What is the expected increase in serum sodium level after administration of a bolus of hypertonic saline (sodium chloride) solution?

From the Guidelines

A bolus of 3% hypertonic saline typically raises serum sodium by approximately 2-4 mEq/L for every 100 mL administered in adults. The exact increase depends on several factors including the patient's weight, current sodium level, and total body water. For practical application, clinicians often use the formula: change in serum Na+ = [(infusate Na+ - serum Na+) ÷ (total body water + 1)] × (volume of infusate in L) 1.

Key Considerations

• For a 70 kg adult with approximately 42 L of total body water, a 100 mL bolus of 3% saline (containing 513 mEq/L of sodium) would raise serum sodium by about 1-2 mEq/L.
• When treating severe hyponatremia, the goal is typically to increase sodium by 4-6 mEq/L in the first 24 hours to prevent osmotic demyelination syndrome, while addressing life-threatening symptoms, as recommended by the American Association for the Study of Liver Diseases in 2021 1.
• Frequent monitoring of serum sodium levels (every 2-4 hours initially) is essential during hypertonic saline administration to avoid overly rapid correction.

Clinical Application

• The use of hypertonic saline is reserved for short-term treatment of patients with symptomatic or severe hyponatremia or those with imminent liver transplant, according to the 2021 practice guidance by the American Association for the Study of Liver Diseases 1.
• It is crucial to weigh the benefits of correcting hyponatremia against the risk of osmotic demyelination syndrome, particularly in patients with severe hyponatremia (<120 mEq/L) at the time of liver transplant 1.

From the FDA Drug Label

Inadvertent direct injection or absorption of concentrated sodium chloride solution may give rise to sudden hypernatremia and such complications as cardiovascular shock, central nervous system disorders, extensive hemolysis and cortical necrosis of the kidneys.

The amount by which a bolus of hypertonic saline will raise serum sodium is not directly stated in the provided drug labels.

• Key point: The labels warn of the potential for sudden hypernatremia with inadvertent direct injection or absorption of concentrated sodium chloride solution, but do not provide a specific amount of increase in serum sodium levels.
• The labels do mention the risks associated with excessive sodium chloride administration, including electrolyte disturbances and hypernatremia, but do not quantify the expected rise in serum sodium levels 2.

From the Research

Effect of Hypertonic Saline on Serum Sodium

• The effect of hypertonic saline on serum sodium levels is a critical consideration in the treatment of hyponatremia 3, 4, 5, 6, 7.
• Hypertonic saline has been used for nearly a century to treat hyponatremia, particularly in patients with moderate or severe symptoms to prevent neurological complications 3.
• The administration of hypertonic saline can help raise serum sodium levels, but careful monitoring is required to avoid overcorrection and complications such as osmotic demyelination 4, 5, 6, 7.
• The rate of correction of serum sodium levels is crucial, as overly rapid correction can cause osmotic demyelination syndrome 6, 7.
• The use of desmopressin or vasopressin inhibitors may be considered in conjunction with hypertonic saline to prevent rapid correction of serum sodium levels 5.

Administration and Monitoring

• The administration of hypertonic saline should be guided by the severity of symptoms and the underlying disease state 3, 4, 5, 6, 7.
• Frequent monitoring of serum sodium levels is essential to avoid overcorrection and complications 4, 5, 6, 7.
• The use of vasopressin antagonists may be considered in the treatment of hyponatremia, particularly in patients with euvolemic or hypervolemic hyponatremia 4, 5.