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Author Topic: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
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Post Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: August 28, 2011, 16:08
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This is a question asked on the YouTube discussion channel about the following video: http://www.youtube.com/watch?v=7Jhd4f9sPoQ

Why are you using the total body water and not the extracellular fluid volume?

The sodium concentrations you are using (110 vs. 140) are for ECV measurements. This is a disconnect for me.

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Post Re: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: August 28, 2011, 16:16
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This is a great question. I'll give you a simple answer to help explain this a little better.

Simple answer:
The sodium concentrations used in the 10-minute rounds video (110 and 140 meq/L) are measured in the extracellular compartment. Thus, one would believe that the total sodium (in meq) would be the product of the extracellular fluid volume (ECF vol) * the sodium concentration. However, the [Na+] is not a measure of ECF volume. It is a surrogate measure of the intracellular (or total body) water content.

Multiplying ECF volume with [Na+] would be a misuse of the [Na+] because the latter reflects body water. Thus, total sodium (in meq; not meq/L) would be calculated by multiplying body water * [Na+].

I recommend going through the following teaching resource to understand the difference between [Na+] (and what it measures) versus total sodium content (in meq) and what it measures.

http://blog.ecu.edu/sites/nephrologyondemand/?p=6205

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Post Re: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: June 16, 2013, 09:09
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I have read all this and I still do not understend something? If there are diffrent concentrations of sodium in exctracelular and inracelular spaces, how can there be so simple equation, using only contration in extracellular space? That does not make abosolutely any sense to me. Can anybody help?

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Post Re: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: June 16, 2013, 10:21
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You're right that the equation we use is very simple. The simplicity is intentional to make it easier for clinicians. A quadratic or differential equation would be more mathematically correct but more difficult to use on the wards.

From my clinical experience these simple equations work well and help us accurately predict the response to IV fluid administration.

But I'd like to read your thoughts and share your equations with the whole group.

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Post Re: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: June 18, 2013, 15:24
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No I did not think like that, newetheless if you mention, no matter how complicated equations would be, it wuld be always possible to do program, where you woul just inest relevant numbers, which would be pretty resonable if that would be better for patents, wouldnt it?

But as I say I did not think like that. With simplicity I meant our physiological model. I think it is not accuarte enuof. But I will try to ask again.

Consider two statments:

1. Human body is made of some percent of water and that whater is in diffrent comparmnets(cells, extracelular,....)

2. There are some important diffrences in concentration of ions in diffrent compartmen.(For example sodium)

Now if you agre wuth 1 and 2 than my question is:

How is it possible to absulotly ignore statment 2 in patients with hyponatriemia?

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Post Re: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: September 30, 2013, 07:26
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Nice Post

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Post Re: Question about a 10-minute rounds video on Hyponatremia (Calculating the amount of water lost)
on: October 12, 2013, 08:17
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This is just great. I love your blog.

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