In this episode, I’ll discuss the rare case when a very hypotonic solution may be indicated.
A recent commentary published in AJHP argues for abandoning the use of extremely hypo-osmolar intravenous solutions to treat hypernatremia. The authors consider extremely hypotonic solutions to be 0.225% sodium chloride (also called one-quarter normal saline) and sterile water for injection. Both of these solutions have a high risk of hemolysis. In addition, 0.225% sodium chloride must be compounded which comes with a risk of compounding error.
The authors correctly point out that dextrose 5% in water is an isotonic solution that provides the necessary free water to treat acute hypernatremia without the risk from extremely hypotonic solutions. The risk with the administration of extremely hypotonic fluids is hemolysis. Death has occurred with the administration of sterile water and hemolysis of about 25% appears to occur with 1/4 normal saline.
In addition, the authors make the point that avoiding dextrose-containing solutions in patients with hypernatremia and hyperglycemia out of concern for worsening hyperglycemia is not worth the risk of hemolysis when glucose levels can be so easily controlled with insulin infusion protocols.
The authors conclude:
For treatment of hypernatremia, the time has come to abandon the use of sterile water for injection and sodium chloride solutions of less than 0.45% that require sterile compounding. There is only anecdotal evidence purporting their benefits, which is offset by anecdotal evidence documenting their substantial potential for harm.
These are reasonable recommendations and using dextrose 5% instead of sterile water or 0.225% saline will effectively provide enough free water to treat hypernatremia in almost all patients.
There is however a rare instance where 5% dextrose might not lower a patient’s sodium at all and a more hypotonic solution will be required.
If the rate of dextrose infusion is high enough, and insulin is not able to control a patient’s hyperglycemia it is possible for glycosuria to develop. Glycosuria will increase electrolyte-free water loss and slow down or stop altogether the rate of decrease in serum sodium.
If this occurs, it should first be managed by slowing down the rate of dextrose infusion. However, that may also slow the rate of sodium correction.
In such a scenario, a hypotonic solution with less than 5% dextrose may need to be used. I have encountered this scenario only once in my practice, and the patient was treated instead with dextrose 2.5%. Unfortunately, the data for this is limited to anecdotes and expert opinion only.
Whether hemolysis would occur with 2.5% dextrose is unknown as far as I can tell. If using this therapy I’d strongly consider monitoring the H&H and looking for signs of hemolysis, and switching back to 5% dextrose as soon as possible.
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