From the Guidelines
A bolus of hypertonic saline typically raises serum sodium by approximately 1-2 mEq/L for every 100 mL of 3% hypertonic saline administered. For more precise calculations, the change in serum sodium can be estimated using the Adrogue-Madias formula: change in serum sodium = [(infusate sodium - serum sodium) ÷ (total body water + 1)], as noted in general medical practice 1. Total body water is estimated as 0.6 × weight in kg for men and 0.5 × weight in kg for women. When administering hypertonic saline, it's crucial to monitor serum sodium levels frequently, typically every 2-4 hours initially, to avoid overly rapid correction.
Key Considerations
- The rate of sodium correction should generally not exceed 8-10 mEq/L in 24 hours (or 0.5-1 mEq/L/hour) to prevent osmotic demyelination syndrome, particularly in patients with chronic hyponatremia 1.
- Hypertonic saline is typically administered as a 100-150 mL bolus of 3% solution over 10-20 minutes, which can be repeated if necessary based on clinical response and sodium measurements.
- The physiological basis for this therapy is that hypertonic saline increases serum osmolality, drawing water from the intracellular to the extracellular space, thereby reducing cerebral edema and raising serum sodium concentration.
Administration Guidelines
- To prevent rapid increase in serum sodium and the risk of developing central pontine myelinolysis, guidelines recommend a serum sodium increase of up to 5 mmol/L in the first hour with a limit of 8–10 mmol/L every 24 hours thereafter until the serum sodium concentration reaches 130 mmol/L 1.
- It is best reserved for those with severely symptomatic acute hyponatraemia, especially if a transplant is imminent 1.
From the Research
Correction of Hyponatremia with Hypertonic Saline
- The provided studies do not directly address the question of how much a bolus of hypertonic saline will raise serum sodium levels 2, 3, 4, 5, 6.
- However, it is known that hypertonic saline is used to treat hyponatremia, especially in patients with moderate or severe symptoms, to prevent neurological complications 3.
- The rate of sodium correction is crucial, as overly rapid correction can lead to osmotic demyelination syndrome (ODS) 2, 4, 5, 6.
- The definition of rapid sodium correction varies, but it is generally considered to be an increase of more than 8-12 mmol/L within 24 hours 2.
- The use of hypertonic saline, desmopressin, and vasopressin inhibitors are discussed as treatment options for hyponatremia, but the exact effect of a bolus of hypertonic saline on serum sodium levels is not specified 3, 5, 6.
Key Considerations
- The risk of ODS is associated with the rate of sodium correction, highlighting the need for careful monitoring and management of serum sodium levels 2, 4.
- The choice of treatment for hyponatremia depends on the underlying cause, severity, and symptoms, as well as the patient's individual response to treatment 3, 5, 6.
- Further research is needed to fully understand the relationship between sodium correction and the development of ODS, as well as to determine the most effective treatment strategies for hyponatremia 2, 4.