium Deficit
Formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1, 4
Management of Overcorrection
If sodium correction exceeds 8 mEq/L in 24 hours, act immediately to prevent osmotic demyelination syndrome. 1
Rescue Protocol
- Discontinue current fluids immediately 1
- Switch to D5W (5% dextrose in water) 1
- Administer desmopressin (dDAVP) to slow or reverse rapid rise 1, 6
- Goal: Relower sodium to bring total 24-hour correction to ≤8 mEq/L 1
Osmotic Demyelination Syndrome (ODS)
- Occurs 2-7 days after overly rapid correction 1
- Symptoms: Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, parkinsonism 1, 7
- Risk: 0.5-1.5% in liver transplant recipients 1
Common Pitfalls to Avoid
- Ignoring mild hyponatremia (130-135 mEq/L): Associated with increased falls (21% vs 5%), fractures, and mortality 1, 7
- Using fluid restriction in CSW: Worsens outcomes, especially in subarachnoid hemorrhage 1
- Correcting chronic hyponatremia too rapidly: Exceeding 8 mEq/L in 24 hours risks ODS 1, 7
- Using hypertonic saline in hypervolemic hyponatremia without severe symptoms: Worsens edema and ascites 1
- Inadequate monitoring during active correction: Check sodium every 2 hours for severe symptoms, every 4 hours for mild symptoms 1
- Failing to distinguish SIADH from CSW in neurosurgical patients: They require opposite treatments 1
- Using normal saline in SIADH: May worsen hyponatremia through dilution 1