IV fluids (also known as intravenous fluids) are special fluids administered to the intravascular compartment, which is part of the extracellular compartment space. Intravenous fluids are an extremely common treatment ordered for patients in the hospital setting.
Nurses administer IV fluids per the healthcare provider orders to help treat fluid volume deficits via dehydration, electrolyte imbalances, and other conditions.
Therefore, as the nurse you want to be familiar with the types of IV fluids (hypertonic, hypotonic, and isotonic), how they work, and what you must watch for while administering IV fluids.
However, before we can understand the different types of IV fluids and how they work, we must first review the body fluid compartments these fluids affect and the process for how they do this (osmosis).
Nurse Sarah’s Notes and Merch
Just released is “Fluid and Electrolytes Notes, Mnemonics, and Quizzes by Nurse Sarah“. These notes contain 84 pages of Nurse Sarah’s illustrated, fun notes with mnemonics, worksheets, and 130 test questions with rationales.
You can get an eBook version here or a physical copy of the book here.
Body Fluid Compartments
The average adult body is made up of around 60-70% water. The fluid is stored in compartment spaces.
There are two main compartments you want to be familiar with: intracellular and extracellular compartments.
Intracellular
Intra means inside and cellular means cell = inside the cell
This is the compartment inside of the cell and accounts for a 2/3 of our body water. Memory Tip: most of our fluid is inside the cell.
Extracellular
Extra means outside of and cellular means cell = outside of the cell
This is the compartment outside of the cell, and it accounts for 1/3 of our body water.
It includes 3 fluid compartments:
Interstitial
This is the fluid that surrounds the outside of the cells or found in between the cells.
It plays a vital role in helping be a medium for electrolytes and other substances to move to and from the cell to the plasma with the assistance of the capillaries.
Intravascular
Also known as the plasma
This is the fluid found inside the blood vessels and contains so many important substances like electrolytes, blood cells, and so forth.
Transcellular
Smallest compartment
This is the fluid found in certain body cavities like the spinal fluid, fluid around the heart/lungs, and joints etc.
What’s the Big Deal about these Compartments?
These compartments are all interconnected with their own amount of electrolytes and water.
They work together to maintain a homeostatic environment in the body by shifting around water, electrolytes, and other nutrients to help keep a balanced environment via different types of transport processes, such as osmosis.
Body Fluid Compartments + Osmosis + IV fluids = Shifting of Body Water
Connecting the Dots:
In healthcare, we administer IV fluids to the intravascular compartment to help expand it (if we need to) or shift fluids around in these compartments via a process called osmosis to help correct fluid imbalances or other problems that can occur with the intracellular and extracellular spaces.
Osmosis and Osmolarity
- Passive type of water transport
- Water molecules move through a semi-permeable membrane that only allows water through.
Look at osmosis these two ways:
Water will move from a fluid of a higher water concentration to a fluid of lower water concentration.
OR
Water will move from a lower solute concentration fluid to a higher solute concentration fluid.
Simplified: Water is drawn to the fluid that has the MOST solutes.
What is a solute?
A solid dissolved in a liquid.
Many substances can be a solute. For example, sodium and chloride are solutes in a bag of IV fluids. They are also considered electrolytes in this form.
The liquid or the solution that contains the solutes is known as the solvent.
Osmosis is influenced by how concentrated a fluid is of solutes, hence its osmolarity.
Osmolarity
The total concentration of solutes in a solution (per liter).
IV fluids can have an equal, high, or low osmolarity when compared to the blood plasma.
High osmolarity = high amount of solutes in a solution but low amount of water
Example: hypertonic solutions
Low osmolarity = low amount of solutes in a solution but high amount of water
Example: hypotonic solutions
Connecting the dots:
We can use the principles of osmosis and osmolarity to help treat patients who need fluids replaced based on what fluid compartment needs to be treated by shifting fluids around. This can be done by administering various types of IV fluids that have different osmolarities or solute concentrations, which will move water in or out of these fluid compartments.
IV Fluid Types
There are three main types of IV fluids: isotonic, hypotonic, and hypertonic
The prefix and suffix of the fluid type’s name tells you about how the fluid works.
The prefix: iso, hypo, hyper tells us about the concentration of solutes in that fluid
Iso: means “equal” and this means this fluid’s solute concentration matches or is equal to that of the blood plasma
Hyper: means “high” and this means this fluid’s solute concentration is higher than the blood plasma
Hypo: means “low” and this means this fluid’s solute concentration is lower than the blood plasma
The suffix tonic is for tonicity.
This refers to that STRENGTH of that fluid. It tells us about how that fluid entering the extracellular compartment (hence that intravascular space) will affect the intracellular compartment. Will it move water in or out of the cell or keep it equal?
This is all based on the concentration of electrolytes (hence solutes) in the IV fluid.
Isotonic IV Fluids
Same osmolarity as the blood (same concentration of solutes)
Result? Water will equally transfer in and out of the cell (no swelling or shrinkage of the cell)
Help expand plasma (intravascular) which is part of the extracellular compartment
Benefits?
Experiencing a loss fluid here in the extracellular compartment due to vomiting, diarrhea (need some sodium and chloride back), hypovolemic shock, burns, or prior to surgery (will be losing ECF in surgery)
Some fluids that are isotonic:
0.9% Normal Saline
Lactated Ringer’s solution (LR)
5% Dextrose in water*
Things to Remember:
0.9% Normal Saline: replaces water, sodium, and chloride
The ONLY solution administered with blood transfusion.
Watch for:
fluid overload- putting too much fluid back into the extracellular compartment (especially in patients with kidney and heart failure):
Increase in sodium and chloride levels
Dextrose 5% in Water (D5W) *: replaces water and glucose
Starts out as isotonic but turns into a hypotonic solution
Why? Dextrose will be used by the body (metabolized) and what is left over is not very concentrated. It’s free water (low osmolarity) so it becomes hypotonic.
Not for fluid resuscitation situations (it can cause an increase in blood glucose)
Helps with hypernatremia
Lactated Ringer’s solution (LR): contains water, potassium, sodium, chloride, calcium, and lactate
- The lactate in the fluid helps increase the blood’s pH by converting to bicarbonate, which is needed to correct acidotic conditions like mild cases metabolic acidosis.
- Not for patients with liver disease because their liver can’t covert lactate to bicarbonate or for patients who are experiencing lactic acidosis (high amount of lactic acid in the body).
- Hyperkalemia risk, especially in patients with renal failure
Hypertonic IV Fluids
Higher osmolarity than the blood (higher concentration of solutes in the fluid)
Result? Water will leave the intracellular space and move to extracellular space. This shrinks or dehydrates the cell.
Helps expand the extracellular space
Benefits?
Cases of severely low sodium levels (hyponatremia): by adding a hypertonic saline solution to the plasma this will increase sodium blood levels
Brain swelling (cerebral edema): hypertonic solutions will pull water from the brain cells and decrease swelling.
Some Hypertonic Solutions Include:
3% Saline
Dextrose 10% in water
Dextrose 5% in 0.9% Normal Saline
Dextrose 5% in 0.45% Normal Saline
Things to Remember:
Use cautiously: may overload the extracellular space leading to pulmonary edema (fluid in the lungs) and hypertension
May cause hypernatremia
Always check with facility’s protocol for how to properly administer these hypertonic solutions.
May need a central line for administration due to extravasation risk.
Hypotonic IV Solutions
Lower osmolarity than the blood (lower concentration of solutes in the fluid)
Results? Water moves from the extracellular compartment to the intracellular and can swell the cell (risk of rupture)
Helps replenish water to the inside of the cell
Benefits?
Too much solute concentration in the blood example: sodium (hypernatremia), helps provide free water to the kidneys so they can excrete waste, prevent dehydration
Some Hypotonic Solutions Include:
0.45% Saline (1/2 Normal Saline)
0.225% Saline
0.33% Saline
5% Dextrose in Water* starts out as isotonic but turns hypotonic
Things to Remember:
Risk of swelling the cell because fluid leaves the extracellular space and goes inside the cell which can lead to brain swelling:
Monitor for mental status changes, low blood pressure, hypovolemia
Hyponatremia (too much fluid in ECF)
Monitor in fluid sensitive patients: heart and renal failure (can handle the extra free water)
Now test your knowledge with this IV fluids types quiz.
References:
Dengue Clinical Case Management E-learning. (2023). Crystalloid IV Solutions: Intravenous Fluids. Retrieved from https://www.cdc.gov/dengue/training/cme/ccm/page70749.html.
Merriam-Webster. (n.d.). Osmolarity. In Merriam-Webster.com dictionary. Retrieved March 08, 2023, from https://www.merriam-webster.com/dictionary/osmolarity
NCI Dictionary: Osmotic. National Cancer Institute. (n.d.). Retrieved March 8, 2023, from https://www.cancer.gov/publications/dictionaries/cancer-terms/def/osmotic