Isotonic fluids are those that are a similar osmolarity to the blood such as normal saline (NS), lactated ringers (LR), and 5% dextrose in water (D5 or D5W). These fluid choices are great for treating volume depletion because they will not cause any significant shift in electrolytes or changes in the osmolarity of the blood.
In most cases, you can use NS and LR interchangeably, but the newest research favors LR unless you are trying to increase the sodium (Na) level, in which case you can use NS, because eventually, NS will cause the Na level to rise.
Hypertonic fluids are used to treat very diluted blood or low osmolarity in the blood. The best way to quickly determine if the blood is diluted is based on the electrolyte levels, mainly Na. If the Na is very low, then your blood is diluted (low osmolarity), and if it is very high then the blood is very concentrated (high osmolarity).
Hypertonic fluids work by pulling fluid out of the cells due to the increased osmotic gradient that you have created outside of the cell. This helps swollen cells reduce their size back to normal by getting rid of the excess fluid. These patients may be overhydrated, or have some issue causing their Na level to be very low.
Typical hypertonic solutions are 3% NS and 10% dextrose in water (D10). You can also consider doing a fluid restriction which will naturally lower the osmolarity by getting rid of water.
Hypotonic fluids are used to treat high osmolarity (highly concentrated, high Na) in the blood. Hypotonic fluids will swell up the cells due to the higher osmotic gradient inside of the cells drawing fluids in and can be useful in times when patients are dehydrated.
Typical hypotonic solutions include half NS (1/2NS) or 2.5% dextrose in water.
Test your knowledge
- A patient has a sodium of 125. What fluid orders should the nurse anticipate?
- A patient has a sodium of 140 and is hypovolemic. What fluid orders should the nurse anticipate?
- A patient has a sodium of 155. What fluid orders should the nurse anticipate?