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Isotonic, hypotonic and hypertonic IV solutions
Isotonic IV fluids (0.9% sodium chloride, lactated Ringer's) stay in the bloodstream and expand volume; hypotonic fluids (0.45% sodium chloride) move water into the cells; hypertonic fluids (3% sodium chloride) pull water out of the cells into the blood. Choose the fluid by where the body needs water.
What happens to the cell
| Type | Water moves | Cell |
|---|---|---|
| Isotonic | No net shift | Stays the same size |
| Hypotonic | From the blood into the cells | Swells |
| Hypertonic | From the cells into the blood | Shrinks |
Examples and uses
| Type | Examples | Common uses | Watch for |
|---|---|---|---|
| Isotonic | 0.9% sodium chloride (normal saline), lactated Ringer's | Fluid volume deficit, blood loss, dehydration from vomiting or diarrhea, with blood transfusions (normal saline only) | Fluid overload in heart failure and kidney disease: crackles, edema, weight gain |
| Hypotonic | 0.45% sodium chloride (half normal saline) | Cellular dehydration, such as hypernatremia | Avoid in increased intracranial pressure, stroke, low blood pressure, burns, trauma or liver failure: water shifts into brain cells and out of the vessels |
| Hypertonic | 3% sodium chloride | Severe symptomatic hyponatremia, cerebral edema (per protocol) | Fluid overload and a too-fast sodium rise; usually given in critical care, often through a central line, with frequent sodium checks |
The D5W exception
- 5% dextrose in water (D5W) is close to isotonic in the bag (about 252 mOsm/L), but the body uses the dextrose quickly, leaving free water.
- Inside the body it acts like a hypotonic fluid, so it is not used for volume replacement or for clients with increased intracranial pressure.
How to remember it
- Hypo: water goes into the cell and makes it swell like a hippo.
- Hyper: water is pulled out and the cell shrinks.
- Iso: the same tonicity as blood, so nothing moves.
NCLEX tip: Classic NCLEX trap: a client with a head injury should not receive a hypotonic fluid such as 0.45% saline or D5W, because water would move into the brain cells and raise intracranial pressure.
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Frequently asked questions
Is lactated Ringer's isotonic?
Yes. Lactated Ringer's is an isotonic solution used for volume replacement, such as after blood loss or burns.
Is 0.45% normal saline hypotonic?
Yes. 0.45% sodium chloride (half normal saline) is hypotonic, so it moves water into the cells.
When is hypertonic saline used?
For severe, symptomatic hyponatremia and for cerebral edema, usually in critical care with frequent sodium levels.
Is 3% saline hypertonic or hypotonic?
Hypertonic. 3% sodium chloride pulls water out of cells into the blood, so it is used for severe symptomatic hyponatremia and cerebral edema, usually in critical care with frequent sodium checks.
Which IV fluids are isotonic, hypotonic, and hypertonic?
Isotonic: 0.9% sodium chloride and lactated Ringer's. Hypotonic: 0.45% sodium chloride. Hypertonic: 3% sodium chloride. D5W is close to isotonic in the bag but acts hypotonic in the body once the dextrose is used.
Keep studying
Sources
- Clinical Nursing Skills, 13.3 Intravenous Infusion, OpenStax
- Crystalloid Solutions in Intravenous Fluid Therapy, StatPearls, NCBI Bookshelf
For study only, not medical advice. Ranges and protocols vary by facility; follow your program, your facility's policies and the provider's orders.