What is the initial approach to treating a patient with chronic hyponatremia?

Initial Approach to Chronic Hyponatremia Treatment

For chronic hyponatremia (>48 hours duration), the cornerstone of initial management is determining volume status and correcting sodium slowly—never exceeding 8 mmol/L in 24 hours—to prevent osmotic demyelination syndrome. 1

Immediate Assessment and Classification

Obtain serum sodium, serum osmolality, urine osmolality, and urine sodium concentration to establish the diagnosis and differentiate causes 1. Hyponatremia is defined as serum sodium <135 mmol/L, with treatment warranted when levels fall below 131 mmol/L 2, 1.

Assess extracellular fluid volume status through physical examination:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic signs: no edema, normal blood pressure, moist mucous membranes 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention 1

Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%), so laboratory confirmation is essential 1.

Critical Correction Rate Guidelines

The single most important principle: never correct chronic hyponatremia faster than 8 mmol/L in 24 hours 2, 1. Overly rapid correction causes osmotic demyelination syndrome, manifesting as dysarthria, dysphagia, oculomotor dysfunction, spastic quadriparesis, or death, typically 2-7 days after overcorrection 1.

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

• Advanced liver disease 1
• Alcoholism 1
• Malnutrition 1
• Prior encephalopathy 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion 1. Urine sodium <30 mmol/L predicts good response to saline with 71-100% positive predictive value 1.

Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1. Discontinue diuretics immediately if sodium <125 mmol/L 1.

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is first-line treatment 2, 1, 3. Nearly half of SIADH patients fail fluid restriction alone 4.

For refractory cases, add oral sodium chloride 100 mEq three times daily 1. Second-line pharmacological options include:

• Urea (effective and safe) 4
• Tolvaptan 15 mg once daily, titrated to 30-60 mg 3
• Demeclocycline or lithium (less commonly used due to side effects) 1

Critical caveat: Tolvaptan must be initiated in hospital with frequent sodium monitoring due to risk of overly rapid correction 3. The FDA label explicitly warns that 7% of patients with sodium <130 mEq/L had increases >8 mEq/L at 8 hours 3.

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1. Temporarily discontinue diuretics until sodium improves 1.

For cirrhotic patients, consider albumin infusion alongside fluid restriction 1. Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1.

Important distinction: In cirrhosis, sodium restriction (not fluid restriction) produces weight loss, as fluid passively follows sodium 1.

Special Considerations for Neurosurgical Patients

Distinguish SIADH from cerebral salt wasting (CSW)—they require opposite treatments 2, 1:

SIADH characteristics:

• Euvolemic state 1
• Urine sodium >20-40 mmol/L 1
• Treatment: fluid restriction 2, 1

CSW characteristics:

• True hypovolemia with low CVP (<6 cm H₂O) 1
• Urine sodium >20 mmol/L despite volume depletion 1
• Treatment: volume and sodium replacement, NOT fluid restriction 2, 1

For subarachnoid hemorrhage patients at risk for vasospasm, never use fluid restriction 2, 1. Consider fludrocortisone 0.1-0.2 mg daily to prevent vasospasm 2, 1.

Monitoring Protocol

Check serum sodium every 24 hours initially for asymptomatic patients 1. Monitor daily weights and strict intake/output 1.

Watch for signs of osmotic demyelination syndrome: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, typically appearing 2-7 days after rapid correction 1.

Common Pitfalls to Avoid

Never ignore mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk 21% vs 5% in normonatremic patients and carries 60-fold increased mortality 1, 5.

Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1, 6.

Never use hypertonic saline for chronic asymptomatic hyponatremia—reserve for severe symptomatic cases only 1, 7.

Inadequate monitoring during active correction leads to overcorrection and osmotic demyelination 1.

Failing to identify and treat the underlying cause results in recurrence 1.