Intravenous Fluids: Types of IV Fluids

William Kelly, MSN, FNP-C

Updated June 2026 · Medically reviewed for nurses

11 min read

Intravenous fluids are everywhere in hospitals and emergency departments — used both as rapid boluses and slow maintenance drips. Telling the types apart can be confusing, but as a nurse it's essential to understand.

This guide walks through when to give IV fluids, the difference between maintenance and bolus, the key concepts of tonicity, and every common fluid you'll hang at the bedside — with its uses, cautions, and contraindications.

Indications for Intravenous Fluids

IV fluids are one of the most commonly used interventions in healthcare. Most often they're used to hydrate patients with dehydration, but they also support blood pressure in those with hypotension or sepsis, and act as maintenance fluids for patients who can't take in enough hydration on their own.

In the ER, IV fluids are commonly ordered for nausea and vomiting, diarrhea, dehydration, acute kidney injury, abdominal pain, headaches, bleeding, and infections.

Maintenance Fluids vs IV Bolus

The same bag of fluid behaves very differently depending on how fast you run it. Maintenance fluids run slowly to cover decreased intake or expected losses; a bolus runs wide-open to rapidly restore volume.

Maintenance Fluids

Run at a slower rate to account for decreased PO intake or ongoing losses. Common for NPO patients and those with fevers, vomiting, diarrhea, drains, burns, or pancreatitis.

IV Bolus

Given rapidly over a short time, mainly in acute care for unstable patients with low blood pressure. Helps support BP and correct hypotension.

Ongoing fluid losses occur with many conditions. Fevers increase maintenance needs through "insensible water losses" from sweating and increased metabolism. Frequent vomiting, diarrhea, and high-output drains all demand extra fluid, and patients with burns or pancreatitis often require large volumes. Those admitted with dehydration, mild hyponatremia, or acute renal failure usually get maintenance fluids to slowly correct hydration, sodium, and renal function.

An IV bolus is fluid given rapidly over a short time, used most in acute settings like the ER or ICU for unstable patients with low blood pressure. A 1-liter bolus is commonly ordered on patients first arriving to the ER, since fluids help so many conditions. You'll typically see 1–3 liters of boluses for dehydration, sepsis, shock, migraines, abdominal pain, and n/v/d.

In sepsis, 30 mL/kg boluses are commonly ordered. Hang the bolus (usually 1 L bags) by gravity and open the clamp wide open. Make sure the patient keeps their arm straight if the IV is in the AC, or the bolus won't flow.

Important Fluid Concepts to Understand

Before diving into the fluids themselves, a few underlying concepts make the whole topic click: tonicity, osmolarity, and osmosis.

Osmolarity

The total concentration of solutes within a solution. The more solutes, the higher the osmolarity.

Osmosis

Water flows across the semi-permeable cell membrane from lower to higher solute concentration, balancing the two sides. Electrolytes (Na, Cl, K) can't cross freely; water can.

Tonicity

A fluid's ability to move water into or out of cells, related to its osmolarity relative to the inside of the cell.

Isotonic

Nearly the same osmolarity as intracellular fluid, so there's no significant net shift of water into or out of cells.

Hypotonic

Lower osmolarity than the cell, so water shifts into cells and they swell. Can be deadly in severe head injury and increased ICP.

Hypertonic

Higher osmolarity than the cell, so water shifts out of cells, causing cellular dehydration and shrinking.

Types of IV Fluids

There are many fluids that can be ordered, and knowing the difference matters — certain fluids are ideal for certain situations, and others can be harmful. As a nurse you need the basics; as a nurse practitioner you'll be ordering them, making it even more important to understand.

Isotonic Fluids: Normal Saline & Lactated Ringers

Normal Saline (0.9% NS)the standard isotonic fluid

Normal Saline (NS / NSS) is the standard fluid given both as boluses and maintenance. It contains sodium chloride (NaCl) and is isotonic, so there's no net movement of fluid or electrolyte into or out of cells — no unnecessary swelling or shrinking. It's the cornerstone IV fluid because it works for most situations:

• Hydration & maintenance fluids
• Hyponatremia
• Hypotension or shock
• Sepsis
• With blood transfusions

NS is cheap, doesn't cause allergic reactions, and almost all medications are compatible with it.

Lactated Ringers (LR)buffered isotonic fluid

LR is another commonly given isotonic fluid — the fluid of choice for surgeons. Some consider it slightly better than NS, but the general consensus is that "one is not better than the other." Unlike NS, LR contains not just sodium chloride but also sodium lactate, potassium chloride, and calcium chloride. Because LR is buffered, it won't cause the hyperchloremic metabolic acidosis large volumes of NS can, and some studies suggest improved renal function in critically ill patients on LR (though evidence is mixed).

• Same indications as NS: dehydration, NPO maintenance, ongoing losses, sepsis, allergic reactions
• Preferred over NS in: pancreatitis, burns, surgical patients, sepsis
• Avoid in: severe liver or renal failure, metabolic alkalosis > 7.5, hyperkalemia or hypercalcemia, and blood transfusions (precipitates if run in the same line)

Hypotonic Fluids: Half Normal Saline (0.45% NS)

Half normal saline has half the tonicity of NS, so it's hypotonic — a lower osmolarity than the fluid inside the cells. This causes water to shift into cells, making them swell, which can be helpful in some situations and dangerous in others.

Half Normal Saline (0.45% NS)hypotonic

Rarely given alone — usually combined with potassium or dextrose. You may see slower rates in conditions causing significant cellular dehydration, such as:

• Hypernatremia
• Severe DKA

Run alone, Half-NS is the wrong choice for most other scenarios, since it can deplete intravascular volume and cause cellular edema.

Hypertonic Saline (3% NS)

Hypertonic saline is given for severe hyponatremia or increased intracranial pressure. It's used carefully and selectively, because correcting sodium too quickly can cause osmotic demyelination syndrome and irreversible neural damage.

Hypertonic Saline (3% NS)severe hyponatremia / raised ICP

Used when severe hyponatremia comes with symptoms of cerebral edema — seizures, severe headaches, decreased LOC, or tremors. The usual dose is a 100 mL bolus over 10 min (a rate of 600 mL/hr), which can be repeated twice if needed. It's also given in severe head injury to reduce intracranial pressure.

Dextrose, Potassium & Bicarbonate Solutions

Dextrose-Containing Solutionshypoglycemia & maintenance

Dextrose can be added to any fluid above or to water. It's osmotically active and raises tonicity, shifting fluid out of cells — but dextrose is rapidly metabolized, so the effective osmolarity ends up higher than the base fluid yet lower than the calculated value. Common solutions: D5W, D10W, D5NS, D5 ½NS, D5LR.

• Add dextrose in: hypoglycemia, alcohol intoxication, starvation ketosis
• Avoid dextrose in: hyperglycemia, hypokalemia

An amp (25 g) of 50% Dextrose (D50) is often given IV push for profound hypoglycemia or alongside IV insulin to lower potassium. D5W and D10W are used for slow correction of chronic hypernatremia or over-rapidly corrected hyponatremia. Monitor blood sugar and electrolytes; never give dextrose solutions as a bolus (except D50 as above).

Potassium-Containing Solutionshypokalemia & ongoing losses

Potassium may be added to each liter bag for hypokalemia, ongoing potassium losses, or DKA / severe hyperglycemia. Potassium is as osmotically active as sodium, so it raises osmolarity and makes the fluid more hypertonic — adding it to an isotonic fluid makes it hypertonic, a poor choice in cellular dehydration like DKA. A hypotonic base (e.g., D5 ½NS with potassium) is a great alternative there.

Bicarbonate-Containing Solutionsmetabolic acidosis

Bicarb can be added to IV fluids to help with significant metabolic acidosis. This isn't common outside of the ICU.

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