Hypothetical scenerio involving hypotnatremia vs. heat stress injury

[Just Steve]

So a PA friend of mine just attended a wilderness medicine conference down in Tucson and was posting on Facebook about some of the intricacies of differentiating between heat stress injury versus hyponatremia in a wilderness setting. This of course started a conversation about things around that foci and the eventual question was asked "why don't we treat all possible heat stress related injuries with electrolyte drink until we can get to definitive diagnosis back in the lab?"

 

A person is crossing 80 miles of desert with just the clothes on their back. Haven't eaten in three or four days, but does happen across a rescue water station that have been placed along our southern border. That person drinks until they are bursting at the seams with water. They fill their water jug and continue on their trek. They are soon discovered by US Border Patrol. They note that the person is acting erratic, assume their detainee is dehydrated, and gives them a sports drink. What sort of untoward metabolic issues may we anticipate if any?

 

I am just a neophyte student who should be studying other body systems right now for the test on Tuesday, but this has me curious...what say ye, founts of knowledge?

[Acebecker]

One would think that we would wan to give a hypertonic saline solution, right? In theory, yes. However, the fluid/electrolyte balance shift that could potentially occur may be disastrous for that patient. The hypertonic solution would begin to lyse RBCs causing serum K+ to elevate as well as a potentially significant anemia. Thus, in practice (at least where I trained clinically) an isotonic saline soln is the Tx of choice. Basically we fluid support the kidneys so they can do their job of dumping the excess water. A sports drink would work just fine as long as there was enough intravascular volume to allow proper processing. If the pt is already in a pre-renal failure from lack of blood volume, you won't accomplush a lot with PO fluid and perenteral becomes necessary.

 

At least this is my take on it.

 

Andrew

[ventana]

look for horses not zebra's

 

hyponatremia due to over ingesting H2O is pretty darn rare - it does happen but not with any of the frequency of heat injury...

[flyingsquirrel]

Our treatment of choice (level one trauma center/critical care transport) for adults is to give 100ml 3% saline over 10-20 minutes if the patient has signfigant neurological symptoms (altered mental status, seizures, herniation etc). This should raise serum sodium by 2 mEq/L. If needed, this can be repeated ONCE. After that, fluid restrict, consult nephrology. Don't give NS, don't try to correct the K.

We usually have access to labs/iStat but often we can differentiate acute hyponatremia from heat stroke by H&P.

[Just Steve]

I appreciate the input. Perhaps I wasn't quite clear enough in my description. The situation is one of a zebra nature, I agree there. It is very rare that a person is volume adequate but electrolyte depleted. That is one of the fun things about wilderness medicine...there is a need to do a little zebra scouting as we are typically far removed from the luxuries that tertiary medical centers have to offer. Failure to anticipate can be even more dramatic as we lack most of the tools to help catch up if we fall off the proper path.

 

The background on the scenario is that a PA friend of mine who is the medical leader for a search/rescue group down in southern Arizona is a Fellow in the Academy of Wilderness Medicine ( http://wms.org/fawm/masters.asp ). During the recent directors meeting of the wilderness medical conference, they spent an afternoon discussing this very situation. So via Facebook, he shared the scenario for us to digest. I was just digging around for thoughts on the potential pitfalls. I won't say he "pimped" me per se', but there was some encouragement directed towards me to figure this out.

 

The assumption is that the rescue team came across this desert wanderer who is adequately hydrated but has been without food. It can be a desert hiker, it can be a victim of an earthquake region in the heat of summer, it can be a cholera patient who now has access to water but can't retain food. Pick your favorite situation. The premise is that a hospital is not an option in the immediate future.

 

I went with the issue being running a risk of fluid overload. Sports drinks are actually just a little hypotonic. There isn't enough electrolytes in them to remedy the hyponatremia. So the fluid intake climbs and the osomotic receptors still sense a hypotonic blood solution, they continue to stimulate ADH, the kidneys still retain all the fluid, and eventually we go down the path of fluid overload, plus still not correcting the issues of hyponatremia. It is my understanding that the ANP/BNP processes are overridden by the ADH.

 

So, to differentiate hyponatremia vs heat stress injury is to observe for persistent altered mental status who is producing sufficient urine, with normo to hypertensive blood pressure. (S&R teams do carry BP cuffs). If the patient is peeing great, but still goofy, think sodium imbalance.

 

That's my angle on it...

[pahopeful]

look for horses not zebra's

 

hyponatremia due to over ingesting H2O is pretty darn rare - it does happen but not with any of the frequency of heat injury...

 

This summer in the extreme Texas heat, I had several people come in with hyponatremia d/t over ingestion of water. Pretty interesting, but not too rare in these parts.

[NoClinic4Me]

Agree that it's rare except in schizophrenics on antipsychotic drugs. I've seen those folks drink 10 gallons of water and take their sodium down to 110. Called psychogenic polydipsia. I used to admit a couple of these a month from the neighborhood county psych hospital. Skewed population for sure, I get that.

In this context, I'd agree with you however.

[EMEDPA]

Agree that it's rare except in schizophrenics on antipsychotic drugs. I've seen those folks drink 10 gallons of water and take their sodium down to 110. Called psychogenic polydipsia. I used to admit a couple of these a month from the neighborhood county psych hospital. Skewed population for sure, I get that.

In this context, I'd agree with you however.

 

I have seen this as well with psych folks presenting with seizures and NA of 105.