About this Calculator – Custom Sodium Solution Calculator

This custom sodium solution calculator is designed to assist veterinarians in creating a custom sodium-containing solution using the following formula:

Vx = [(C1 – C2) x V1]/(C3 – C2)

This formula helps determine the volume of a higher sodium concentration solution (e.g., hypertonic saline) needed to achieve a desired final sodium concentration in a baseline solution.

C1: Desired Na+ concentration in the final solution

C2: Current Na+ concentration in the baseline solution

V1: Desired volume of the final solution

C3: Na+ concentration in the hypertonic or other higher sodium solution

Vx: Volume of the hypertonic or higher Na+ solution to be added to the baseline crystalloid

For more in-depth guidance on managing hypernatremia, check out this blog post.

Example:

You’re treating a 10 kg dog with a plasma sodium of 185 mmol/L. The patient is hypovolemic, and you plan to administer a 20 mL/kg fluid bolus using a solution that is isotonic to the dog’s current sodium level.

You have:

• A 500 mL bag of LRS (Na⁺ = 130 mmol/L)

• 7.2% NaCl (Na⁺ = 1232 mmol/L)

To calculate how much 7.2% NaCl to add, use the formula:

Vx = [(C₁ – C₂) × V₁] / (C₃ – C₂)

Where:

• C₁ = target Na⁺ (185 mmol/L)

• C₂ = baseline fluid Na⁺ (130 mmol/L)

• C₃ = hypertonic Na⁺ (1232 mmol/L)

• V₁ = total final volume (500 mL)

Vx = [(185 – 130) × 500] / (1232 – 130) = 24.9 mL

Conclusion:
Withdraw 24.9 mL from the LRS bag and replace it with 24.9 mL of 7.2% NaCl. This gives you 500 mL of custom fluid with a sodium concentration of 185 mmol/L, appropriate for safe bolus administration in this hypernatremic dog.

In general, if a dysnatremic patient is hypovolemic and requires a fluid bolus, choose a fluid with a sodium concentration within ±5-10 mmol/L of the patient’s plasma sodium to avoid rapid shifts and reduce the risk of neurologic complications, especially in cases of moderate-to-severe hypo- and hypernatremia. Improve your efficiency with the custom sodium solution calculator.

Read more about hypernatremia here.

VETEMCRIT ACADEMY

VetEmCrit Academy is dedicated to advancing veterinary medicine by providing practical, evidence-based resources for veterinarians and veterinary students. Focusing on areas such as electrolyte and acid-base disorders, VetEmCrit Academy helps professionals go from novice to expert with step-by-step guides and case-based learning. By simplifying complex medical topics, the academy aims to empower veterinary teams to make informed decisions, improving patient outcomes and mastering the intricacies of small animal emergency and critical care.

WATCH VIDEO ON THE CUSTOM SODIUM SOLUTION CALCULATOR:

Disclaimer

This veterinary custom sodium solution calculator is intended for informational and educational purposes only.

The creator of this tool is not responsible for clinical decisions or medical errors resulting from its use.

Users are encouraged to consult with a licensed veterinarian or medical professional to make informed decisions.

References

1. Ueda Y, Hopper K, Epstein SE. Incidence, severity and prognosis associated with hypernatremia in dogs and cats. J Vet Intern Med. 2015 May-Jun;29(3):794-800. doi: 10.1111/jvim.12582. PMID: 25996661; PMCID: PMC4895431.
2. Muhsin SA, Mount DB. Diagnosis and treatment of hypernatremia. Best Pract Res Clin Endocrinol Metab. 2016 Mar;30(2):189-203. doi: 10.1016/j.beem.2016.02.014. Epub 2016 Mar 4. PMID: 27156758.
3. DiBartola SP. Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 4th ed. St. Louis, MO: Elsevier Saunders; 2012.