Drinking 0.9% Sodium Chloride Solution.

Factual Questions
1

I was in a medical company when I was in the army long ago. One sweltering day we were working in the motor pool organizing medical chests and I didn’t have anything to drink. Nothing, that is, except for some bags of 0.9% sodium chloride solution, more commonly reffered to as saline. I ripped one open and took a big gulp and nearly puked. I didn’t realize 1% could make the water so salty. Anyway, it got me thinking…

I know you can’t survive for long drinking sea water which, from what I understand, has ~3.5% salinity(is that figure right?). The cells break down, electrical impulses in the heart and brain get messed up, you get dehydrated, kidneys malfunction, etc. But, can you survive drinking saline? I searched far and wide for blood plasma salinity levels but couldn’t find anything. We commonly pump people full of this stuff though, so it would make sense that you’d be able to drink it as well. I would assume it was true except for the small margin between the salinities of sea water and normal saline.

Thanks in advance,

Demo

2

Salinity of human blood is .085%. Or rounded, call it 0.9% just like the bags of saline you were talking about. That’s why it’s usually just referred to as “normal saline” by medical personnel. I use it all the time in the blood bank. However I’ve never had any to drink so I can’t vouch for that aspect.

3

If memory serves, a person with healthy kidneys can excrete urine with a maximum salinity of about 2%, so I guess drinking one litre of 1% saline would be about as replenishing as drinking a half litre of unsalted water. In humans, drinking sea water leads to a net loss of water, but aquatic mammals have large specialized kidneys that excrete urine saltier than sea water.

4

What is the salinity of Gatorade?

5

I’ll take a stab at this.

The concentration of Na[sup]+[/sup] in “normal” saline is 154 mmol/L.
The concentration of Na[sup]+[/sup] in the bloodstream is slightly less, about 140 mmol/L.

So, if a person ingests only normal saline, they will probably wind up with a blood Na[sup]+[/sup] concentration about 10% higher than physiological. They’d be very thirsty and possibly a bit delirious, but I think they’d survive for a good while.

To put this into some perspective, if a person is in a coma and has no access to water, his blood sodium concentration can become grossly elevated (I’ve seen many old folks who collapsed at home, had no way to get to the tap, and who were found days later, to have Na[sup]+[/sup] concentrations in the 180 range). For these type of people, normal saline (with its Na[sup]+[/sup] concentration of 155) would actually be a great improvement.

The issue is more complicared than this, though. The Na[sup]+[/sup] concentration in the blood reflects the amount of water in the blood. So, a high Na[sup]+[/sup] indicates too little water, and a low Na[sup]+[/sup] concentration means too much water. On the other hand, the total amount (not concentration) of Na[sup]+[/sup] in the blood dictates a person’s “blood volume” (related to the blood pressure).

So, there are permutations where you can have purely too little water, purely too much water, too little blood volume but too much water, and too little volume with too little water, etc.

Taken together, urine, sweat, feces, and exhaled air contain both water and Na[sup]+[/sup] (with more water lost than Na[sup]+[/sup] ). Thus, a person denied access to both water and Na[sup]+[/sup] replenishment will eventually wind up in need of both. His blood Na[sup]+[/sup] concentration will be elevated because of the water lack, and his blood volume will be down due to lack of Na[sup]+[/sup] .

6

Wow. KarlGauss, how did you learn all that? Awesome.

7

0.085 would round to 0.09, or 0.1, not 0.9.

8

The trick is in how saline your urine is. If it is saltier than the saline solution you can get a net increase of water. If it is less salty than the saline, then every drink will dehydrate you.

9

About 0.17% according to this page. Water evaporating from the lungs don’t carry away salt. Also, I don’t think sweat evaporating directly from our skin removes salt from the blood. (Anybody know for sure?)

Tengu, I’m sure dwyr meant to say 0.85%. 0.085% is clearly wrong.

10

Here’s an experiment for you:
[ul][li]Have a shower[/li][li]lick your skin, and write down how it tastes[/li][li]Run a marathon.[/li][li]Lick your skin, and again write down how it tastes[/li][/ul]
By comparing the saltiness measured in step 2 and step 4, I think you will find that the salinity of your skin has increased.
I believe that that salt originated as sweat, the salt of which previously was in your bloodstream.

But I might be wrong :wink:

11

Sorry if I implied that salt was given off when we breath. I was simply lumping together the various sources of salt and/or water loss from the body.

In terms of salt loss from sweating, indeed it must come from the blood. Unless the sweat glands are manufacturing salt (and they’re not), their only source of new, replacement, salt is via the circulation.

For those who are interested in such things, much of the salt (i.e. Na[sup]+[/sup]) in the body is neither in the blood stream or in the cells themselves. About 75% of the Na[sup]+[/sup] in the body is located in the “interstitium”, a space outside the cells, but not in the circulation/bloodstream. In many disease states, there is an inappropriate flux of Na[sup]+[/sup] from the bloodstream into this interstitial space. Since Na[sup]+[/sup] pulls water with it, the patient winds up with swelling (edema) or accumulations of fluid in what were previously only “potential” spaces.

12

Guilty as charged. It was pretty much a drive-by post while I was at work. I did mean 0.85%.