When is 0.45% Normal Saline (NS) used?

When to Use 0.45% Normal Saline (Half-Normal Saline)

0.45% normal saline is primarily used as a maintenance fluid for patients who need free water replacement along with some sodium, particularly in pediatric populations and specific clinical scenarios where hypotonic fluid is indicated, but it should NOT be used for volume resuscitation or initial fluid management in most acute settings.

Primary Clinical Indications

Maintenance Fluid Therapy

• 0.45% NS serves as a maintenance fluid when patients require both free water and modest sodium replacement, typically in stable patients who are NPO but not acutely volume depleted 1
• This hypotonic solution provides approximately 77 mEq/L of both sodium and chloride, making it suitable for ongoing fluid needs rather than acute resuscitation 1

Hypernatremia Management

• In pediatric patients with diarrhea-related hypernatremic dehydration, 0.45% NS (often as D5 0.45% NS) can be used after initial volume expansion to provide gradual correction of elevated sodium levels 2
• The solution helps dilute serum sodium while providing some volume support, though initial resuscitation should use isotonic fluids 2
• D5 half-normal saline is recommended as an alternative to lactated Ringer's for managing hyperchloremia, as it provides lower chloride load while helping dilute serum chloride 1

Specific Avoidance Scenarios

• Never use 0.45% NS for initial fluid resuscitation in sepsis, shock, or acute volume depletion - balanced crystalloids or normal saline are indicated 3, 4
• Avoid hypotonic solutions like 0.45% NS in patients with traumatic brain injury or severe head trauma to prevent fluid shift into damaged cerebral tissue and worsening cerebral edema 3, 1, 5
• Do not use for perioperative fluid management where balanced crystalloids are strongly preferred 6

Critical Clinical Considerations

Volume Resuscitation Context

• For any acute resuscitation needs (sepsis, hemorrhage, perioperative), balanced crystalloids such as lactated Ringer's or Plasma-Lyte are strongly recommended over both normal saline and hypotonic solutions 6, 3, 4
• Balanced crystalloids reduce mortality (OR 0.84,95% CI 0.74-0.95) and major adverse kidney events compared to normal saline in critically ill patients 3
• Initial fluid resuscitation with lactated Ringer's versus 0.9% saline showed improved survival (adjusted HR 0.71,95% CI 0.51-0.99) in sepsis-induced hypotension 4

Monitoring Requirements

• When using 0.45% NS, monitor serum electrolytes every 4-6 hours, particularly sodium and chloride levels, along with renal function and urine output 1
• Watch for signs of hyponatremia development, especially in patients with ongoing losses or SIADH 7

Practical Algorithm for Fluid Selection

For acute/resuscitation scenarios:

1. Use balanced crystalloids (lactated Ringer's or Plasma-Lyte) as first-line 3, 5
2. Limit normal saline to maximum 1-1.5 L if balanced solutions unavailable 1, 5
3. Never use hypotonic solutions like 0.45% NS 3, 5

For maintenance therapy in stable patients:

1. Consider 0.45% NS (often with dextrose) for ongoing fluid needs when free water replacement needed 1
2. Avoid in traumatic brain injury patients 1, 5
3. Monitor electrolytes closely 1

For hypernatremia correction:

1. Initial volume expansion with normal saline if needed 2
2. Transition to 0.45% NS or balanced solutions for gradual sodium correction 1, 2
3. Target sodium drop of approximately 0.5 mEq/L/hour 2

Common Pitfalls to Avoid

• Do not confuse maintenance fluid needs with resuscitation needs - 0.45% NS is inadequate for volume expansion and can worsen hypotension 3, 1
• Avoid using 0.45% NS in neurosurgical patients or those with increased intracranial pressure due to risk of cerebral edema from hypotonic fluid administration 1, 5
• Do not use as the primary fluid in perioperative settings where near-zero fluid balance with balanced crystalloids is recommended 6
• Remember that dextrose in D5 0.45% NS is rapidly extravasated from intravascular space, making it inappropriate for volume replacement despite the dextrose component 1