Difference between saline and dextrose?

Question

How comes with saline, less fluid leaves the intravascular space into the interstital fluid, than when using dextrose?

I know it has something to do with the Na+ ions but i'm not quite sure.

Thanks :o)

Answer 1

The difference between these fluids that is that sugar is a rapidly regulated and metabolized compound in the bloodstream. As the sugar is metabolized, or is removed from circulation by the liver making it into glycogen, what remains is free water, which is hypotonic and therefore tends to cross membranes out of the vascular space until osmotic equalibrium is reachieved.

That's the simple answer. However, it is incomplete. It's a highly theoretical answer, because nobody would ever use enough D5 water on a patient that they would have measurable volume status changes!

"Normal saline", which is a 0.9% solution of sodium chloride, is essentially isotonic. That is, it has about the same amount of salt as the plasma it mixes with when it enters the vein. For this reason, it can almost always be used when a patient requires volume expansion. We can deliver it slowly or rapidly without any concern about the osmotic forces across blood cell membranes.

D5 water is a 5% sugar solution. There is no salt in it whatsoever. Although the osmotic force of the sugar helps to counteract the lack of salt at the point of injection, it does nothing for the eventual electrolyte imbalances that would come from the free water infusion, if this solution was to be used in the same manner as normal saline is used. The fact is, we just don't use D5 as a volume expander. It is used in small amounts, on occassion, to correct "free water deficits" when we need to bring down a patient's high sodium level, and when using the intestines to absorb water is for some reason not an option.

When crystalloid solutions such as saline or LR (lactated ringer's - look it up) are infused, they invariably follow a 2/3 - 1/3 rule. When the fluid shifts have stabilized, 2/3 of the infused volume will escape into the interstitial fluid, and 1/3 will remain intravascular. This is, of course, worsened if the infused fluid is hypotonic such as "half-normal saline". Thus hypotonic solutions are not used for volume resuscitation, only for maintenance and fluid replacement while patients are unable to meet their fluid requirements orally.

D5 water, unlike half-normal saline, is never used as an ongoing IV fluid at all. It is only used in small individual measured infusions. The consquences of leaving D5 running as an ongoing IV fluid could easily be mortal.

For this reason, the practical answer to your question is that crystalloid solutions are expected to leave the intravascular space. The ratio is 2/3 interstitial, 1/3 intravascular. This clearly happens with normal saline and LR, our two work-horse resuscitation fluids, which are given in high volumes (10's of liters) to some patients. A large volume infusion of D5 would be half a liter. People who have free water deficits do not have intravascular depletion; they are stable and euvolemic. For calculated free water deficits in the multiple liters, small infusions are given serially, timed over days, with re-evaluations of electrolyte levels in between. Although this fluid would theoretically leave the intravascular space in higher percentage, we don't see it because the fluid shifts are small and the patient already has a normal circulating volume. Because of this, the 2/3 - 1/3 rule doesn't enter our thinking with D5 because we're not treating the intravascular volume, we're treating the total body water.

... I hope that helps!

Contact me if you have questions.

Answer 2

D5 Dextrose

Answer 3

right it has to do with the electrolytes found in saline mainly sodium as the concentration of sodium present in the extracellular fluid determines the amount of water that moves between compartments by osmosis.so since dextrose has no electrolytes and only sugar which gets metabolized very fast what remains is literaly distilled water which moves out to where there is more concentration of sodium which in this case is the extra vascular space(when the fluid is given intravenously)

Answer 4

the difference between saline and dextrose is
saline is a salt and mineral solution and dextrose is a sugar solution,so when dextrose is used the body sands it's natural filter system into action thus drawing out most of the fluid.!

Answer 5

In medicine, saline is a solution of sodium chloride in sterile water, used commonly for intravenous infusion, rinsing contact lenses, and nasal irrigation or jala neti. Sodium chloride (NaCl) is ordinary salt. Saline solutions are available in various concentrations for different purposes.
Glucose (Glc), a monosaccharide (or simple sugar), is one of the most important carbohydrates in biology. The cell uses it as a source of energy and metabolic intermediate.
Please see the webpages for more details on Saline and Dextrose (Glucose).

Answer 6

fluid moves with the osmotic gradient from low to high concentration. dextrose is not an osmotic compound, i guess. so fluid stays where the salt is higher in concentration in the intravascular.

Answer 7

saline is a salt solution and dextrose is sugar based

Answer 8

ones salt the other is sugar

Answer 9

You are right. It's all because of the sodium.

Answer 10

not a clue