Aim of Hypertonic Saline in Symptomatic Hyponatremia
The primary aim of hypertonic saline in symptomatic hyponatremia is to rapidly increase serum sodium levels to reverse life-threatening neurological symptoms while preventing osmotic demyelination syndrome by controlling the rate of correction.
Indications and Goals
Hypertonic saline (3%) is indicated for:
Severe symptomatic hyponatremia with neurological manifestations such as:
- Seizures
- Altered consciousness
- Coma
- Cardiorespiratory distress 1
The immediate goal is to:
- Increase serum sodium by 4-6 mEq/L within 1-2 hours to reverse hyponatremic encephalopathy
- Stay within correction limits of no more than 10 mEq/L in the first 24 hours 1
Administration Protocol
For severe symptomatic hyponatremia:
- Administer up to three 100 mL boluses of 3% hypertonic saline spaced at 10-minute intervals to correct symptoms 2
- Use a sliding-scale protocol to minimize variability and achieve safe correction rates 3
For acute hyponatremia (<48 hours):
- More rapid correction is generally safer as brain adaptation hasn't fully occurred
- Prompt correction is crucial when symptoms are present 4
For chronic hyponatremia (>48 hours):
- Limit correction to ≤15 mEq/L in 24 hours
- Further limit to ≤10 mEq/L in 24 hours for high-risk patients (hypokalemia, liver disease, malnutrition, alcoholism) 4, 2
Mechanism and Benefits
Hypertonic saline works by:
- Creating an osmotic gradient that pulls water from intracellular to extracellular space
- Rapidly reducing cerebral edema and intracranial pressure
- Increasing regional cerebral blood flow, brain tissue oxygen, and pH in patients with high-grade subarachnoid hemorrhage 5
Monitoring and Safety Considerations
To prevent complications:
- Monitor serum sodium levels frequently during correction
- Consider using a standardized protocol that has shown 84.3% time in goal sodium range (136-145 mEq/L) with minimal overshoot 3
- Be vigilant for signs of overly rapid correction
- Consider prophylactic desmopressin in high-risk cases to prevent overcorrection 6
Avoiding Osmotic Demyelination Syndrome
Overly rapid correction of chronic hyponatremia can lead to osmotic demyelination syndrome:
- If correction exceeds target rates, consider administering hypotonic fluids and desmopressin to re-lower sodium 4
- Patients with alcoholism, malnutrition, or liver disease require more cautious correction 2
- Never correct to normonatremia or hypernatremia in a single treatment session 7
Alternative Approaches
For less severe cases:
- Oral hypertonic solutions may be considered for mild to moderate symptomatic hyponatremia if the patient can tolerate oral intake 2
- Urea can be an effective alternative treatment for syndrome of inappropriate antidiuresis but has poor palatability and may cause gastric intolerance 1
Hypertonic saline remains the cornerstone of treatment for symptomatic hyponatremia, with the dual goals of rapidly reversing life-threatening symptoms while preventing neurological complications from overly aggressive correction.