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Hypotonic vs hypertonic vs isotonic IV fluids: a chart for nurses

Which way water moves with each IV fluid, with examples: 0.9% and 0.45% NaCl, lactated Ringer's, D5W and 3% NaCl, plus the nursing cautions the NCLEX tests.

Key points
  • Isotonic fluids stay in the vessels: 0.9% NaCl, lactated Ringer's.
  • Hypotonic fluids swell cells: 0.45% NaCl. Avoid them with raised intracranial pressure.
  • Hypertonic fluids shrink cells: 3% NaCl. Raise sodium slowly.
  • Blood goes with 0.9% NaCl only.

Tonicity tells you which way water moves when an IV fluid enters the blood. Water moves toward the side with more dissolved particles. Learn that one rule and the chart below makes sense: which fluids swell cells, which shrink them, and when each is dangerous.

Sources checked 18 October 2026.

The short answer

  • Isotonic fluids have about the same concentration as blood. They stay in the extracellular space and expand blood volume. Examples: 0.9% sodium chloride, lactated Ringer's.
  • Hypotonic fluids are more dilute than blood. Water moves into the cells and the cells swell. Example: 0.45% sodium chloride. D5W acts as hypotonic once the dextrose is used.
  • Hypertonic fluids are more concentrated than blood. Water moves out of the cells into the vessels and the cells shrink. Example: 3% sodium chloride.

How water moves

Three red blood cells. In a hypotonic solution, water moves in and the cell swells. In an isotonic solution, the cell keeps its size. In a hypertonic solution, water moves out and the cell shrinks.HypotonicIsotonicHypertonic
Water moves toward the side with more particles. Arrows show which way it goes.

Normal serum osmolality is roughly 275 to 295 mOsm/kg. A fluid near that value is isotonic. The numbers in the chart are the osmolarity of the fluid in the bag.

IV solutions chart

SolutionTonicityUsed forWatch for
0.9% NaCl (normal saline), 308 mOsm/LIsotonicVolume replacement, dehydration, with blood transfusionsFluid overload. Large volumes can cause hyperchloremic acidosis.
Lactated Ringer's, 273 mOsm/LIsotonicVolume replacement in surgery, trauma and burnsContains potassium, calcium and lactate. Not in the same line as blood. Use caution in liver dysfunction.
D5W (5% dextrose in water), 252 mOsm/LIsotonic in the bag, hypotonic in the bodyFree water, hypernatremiaNot for volume resuscitation. Avoid in hyperglycemia and raised intracranial pressure.
0.45% NaCl (half normal saline), 154 mOsm/LHypotonicHypernatremia, cellular dehydrationCerebral edema. Can deplete the vessels further in a client who is already hypovolemic.
3% NaCl, about 1026 mOsm/LHypertonicSevere hyponatremia with neurologic symptoms, cerebral edemaHypernatremia, fluid overload, pulmonary edema, too-rapid correction. Central line preferred.
D5 0.45% NaCl, D5NS, D5LRHypertonic in the bagMaintenance fluids with some caloriesAfter the dextrose is used, D5 0.45% NaCl acts as hypotonic. D5NS and D5LR act as isotonic. Avoid in hyperglycemia.

Nursing cautions for each type

Isotonic: the risk is too much volume. Check lung sounds, blood pressure, edema, weight and intake and output, especially in clients with heart failure or kidney disease.

Hypotonic: the risk is water moving out of the vessels and into the cells. Brain cells swell, so avoid hypotonic fluids with a head injury, a stroke or raised intracranial pressure. Watch for confusion, headache and a falling level of consciousness.

Hypertonic: the risk is too much water pulled into the vessels and sodium corrected too fast. Use an infusion pump, check sodium levels as ordered, and listen for crackles.

Which fluid for which client

ClientFluid type usually chosen
Hypovolemia from bleeding, vomiting or diarrheaIsotonic: 0.9% NaCl or lactated Ringer's
Blood transfusion0.9% NaCl only
Hypernatremia, water lossHypotonic, such as D5W or 0.45% NaCl
Severe hyponatremia with seizures or confusionHypertonic 3% NaCl, closely monitored
Head injury or raised intracranial pressureNot hypotonic
HyperglycemiaNot a dextrose solution

The provider orders the fluid. On the exam, the nurse's job is to know why it was chosen and to question an order that does not fit the client.

How to remember it

  • Hypo-tonic, hippo cell. In a hypotonic fluid the cell swells up like a hippo.
  • Hyper-tonic, cell shrinks. A hypertonic fluid pulls water out.
  • Iso means equal. Nothing moves in or out. The fluid stays in the vessels.
  • Only saline with blood. Not lactated Ringer's, not dextrose.

More on fluids and electrolytes

Practice questions

  1. Question 1Multiple choicePharmacological and Parenteral Therapies
    A client with a traumatic brain injury has signs of rising intracranial pressure. Which IV fluid order should the nurse question?
  2. Question 2Multiple choicePharmacological and Parenteral Therapies
    The nurse is preparing to give a unit of packed red blood cells. Which solution should the nurse hang with the blood?
  3. Question 3Multiple responsePharmacological and Parenteral Therapies
    A client with severe hyponatremia and confusion is receiving 3% sodium chloride. Which actions are appropriate? Select all that apply.
  4. Question 4Multiple choicePharmacological and Parenteral Therapies
    A nursing student asks why 5% dextrose in water (D5W) is not used to restore blood volume. Which answer is correct?
  5. Question 5Multiple choicePhysiological Adaptation
    A client is receiving a hypotonic IV solution. Which describes the fluid shift the nurse expects?
Sources
  1. StatPearls: Crystalloid Solutions in Intravenous Fluid Therapy
  2. Open RN Nursing Fundamentals: Fluids and electrolytes
  3. NCSBN: 2026 NCLEX-RN Test Plan

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