Fluid deficits and replacement

[jammed]

Hey everyone,

I'm on my surgery rotation and trying to figure out fluid deficits and replacements. I understand the fluid deficit equation in hypernatremia (wt in kg x .6 ((measured na/140)-1)), but am trying to figure out a standard for replacement therapy. I am also having trouble finding working out hyponatremia. I know the sodium deficit = Total Body Water * Normal Wt in kg * (Desired Na - Pt's Na), but how do you calculate sodium replacement. Both of these are probably important to know considering too quick of a fix to hypernatremia (fluid deficit) can cause cerebral edema and too quick of a fix to hyponatremia can cause central pontine myelinolysis. Any help on the replacement of these deficits would be awesome! Also, if anyone has a good website to help walk through the steps when assessing a patient with these deficits let me know. Thanks for everyone's help!!

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[BigRedBeta]

You're on your way if you can calculate the deficit. The next step is simply to figure out how much volume of NS (or if the patient is symptomatic and you need to use 3% Hypertonic Saline) is knowing that NS has 154 mEq of NaCl per liter (3% is 513 mEq/liter). At that point put the deficit mEq over x, cross multiply and divide to figure out the volume (may be easier to use 1000mL instead of 1L).

Once you know the total volume needed to replace the sodium, it's a matter of picking your fluid rates and for how long. Most people probably give 1/2 of the volume over the first 8 hours, and the remainder over the next 16.

Central Pontine Myelinolysis is a concern, so frequent lytes are important, particularly if your patient is the textbook patient (young female). There are some articles out there that suggest that CPM is more of a theoretical concern than reality, but at the same time there's not a lot of great reasons to be risky.

 

[Rendar5]

Hey everyone,

I'm on my surgery rotation and trying to figure out fluid deficits and replacements. I understand the fluid deficit equation in hypernatremia (wt in kg x .6 ((measured na/140)-1)), but am trying to figure out a standard for replacement therapy. I am also having trouble finding working out hyponatremia. I know the sodium deficit = Total Body Water * Normal Wt in kg * (Desired Na - Pt's Na), but how do you calculate sodium replacement. Both of these are probably important to know considering too quick of a fix to hypernatremia (fluid deficit) can cause cerebral edema and too quick of a fix to hyponatremia can cause central pontine myelinolysis. Any help on the replacement of these deficits would be awesome! Also, if anyone has a good website to help walk through the steps when assessing a patient with these deficits let me know. Thanks for everyone's help!!

The reason you're having problems with hyponatremia is that it's a complex issue with a huge differential whereas hypernatremia has a much more limited differential and easy treatment. If the pt is profoundly hyponatremic, you give normal saline (154meq) and you adjust the rate for a steady rise in sodium. This is the case of the symptomatic pt. My training (and I need to research it) is to reserve hypertonic saline (which requires a central line) for hyponatremic seizures. Your standard asymptomatic pt you get a nephrology consult and start the workup to figure out the cause. The cure is dependent on it (fluid restriction v. NS) and can wait. I say this as an ED resident who deals with the initial management and not the continuing management. Inpt treatment is as discussed much better above me.

 

[BigRedBeta]

. My training (and I need to research it) is to reserve hypertonic saline (which requires a central line) for hyponatremic seizures.

As a pediatric resident, I will use hypertonic saline even in asymptomatic patients if the required volume of NS results in an excessive volume or hourly rate.

 

[km11]

As a pediatric resident, I will use hypertonic saline even in asymptomatic patients if the required volume of NS results in an excessive volume or hourly rate.

Are you somehow implying kids are not just miniature adults?

 

[McGillGrad]

Are you somehow implying kids are not just miniature adults?

 

[jdh71]

The reason you're having problems with hyponatremia is that it's a complex issue with a huge differential whereas hypernatremia has a much more limited differential and easy treatment. If the pt is profoundly hyponatremic, you give normal saline (154meq) and you adjust the rate for a steady rise in sodium. This is the case of the symptomatic pt. My training (and I need to research it) is to reserve hypertonic saline (which requires a central line) for hyponatremic seizures. Your standard asymptomatic pt you get a nephrology consult and start the workup to figure out the cause. The cure is dependent on it (fluid restriction v. NS) and can wait. I say this as an ED resident who deals with the initial management and not the continuing management. Inpt treatment is as discussed much better above me.

Interesting. We also reserve 3% for the symptomatic, but pass on the central line and the knee jerk nephro consult. I know you need the line for more concentrated solutions, like the stuff used for decreased ICP (23.4%), but I don't remember ever using it for mere 3%. Nephro is busy and will yell at me if I make them do my thinking for me

 

[Rendar5]

Never called a nephro consult for it from the ED, wouldn't add anythin to the care. Different hospitals I've been inpatient care at do get nephro consults for hyponatremia of unknown origin as backup to make sure nothing's missed. And yes, all the consult is doing is doing your thinkin for you and it is a knee-jerk reaction.

 

[Rendar5]

Interesting. We also reserve 3% for the symptomatic, but pass on the central line and the knee jerk nephro consult. I know you need the line for more concentrated solutions, like the stuff used for decreased ICP (23.4%), but I don't remember ever using it for mere 3%. Nephro is busy and will yell at me if I make them do my thinking for me

Any bad experiences ever with running 3% through a peripheral line? I don't know if it's my hospital's culture to require it or a significant risk (5% or greater).

 

[jdh71]

Never called a nephro consult for it from the ED, wouldn't add anythin to the care. Different hospitals I've been inpatient care at do get nephro consults for hyponatremia of unknown origin as backup to make sure nothing's missed. And yes, all the consult is doing is doing your thinkin for you and it is a knee-jerk reaction.

I was just teasin'. Hope you didn't take offense.

The cultures at some places is such that consults get called much more easy than others because it's an opportunity for everyone to learn 1* and specialist team. Other places, especially if VERY busy, get grumpy for a consult if the 1* hasn't tried to figure it out first and is really at a loss of which way to go or wants an expert opinion regarding specific treatment.

 

[jdh71]

Any bad experiences ever with running 3% through a peripheral line? I don't know if it's my hospital's culture to require it or a significant risk (5% or greater).

No bad experiences yet in the handful of cases where we've used it on the floor. Anything above 3% need the central access. Although, I'd probably say that most of the cases where a patient is actually sick enough get hyponatremic causing seizures, they find themselves in the unit with a central line simply by the nature of everything else going on . . .

 

[Rendar5]

I was just teasin'. Hope you didn't take offense.

The cultures at some places is such that consults get called much more easy than others because it's an opportunity for everyone to learn 1* and specialist team. Other places, especially if VERY busy, get grumpy for a consult if the 1* hasn't tried to figure it out first and is really at a loss of which way to go or wants an expert opinion regarding specific treatment.

Nah, no offense taken, just wanted to clarify which settings I was talking about.