In a patient with chronic hyponatremia, how should sodium chloride be used for treatment and what are the safe limits for serum sodium correction?

Management of Chronic Hyponatremia with Sodium Chloride

In chronic hyponatremia, sodium chloride should be used cautiously with correction rates never exceeding 8 mmol/L in 24 hours, and even slower (4-6 mmol/L per day) in high-risk patients with liver disease, alcoholism, or malnutrition to prevent osmotic demyelination syndrome. 1

Critical Correction Rate Limits

The single most important safety principle is the maximum correction rate:

• Standard-risk patients: 4-8 mmol/L per day, absolute maximum 8 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, chronic alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, never exceeding 8 mmol/L in 24 hours 1
• Risk of osmotic demyelination: 0.5-1.5% even with careful correction in liver transplant recipients 1

The distinction between acute (<48 hours) and chronic (>48 hours) hyponatremia is critical because chronic hyponatremia requires slower correction due to brain adaptation 2. Even mild chronic hyponatremia (130-135 mmol/L) is associated with 60-fold increased mortality risk and should not be ignored 3.

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Use isotonic saline (0.9% NaCl) for volume repletion:

• 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
• Urine sodium <30 mmol/L predicts 71-100% positive response to saline 1
• Monitor for euvolemia: absence of orthostatic hypotension, normal skin turgor, moist mucous membranes 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction is first-line, NOT sodium chloride:

• Restrict fluids to 1 L/day (or <800 mL/day for refractory cases) 1
• If fluid restriction fails after 24-48 hours, add oral sodium chloride 100 mEq (2.3 grams) three times daily 1
• Consider urea or vaptans as second-line therapy 4
• Never use normal saline in SIADH as it can worsen hyponatremia through dilution 1

Hypervolemic Hyponatremia (Cirrhosis, Heart Failure)

Fluid restriction is primary therapy, avoid sodium chloride:

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion (8 g/L of ascites removed) in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms as it worsens ascites and edema 1
• Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss in cirrhosis 1

Severe Symptomatic Hyponatremia

For seizures, coma, or altered mental status, use 3% hypertonic saline:

• Administer 100 mL boluses of 3% NaCl over 10 minutes, repeat up to 3 times 1, 5
• Target correction: 6 mmol/L over first 6 hours or until symptoms resolve 1
• Still respect the 8 mmol/L/24-hour limit even in emergencies 1
• Check sodium every 2 hours during initial correction 1
• ICU admission required for close monitoring 1

Monitoring Protocol

Frequency of sodium checks:

• Severe symptoms: every 2 hours during initial correction 1
• After symptom resolution: every 4 hours 1
• Asymptomatic/mild: every 24-48 hours initially 1

Watch for osmotic demyelination syndrome signs (typically 2-7 days after correction): dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1

Management of Overcorrection

If sodium rises >8 mmol/L in 24 hours:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider desmopressin to slow or reverse rapid sodium rise 1, 6
• Target: bring total 24-hour correction back to ≤8 mmol/L from baseline 1

Three desmopressin strategies exist: proactive (early administration), reactive (based on sodium changes), and rescue (after exceeding targets), with proactive showing lower incidence of exceeding correction targets in small case series 6.

Calculating Sodium Deficit

Formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

This helps determine the amount of sodium supplementation needed, but always prioritize correction rate limits over achieving target sodium levels quickly 1.

Common Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours regardless of initial severity 1, 5
• Never use normal saline in SIADH or hypervolemic states as it worsens hyponatremia 1
• Never ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk and mortality 3
• Never use fluid restriction in cerebral salt wasting as it worsens outcomes 1
• Never fail to distinguish between acute and chronic hyponatremia as treatment strategies differ fundamentally 2
• Inadequate monitoring during active correction is a critical error 1

Even when overall 24-hour correction rates appear safe, short bursts exceeding 0.5 mmol/L per hour within that period can still cause osmotic myelinolysis, particularly in severely malnourished patients 7. This emphasizes the need for uniformly slow correction rather than just meeting overall daily targets 7.