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IV Fluids: Types, Ingredients, Uses & Benefits

 [Medically Reviewed, 2023]

Written by Micaela Strevay (CNO, FNP-C), Family Practitioner

What are IV Fluids



IV fluids consist of fluids that are injected into veins to treat dehydration or prevent it. Additionally, intravenous rehydration is a simple, safe, and common procedure for people of all ages who are ill, injured, suffering from severe dehydration due to heat or exercise, or undergoing surgery. It is also increasingly used in intravenous therapy.

What's in IV Fluids: Ingredients


The 4 common types of IV fluids include:


  1. Normal Saline
  2. Half Normal Saline
  3. Lactated Ringers
  4. Dextrose

What do IV Fluids do?

Dehydration and electrolyte imbalance can be treated with IV fluids: liquids injected into veins through an intravenous tube.
Let's first cover a few basic definitions to understand better what the IV fluid is doing to your cells before we move on to types of IV fluids.


Osmosis
The osmosis process involves the movement of solvent molecules across a semipermeable membrane from a dilute solution to a concentrated solution. This regulates the concentration of solutes on both sides of the membrane.

By moving molecules into or out of a membrane, they either create a more concentrated solution or a more diluted solution, depending on the circumstances.

As the most common cause of osmosis, water likes to balance itself out (i.e. rush to places where there isn't water). Consequently, a cell with low water levels would rush water molecules into it, which would be regulated by the cell membrane. Water molecules would rush out if the inside of the cell had more water molecules than the outside.

Osmotic Pressure
Osmotic pressure regulates osmosis, which is the pressure that stops water from flowing into a membrane. This protects a cell from taking in more water than it can handle, which would cause the cell to burst. Simply put, it's the pressure necessary to prevent osmosis from taking place.

The Basics of IV Fluids


It is important to understand the role that osmosis and osmotic pressure play in IV fluids' interaction with your cells. In fact, IV fluids are specifically designed to create certain reactions in your cells based on osmosis.

Basically, whether something flows into or out of your cells significantly impacts how your body responds to it. So when we talk about IV fluids and intravenous solutions, we’re discussing how these solutions affect osmosis and osmotic pressure in your cells.

IV fluids are either crystalloids or colloids. A crystalloid or colloid solution can also be isotonic, hypotonic, or hypertonic, directly affecting what that solution is used for.

What happens after IV Fluids for Dehydration?


Our bodies contain almost 60% water essential to our survival. You're dehydrated when you don't have enough water in your body. Dehydrated people require IV fluids.
Severe dehydration can occur if you:

  • Have diarrhea or vomiting
  • Have overexertion or prolonged heat exposure without sufficient hydration
  • Have suffered a serious injury or burns
  • Have had surgery, and/or you have been unconscious and unable to eat or drink.


By rehydrating the cells through the bloodstream, someone who is dehydrated will feel better quickly:

  • Nausea dissipates
  • Vomiting and diarrhea stop
  • Their energy level will increase


 Types of IV Fluids

These solutions can be classified as crystalloid or colloid and as isotonic, hypotonic, or hypertonic, directly impacting how the fluids can be used. Crystalloid solutions remain the most common, largely due to the overwhelming presence of normal saline in most hospitals and healthcare settings. The fluid of choice depends on the patient's needs.

Crystalloids

Small molecules found in crystalloid solutions can easily pass through semipermeable membranes. Think of your cell membrane as a strainer. As crystalloid solutions (or particles in crystalloid solutions) are small enough, they can pass through cell membrane holes.
As a result, crystalloid solutions are readily available to your cells once they travel in. Therefore, crystalloids are commonly used in the case of hypovolemia (loss of plasma) resulting from burns, trauma, or postoperative recovery when healthcare professionals want to increase fluid volume and intravascular space.


1. Normal Saline

Normal saline is also called 9% normal saline, NS, or 0.9NaCL.
As a sterile, nonpyrogenic fluid, normal saline is easy to pass through cell membranes and is generally isotonic.
Fluid resuscitation in extracellular spaces is the most common use of this fluid due to its high effectiveness in treating various conditions, including hemorrhage, vomiting, diarrhea, or even shock.
This procedure increases the circulating plasma volume (assuming sufficient red blood cells in the patient).

Blood transfusion
Fluid replacement for patients suffering from diabetic ketoacidosis
Metabolic alkalosis
Hypercalcemia
Hyponatremia

Furthermore, normal saline is the only fluid used when administering blood. The high sodium content can cause excess fluid retention, further stressing the already weak heart and kidneys, so it must be used cautiously in patients with cardiac or renal complications.

2. Half Normal Saline

Also called 0.45NaCl or 45% normal saline, half normal saline is widely used.
Half normal saline contains half the chloride concentration of normal saline and is a hypotonic, crystalloid solution of sodium chloride in sterile water.


It’s designed to treat patients suffering from cellular dehydration and can be used for things like:


  • Raising your overall fluid volume
  • Water replacement
  • Sodium chloride depletion
  • Gastric fluid loss
  • DKA after normal saline and before dextrose infusions


Patients who are diabetics and cannot handle glucose solutions are especially benefitted from it. In patients with burns, liver disease, or trauma, the solution must always be avoided since it depletes intravascular fluids to the degree that can be dangerous. A person with cardiovascular disease or elevated intracranial pressure may be at risk from the solution, just like they would with normal saline. Although half normal saline has half the sodium chloride concentration as normal saline, it still has uses in maintaining daily fluid levels, just as normal saline does.

3. Lactated Ringers

Another highly common IV fluid used in fluid resuscitation is lactated Ringer's. If you've been injured and received surgery, you've probably received an injection of lactated ringers. It's often used as an alternative to normal saline.

The lactates are named after the physician who invented them, Sydney Ringer, who developed a solution containing sodium, chloride, calcium, and potassium in the late 1800s. The "lactated" part of Lactated Ringers comes from one Alexis Hartmann, who discovered that adding lactate to the solution made it more suitable for pediatric patients.

It is most commonly found in milk, but it is also produced by our muscles when we exercise.
A saline solution with electrolytes and a buffer (lactate) makes it isotonic since it contains electrolytes and a buffer.

Since it contains no magnesium, unlike serum, it's the closest thing to the body's natural plasma and serum concentration.

  • Severe or mild Dehydration
  • Burn victims
  • Hypovolemia resulting from third-space fluid shifts
  • Fluid loss in the lower gastrointestinal tract
  • Acute blood loss
  • Replacement of fluid and pH buffers


Because Lactated Ringer’s contain potassium, it cannot be used in patients with renal failure or renal complications as it can result in hyperkalemia. It also should not be used in patients with liver disease, as they cannot successfully metabolize the lactate. It also should not be administered if patients have a pH above 75.

4. Dextrose

Finally, there are many variations of dextrose.
Dextrose itself is a type of simple sugar made from corn. It’s chemically identical to glucose, which you should recognize as your old pal sugar. It’s often used in processed foods and added to baking products as a sweetener, but it has several uses in a medical setting.
It’s useful specifically because it’s a simple sugar, so your body can quickly use it for energy.
There are three main versions of dextrose solutions:


  • Dextrose in water
  • Dextrose in saline
  • Dextrose in Lactated Ringer’s



Regardless of the type of dextrose solution, the basic principle is the same. The IV fluid acts as a carrier for dextrose, which acts as sugar readily available for cells to gobble up and use as energy.

5. Dextrose in Water

One of the more common iterations of dextrose is a solution of dextrose in water.
Dextrose in water is a crystalloid solution. In the bag, it’s isotonic, but the solution is physiologically hypotonic. That’s a fancy way of saying that it enters your body as an isotonic solution (when there’s still sugar in the solution), but when the sugar is absorbed by your cells, you’re left with a hypotonic solution.
Unlike other fluids we’ve listed thus far, dextrose in water is not used in fluid resuscitation, as it can cause hyperglycemia. Instead, it is used to:


  • Correct a fluid volume deficit
  • Rehydration
  • Hypernatremia (an electrolyte problem caused by a decrease in total body water relative to electrolyte content)


Dextrose in water is often used to treat diabetic patients without eating anything by mouth for various reasons. Although the solution contains about 170 calories per liter, it is insufficient to replace normal daily calories and should not be used for long-term food replacement.

Interestingly, it’s sometimes used as a diluent for preparing injectable medications for an IV bag (a lot of fluid to dilute a small dose of medicine). This is likely because dextrose is absorbed so readily. It should always be avoided in patients with cardiac problems, renal failure, and increased intracranial pressure (much like the other fluids on this list), as it can cause fluid overload.

6. Dextrose in Saline

It’s a sterile, nonpyrogenic solution. As the name implies, it's a solution of 5% dextrose in normal saline. Like normal saline, it’s isotonic at first, but it becomes hypertonic when the dextrose is absorbed (remember earlier when we said that hypertonic fluids are particularly risky to work with?)

Because dextrose in saline is such a specialized fluid, it’s used for extremely specific cases, including:


  • Temporary treatment of circulatory insufficiency, but only if other plasma expanders are unavailable
  • Hypotonic dehydration
  • Addisonian crisis (a potentially life-threatening condition resulting from acute insufficiency of adrenal hormones)
  • Syndrome of inappropriate antidiuretic hormone/SIADH (when the brain makes too much antidiuretic hormone)


Like many other fluids on this list, dextrose in saline should not be used in patients with renal or cardiac complications, as it can cause heart failure or pulmonary edema.

7. Dextrose in Lactated Ringers

Finally, dextrose in Lactated Ringer’s is exactly what the name implies.
It’s a solution of 5% dextrose in Lactated Ringer’s, a sterile, nonpyrogenic solution used for fluid and electrolyte replenishment. Like other dextrose solutions, it’s isotonic until the dextrose is absorbed. This particular solution becomes hypotonic fluid after the dextrose is metabolized.

It serves much the same purpose as Lactated Ringer’s, adding 180 calories per liter, though it can be used as an alkalinizing agent. Because it’s Lactated Ringer’s with dextrose, it has many of the same contraindications as Lactated Ringer’s. It isn’t advisable in patients with renal issues due to hyperkalemia concerns, nor should it be used in patients with liver failure (again, they cannot metabolize the lactate).

The addition of dextrose means that it should be used with care if patients have issues with glucose (i.e., diabetics). It also should not be used in infants less than 28 days old, even if separate infusion lines are used.


Colloids


Due to their larger molecules, colloidal solutions cannot cross semipermeable membranes as crystalloid solutions do.
In healthcare terms, this means that colloid solutions, unlike crystalloid solutions, remain intravascular. This means they stay in your bloodstream rather than entering your cells. For this reason, they are used as plasma expanders as a form of fluid resuscitation in cases of severe hypovolemic shock.

Isotonic, Hypotonic, and Hypertonic - What's The Difference


Colloid and crystalloid solutions can be isotonic, hypotonic, or hypertonic.
Since isotonic solutions have different solute concentrations than your cells, they won't expand or shrink in the presence of isotonic solutions because the solute concentrations are different.

Soluble concentrations in hypotonic solutions are lower than those in your cells. Therefore, water will rush into the cell to balance the solute concentration, causing it to expand.
A hypertonic solution has a higher concentration of solutes than the cells in your body, which causes your cells to shrink to balance the solution.

A professional will make a choice between isotonic, hypotonic, and hypertonic solutions based on which way they want osmosis to work. Isotonic solutions, for example, maintain osmotic pressure inside and outside the cell, making them ideal for treating vomiting, diarrhea, shock, and metabolic acidosis.
However, hypotonic solutions cause cell swelling, so patients should be monitored for hypovolemia and hypertension if they receive them. It is not recommended to administer these solutions to patients with high intracranial pressure, as they may worsen cerebral edema (swelling of the brain).

A hypertonic solution draws fluid out of the cells, so patients need to be monitored closely. Although IV solutions come with their own risks, hypertonic solutions are especially risky because they can cause intravascular fluid overload and pulmonary edema (excess fluid in the lungs). As a result, hypertonic solutions cannot be used for an extended period of time.


What Benefits and Risks do IV Fluids have?


IV rehydration is a common, simple, and safe procedure that can make you feel better quickly and help save your life if you are seriously ill. But rare complications can occur, including:


Infiltration

There is a risk of extracellular fluid entering interstitial or intracellular space around the vein if the needle moves or becomes dislodged. This can cause stinging and bruising but is usually harmless.


Fluid volume overload

A large amount of fluid is given too quickly, causing headaches, high blood pressure, and difficulty breathing. This usually resolves with an adjustment of fluid levels, but it can be dangerous.


Phlebitis

Having an IV in your arm can cause a swollen vein, which can be treated by removing the IV, applying a warm compress, and elevating your arm.


Collapsed vein

Having an IV in your arm can cause a swollen vein, which can be treated by removing the IV, applying a warm compress, and elevating your arm.


Infection

The area around the needle may become infected if the area is not clean or the needle is not inserted properly. Antibiotics can usually be prescribed to treat infections.


Hematoma

Hematomas occur when blood leaks from a blood vessel into nearby tissues. They usually disappear within a few weeks.


Air embolism

When an IV pushes too much air into the vein, it causes an air embolism. It's rare but can have serious consequences, including death.


Where Can You Get an IV?

Getting an IV is simple. You can get an IV at:

  • The hospital
  • A clinic
  • At home using mobile IV fluid therapy services


FAQ about IV Fluids


When should you get IV fluids?


Approximately 60% of our bodies are made up of water. Dehydration is when the body lacks enough water. When dehydration becomes dangerous, IV fluids are needed.
It is possible to suffer from a serious case of dehydration if you:


  • Having a bad case of the flu or other illness (vomiting and diarrhea)
  • Spend too much time in the sun without drinking enough water, or exercise too much
  • Injuries or burns that are serious in nature
  • Have undergone surgery, or are unconscious and can't eat or drink for a long time.


Which IV fluid is best for weakness?


The best dextrose solution to treat weakness is dextrose in Lactated Ringer's. It is a nonpyrogenic, sterile solution to replenish extracellular fluid, intracellular fluid, and electrolytes.


How long do IV fluids stay in the body?


A controlled rate of amino acids, vitamins, minerals, and fluids is provided through IV fluid therapy. The length of your IV treatment depends on why you are receiving it. It usually lasts 45 minutes to an hour. Once connected to the IV, it is usually a quick and simple process.

The effect of IV therapy depends on the reason you are receiving it. In some cases, you may feel the effects almost immediately. In other cases, it may take a while to feel the effects. For example, some mobile IV therapies energize and refresh your body immediately. It depends on your hydration level, your body's natural metabolic rate, and the IV package you received. However, the effects can last several days after the procedure has been completed.


What IV is used for low blood pressure?


Although rare, side effects of IV therapy include light bruising and soreness around the injection area. Some people may also experience a cool feeling in the arm, a metallic taste in the mouth, and a flushing feeling.


Are there age requirements for IV therapy?


Isotonic fluids: During shock or hypovolemia, isotonic crystalloid fluids are given to replenish intravascular space.


Which IV fluid is best for diabetic patients?


The best-balanced crystalloid is Ringer's lactate. The chloride concentration in balanced crystalloids is similar to that in human plasma; therefore, treatment with balanced crystalloids may lead to a faster recovery from DKA. That said, half-normal saline solution is also used in IV therapies.

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