How much will 250 cc of D5 (Dextrose 5% in Lactated Ringer's) lower sodium levels?

Effect of 250 cc of D5 LR on Sodium Levels

A 250 cc infusion of D5 LR will lower serum sodium by approximately 0.8-1.0 mEq/L in an average adult. This effect is transient and relatively modest compared to larger volumes of hypotonic fluids.

Mechanism of Sodium Reduction

When administering D5 LR (5% dextrose in Lactated Ringer's solution), two key factors affect serum sodium:

1. Free Water Effect: The 5% dextrose component (50g/L) is metabolized rapidly, effectively creating free water that dilutes serum sodium
2. Sodium Content: Lactated Ringer's contains approximately 130 mEq/L of sodium, which is hypotonic relative to normal serum sodium (135-145 mEq/L)

Calculation Approach

The sodium-lowering effect can be estimated using the following principles:

• 250 cc of D5 LR contains approximately 12.5g of dextrose
• After metabolism, this creates 250 cc of effectively hypotonic fluid
• For an average 70kg adult with total body water of approximately 42L (60% of body weight)
• The dilutional effect can be calculated as the change in sodium concentration after adding this volume

Clinical Considerations

Factors Affecting Sodium Reduction

• Patient Size: The effect will be greater in smaller patients and less in larger patients
• Baseline Sodium Status: Patients with higher baseline sodium may show a slightly greater absolute decrease
• Rate of Administration: Rapid infusion causes more immediate but transient changes
• Renal Function: Impaired kidney function may prolong the effect

Safety Considerations

In patients with hyponatremia, careful consideration should be given before administering D5 LR:

• For severe hyponatremia (Na <120 mEq/L), D5 LR should be avoided as it may worsen the condition 1
• In patients requiring CRRT (Continuous Renal Replacement Therapy), D5W is sometimes used prefilter specifically to prevent overcorrection of hyponatremia 2

Comparison with Other Fluids

• Normal saline (0.9% NaCl) typically does not lower serum osmolality 3
• D5W has a more pronounced effect on lowering serum sodium than D5 LR 4, 5
• Hypotonic solutions like 0.45% saline and D5W can worsen cerebral edema after head trauma, while isotonic solutions like normal saline do not 5

Clinical Applications

• In most clinical scenarios, 250 cc of D5 LR is too small a volume to cause clinically significant hyponatremia in adults with normal renal function
• For patients requiring fluid resuscitation with concerns about cerebral edema, normal saline may be preferred over D5 LR 1
• In diabetic ketoacidosis management, fluid selection should prioritize correcting volume depletion, with careful monitoring of electrolytes 1

Monitoring Recommendations

When administering D5 LR in patients with electrolyte concerns:

• Check serum sodium before and after administration if clinically indicated
• Monitor for symptoms of rapid sodium changes (headache, altered mental status, seizures)
• In patients with traumatic brain injury, avoid hypotonic solutions that may worsen cerebral edema 4

Remember that the effect of a single 250 cc bolus of D5 LR on serum sodium is typically minimal in most adults with normal renal function, but the cumulative effect of multiple boluses or continuous infusions should be considered in your fluid management strategy.