When is 0.45% (normal saline) recommended for maintenance fluid therapy?

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

0.45% normal saline should be used primarily in hyperglycemic crises (DKA/HHS) when corrected sodium is normal or elevated, and should be avoided in most other acute settings including traumatic brain injury, hyponatremia, and general resuscitation. 1, 2, 3

Primary Indications

Hyperglycemic Crises (DKA/HHS)

• Use 0.45% NaCl at 4-14 ml/kg/h when corrected sodium is normal or elevated after initial resuscitation with 0.9% saline 1, 3
• Calculate corrected sodium using: Corrected [Na+] = Measured [Na+] + 1.6 × ([Glucose in mg/dL - 100]/100) 1, 3
• If corrected sodium is LOW, use 0.9% NaCl instead 1
• Once serum glucose reaches 250 mg/dl, switch to 5% dextrose with 0.45% NaCl 1

Pediatric Maintenance Fluids (Historical Use - Now Discouraged)

• The AAP now strongly recommends AGAINST hypotonic solutions like 0.45% saline for maintenance fluids in children 28 days to 18 years 1
• Isotonic solutions should be used instead to prevent hyponatremia and neurologic complications 1
• This represents a major shift from historical practice where 0.45% saline was commonly used for maintenance 2

Absolute Contraindications

Traumatic Brain Injury and Neurosurgical Patients

• Never use hypotonic solutions like 0.45% saline in patients with severe head trauma or increased intracranial pressure 2, 3
• Hypotonic fluids cause fluid shift into damaged cerebral tissue, worsening cerebral edema 2, 3
• Use 0.9% saline as first-line fluid therapy in traumatic brain injury 2

Hyponatremia

• Avoid 0.45% NaCl in any patient with hyponatremia - use isotonic solutions instead 3
• Hypotonic solutions will worsen existing hyponatremia and risk neurologic complications 1, 3

Acute Resuscitation

• 0.45% saline is inadequate for volume expansion and should never be used for resuscitation 2
• Balanced crystalloids (lactated Ringer's, Plasma-Lyte) are preferred over both normal saline and hypotonic solutions for acute resuscitation 1, 2

Clinical Decision Algorithm

Step 1: Identify the clinical scenario

• Hyperglycemic crisis? → Calculate corrected sodium 1, 3
• Traumatic brain injury/neurosurgical patient? → Absolute contraindication 2, 3
• Hyponatremia present? → Absolute contraindication 3
• Acute resuscitation needed? → Use balanced crystalloids instead 1

Step 2: For hyperglycemic crises only

• If corrected sodium is normal or elevated → 0.45% NaCl at 4-14 ml/kg/h 1, 3
• If corrected sodium is low → Use 0.9% NaCl 1
• Monitor serum osmolality changes (should not exceed 3 mOsm/kg/H2O per hour) 1

Step 3: Monitor closely

• Check electrolytes every 4-6 hours when using 0.45% saline 2
• Monitor for signs of fluid overload 3
• Reassess volume status and sodium levels frequently 1

Critical Pitfalls to Avoid

Confusing Maintenance with Resuscitation

• Do not confuse maintenance fluid needs with resuscitation needs - 0.45% NS is inadequate for volume expansion and can worsen hypotension 2
• Initial resuscitation should always use isotonic or balanced crystalloid solutions 1

Pediatric Hyponatremia Risk

• The widespread historical use of hypotonic maintenance fluids in children caused significant iatrogenic hyponatremia and neurologic injury 1
• This practice has been abandoned - isotonic solutions are now standard for pediatric maintenance fluids 1

Cerebral Edema in Vulnerable Populations

• Hypotonic solutions contribute to cerebral edema in patients with traumatic brain injury, neurosurgical conditions, or acute neurologic injury 2, 3
• Even in hyperglycemic crises, the rate of osmolality correction must be controlled to prevent cerebral complications 1

Modern Fluid Therapy Paradigm

Balanced crystalloids are generally superior to both normal saline and hypotonic solutions in most clinical scenarios 1:

• Balanced crystalloids reduce mortality (OR 0.84,95% CI 0.74-0.95) compared to normal saline 2
• They reduce major adverse kidney events in critically ill patients 2
• The 2024 perioperative guidelines recommend buffered crystalloid solutions over 0.9% saline (98% agreement) 1

The role of 0.45% saline has become extremely limited - essentially restricted to the specific scenario of hyperglycemic crises with normal/elevated corrected sodium after initial resuscitation 1, 3