hypertonic solution, retain fluid or expell fluid

Daytonite, BSN, RN · Dec 6, 2008

remember that the gi track is an enclosed tube. when a hypertonic tube feeding gets sloshed into it peristaltic action washes it down, down, down. what do we know about hypertonic fluids? they are solutions with higher osmolality. usually, something with a lot of carbohydrate or salt in it will do that. and, if the tube has somehow gone past the pyloric sphincter (which has the ability to slow down what gets passed into the intestines) its like a roller coaster ride for these hypertonic tube feedings that get directly deposited into the duodenum. so, what happens when hypertonic meets gi track? the body naturally wants to achieve homeostasis. it starts sending water into the intestine to dilute this tube feeding to a more isotonic state that it would rather have. the body always wants to achieve a normal state. in so doing, the contents of the intestine increase dramatically. the other problem is that the ph of this hypertonic tube feeding is on the acidic side making it pretty irritating to the lining of the small intestine. the first thing the intestinal track wants to do is get this tube feeding out of it and so its motility increases. so, you have some increased intestinal motility and increased fluid coming along. and, it all starts moving down the pipe rather quickly. that is the pathophysiology of dumping syndrome. in about 2 hours it is all literally going to "blow" meaning this person is going to have diarrhea.

osmotic laxatives work the same way because they pull fluid into the intestinal track to dilute down the electrolyte content.

it's all about the osmolality with the added bonus of the physical irritability caused by the hypertonicity of the solutions. try tasting some oral fleet's enema solution. i've had to take it for colonoscopy preps and it burns the back of my throat. i also have had gastric bypass surgery. if i eat too much ice cream which is loaded with pure sugar i get dumping syndrome. i can hear the gurgling in my gut and i know i am going to dump. i also get the symptoms of hyperglycemia in about an hour because so many calories get absorbed into my blood stream at one time (i don't have a pyloric valve to contain it all in my stomach anymore so it all goes directly into the jejunum where all that galactose and added sugar is absorbed directly and rapidly into the blood stream) and diarrhea in about 2 to 3 hours. depending on how much of a pig i was will determine how sick i will feel.

other stuff that will give you dumping syndrome are eating too many sugar free candies that are sweetened with things like sorbitol. they are also sugars that are very irritating to the lining of the intestinal track, have high osmolarities and act just like laxatives if you eat enough of them at one time.

so in what situation does an ingested hypertonic solution cause excess fluid to be retained in the body or fluid to be taken from the body into the gi tract?

fluid is going to be pulled into the gi track from the immediate local tissues. fluid release from tissues is of two types. there is fluid moved by hydrostatic and oncotic pressures that involves the circulatory system. then, there is fluid movement due to chemical osmosis which is a more passive effort to equalize the pressure and involves the amount and composition of particles dissolved in the solutions. what you have going on with the scenario you presented is more of an osmosis situation. any fluid stuck in body tissues, as in edema, is probably going to remain there since edema occurs because of a problem with hydrostatic and oncotic pressures that is a systemic situation. a one time hypertonic tube feeding is a local gi problem confined to the gi track. it wouldn't become a systemic problem until it was an ongoing tube feeding being given consistently and the person's electrolytes started showing they were getting messed up enough to effect the body's hydrostatic and oncotic pressures. you'd start to see b/p changes and signs and symptoms of dehydration body wide.

kikoricco · Dec 7, 2008

Thank you for your reply,

I have a clearer picture of the dumping syndrome now. What still confuses me is when it is said that eating a diet high in sodium can cause Fluid retention. This says a totally opposite thing! I know there must be some A&P to explain that.

hypocaffeinemia, BSN, RN · Dec 7, 2008

Interesting study, somewhat related:

http://ajprenal.physiology.org/cgi/content/full/278/4/F585

Daytonite, BSN, RN · Dec 7, 2008

What still confuses me is when it is said that eating a diet high in sodium can cause Fluid retention. This says a totally opposite thing! I know there must be some A&P to explain that.

Water follows sodium. Think of water and sodium as partners holding hands. Where one goes, the other is tagging along. A diet high in sodium causes the person to retain fluid. Symptoms of hypernatremia, which is systemic, are the symptoms of overhydration:

Elevated blood pressure (hypertension)
Elevated pulse (tachycardia)
Elevated temperature
Elevated respiratory rate, possible dyspnea
Increased body weight
Bounding peripheral pulses
Moist mucous membranes
Moist respiratory secretions
Crackles in lungs on auscultation
Fever
Edema (may be pitting)
Dry skin
Weakness
Restlessness/agitation
Disorientation
Delusions
Hallucinations
Lethargic when undisturbed
Irritable when stimulated
Muscle irritability
Diminished or absent DTRs
High pitched cry in infants
Seizures
Coma (due to swelling of brain cells)
Respiratory arrest due to increased osmotic pressure