How much hypertonic saline should I give?

You have a patient with hyponatremia and you’ve determined that salt tabs and normal saline just won’t do, they need some 3% hypertonic saline. Great! You go to write the order…how many cc’s should they get? At what rate? Is there a better way of calculating it rather than just saying, give 50 cc x1 and hope for the best? 

As it turns out, giving 50 cc boluses and checking Na every 2 hours is an accepted form of empiric treatment. But if that makes you uneasy, there is a more mathematical solution. (Reference

You are solving for “predicted Na.” 513 refers to the amount of Na in 1 L 3% NS. Total body water is kg x0.5 for women, kg x0.6 for men

Example: a 60 kg woman with an Na of 108. Your goal is to increase her Na by 4 mmol over the next 4 hours. 

So far, your answer should be: the predicted change in Na will be 13.06 for every 1 L 3% NS. Therefore, to increase Na from 108 to 112 over four hours: 

=0.294 L or 294 mL. However, because you want to run this over 4 hours, 294/4=73.5 mL/hour. And that’s your hypertonic saline infusion rate!

Remember your Na correction goals:

  • 2-4 mEq in the first 2-4 hours (if you go over that, consider giving some free water back)
  • <8-10 mEq over 24 hours
  • You can stop being aggressive about correction around the time Na >125 mmol/L

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