Administering IV fluids is a task acute care nurses perform every shift. It may seem like a simple action without much risk, but IV fluids have the potential to affect patients in positive and negative ways. Understanding the different types of solutions, what they are used for, and the intended or adverse outcomes is crucial to safe IV fluid administration.
In this article, we will discuss the three types of crystalloid fluids: Isotonic, hypotonic, and hypertonic.
In this article:
- Osmosis and Fluid Shifts
- Isotonic Solutions
- Hypotonic Solutions
- Hypertonic Solutions
- Cheat Sheet For IV Fluids
- Clinical Application: IV Solution Example Question
- Conclusion
- References
Osmosis and Fluid Shifts
Before we dive into the different types of solutions, let’s refresh your memory about the concept of osmosis. You probably learned about this in biology class, but it is still relevant in nursing school. Osmosis is the movement of water across cell membranes with the goal of equalizing solute concentrations. The type of IV fluid you administer determines whether solutes (sodium, potassium, glucose, etc.) move into or out of the cell.
Isotonic Solutions
Isotonic solutions are the most common fluids you will administer. They have the same osmolality (concentration of solutes) as blood, so there is no fluid shift between cells, and fluid stays within the intravascular compartment (blood vessels).
When To Use: Administer these solutions to replace lost fluids, such as during hemorrhaging, severe vomiting or diarrhea, and dehydration.
Examples: 0.9% Normal Saline (NS), Lactated Ringer’s (LR).
Precautions: Excessive isotonic fluids can result in fluid overload, especially in patients with heart or kidney failure.
What To Monitor: Assess for hypertension, edema, or bounding pulses that indicate hypervolemia.
Hypotonic Solutions
Hypotonic solutions have fewer solutes than blood plasma, so fluid will shift into the cells from the intravascular space. This causes cells to swell with the goal of hydrating the intracellular fluid.
When To Use: These solutions are used to treat cellular dehydration, such as with severe hypernatremia or diabetic ketoacidosis (DKA).
Examples: 0.45% NS, Dextrose 5% in Water (D5W)*
Precautions: If brain swelling is suspected or confirmed (head trauma, stroke, etc.), do not administer hypotonic solutions as they can worsen cerebral edema.
What To Monitor: Closely monitor for new or worsening neurological findings, such as confusion, headache, or decreased level of consciousness (LOC).
Note: D5W is technically isotonic in the bag, but it becomes hypotonic as the body quickly metabolizes glucose.
Hypertonic Solutions
Hypertonic solutions have more solutes than blood, so fluid moves out of the cells and into the intravascular space, causing cells to shrink.
When To Use: These fluids are used to treat severe hyponatremia or hypoglycemia and reduce intracranial pressure.
Examples: 3% or 5% NS, Dextrose 10% in Water (D10W), Dextrose 50% in Water (D50W).
Precautions: These are high-alert solutions that require close monitoring. It is recommended that they be infused using a central line.
What To Monitor: Fluid overload is a concern with these fluids, so monitor for hypertension, lung crackles, and imbalanced intake and output. Closely monitor the sodium level to prevent hypernatremia.
Cheat Sheet For IV Fluids
It can be confusing trying to remember how each type of fluid affects the cells. Use this easy reminder:
- Isotonic fluids → Stay where I put them.
- HypOtonic fluids → Move Out of the vessel and into the cells.
- HypErtonic fluids → Enter the vessel from the cells.
Now, to recall examples of each solution, you only need to remember that 0.9% NS is isotonic. Use that number as your baseline for comparison:
- Hypotonic: Any saline solution less than 0.9% (e.g., 0.45% NS).
- Hypertonic: Any saline solution greater than 0.9% (e.g., 3% NS).
- Dextrose Rule: Any dextrose concentration greater than 5% is typically hypertonic (e.g., D10W, D50W).
Clinical Application: IV Solution Example Question
Scenario: A 65-year-old patient is admitted with severe dehydration secondary to a 48-hour gastrointestinal illness. They are hypotensive and tachycardic, with poor skin turgor. Their sodium level is 150 mEq/L. The provider orders 1 L of IV fluids to run over 2 hours.
Question: Which type of IV solution (isotonic, hypotonic, or hypertonic) is the most appropriate initial choice for this patient, and why?
Answer and Rationale:
The most appropriate initial choice is an isotonic solution (e.g., 0.9% NS or LR).
- Prioritize Volume: The patient is hypotensive and tachycardic, indicating hypovolemia (low vascular volume). Isotonic fluids stay in the vascular space to raise blood pressure and treat shock.
- Addressing Hypernatremia: While the patient has hypernatremia (high sodium), using a hypotonic solution right away could shift water into the cells too quickly, potentially causing cerebral edema. Once the patient is hemodynamically stable, the nurse can safely transition to a hypotonic solution (0.45% NS) to slowly correct the cellular dehydration caused by the hypernatremia.
Conclusion
Understanding how fluids work is detrimental to safe nursing practice. While the physician will prescribe the solution, the nurse serves as a second check to ensure the fluid is appropriate for the patient and is not contraindicated based on their health status or comorbidities. IV fluids are still medications, and they require your expertise and judgment during administration.
References
- Alexi Mason; Ahmad Malik; Jacob G. Ginglen. Hypertonic Fluids. November October 2025. https://www.ncbi.nlm.nih.gov/books/NBK542194/
- Levi D. Procter. Intravenous Fluid Resuscitation. Accessed November 2025. https://www.msdmanuals.com/professional/critical-care-medicine/shock-and-fluid-resuscitation/intravenous-fluid-resuscitation
- National Institute for Health and Care Excellence (NICE). Intravenous fluid therapy in adults in hospital (CG174). Accessed November 2025. https://www.nice.org.uk/guidance/cg174
- Preeti Patel; Paul Tonog; Anand D. Lakhkar. Normal Saline. Accessed November 2025. https://www.ncbi.nlm.nih.gov/books/NBK545210/
- Preeti Rout; Preeti Patel; David Davis. Ringer’s Lactate. Accessed November 2025. https://www.ncbi.nlm.nih.gov/books/NBK500033/
