Help Hypotonic, Isotonic, & Hypertonic Solutions

[VickyRN]

Tonicity refers to the solute concentration of a solution outside a cell and its effect on cellular fluid volume. The osmolarity of the solution determines the direction of water flow into or out of the cell. In normal body situations, solute concentration within and outside of the cell is usually nearly the same (isotonic).

tweetym_22 said:

Can anyone please help me understand the use of these solutions?

Isotonic:

Same osmolarity as the cells (270 - 300 mmol/l). Equal solute and water--exact same number of particles in both solutions--no net movement of water. Does not change cell volume.

Higher solute concentration surrounding cells pulls water out of the cells.

Hypertonic:

Higher osmolarity than cells (> 300 mmol/l). Greater solute, less water--water moves out of cells. The cell will shrink.

Lower solute concentration surrounding cells causes water to move into the cells.

Hypotonic:

Lower osmolarity than cells (< 270 mmol/l). Less solute, more water--water moves into cells. The cell will swell.

Isotonicity:

If the concentrations of electrolytes are the same in the cell and surrounding fluid, the situation is balanced (homeostatic). The cell fluid volume remains the same.

Hypertonicity:

The cell will shrink (crenation) by loss of its fluid to the surrounding hypertonic environment. High osmotic pressure of surrounding fluid pulls fluid out of the cell.

Hypotonicity:

In a hypotonic environment, fluid will enter a cell and cause it to swell and burst. The inside of the cell has higher osmotic pressure than the surrounding fluid, so fluid is drawn into the cell.

Both hypertonicity and hypotonicity in the extracellular fluids will destroy cells.

Need isotonicity for cell homeostasis, for balance.

NS IV is hypotonic relative to cells. Fluid moves from the vascular space into the cells. When a liter of NS is administered intravenously, it will go into the cells and very little will remain in the blood vessel (since it is hypotonic).

If you put two isotonic solutions side by side, no fluid shift occurs. A liter of normal saline or ringer's lactate is limited to the extracellular space and will expand the blood volume.

5% dextrose in NS is hypertonic compared to cells; pulls water into the vascular space from the cells or interstitium.

Hope this explanation helps .

[xtxrn, ASN, RN]

fmeu6038 said:

Hi need more understanding..if d5% becomes hypotonic or free water as soon as its infused (VickyRN), then why can't we just infuse bottled or mineral water??

They're hypotonic as well- besides being for oral use and not sterile.... too much free water puts the patient at risk for cerebral edema, CHF, and other excess fluid issues.

[ELIZABETH KUSI]

I am very happy to join this learning network

[ELIZABETH KUSI]

I am confused of how excessive administration of d5w can cause increased intracranial pressure

[choralguy]

I am in A&P and have a question...A woman is passing blod clots. Her hemoglobin level is 10.4 and she has been diagnosed as slightly anemic. Admissions orders include starting an IV solution of dextrose 5% and lactated Ringer's solution.

Do you expect the IV solution to be hypertonic, hypotonic, or isotonic? Why?

A. Hypertonic - to decrease the size of the red blood cell

B. Isotonic - becacuse this solution does not change the size of the red blood cell

C. Hypotonic - to increase the size of the red blood cell and thus enable it to carry more oxygen

D. Hypertonic - to cause fluid shifts from the intracellular space to the extra-cellular space and thus replace the blood lost by the patient from the uterine bleeding.

I do not see how A could help. B would make sense for most IV fluids from what I can tell. C would be helpful if it is true that a larger cell carries more oxygen. I do not understand how D would cause the added water content to turn to blood.

I really desire to learn this stuff, so if you could explain why one of these is the best answer, I would greatly appreciate it.

[turnforthenurse, MSN, NP]

xtxrn said:

They're hypotonic as well- besides being for oral use and not sterile.... too much free water puts the patient at risk for cerebral edema, CHF, and other excess fluid issues.

Plain 'ole free water just isn't safe to give, period. D5W becomes hypotonic once it enters the body because the dextrose is metabolized...but that is a safe way of giving free water. The IV solution also has a little bit of calories because of the dextrose.

choralguy said:

I am in A&P and have a question...A woman is passing blod clots. Her hemoglobin level is 10.4 and she has been diagnosed as slightly anemic. Admissions orders include starting an IV solution of dextrose 5% and lactated Ringer's solution.

Do you expect the IV solution to be hypertonic, hypotonic, or isotonic? Why?

A. Hypertonic - to decrease the size of the red blood cell

B. Isotonic - becacuse this solution does not change the size of the red blood cell

C. Hypotonic - to increase the size of the red blood cell and thus enable it to carry more oxygen

D. Hypertonic - to cause fluid shifts from the intracellular space to the extra-cellular space and thus replace the blood lost by the patient from the uterine bleeding.

I do not see how A could help. B would make sense for most IV fluids from what I can tell. C would be helpful if it is true that a larger cell carries more oxygen. I do not understand how D would cause the added water content to turn to blood.

In regards to blood administration and hanging fluids, you should always hang an isotonic solution - 0.9% NS. A hypertonic or hypotonic solution will damage the blood cells.

As for D5LR, the solution itself is hypertonic. A hypertonic fluid will pull fluid from the cells (cells shrink) and into the intravascular space. It wouldn't "turn to blood" but will help restore intravascular volume.