Will 5% dextrose in lactated Ringer's solution lower serum sodium?

Will D5LR Fluids Decrease Sodium?

Yes, D5LR (5% dextrose in lactated Ringer's solution) can decrease serum sodium, particularly in maintenance fluid scenarios, because lactated Ringer's is slightly hypotonic (osmolarity ~273-277 mOsm/L) and the dextrose component becomes functionally hypotonic once metabolized. 1, 2

Understanding the Tonicity of D5LR

• Lactated Ringer's solution has a measured osmolarity of approximately 273-277 mOsm/L, making it hypotonic compared to plasma (275-295 mOsm/L), which creates a gradient that can drive water into cells and dilute serum sodium. 2

• When 5% dextrose is added to lactated Ringer's, the glucose is rapidly metabolized, leaving behind the hypotonic electrolyte solution—this functionally increases the hypotonicity of the fluid. 2

• In healthy volunteers receiving 50 mL/kg of lactated Ringer's over 1 hour, serum osmolality decreased by 4±3 mOsm/kg, demonstrating the hypotonic effect even with rapid infusion. 3

Critical Clinical Context: When Sodium Lowering Becomes Dangerous

The risk of hyponatremia from D5LR is particularly concerning in specific patient populations:

• Pediatric patients receiving maintenance fluids are at highest risk—hypotonic solutions like D5LR markedly increase hospital-acquired hyponatremia with a number-needed-to-harm of approximately 7.5 (one case per 7-8 children). 1

• The American Academy of Pediatrics strongly recommends against using hypotonic maintenance solutions in hospitalized children and instead advocates for isotonic solutions (sodium 130-154 mEq/L) with 2.5-5% dextrose. 1

• Patients with edema or impaired free water excretion (cardiac dysfunction, nephrotic syndrome, hepatic failure) are at heightened risk because they cannot adequately excrete the free water load, making the sodium-lowering effect more pronounced. 1

• Patients with severe traumatic brain injury or increased intracranial pressure should never receive D5LR because the hypotonic nature can worsen cerebral edema and raise intracranial pressure; 0.9% normal saline is the only appropriate crystalloid in this setting. 2

When D5LR May NOT Lower Sodium

There is one important exception where the volume expansion effect can paradoxically increase sodium:

• In hypovolemic hyponatremia, the volume expansion from D5LR can outweigh its hypotonic nature, resulting in a net increase in serum sodium by correcting the volume deficit that triggered water retention and dilutional hyponatremia. 4

• The American Association for the Study of Liver Diseases specifically recommends lactated Ringer's (with or without dextrose) as the preferred crystalloid for fluid resuscitation in hypovolemic hyponatremia in cirrhotic patients. 4

Practical Algorithm for Fluid Selection

For maintenance fluids in hospitalized patients:

• Use isotonic solutions (0.9% saline or balanced crystalloids with sodium 130-154 mEq/L) with 2.5-5% dextrose added. 1
• Avoid D5LR for maintenance therapy due to hyponatremia risk. 1

For resuscitation in hypovolemic hyponatremia:

• D5LR or lactated Ringer's without dextrose is appropriate because volume expansion corrects the underlying pathophysiology. 4

Absolute contraindications to D5LR:

• Severe traumatic brain injury or increased intracranial pressure—use 0.9% saline only. 2
• Patients with edema or impaired free water excretion—use isotonic solutions without the hypotonic component. 1

Monitoring Requirements

• When D5LR must be used, check serum sodium, potassium, and glucose every 12-24 hours initially to detect emerging hyponatremia or other electrolyte abnormalities. 1

• In edematous patients receiving any intravenous fluids, reduce the maintenance infusion rate by 50-75% if signs of fluid overload appear (increased work of breathing, hepatomegaly, worsening peripheral edema). 1

Common Pitfalls to Avoid

• Do not assume that restricting the infusion rate of D5LR will prevent hyponatremia—the hyponatremia risk persists even at reduced rates because the tonicity of the solution remains hypotonic. 1

• Do not use D5LR in pediatric maintenance fluid protocols—the AAP guideline is explicit that hypotonic solutions should never be used in hospitalized children. 1

• Do not confuse resuscitation scenarios (where volume expansion may raise sodium) with maintenance scenarios (where hypotonic fluids will lower sodium)—the clinical context determines the net effect on serum sodium. 4