Is water given orally ever a bad idea with dehydration

With starvation, the body adapts to a lack of food and if you give someone who has been starving for too long rich food it can make them sick or kill them.

Does something similar exist for dehydration, can a person reach a point where oral rehydration does more harm than good (and you have to do IV rehydration)? Or is it such that no matter how dehydrated someone is (stuck in the desert for 2 days, near death, etc) oral rehydration (without added electrolytes, for argument’s sake) is still a good idea?

In many years of Wilderness F/A training I’ve never heard of a situation where you don’t want to hydrate orally. The main thing would be to avoid a situation where you would get vomiting due to overwhelming a distressed system. In general, small sips of water is best for anyone in possible chance of distress.

Total second hand anecdote here, but a friend who is/was in the Army mentioned that they would, on occasion, rehydrate folks… um… from the other end. The explanation he gave was just about speed of absorption, though.

My MIL had a stroke and it damaged the portion of her brain that controlled swallowing(no one knew until close to her death).

She couldn’t swallow and became dehydrated and emaciated, and when she was hospitalized every time they would put her on a IV drip and no matter how low they regulated the drip she would balloon up and bloat with water to the point it was like edema. You could touch her skin and leave a dent, like she was a bag of water.

They said her kidneys had become so adapted to conserving water they were not functioning normally.

I just mention this because yes apparently your kidneys can lose the ability to correctly maintain water balance in the body.

Well you don’t want to re-hydrate with ice or snow if you are out in the cold. That could lower your internal body temp quickly and dangerously.

There is a condition called water intoxication or water poisoning. The scientific name is dilutional hyponatremia. It can kill in the worse case scenario by causing an electrolyte imbalance. It happens from drinking plain water when sweating as the sweat often contains a lot of salt in it. The brain and other body parts swell up as salt helps regulate the amount of water in the body. That’s why sports drinks and IV fluids have electrolytes in them such a salt and potassium.

Apparently the first aiders on yacht cruises use a hosepipe analy (or at least the threat of it) to rehydrate passengers who fail to drink enough.

It can be a bad idea in that gulping water or drinking chilled water can make a dehydrated person vomit, and thus lose more water than they took in. It can also delay the decision to place an IV in an actual emergency. Small frequent sips, as already mentioned, are better than chugging. I’m personally a fan of enema rehydration in first aid situations, as well; it’s faster than oral, it’s easier to get lightly salted water up the bum than down the throat, and it won’t trigger vomiting.

I vaguely remember a medical public service announcement stating how sometimes those suffering from…something: maybe heat exhaustion…rehydration by drinking won’t work; you’d just piss it out as fast as it went in, so you must rehydrate intraveneously.

Especially in hospitalized or institutionalized patients (who may not have the ability to drink when they are thirsty), we often encounter people who are so dehydrated that the salts in their blood have become extremely concentrated. The key salt to consider in such a situation is sodium.

When sodium in the bloodstream has become too concentrated (hypernatremia), that in itself is a bad thing and can lead to quite profound depression of consciousness.

That said, if someone is identified as having a very high sodium concentration, it is usually not a good idea to immediately provide sufficient water to dilute their sodium back down to normal levels. If you do, there is a real risk of causing brain swelling (cerebral edema). I imagine the risk would exist whether you give the water by mouth or by IV.

The reason that suddenly restoring someone’s blood sodium concentration back to normal by providing them with the water they lack can cause brain swelling has to do with the role that sodium concentration plays in pulling water in and out of body compartments.

For example, when blood sodium levels rise, the result (by osmosis) is to pull water out of the body’s cells (and into the blood). In the case of the brain, the same thing occurs, with high sodium concentration in blood tending to pull water out of the brain cells. That would lead to brain (and brain cell) shrinkage which is something your body guards against. It does so by generating intracellular osmoles in the brain which serve to balance the osmotic pull of the high sodium concentration in the blood, i.e. those extra brain cell osmoles allow the brain cells to retain their water in the face of high sodium, and thus high osmolality, in the blood.

If, at a time when the brain cells have generated such extra osmoles you intervene to lower the blood sodium concentration by providing water to the patient, you will, of course, lower the osmolality in the blood. But, because of those intracellular osmoles in the brain cells, a gradient is thereby created where water will flow from the blood and into the brain cells. Brain swelling can occur with fatal consequences.

What you must do is only slowly give back the ‘missing’ water and thus only gradually lower the blood sodium concentration and osmolality. That gives time for the brain cells to dissipate any osmoles they generated in the face of the high sodium in the blood (which would have pulled water from the brain cells if they hadn’t been produced).

Again, the key is to do it slowly. Empirically, restoring an elevated blood sodium concentration to normal by the administration of water over 48 to 72 hours provides sufficient time for the brain cells to get rid of their extra osmoles, and prevents brain swelling.

I see no reason why the above would not apply pretty much equally for water given IV or by mouth and have to admit that I, too, have wondered whether people who had been dying of thirst (i.e. whose blood sodium was too concentrated) would be at risk if able to suddenly take in all their ‘water deficit’ by mouth. I know they are (as above) if they get the water by IV.

(NB: the above ‘explanation’ takes some liberties by equating blood with the extracellular space which is not strictly the case, but the general idea is not affected by doing so)

I did a mental ‘WTF?’ when I read that as horsepipe. That would be quite a threat.


It sounds more like your MIL was probably nutritionally depleted due to her inability to take in adequate food. When that happens, you can lose a lot of what’s called oncotic pressure. Oncotic pressure is part of what keeps blood in your blood vessels and not everywhere else. When that is really lose, people commonly swell up. This occurs often in liver failure patients (cirrhosis). It’s a lot more complicated than that, but they have such low oncotic pressure that they can be simultaneously fluid overloaded, that is swollen like your MIL was, while also being intravascularly depleted to the point their kidneys start to shut down.
As an aside, to add to what Karl Gauss wrote, it’s actually usually okay to more rapidly correct sodium imbalances if initially occurred over a very short period of time. This can happen in people who are otherwise healthy but become very dehydrated over a short period of time due to illness or exercise. If you know it happened acutely like that, then the thought is that there hasn’t been time for the cells to all have reset to the new balance and there’s less danger.

(emphasis added)

Thanks for bringing this up. You are absolutely correct that if the dehydration/high sodium concentration (hypernatremia) developed only in the last day or so, then it is likely safe to correct it quickly as opposed to doing it over several days. And, just to restate what you mentioned, the reason that it is safe to quickly correct acute hypernatremia is that in such a situation there has not been time for the brain cells to generate those extra osmoles.

This is how it was done before people routinely had IVs.

Some women with that most feared pregnancy complication, hyperemesis gravidarum, must be hydrated and fed via IV because oral intake is beyond pointless.

:smiley: One of the funniest things I’ve read on the boards.

Spoken like a person who’s never had gastroenteritis. :wink: My neighbor the nurse was my favorite person that day, when she showed up with an enema bag and a huge bottle of saline and told me where to shove it! :smiley: Seriously, it was amazing how much better I felt, almost immediately. Saved me an ER trip, too.