What is the initial approach to treating chronic hyponatremia?

Initial Approach to Chronic Hyponatremia

For chronic hyponatremia, the initial approach depends critically on volume status assessment and symptom severity, with fluid restriction as the cornerstone for euvolemic/hypervolemic states and isotonic saline for hypovolemic states, while always limiting correction to ≤8 mmol/L per 24 hours to prevent osmotic demyelination syndrome. 1

Immediate Assessment Required

Determine chronicity and symptom severity first:

• Chronic hyponatremia is defined as >48 hours duration or unknown timing 1
• Assess for severe symptoms: seizures, coma, altered mental status, or cardiorespiratory distress 1
• Even mild chronic hyponatremia (130-135 mmol/L) increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L) 1, 2

Essential initial workup includes: 1

• Serum and urine osmolality
• Urine sodium and electrolytes
• Serum uric acid (level <4 mg/dL suggests SIADH with 73-100% positive predictive value)
• Extracellular fluid volume status assessment
• TSH and cortisol to exclude hypothyroidism and adrenal insufficiency

Volume Status Classification and Treatment

Hypovolemic Hyponatremia

Clinical signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1

Laboratory findings: Urine sodium <30 mmol/L (71-100% positive predictive value for saline responsiveness) 1, 3

Treatment approach: 1

• Discontinue diuretics immediately
• Administer isotonic saline (0.9% NaCl) for volume repletion
• Correct at 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours
• Monitor sodium every 4 hours initially

Euvolemic Hyponatremia (SIADH)

Clinical signs: No edema, no orthostatic hypotension, normal skin turgor, moist mucous membranes 1

Laboratory findings: Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg, serum uric acid <4 mg/dL 1

Treatment approach: 1, 2

• Fluid restriction to 1 L/day is the cornerstone of treatment
• If no response after 48-72 hours, add oral sodium chloride 100 mEq three times daily
• For resistant cases, consider urea (15-30g/day), demeclocycline, or tolvaptan 15 mg once daily
• Avoid correction >8 mmol/L in 24 hours

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Clinical signs: Peripheral edema, ascites, jugular venous distention, pulmonary congestion 1

Treatment approach for sodium <125 mmol/L: 1

• Fluid restriction to 1-1.5 L/day
• Discontinue diuretics temporarily until sodium improves
• In cirrhosis: add albumin infusion (6-8g per liter of ascites drained)
• Avoid hypertonic saline unless life-threatening symptoms present (worsens edema and ascites)
• Sodium restriction (2-2.5 g/day) more important than fluid restriction for weight loss

Critical Correction Rate Guidelines

Standard correction limits: 1

• Maximum 8 mmol/L in 24 hours for all patients
• Target 4-6 mmol/L per day for safer approach

High-risk patients requiring slower correction (4-6 mmol/L per day): 1

• Advanced liver disease or cirrhosis
• Alcoholism or malnutrition
• Prior encephalopathy
• Severe hyponatremia (<120 mmol/L)
• Hypokalemia or hypophosphatemia

Monitoring Protocol

For asymptomatic/mild symptoms: 1

• Check sodium every 4-6 hours during initial correction
• Daily monitoring once stable
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically 2-7 days post-correction

Calculate sodium deficit: 1

• Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg)
• This helps determine total sodium supplementation needed

Special Considerations for Neurosurgical Patients

Distinguish SIADH from Cerebral Salt Wasting (CSW): 1

• CSW requires volume and sodium replacement, NOT fluid restriction
• CSW signs: True hypovolemia, CVP <6 cm H₂O, urine sodium >20 mmol/L despite volume depletion
• CSW treatment: Isotonic or hypertonic saline + fludrocortisone 0.1-0.2 mg daily
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm

Common Pitfalls to Avoid

• Never correct chronic hyponatremia >8 mmol/L in 24 hours (risks osmotic demyelination syndrome) 1
• Never use fluid restriction in CSW (worsens outcomes) 1
• Never ignore mild hyponatremia (130-135 mmol/L) as clinically insignificant 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Never fail to identify and treat the underlying cause 1

When to Use Hypertonic Saline (3%)

Reserved ONLY for severe symptomatic hyponatremia: 1

• Seizures, coma, altered mental status requiring urgent intervention
• Target: 6 mmol/L correction over 6 hours or until symptoms resolve
• Then switch to slower correction to stay within 8 mmol/L total in 24 hours
• Monitor sodium every 2 hours during hypertonic saline administration