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Hypotonic MIVF

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WheezyBaby

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Is D51/2NS still widely used at your institution? I've never really understood the logic, and the evidence seems to be pointing pretty clearly toward increased risk with its use relative to isotonic fluids, though I'm certainly not an expert in the area. Just a matter of old habits at this point?
 

SurfingDoctor

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    The "logic" of hypotonic fluids is based on the Holliday-Segar methods of calculation for the daily needs of water and solutes based off normal, healthy adults and children. That being said, by definition of being hospitalized, a patient is not healthy and people argue (rightly so), that one shouldn't extrapolate healthy calculations into sick patients.

    The risk of hypotonic fluids is the development of hyponatremia. This is a well documented phenomenon. This is likely a combination of the fluid themselves and the patients pathology. Considering respiratory symptoms (pneumonia, brochiolitis, asthma) are the most common causes of pediatric hospitalizations, and that lung pathology causes ADH release (through unclear mechanism) and can cause patients to have SIADH, the use of hypotonic fluids does have an increase risk of hyponatremia and hyponatremic seizures (I've seen it several times before).

    However, patients who are ill, especially those with vomiting/diarrhea/increased urinary loss/insensible loss have free water deficits for which isotonic fluids may be inappropriate. Additionally, you have to remember that NS also has 154 mEq/L of Cl- which can induce a non-gap metabolic acidemia (though it is typically harmless). So the use of isotonic versus hypotonic fluids really depends on the patient and the pathology. Just like most of medicine, one size doesn't fit all.

    I'm a big fan of Plasmalyte or LR. However, NS and versions of it are simply easier and cheaper to make, can be customized, and are most compatible with other drugs (due to lack of Ca++ and Mg++), and thus are more commonly used. I personally think it is okay to use 1/2 NS (but not 1/4 NS unless to are specifically correcting a free water deficit for a finite period of time... like diabetes insipidus) for short durations, but if one does so, they need to follow Na++ levels.
     
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    WheezyBaby

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    The "logic" of hypotonic fluids is based on the Holliday-Segar methods of calculation for the daily needs of water and solutes based off normal, healthy adults and children. That being said, by definition of being hospitalized, a patient is not healthy and people argue (rightly so), that one shouldn't extrapolate healthy calculations into sick patients.

    The risk of hypotonic fluids is the development of hyponatremia. This is a well documented phenomenon. This is likely a combination of the fluid themselves and the patients pathology. Considering respiratory symptoms (pneumonia, brochiolitis, asthma) are the most common causes of pediatric hospitalizations, and that lung pathology causes ADH release (through unclear mechanism) and can cause patients to have SIADH, the use of hypotonic fluids does have an increase risk of hyponatremia and hyponatremic seizures (I've seen it several times before).

    However, patients who are ill, especially those with vomiting/diarrhea/increased urinary loss/insensible loss have free water deficits for which isotonic fluids may be inappropriate. Additionally, you have to remember that NS also has 154 mEq/L of Cl- which can induce a non-gap metabolic acidemia (though it is typically harmless). So the use of isotonic versus hypotonic fluids really depends on the patient and the pathology. Just like most of medicine, one size doesn't fit all.

    I'm a big fan of Plasmalyte or LR. However, NS and versions of it are simply easier and cheaper to make, can be customized, and are most compatible with other drugs (due to lack of Ca++ and Mg++), and thus are more commonly used. I personally think it is okay to use 1/2 NS (but not 1/4 NS unless to are specifically correcting a free water deficit for a finite period of time... like diabetes insipidus) for short durations, but if one does so, they need to follow Na++ levels.

    That was a great post, thank you! I'm also a fan of the notion of "being physiologic" and using ringers or plasmalyte, but I suppose it's just more to think about when it doesn't tend to matter all that much outside of large volume resuscitation, which has its own issues.
     
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