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#1
Old 01-22-2011, 02:54 AM
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could you really filter saltwater via your rectum?

I recently read an TSD article entitled "Is strength of will in fighting illness a factor in whether you live or die?".

At the end of the article Cecil writes

Quote:
Finally, let's not overlook the story of Dougal and Lynn Robertson. While stranded at sea for 38 days with only small amounts of rainwater to drink, they gave brackish-water enemas to themselves and others on their life raft on the theory that their rectums would filter out the salt and absorb enough water to keep them alive. The book I found this story in (Surviving the Extremes: A Doctor's Journey to the Limits of Human Endurance by Kenneth Kamler, 2004) doesn't make clear how important rectal desalination was to the Robertsons' survival.
As a 'survival' fan, I was curious about this, and want to know if this is something that could be used if stranded at sea / on an island, with no freshwater. Could someone survive by way of seawater enemas?
#2
Old 01-22-2011, 05:27 AM
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I don't see how. The colon's natural function (one of them) is to absorb water and salts from pre-fecal material. But, pretending for a moment that the colon is permeable only to water...

Water purification by reverse osmosis, which appears to be the mechanism here, requires physical pressure to counteract the osmotic pressure, which for seawater is roughly 26 atmospheres. I don't think that kind of pressure can be generated in the rectum, much less the colon.
#3
Old 01-22-2011, 06:15 AM
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Whether or not this is actually effective, Bear Grylls did this in one of his Man vs Wild episodes in a raft in the middle of the ocean.

Last edited by cochrane; 01-22-2011 at 06:16 AM.
#4
Old 01-22-2011, 06:50 AM
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I would have thought that water moves from the most diluted to the least diluted, when separated by a membrane. So a saltwater enema would actually dehydrate you.

Other than Bear Grylls being a total tosser, who carries an enema in their survival kit?
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#5
Old 01-22-2011, 07:00 AM
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I read the Book where Dougal and Lynn Robertson, tell the story of their ordeal after being attacked on their Boat by Killer Whales off the Galapagos Islands, there was also a Student on Board that did not belong to the Family that refused to have the enemas, at the time of the rescue that did not seem to have made a difference.
#6
Old 01-22-2011, 07:21 AM
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The colon does not have the ability to extract free water and leave behind solutes to a sufficient degree. It is, essentially, a semipermeable membrane. As such hypertonic solutions would not be effective in adding net free water to a dehydrated individual if administered as enemas.

As far as using a rectal route as a means to filter out other contaminants such as mechanical debris or pathogens, an oral route would be much preferable. The upper gut is designed to take in contaminated food and fluid much better than is the colon. Just because the colon is full of bacteria does not make it an appropriate receptacle for dirty things, physiologically speaking.
#7
Old 01-22-2011, 07:25 AM
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The colon does not have the ability to extract free water and leave behind solutes to a sufficient degree. It is, essentially, a semipermeable membrane. As such hypertonic solutions would not be effective in adding net free water to a dehydrated individual if administered as enemas.

As far as using a rectal route as a means to filter out other contaminants such as mechanical debris or pathogens, an oral route would be much preferable. The upper gut is designed to take in contaminated food and fluid much better than is the colon. Just because the colon is full of bacteria does not make it an appropriate receptacle for dirty things, physiologically speaking.

As to the survival of folks who have apparently tried this, I make two comments. First, I don't see where the relative tonicity of the fluid was measured. Second, there was no control to see whether or not per os would have been just as effective. And, of course, there is the post hoc ergo propter hoc fallacy. After all, many people in years past survived blood-letting. That does not mean they survived because of it...

Last edited by Chief Pedant; 01-22-2011 at 07:25 AM.
#8
Old 01-22-2011, 07:41 AM
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Quote:
Originally Posted by cochrane View Post
Whether or not this is actually effective, Bear Grylls did this in one of his Man vs Wild episodes in a raft in the middle of the ocean.
He did not use sea water, but rancid water.
#9
Old 01-22-2011, 02:30 PM
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The colon is where most of the water we take in gets absorbed, anyway, regardless of which end the water entered through. If it were capable of filtering water administered from below, then it would be equally capable of filtering water administered from above.
#10
Old 01-22-2011, 03:40 PM
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Originally Posted by Chronos View Post
The colon is where most of the water we take in gets absorbed, anyway, regardless of which end the water entered through. If it were capable of filtering water administered from below, then it would be equally capable of filtering water administered from above.
Unless the saltiness of the water caused the person to wretch.

Of course, that the body wretched it back out might be an indication that the human body has evolved to naturally determine that salt water is a net negative.
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Old 01-22-2011, 04:47 PM
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Nearly the same discussion in this thread starting with post #8. It includes the following:

Quote:
Originally Posted by Qadgop the Mercotan View Post
Sorry, a big NO!! for this one. And I am a doctor.

A seawater enema would pull water out of the body via the colon. And accelerate dehydration.

In fact, a standard recipe for salt water enemas is 1 tsp. of salt in 1 quart of fresh water. When given, it doesn't overload the kidneys so much as a pure fresh water enema would, because much less water is absorbed due to that very small amount of salt! Double the concentration of salt in that recipe, and it will begin to pull fluids out of the body. A quart of seawater has close to 10 times that much salt in it!

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Originally Posted by Sage Rat View Post
Unless the saltiness of the water caused the person to wretch.
It's "retch."
#12
Old 01-22-2011, 04:57 PM
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Originally Posted by orcenio View Post
He did not use sea water, but rancid water.
You're right, I do remember now. At the time I posted, I forgot to make the distinction. Mea culpa.
#13
Old 01-23-2011, 12:31 AM
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Quote:
Originally Posted by Chronos View Post
The colon is where most of the water we take in gets absorbed, anyway, regardless of which end the water entered through.
That simply isn't correct in any way at all. Most water gets absorbed in the stomach and the duodenum, a bit in the rest of the small intestine, and very, very little in the colon.
#14
Old 01-23-2011, 04:44 AM
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Thanks very much for the words folks

I'm glad I didn't accidentally get stranded at sea without checking this first
#15
Old 01-23-2011, 06:26 AM
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In regard to Cecil's article I am of the impression from Dougal Robertson's own account Survive the Savage Sea that only 2 enemas were administered. The first, as indicated, to make use of an unpalatable mix of mostly rain water, turtle blood and a little sea water. They simply wanted to not waste it even though it was undrinkable. No reference is made to the bowel filtering in any way, they simply hoped to absorb the water through the bowel walls. Each had an enema of one to two pints which they would not have been able to drink anyway due to their shrunken stomachs.

On the second occasion the enemas were administered to those who hadn't had a bowel motion despite eating solids. they were for the purpose of preventing an obstruction.

Robin's health may have been aided by the fact that, as he was the largest in the group and the only non family member, Robertson gave him larger rations as it would be natural for Robin to be looking for signs of discrimination. His own family were often angry about this.
#16
Old 01-24-2011, 04:33 AM
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Quote:
Originally Posted by Blake View Post
That simply isn't correct in any way at all. Most water gets absorbed in the stomach and the duodenum, a bit in the rest of the small intestine, and very, very little in the colon.
?? I've taken several anatomy and physiology classes in university (currently I'm a third-year nursing student), and my understanding is that the primary function of the large intestine is to absorb water. If the colon doesn't absorb all the water it's supposed to, diarrhea occurs.

Edited to add: I googled and found the following information. It's true that the stomach and small intestine secrete a large amount of fluid and absorb fluid as well. But it isn't true that the colon absorbs "very, very little" water. It looks like it absorbs about a litre per day.

From this site:
Quote:
An important function of both small intestine and colon is the absorption of water and electrolytes. Approximately 2000 ml of food and drink is ingested daily, and the volume of gastrointestinal secretions (salivary, gastric, biliary, pancreatic and intestinal) is about 8,000 ml daily; therefore, approximately 10 liters of fluid enters the intestine each day. Of the 8 liters secreted, about 1-1.5 liters enter as saliva, 2-3 liters are secreted by the stomach, about 2 liters enter as bile and pancreatic secretion (about 1 liter each), and about 2 liters are secreted by the small intestine. (Please note that these figures are approximate, not absolute. Volumes may vary, depending on experimental method and conditions.) Of the 10 liters which enters the gut each day, only about 1 liter passes into the colon, about 90% having been absorbed across the small intestinal epithelium. Only about 150 ml is lost in the feces daily, with the remainder being absorbed by the colon. It should be obvious that any derangement in intestinal fluid absorption would profoundly influence the balance of fluid and electrolytes in the body, and that the normal functioning of the intestines plays a significant role in regulating water and electrolyte balance.

Last edited by Waenara; 01-24-2011 at 04:37 AM.
#17
Old 01-24-2011, 05:42 AM
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Quote:
Originally Posted by Nametag View Post
Water purification by reverse osmosis, which appears to be the mechanism here, requires physical pressure to counteract the osmotic pressure, which for seawater is roughly 26 atmospheres. I don't think that kind of pressure can be generated in the rectum, much less the colon.
Looks like someone has never won a Taco Bell eating contest.
#18
Old 01-24-2011, 10:30 AM
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Quote:
Originally Posted by cochrane View Post
Whether or not this is actually effective, Bear Grylls did this in one of his Man vs Wild episodes in a raft in the middle of the ocean.
I think that Man vs Wild is a very good show on survival, if you just remember to actually do the opposite of everything Bear Grylls does.
#19
Old 01-24-2011, 09:10 PM
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Quote:
Originally Posted by Blake View Post
That simply isn't correct in any way at all. Most water gets absorbed in the stomach and the duodenum, a bit in the rest of the small intestine, and very, very little in the colon.
Sorry, not true. You've got it backwards. The colon is primarily responsible for absorbing fluids. Very little absorption of anything takes place in the stomach; it's for breaking foods down. The small bowel is where the nutrients are absorbed, along with some fluid absorption.

I've got patients with ileostomies (meaning they have no colon, but excrete directly from the small bowel); their stools are very liquidy; they have to drink a lot of fluids to absorb enough to stay hydrated.

And the OP has already been adequately answered by previous posters. No, you can't filter saltwater (or toxins) through your rectum.
#20
Old 01-25-2011, 04:58 AM
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Quote:
Originally Posted by Qadgop the Mercotan View Post
Sorry, not true. You've got it backwards. The colon is primarily responsible for absorbing fluids. Very little absorption of anything takes place in the stomach; it's for breaking foods down. The small bowel is where the nutrients are absorbed, along with some fluid absorption.

I've got patients with ileostomies (meaning they have no colon, but excrete directly from the small bowel); their stools are very liquidy; they have to drink a lot of fluids to absorb enough to stay hydrated.
No, I'm sorry, you are wrong. This has actually been described as the "fact" that is most commonly misunderstood by medical students, so it's not a surprise.

The colon does indeed regulate water balance in the faeces by either secreting or absorbing water. However that is its sole role as it pertains to water: to regulate faecal consistency. If the faeces are excessively moist then it will absorb water, if they are dry it will secrete water. However the amount of water involved in very minor.

There is certainly no justification in the claim that "The colon is primarily responsible for absorbing fluids"

You can reason this out for yourself if you think about it for a few seconds.

In a healthy person, ingested material takes several hours to reach the colon.

When you are thirsty and drink, how long does it take before the thirst is quenched? Is it 6 hours, or is it closer to 6 minutes? Heck, if you drink excessively following dehydration, how long is it before you urinate? Minutes or hours?

Where you have gone wrong is conflating "the bowel regulates water balance in the faeces" with "the bowel is where most water absorption occurs". Of course the two are almost completely unrelated.
#21
Old 01-25-2011, 10:24 AM
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Blake, you are indeed correct that far more water is absorbed in the small intestine than in the colon. I had thought the ratio was about 25% small bowel, 75% colon while in fact it is more like 90/10%. So thanks for the correction. (Less than 2% of water gets absorbed in the stomach; alcohol is somewhat better absorbed there).

As a side note, the large colon is not real good at secreting water. Colonic distension does trigger some secretion of fluids to try to correct the distension, but in most folks it's not a large amount. Hence the problems of chronic constipation. Reabsorbtion is chiefly what the colon does with water.

Last edited by Qadgop the Mercotan; 01-25-2011 at 10:26 AM.
#22
Old 12-14-2012, 08:35 PM
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Someone years ago told me about a book he read by a seasoned mariner. He said that due to the characteristics of the kidney (its ability to remove salt from the blood, obviously inferior to sea animals), it is nevertheless possible to live on sea water but only if you are never at all dehydrated and drink very large amounts of seawater multiple times a day. I don't know the details of how much and how often - probably just about as much and as often as you can stand I would guess. Once you get to a small level of dehydration it's too late, your kidneys can't recover the situation and you will die without fresh water.

He even went out on a small boat for 2 weeks drinking ony seawater to test his theory and said it worked. I wish I knew who it was, I suppose it would be easy enough to find the relevant number(s) that describe the kidney's characteristics and maybe figure out what he was talking about. Maybe sea water is slightly less concentrated than the salt concentration the kidney is capable of producing?
I haven't really thought about the theory much.

On the debate about colon water absorption, if we are to believe the textbook quotation someone posted it states 8l is secreted, 10 l passes throgh and 1 l is absorbed by the LI/colon. That suggests that 50% is absorbed by the LI/colon so the debate may be a draw. but the OP only talks about the colon so taht's a bit different.

Last edited by paddo; 12-14-2012 at 08:36 PM.
#23
Old 12-15-2012, 12:40 AM
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Quote:
Originally Posted by paddo View Post
Someone years ago told me about a book he read by a seasoned mariner. He said that due to the characteristics of the kidney (its ability to remove salt from the blood, obviously inferior to sea animals), it is nevertheless possible to live on sea water but only if you are never at all dehydrated and drink very large amounts of seawater multiple times a day. I don't know the details of how much and how often - probably just about as much and as often as you can stand I would guess. Once you get to a small level of dehydration it's too late, your kidneys can't recover the situation and you will die without fresh water.
I have a book titled Survival: How to Prevail in Hostile Environments by Xavier Maniguet that agrees with this theory and argues in favor of drinking modest amounts of salt water in a survival crisis. (Perhaps it is the very book your friend was talking about.)

The book features two charts. One shows a person's degree of dehydration without drinking any water over a period of days. The other shows the degree of dehydration resulting from drinking small amounts of salt water. Both charts predict that a person would die around Day 10. But the while the non-drinker declines steadily over time, losing consciousness at Day 4, the salt-water drinker remains fully functional until Day 7; then he crashes, losing consciousness too, and eventually giving up the ghost.

But during those functional seven days, the author argues, the salt-water drinker can do a far better job of securing fresh water sources that will save his life in the long term.
#24
Old 12-15-2012, 12:59 AM
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Quote:
Originally Posted by Blake View Post

There is certainly no justification in the claim that "The colon is primarily responsible for absorbing fluids"

You can reason this out for yourself if you think about it for a few seconds.

In a healthy person, ingested material takes several hours to reach the colon.

When you are thirsty and drink, how long does it take before the thirst is quenched? Is it 6 hours, or is it closer to 6 minutes? Heck, if you drink excessively following dehydration, how long is it before you urinate? Minutes or hours?
That was exactly what I was going to post, hell forget the water what about alcohol or other drugs? Clearly most(not all) are being absorbed before reaching the colon.
#25
Old 12-15-2012, 01:32 AM
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Quote:
Originally Posted by Qadgop the Mercotan View Post

And the OP has already been adequately answered by previous posters. No, you can't filter saltwater (or toxins) through your rectum.
So you assert that on the contrary, it would've nearly killed 'em?
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