What are the indications for half normal saline (0.45% sodium chloride solution) as an intravenous (IV) fluid?

Indications for Half Normal Saline (0.45% Sodium Chloride) as IV Fluid

Half normal saline (0.45% sodium chloride) is primarily indicated for patients with hypernatremia or hyperglycemic crises with normal or elevated corrected sodium levels, and should be avoided in patients with traumatic brain injury or hyponatremia. 1

Primary Indications for Half Normal Saline

• Hyperglycemic crises: In diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) with normal or elevated corrected sodium levels, 0.45% NaCl is recommended at 4-14 ml/kg/h 1
• Free water replacement: When patients need both sodium and free water replacement but not in equal proportions 2
• Recovery phase of DKA: May be preferred over normal saline to avoid hyperchloremic metabolic acidosis that can prolong insulin infusion requirements and ICU stay 2
• Pediatric maintenance fluids: Can be used in certain pediatric populations when the risk of hyponatremia is low 3, 4

Clinical Decision Algorithm for Half Normal Saline Use

1. Calculate corrected sodium in hyperglycemic patients:

   • Formula: Corrected [Na+] = Measured [Na+] + 1.6 × ([Glucose in mg/dL - 100]/100) 1
   • If corrected sodium is normal or high: Use 0.45% NaCl
   • If corrected sodium is low: Use 0.9% NaCl 1

2. Assess patient's fluid and electrolyte status:

   • Patients with hypernatremia: Consider 0.45% NaCl to provide free water 2
   • Patients with hyponatremia: Avoid 0.45% NaCl and use isotonic solutions 5

Contraindications and Cautions

• Traumatic brain injury: Hypotonic solutions like 0.45% saline should be avoided in patients with severe head trauma to prevent cerebral edema 5
• Hyponatremia: Half normal saline may worsen existing hyponatremia 4
• Critical illness: Balanced crystalloids or normal saline are generally preferred over hypotonic solutions in critically ill patients 5
• Septic shock: Current guidelines recommend balanced crystalloids over normal saline, with no recommendation for hypotonic solutions like 0.45% saline 5

Special Considerations

• Pediatric patients: While isotonic solutions are increasingly recommended for maintenance fluids in children, some studies show that 0.45% saline may be safe in certain pediatric populations when properly monitored 3, 4
• Monitoring requirements: When using half normal saline, more frequent monitoring of serum electrolytes is recommended, particularly sodium levels 2
• Duration of therapy: Half normal saline is generally more appropriate for short-term use rather than prolonged therapy 2

Potential Complications

• Iatrogenic hyponatremia: Risk increases with prolonged use of hypotonic solutions, particularly in children and postoperative patients 3
• Cerebral edema: Hypotonic solutions may contribute to cerebral edema in vulnerable patients, particularly those with traumatic brain injury 5
• Fluid overload: As with any IV fluid, volume status should be monitored to prevent fluid overload 5

Half normal saline has specific indications but should be used cautiously with appropriate monitoring of electrolytes and volume status. Recent guidelines increasingly favor balanced crystalloids over both normal saline and hypotonic solutions for most clinical scenarios 5.