Understanding the Paradox: What is 5% Dextrose Dehydration?

January 10, 2026 •

4 min read

While often perceived as a hydrating fluid, the paradox is that administering a 5% dextrose solution (D5W) to a dehydrated patient can actually cause or worsen dehydration on a cellular level. This occurs because the body rapidly metabolizes the dextrose, leaving behind only free water, which can dilute electrolytes and cause a dangerous shift of fluid into the cells.

Quick Summary

A 5% dextrose solution can cause or exacerbate cellular dehydration and electrolyte imbalances if used incorrectly for rehydration, as the body processes the glucose, leaving behind hypotonic free water that shifts into cells. It is not suitable for most dehydration cases involving electrolyte loss.

Key Points

Paradoxical Dehydration: Administering 5% dextrose for rehydration can cause paradoxical cellular dehydration by rapidly creating a hypotonic solution.
Hypotonic Effect: After the body metabolizes the dextrose, the fluid becomes hypotonic, causing water to shift out of the blood and into the body's cells.
Electrolyte Imbalance: The influx of free water dilutes existing electrolytes, leading to dilutional hyponatremia, a potentially life-threatening condition.
Not for Volume Replacement: D5W is ineffective at expanding blood volume to correct hypovolemia because most of the water quickly leaves the intravascular space.
Correct Use Cases: D5W is properly used for providing free water, treating hypoglycemia, and acting as a vehicle for medication delivery.
Alternative Fluids: Isotonic solutions like Normal Saline and Lactated Ringer's are the standard for treating most cases of dehydration involving electrolyte loss.

What is 5% Dextrose? The Basic Science

At its core, a 5% dextrose solution, often referred to as D5W (5% dextrose in water), is a sterile intravenous fluid containing 5 grams of glucose per 100 milliliters of water. Dextrose is a simple sugar, a form of glucose, which the body can readily use for energy. When first introduced into the bloodstream, the solution is initially isotonic, meaning it has a similar concentration of dissolved particles (solutes) to blood plasma. However, this balance is temporary and misleading. The body quickly metabolizes the dextrose for fuel, leaving behind only the sterile water. At this point, the solution effectively becomes hypotonic—it has a lower solute concentration than the fluid inside the body's cells.

The Critical Role of Tonicity and Osmosis

Tonicity is a measure of the effective osmotic pressure gradient of a solution. It determines the direction and extent of water movement across a cell membrane. The movement of water across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration is known as osmosis. This fundamental process is where the danger of using D5W for typical dehydration lies.

Initial Isotonicity: Upon infusion, the 50 grams of dextrose per liter initially gives D5W an osmolality of 278 mOsm/L, making it relatively isotonic to plasma.
Rapid Metabolism: The body's cells quickly absorb and use the dextrose, particularly for energy production. This metabolism happens very rapidly.
Becoming Hypotonic: As the dextrose is consumed, the remaining sterile water effectively becomes a hypotonic solution. It now has a lower concentration of solutes than the surrounding blood plasma and interstitial fluid.
Fluid Shift and Swelling: To restore equilibrium, water shifts from the area of lower solute concentration (the blood vessels) into the area of higher solute concentration (the body's cells). This movement can lead to cellular swelling and, if severe enough, can cause dangerous swelling of brain cells, known as cerebral edema.

Why 5% Dextrose is Not Recommended for True Dehydration

True dehydration, especially from vomiting, diarrhea, or excessive sweating, involves a loss of both water and electrolytes, particularly sodium and potassium. Treating this type of fluid and electrolyte depletion with D5W is inappropriate and potentially dangerous. The free water from D5W will dilute the remaining electrolytes in the bloodstream, leading to a condition called dilutional hyponatremia (abnormally low sodium levels).

Clinical Consequences of Incorrect Rehydration

Aggravated Hyponatremia: By adding free water without electrolytes, D5W can further drop sodium levels, which is life-threatening.
Cerebral Edema: Dilutional hyponatremia causes excessive water to move into brain cells, leading to swelling, confusion, seizures, and potentially coma.
No Extracellular Volume Expansion: Because the free water rapidly shifts into the cells, D5W is ineffective at expanding the extracellular fluid volume to correct dehydration-induced hypovolemia (low blood volume).

How D5W is Properly Used in a Clinical Setting

Given its risks in treating general dehydration, D5W has very specific and controlled clinical applications. It is used to provide a small amount of calories and free water, but never to correct significant electrolyte loss.

Free Water Replacement: For patients with pure water deficits and no significant electrolyte loss, D5W provides necessary hydration.
Treating Hypoglycemia: Dextrose is glucose, so D5W is an effective treatment for low blood sugar.
As a Drug Diluent: It is a common carrier fluid for administering compatible intravenous medications.

Comparison of IV Fluids for Rehydration


Feature	5% Dextrose (D5W)	Normal Saline (0.9% NaCl)	Lactated Ringer's (LR)
Tonicity (Initial)	Isotonic	Isotonic	Isotonic
Tonicity (Effective)	Hypotonic (after metabolism)	Isotonic	Isotonic
Composition	Dextrose and sterile water	Sodium chloride (salt) and sterile water	Sodium, potassium, calcium, chloride, and lactate
Electrolyte Content	None	High sodium and chloride	Balanced electrolytes
Primary Purpose	Free water replacement, vehicle for drugs, treat hypoglycemia	Extracellular volume expansion, treat hypovolemia	Extracellular volume replacement, fluid and electrolyte balancing
Suitability for Dehydration	Poor; dangerous for most dehydration cases involving electrolyte loss	Good; primary fluid for volume replacement in dehydration	Excellent; most physiologic option for many dehydration and electrolyte issues
Key Risk (Incorrect Use)	Cellular swelling, dilutional hyponatremia	Hypernatremia or hyperchloremia (with excessive use)	Mild metabolic alkalosis (risk with impaired liver function)

Conclusion

The concept of "5% dextrose dehydration" is a misnomer that highlights a serious clinical risk. While D5W seems like a simple hydrating fluid, its unique metabolic pathway makes it the wrong choice for treating most forms of dehydration that involve electrolyte loss. Instead, this fluid is reserved for specific purposes like providing free water or treating low blood sugar, while balanced electrolyte solutions like Normal Saline or Lactated Ringer's are the standard of care for rehydration. Understanding the physiological difference is crucial for preventing serious complications related to fluid and electrolyte imbalances.

Proper Intravenous Fluid Selection is Critical

Selecting the correct IV fluid is a precise and crucial medical decision that depends on the patient's specific condition and electrolyte status. Healthcare providers consider the type of dehydration, the patient's glucose levels, and any pre-existing conditions before administering any fluid. Always consult a healthcare professional for guidance on proper intravenous fluid therapy.

Symptoms of Cellular Dehydration

When fluids shift from the extracellular space into the cells due to hypotonic infusion, symptoms of cellular dehydration and electrolyte imbalance can manifest.

Excessive Thirst and Dryness: The body signals a need for fluid despite recent administration.
Dizziness and Confusion: Neurological symptoms can be a sign of cerebral edema.
Headaches: Often accompany shifts in fluid balance and cerebral swelling.
Rapid Heart Rate: The cardiovascular system tries to compensate for perceived hypovolemia.
Fatigue and Weakness: Electrolyte imbalances can disrupt muscle and nerve function.
Seizures: A severe symptom of dilutional hyponatremia and cerebral edema.

Frequently Asked Questions

It is potentially dangerous because the body rapidly metabolizes the dextrose, leaving behind free water. This water dilutes the blood's electrolytes, and as a hypotonic solution, it pulls water into the cells, which can worsen cellular swelling and electrolyte imbalance.

The primary risk is dilutional hyponatremia, where the concentration of sodium in the blood becomes dangerously low. This can lead to severe neurological symptoms like confusion, seizures, and cerebral edema.

A 5% dextrose solution is appropriate for treating low blood sugar (hypoglycemia), replacing pure water deficits without electrolyte loss, or as a vehicle to deliver compatible intravenous medications.

An isotonic solution has the same solute concentration as the body's cells, so there is no net movement of water. A hypotonic solution has a lower solute concentration, causing water to move into the cells.

For general dehydration involving electrolyte loss, an isotonic solution like Normal Saline (0.9% NaCl) or a balanced electrolyte solution like Lactated Ringer's is more appropriate, as they replace both fluid and electrolytes.

Yes, if 5% dextrose is used improperly for dehydration, it can cause severe dilutional hyponatremia. The resulting osmotic shift of water into brain cells can cause cerebral edema, or brain swelling.

In patients without diabetes, the plasma half-life of a dextrose bolus is typically no more than 15 minutes, meaning the hypotonic effect can begin very quickly.