Is 0.45% Normal Saline (NS) at 100ml/hr appropriate for maintenance fluids?

0.45% Normal Saline at 100ml/hr is NOT Appropriate for Maintenance Fluids in Pediatric Patients

Isotonic solutions (0.9% saline or balanced crystalloids with sodium 140 mEq/L) should be used instead of hypotonic fluids like 0.45% NS for maintenance IV therapy in hospitalized children, as hypotonic fluids significantly increase the risk of hospital-acquired hyponatremia. 1, 2

Why 0.45% NS is Problematic

Composition and Classification

• 0.45% normal saline is a hypotonic solution with a sodium concentration of approximately 77 mEq/L, which is well below the physiologic sodium concentration of plasma (135-144 mEq/L) 1
• This falls into the category of hypotonic maintenance fluids (sodium 30-100 mEq/L) that have been associated with increased hyponatremia risk 1

Evidence Against Hypotonic Fluids

• The American Academy of Pediatrics provides a Level A (highest quality) recommendation that patients 28 days to 18 years requiring maintenance IV fluids should receive isotonic solutions with appropriate potassium and dextrose 1, 2
• Seventeen randomized clinical trials involving 2,455 patients demonstrated that isotonic fluids were superior to hypotonic fluids in preventing hyponatremia 1
• The number needed to treat with isotonic fluids to prevent hyponatremia is only 7.5 patients 1
• Multiple studies show hypotonic fluids increase hyponatremia incidence to 16.7-20.6% compared to 5.1-7.5% with isotonic fluids 3, 4

Clinical Consequences

• Hyponatremia can lead to hyponatremic encephalopathy, which is a medical emergency that can be fatal or cause irreversible brain injury 2
• Hospital-acquired hyponatremia is a preventable complication that significantly increases morbidity 1

What Should Be Used Instead

Recommended Isotonic Solutions

• 0.9% sodium chloride (normal saline) with sodium concentration of 154 mEq/L 1
• Balanced crystalloids (PlasmaLyte with sodium 140 mEq/L, or Hartmann solution with sodium 131 mEq/L) 1
• Add appropriate dextrose (2.5-5%) and potassium chloride to isotonic base solutions 1, 2

Rate Considerations

• The 100 ml/hr rate may be appropriate depending on patient weight using the Holliday-Segar formula: 4 ml/kg/hr for first 10 kg, plus 2 ml/kg/hr for 10-20 kg, plus 1 ml/kg/hr above 20 kg 1
• However, the composition must be isotonic, not the hypotonic 0.45% NS 1, 2

Important Caveats

When Hypotonic Fluids ARE Indicated

• Hypernatremia correction is the primary indication for hypotonic fluids like 0.45% NS 5
• In frank hypernatremia, hypotonic fluids provide necessary free water to dilute elevated serum sodium 5
• Correction rate must not exceed 10 mEq/L per 24 hours to avoid cerebral edema 5

High-Risk Populations Requiring Extra Vigilance

• Patients with congenital or acquired heart disease, liver disease, renal dysfunction, or adrenal insufficiency are at particularly high risk for hyponatremia 2
• Postoperative and critically ill children have elevated antidiuretic hormone secretion, making them especially vulnerable to hypotonic fluid-induced hyponatremia 1

Monitoring Requirements

• If hypotonic fluids must be used (e.g., for hypernatremia), check serum sodium every 4-6 hours initially 5
• For standard maintenance with isotonic fluids, routine electrolyte monitoring should still be performed based on clinical status 2

Adult Considerations

While the question context suggests pediatrics, in adults undergoing surgery:

• Balanced crystalloids are preferred over 0.9% saline to avoid hyperchloremic acidosis and potential kidney injury 1
• Near-zero fluid balance should be maintained perioperatively, avoiding excessive fluid administration 1
• 0.9% saline in large volumes causes hyperchloremia, renal vasoconstriction, and increased complications 1