What is the recommended rate of correction for hyponatremia in milliliters per hour?

Hyponatremia Correction Rate in mL/hour

For chronic hyponatremia, the correction rate should not exceed 8 mmol/L per 24 hours, which translates to approximately 0.33 mmol/L per hour, and this rate should be achieved through careful fluid management and monitoring rather than a fixed mL/hour infusion rate. 1, 2

Understanding the Correction Rate Framework

The question asks for a rate in "mL per hour," but hyponatremia correction is fundamentally guided by change in serum sodium concentration per unit time, not volume infused. The actual mL/hour rate depends on multiple factors including the patient's body weight, the tonicity of fluid used, and the underlying cause of hyponatremia. 2

Standard Correction Limits

Maximum correction rates to prevent osmotic demyelination syndrome (ODS):

• Standard risk patients: 4-8 mmol/L per 24 hours, not exceeding 10-12 mmol/L in any 24-hour period 1, 2
• High-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia, prior encephalopathy): 4-6 mmol/L per 24 hours, not exceeding 8 mmol/L in any 24-hour period 1, 2
• Hourly rate equivalent: Approximately 0.33 mmol/L per hour maximum for standard patients, 0.25 mmol/L per hour for high-risk patients 2, 3

Calculating Infusion Rates Based on Clinical Scenario

For Severe Symptomatic Hyponatremia (Emergency)

When using 3% hypertonic saline for patients with seizures, coma, or severe neurological symptoms:

• Initial bolus approach: 100 mL of 3% saline over 10 minutes, can repeat up to 3 times at 10-minute intervals until symptoms improve 2, 4
• Target: Increase sodium by 6 mmol/L over 6 hours or until severe symptoms resolve 2, 4, 5
• After initial correction: Switch to slower maintenance rate to avoid exceeding 8 mmol/L total in 24 hours 2, 4

For Chronic Hyponatremia (Non-Emergency)

The approach is NOT continuous hypertonic saline infusion but rather:

• Fluid restriction: 1000-1500 mL per 24 hours (approximately 40-60 mL/hour total fluid intake) for euvolemic or hypervolemic hyponatremia 1, 2
• Isotonic saline for hypovolemic hyponatremia: Rate depends on volume deficit, but correction must still respect the 8 mmol/L per 24-hour limit 2

Practical Monitoring Algorithm

Regardless of the mL/hour rate chosen, mandatory monitoring includes:

• Severe symptoms: Check serum sodium every 2 hours initially 2, 4
• Mild symptoms or asymptomatic: Check serum sodium every 4-6 hours during active correction 2, 4
• After symptom resolution: Check every 4 hours until stable 2

Calculating Sodium Deficit

To determine appropriate fluid volumes, use: Sodium deficit = Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) 2, 6

For example, a 70 kg patient needing 6 mmol/L correction: 6 × (0.5 × 70) = 210 mmol sodium needed.

Critical Safety Considerations

Common pitfalls that lead to overcorrection:

• Spontaneous water diuresis: Can occur unpredictably when treating any cause of hyponatremia, leading to rapid overcorrection even without aggressive treatment 3, 7
• Inadequate monitoring: Failure to check sodium frequently enough to detect rapid rises 2
• Using continuous hypertonic saline without desmopressin backup: Consider concurrent desmopressin (1-2 µg every 6-8 hours) to prevent water diuresis and allow controlled correction 7

If Overcorrection Occurs

Immediate intervention required if sodium rises >8 mmol/L in 24 hours: 1, 2

• Discontinue all sodium-containing fluids immediately
• Switch to D5W (5% dextrose in water) to relower sodium
• Administer desmopressin to terminate water diuresis
• Target: Bring total 24-hour correction back to ≤8 mmol/L from starting point

Treatment Based on Volume Status

Hypovolemic Hyponatremia

• Isotonic (0.9%) saline for volume repletion 2
• Rate determined by hemodynamic status, but respect 8 mmol/L per 24-hour limit
• Monitor for spontaneous water diuresis as volume is restored 2

Euvolemic Hyponatremia (SIADH)

• Primary treatment: Fluid restriction to 1000 mL per 24 hours (approximately 40 mL/hour) 2, 4
• Not hypertonic saline unless severely symptomatic 4
• Add oral sodium chloride 100 mEq three times daily if fluid restriction fails 2, 4

Hypervolemic Hyponatremia (Cirrhosis, Heart Failure)

• Fluid restriction: 1000-1500 mL per 24 hours (40-60 mL/hour) 1, 2
• Avoid hypertonic saline unless life-threatening symptoms present 2
• Consider albumin infusion in cirrhotic patients 1, 2

Special Population: Acute vs. Chronic Hyponatremia

Acute hyponatremia (<48 hours onset): Can be corrected more rapidly (up to 1 mmol/L per hour) without ODS risk, as brain adaptation has not occurred 8

Chronic hyponatremia (>48 hours): Requires strict adherence to 8 mmol/L per 24-hour limit due to completed brain adaptation 1, 2, 3, 8

When timing is unknown: Assume chronic and use conservative correction rates 2, 8