When is 1/2 normal saline (half normal saline) preferred over normal saline (0.9% sodium chloride) for fluid resuscitation?

When to Use Half Normal Saline vs. Normal Saline

Half normal saline (0.45% NaCl) is preferred over normal saline (0.9% NaCl) when the corrected serum sodium is normal or elevated, in patients with edematous states such as congestive heart failure, cirrhosis, or nephrotic syndrome, and when there is concern for hyperchloremic metabolic acidosis. 1

Clinical Decision Algorithm for Fluid Selection

Initial Fluid Resuscitation

• For initial volume expansion and restoration of renal perfusion, normal saline (0.9% NaCl) is the fluid of choice 1
• For adults without cardiac compromise: 15-20 ml/kg/hr during first hour (1-1.5L in average adult) 1
• For pediatric patients: 10-20 ml/kg/hr during first hour (not exceeding 50 ml/kg over first 4 hours) 1

Subsequent Fluid Selection Based on Sodium Status

• Use 0.45% NaCl (half normal saline) when:

  • Corrected serum sodium is normal or elevated 1
  • Rate: 4-14 ml/kg/hr in adults 1
  • Patient has edematous states (CHF, cirrhosis, nephrotic syndrome) 1
  • Risk of hypernatremia is present 2
  • Concern for hyperchloremic metabolic acidosis exists 3

• Use 0.9% NaCl (normal saline) when:

  • Corrected serum sodium is low 1
  • Initial fluid resuscitation is needed 1
  • Treating chloride-responsive metabolic alkalosis 4

Special Populations

Pediatric Patients

• Initial fluid therapy should be with isotonic saline (0.9% NaCl) 1
• For continued rehydration: 0.45-0.9% NaCl (depending on serum sodium) 1
• Once glucose reaches 250 mg/dl in DKA: switch to 5% dextrose with 0.45-0.75% NaCl 1

Patients with Edematous States

• Patients with CHF, cirrhosis, and nephrotic syndrome have impaired ability to excrete both free water and sodium 1
• These patients are at risk for both volume overload and hyponatremia 1
• Half normal saline at restricted rates is preferred to avoid volume overload 1
• Close monitoring is essential in these patients 1

Diabetic Ketoacidosis (DKA)

• Initial resuscitation: 0.9% NaCl 1
• After initial resuscitation, fluid choice depends on corrected serum sodium 1
• Once serum glucose reaches 250 mg/dl: change to 5% dextrose with 0.45-0.75% NaCl 1

Monitoring and Considerations

Electrolyte Monitoring

• Regular monitoring of serum electrolytes is essential when administering IV fluids 4
• Check electrolytes every 4-6 hours until stable 4
• Monitor for development of:
  • Hypernatremia with normal saline (especially in sepsis) 2
  • Hyponatremia with hypotonic solutions 1
  • Hyperchloremic metabolic acidosis with normal saline 3

Volume Status Assessment

• Evaluate for signs of dehydration: dry mucous membranes, decreased skin turgor, postural hypotension 4
• Assess for fluid overload: edema, respiratory distress, worsening heart failure 1
• Target random urinary sodium >20 mmol/L to assess adequate hydration 4

Potential Complications

• Normal saline may cause:
  • Hyperchloremic metabolic acidosis 3
  • Hypernatremia (especially in sepsis patients) 2
  • Vascular and renal function changes 3
• Half normal saline may cause:
  • Hyponatremia if administered too rapidly or in excess 1
  • Inadequate volume resuscitation in hypovolemic states 1

Common Pitfalls to Avoid

1. Using normal saline at typical maintenance rates in patients with edematous states (CHF, cirrhosis, nephrotic syndrome) - this risks volume overload 1

2. Using half normal saline for initial resuscitation in hypovolemic patients - this provides inadequate volume expansion 1

3. Failing to adjust fluid therapy based on corrected serum sodium levels 1

4. Not monitoring for development of hyperchloremic metabolic acidosis with prolonged normal saline administration 3

5. Administering excessive volumes of normal saline in sepsis patients, which increases risk of hypernatremia 2

6. Not considering the patient's acid-base status when selecting fluids 4