What is the IV fluid rate formula for managing hyponatremia?

IV Fluid Rate Formula for Hyponatremia

For severe symptomatic hyponatremia, administer 3% hypertonic saline as 100 mL IV boluses over 10 minutes, repeating every 10 minutes up to three times until symptoms resolve, targeting an initial sodium increase of 4-6 mEq/L within the first hour. 1, 2, 3

Calculating Sodium Deficit and Infusion Rate

The sodium deficit formula is: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg). 1

For continuous infusion of 3% hypertonic saline, the initial infusion rate (mL/kg/hour) = body weight (kg) × desired rate of sodium increase (mmol/L/hour). 4 However, bolus administration is now preferred over continuous infusion for symptomatic cases. 5

3% Hypertonic Saline Specifications

• Sodium content: 513 mEq/L 1
• Each 100 mL bolus provides approximately 51 mEq of sodium 1

Critical Correction Rate Limits

Maximum correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2, 3 This is the single most important safety parameter.

Correction Targets by Symptom Severity

For severe symptoms (seizures, coma, altered mental status):

• Correct by 6 mmol/L over the first 6 hours OR until severe symptoms resolve 1, 2, 3
• If 6 mmol/L is achieved in 6 hours, limit additional correction to only 2 mmol/L in the following 18 hours 2, 3
• Monitor serum sodium every 2 hours during initial correction 1, 3

For asymptomatic or mildly symptomatic hyponatremia:

• Target correction rate of 4-6 mEq/L per day 1, 6
• Slower correction is safer and avoids overcorrection complications 6

Bolus vs. Continuous Infusion Protocol

Bolus administration is preferred for symptomatic hyponatremia: 5

• Give 100-150 mL of 3% saline IV over 10 minutes 3, 5
• Repeat every 10 minutes if symptoms persist, up to three total boluses 3
• Check sodium level after each bolus or at minimum every 2 hours 3

Continuous infusion alternative (less preferred):

• Calculate rate using: body weight (kg) × 1-2 mmol/L/hour (desired correction rate) 4
• Requires more intensive monitoring due to risk of overcorrection 5

High-Risk Populations Requiring Slower Correction

Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require maximum correction of only 4-6 mmol/L per day, not exceeding 8 mmol/L in 24 hours. 1, 3, 6 These populations have significantly higher risk of osmotic demyelination syndrome.

When to Discontinue 3% Saline

Stop 3% hypertonic saline when: 2

• Severe symptoms resolve (primary criterion) 2
• 6 mmol/L correction achieved in first 6 hours 2
• Total correction approaches 8 mmol/L in 24 hours 2

After discontinuation, transition to: 2

• Fluid restriction to 1 L/day for SIADH 2, 3
• Monitor sodium every 4 hours instead of every 2 hours 2
• Continue treatment until sodium reaches 131 mmol/L 2

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours: 1

• Immediately discontinue hypertonic saline and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to halt water diuresis and prevent further correction 1, 6
• Therapeutic relowering of sodium is supported by animal data and small clinical trials 6

Common Pitfalls to Avoid

• Never use continuous infusion without frequent monitoring - bolus administration allows better control 5
• Never exceed 8 mmol/L correction in 24 hours - this risks osmotic demyelination syndrome 1, 2, 3
• Never use 3% saline for asymptomatic hyponatremia - reserve for severe symptoms only 1, 5
• Never use fluid restriction as initial treatment for severe symptomatic hyponatremia - this is a medical emergency requiring hypertonic saline 3
• Inadequate monitoring during active correction leads to overcorrection complications 1