How should I adjust the rate of 3% NaCl in a severely symptomatic adult with hyponatremia (serum sodium <120 mEq/L)?

Adjusting 3% Hypertonic Saline in Severe Symptomatic Hyponatremia

For severe symptomatic hyponatremia (serum sodium <120 mEq/L) with neurological manifestations, administer 3% NaCl as 100 mL boluses over 10 minutes, repeating up to three times at 10-minute intervals, with a target correction of 4-6 mEq/L over the first 6 hours or until symptoms resolve—never exceeding 8 mEq/L total correction in any 24-hour period. 1, 2, 3

Initial Bolus Protocol for Severe Symptoms

Severe symptoms requiring immediate hypertonic saline include seizures, coma, altered mental status, respiratory arrest, or signs of impending herniation. 1, 2

• Administer 100 mL of 3% NaCl intravenously over 10 minutes as the initial bolus 2, 3
• Repeat the 100 mL bolus every 10 minutes for up to three total doses if symptoms persist 2
• Check serum sodium 3 hours after initiating treatment, then every 2-4 hours during the acute correction phase 1, 3
• Target an increase of 4-6 mEq/L over the first 6 hours or until severe neurological symptoms resolve 1, 2, 3

This bolus approach can be safely administered through a peripheral IV and does not require ICU admission in all cases, though close monitoring is essential. 2

Transition to Continuous Infusion

Once severe symptoms improve (typically after 4-6 mEq/L rise), transition from boluses to a continuous infusion protocol:

• Calculate initial infusion rate: Start at approximately 15-30 mL/hour of 3% NaCl 4
• Use a sliding-scale protocol that adjusts the infusion rate based on hourly or 2-hourly sodium measurements 4
• Target serum sodium range of 125-130 mEq/L in the acute phase—do not aim for normonatremia 5, 3

A standardized sliding-scale protocol achieves safe correction rates averaging 0.44 mEq/L per hour, with patients spending 84% of time in goal range (136-145 mEq/L) during maintenance. 4

Absolute Safety Limits

The 8 mEq/L ceiling in 24 hours is inviolable to prevent osmotic demyelination syndrome:

• Maximum correction: 8 mEq/L in any 24-hour period for standard-risk patients 1, 5, 3
• High-risk patients (cirrhosis, alcoholism, malnutrition, chronic severe hyponatremia) require even slower correction at 4-6 mEq/L per day maximum 1
• If you achieve 6 mEq/L correction in the first 6 hours, only 2 mEq/L additional correction is permitted in the remaining 18 hours 1

Monitoring Requirements

• Serum sodium every 2 hours during initial bolus therapy and acute correction phase 1, 3
• Serum sodium every 4-6 hours once symptoms resolve and patient stabilizes 1, 3
• Neurological examination every 1-2 hours to assess symptom resolution 2, 3
• Watch for overcorrection: If sodium rises too rapidly, immediately stop hypertonic saline and administer D5W or desmopressin to lower sodium back within safe limits 1

Adjusting the Rate Based on Response

If sodium is rising too slowly (<0.3 mEq/L per hour):

• Increase 3% NaCl infusion rate by 10-15 mL/hour 4
• Consider additional 100 mL bolus if severe symptoms persist 2

If sodium is rising too rapidly (>0.5 mEq/L per hour or approaching 8 mEq/L total):

• Decrease 3% NaCl infusion rate by 50% 4
• If already at 8 mEq/L rise, stop hypertonic saline completely and switch to D5W 1
• Consider desmopressin to slow correction 1

If sodium reaches 125-130 mEq/L:

• Slow infusion rate significantly or stop hypertonic saline 5, 3
• Transition to maintenance therapy based on underlying etiology (fluid restriction for SIADH, continued volume replacement for cerebral salt wasting) 1

Special Considerations

For patients with heart failure or cirrhosis, hypertonic saline should be used cautiously due to volume overload risk, but severe symptomatic hyponatremia still requires immediate treatment—monitor closely for pulmonary edema. 1

Peripheral IV administration is safe for 3% NaCl boluses and continuous infusions; central access is not mandatory. 2

Avoid fluid restriction during active hypertonic saline therapy in the first 24 hours, as this can lead to unpredictable overcorrection. 1

Critical Pitfalls to Avoid

• Never correct to normonatremia acutely—target 125-130 mEq/L, not 135-145 mEq/L 5, 3
• Never exceed 8 mEq/L correction in 24 hours regardless of symptom severity 1, 5, 3
• Never delay treatment waiting for ICU bed availability—bolus therapy can begin in the emergency department 2
• Never use hypotonic fluids (0.45% NaCl, D5W) during the acute correction phase, as they worsen hyponatremia 1