Effect of 250 mL D5 0.45% NS on Serum Sodium
250 mL of D5 0.45% NS will lower serum sodium by approximately 0.5-1 mEq/L in an average adult patient.
Understanding the Components
D5 0.45% NS (also called D5 half-normal saline) contains:
- 5% dextrose (50 g/L)
- 0.45% sodium chloride (77 mEq/L of sodium)
- Total osmolality: approximately 406 mOsm/L
Mechanism of Action on Serum Sodium
The effect of this fluid on serum sodium occurs through two main mechanisms:
- Dilutional effect: The 250 mL volume expands the extracellular fluid compartment
- Free water effect: The dextrose is metabolized, leaving relatively hypotonic fluid compared to plasma
Factors Affecting Sodium Reduction
The exact reduction in serum sodium depends on several factors:
- Patient's weight: Larger patients experience less sodium reduction with the same volume
- Current sodium level: Baseline sodium affects the magnitude of change
- Hydration status: Dehydrated patients may have different responses
- Renal function: Impaired kidney function alters sodium excretion
- Rate of administration: Faster infusion causes more rapid changes
Clinical Considerations
When administering D5 0.45% NS:
- Monitor serum electrolytes: Especially in patients with pre-existing hyponatremia
- Be cautious in neurological patients: Rapid changes in sodium can lead to neurological complications 1
- Consider alternatives in severe hyponatremia: More isotonic solutions may be safer in patients with significant hyponatremia 2
Safety Precautions
- Avoid rapid correction of sodium (>8 mEq/L/day) to prevent osmotic demyelination syndrome 3
- In critically ill patients, consider using more isotonic solutions to prevent worsening hyponatremia 4
- For pediatric patients, isotonic solutions are generally preferred over hypotonic solutions to reduce the risk of iatrogenic hyponatremia 5
Clinical Application
For most clinical scenarios requiring maintenance fluids:
- D5 0.45% NS at 250 mL is a relatively small volume that poses minimal risk of significant hyponatremia in most adults
- For patients with traumatic brain injury or at risk for cerebral edema, consider more isotonic solutions 1
- In pediatric patients, monitor sodium levels more closely as they may be more susceptible to fluid-induced electrolyte changes 6