Hyponatremia Management Guidelines
Hyponatremia (serum sodium <135 mmol/L) should be evaluated and treated based on symptom severity, volume status, and acuity of onset, with correction rates never exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1
Initial Assessment and Classification
Determine three critical factors immediately:
- Symptom severity: Severe symptoms (seizures, coma, altered mental status) vs. mild symptoms (nausea, headache) vs. asymptomatic 1
- Volume status: Hypovolemic (dehydration, orthostasis) vs. euvolemic (normal exam) vs. hypervolemic (edema, ascites, jugular venous distention) 1
- Acuity: Acute (<48 hours) vs. chronic (>48 hours) 1
Essential initial workup includes: serum and urine osmolality, urine sodium concentration, urine electrolytes, serum uric acid, and assessment of extracellular fluid volume status 1. A urine sodium <30 mmol/L predicts response to normal saline with 71-100% positive predictive value 1.
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)
Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 2 Give 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals 1. Total correction must not exceed 8 mmol/L in 24 hours 1, 2.
- Monitor serum sodium every 2 hours during initial correction 1
- ICU admission is recommended for close monitoring 1
- Calculate sodium deficit: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 3
Mild to Moderate Symptomatic or Asymptomatic Hyponatremia
Treatment depends on volume status and underlying etiology:
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion. 1 Urine sodium <30 mmol/L with clinical signs of dehydration (dry mucous membranes, orthostatic hypotension, decreased skin turgor) confirms this diagnosis 1.
- Correct at a rate not exceeding 8 mmol/L in 24 hours 1
- Once euvolemic, reassess and adjust treatment based on sodium response 1
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of first-line treatment. 1, 3 If no response after 24-48 hours, add oral sodium chloride 100 mEq three times daily 3.
Second-line pharmacological options include:
- Urea: Effective and safe, particularly for chronic SIADH 1
- Vaptans (tolvaptan): Start at 15 mg daily, titrate to 30-60 mg as needed 2. Must initiate in hospital setting with close sodium monitoring 2. Avoid fluid restriction during first 24 hours of vaptan therapy 2
- Demeclocycline or lithium (less commonly used due to side effects) 1
Critical distinction in neurosurgical patients: Differentiate SIADH from cerebral salt wasting (CSW), as CSW requires volume and sodium replacement, NOT fluid restriction 1. CSW presents with evidence of volume depletion (hypotension, tachycardia) and inappropriately high urinary sodium (>20 mmol/L) 1.
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1 Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1.
Additional management:
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- Consider albumin infusion in cirrhotic patients 1
- Treat underlying condition (optimize heart failure management, manage cirrhosis complications) 1
- Important: It is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium 1
Special Populations and High-Risk Considerations
Patients at High Risk for Osmotic Demyelination Syndrome
Use more conservative correction rates of 4-6 mmol/L per day (not exceeding 8 mmol/L in 24 hours) in:
- Advanced liver disease 1
- Alcoholism 1
- Malnutrition 1
- Severe hyponatremia (<120 mmol/L) 1
- Prior encephalopathy 1
Neurosurgical Patients
Cerebral salt wasting treatment: Volume and sodium replacement with normal saline or hypertonic saline based on severity, plus fludrocortisone for severe cases 1. Never use fluid restriction in CSW 1.
Subarachnoid hemorrhage patients at risk for vasospasm: Do not treat with fluid restriction 1. Consider fludrocortisone or hydrocortisone to prevent natriuresis 1.
Cirrhotic Patients
Hyponatremia in cirrhosis increases risk of:
- Spontaneous bacterial peritonitis (OR 3.40) 1
- Hepatorenal syndrome (OR 3.45) 1
- Hepatic encephalopathy (OR 2.36) 1
Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs. 2% placebo) 1.
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours:
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
- Consider administering desmopressin to slow or reverse the rapid rise 1
- Monitor for osmotic demyelination syndrome signs: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis (typically occurring 2-7 days after rapid correction) 1, 2
Common Pitfalls to Avoid
- Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant – even mild hyponatremia increases fall risk and mortality 4, 5
- Using fluid restriction in cerebral salt wasting – this worsens outcomes 1
- Failing to distinguish SIADH from CSW in neurosurgical patients – treatment approaches are opposite 1
- Administering normal saline to SIADH patients – this can worsen hyponatremia 1
- Using hypertonic saline in hypervolemic hyponatremia without severe symptoms – this worsens fluid overload 1
- Inadequate monitoring during active correction – check sodium every 2-4 hours initially 1
- Correcting chronic hyponatremia too rapidly – maximum 8 mmol/L per 24 hours 1, 2
Monitoring Requirements
During active correction:
- Severe symptoms: Every 2 hours initially 1
- After symptom resolution: Every 4 hours 1
- Chronic/asymptomatic: Daily monitoring 1
Watch for signs of osmotic demyelination syndrome: dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures 2