What are the guidelines for using half normal saline (1/2 NS) in the Intensive Care Unit (ICU)?

Half Normal Saline (1/2 NS) in the ICU: Evidence-Based Recommendations

Primary Recommendation

Half normal saline (1/2 NS) should NOT be used as the primary resuscitation or maintenance fluid in adult ICU patients. Balanced crystalloid solutions (Ringer's Lactate or Plasmalyte) are strongly preferred over both 0.9% saline and hypotonic solutions like 1/2 NS for critically ill adults 1, 2.

Fluid Selection Algorithm for ICU Patients

First-Line Choice: Balanced Crystalloids

• Use balanced crystalloid solutions (Ringer's Lactate or Plasmalyte) for resuscitation and maintenance in critically ill patients 1, 2
• These solutions are associated with lower mortality, reduced need for renal replacement therapy, and better acid-base balance compared to 0.9% saline 1, 3
• Recent evidence from sepsis-induced hypotension shows lactated Ringer's solution resulted in 12.2% mortality versus 15.9% with 0.9% saline (adjusted HR 0.71,95% CI 0.51-0.99) 3

Avoid 0.9% Saline Except in Specific Circumstances

• Limit 0.9% saline use to patients with traumatic brain injury or demonstrably injured brain, where it remains the preferred initial fluid 1
• Large volumes of 0.9% saline cause hyperchloremic metabolic acidosis, potential renal dysfunction, and may increase mortality 1, 4, 5

Never Use 1/2 NS for Adult ICU Resuscitation

• 1/2 NS is hypotonic and inappropriate for volume resuscitation in critically ill adults 2
• Hypotonic solutions risk worsening hyponatremia and cerebral edema in vulnerable ICU populations 6

Limited Pediatric Indications

1/2 NS has specific but limited roles in pediatric care only:

• Maintenance fluid in pediatric patients when combined with dextrose (D5 1/2NS) for non-critically ill children 1, 7
• Diabetic ketoacidosis in children after initial resuscitation with normal saline, switch to D5 1/2NS when glucose normalizes 7
• Cerebral malaria in pediatric patients where D5 1/2NS is specifically recommended 7

Critical Contraindications

Avoid 1/2 NS in these ICU scenarios:

• Sepsis or septic shock requiring fluid resuscitation 2, 3
• Hypovolemic shock of any etiology 2
• Acute kidney injury or risk thereof 8
• Traumatic brain injury (use 0.9% saline instead) 1, 7
• Any situation requiring rapid intravascular volume expansion 7

Monitoring Requirements

When any crystalloid is administered in the ICU:

• Reassess hemodynamic status frequently with heart rate, blood pressure, urine output, and lactate levels 2
• Monitor serum electrolytes closely, particularly sodium and chloride 1, 7
• Use dynamic variables (pulse pressure variation, stroke volume variation) over static measures to guide fluid responsiveness 2
• Target mean arterial pressure ≥65 mmHg in patients requiring vasopressors 2

Common Pitfalls to Avoid

• Never use 1/2 NS for initial resuscitation in adult ICU patients—this risks inadequate intravascular expansion and worsening hyponatremia 2, 6
• Avoid fluid overload regardless of fluid type, as positive fluid balance is associated with increased mortality 1, 2
• Do not assume 0.9% saline is "normal" or physiologic—it has no scientific basis for this designation and causes metabolic derangements 4, 5
• Avoid synthetic colloids (hydroxyethyl starch) entirely due to increased renal failure and mortality risk 1, 8

Special Populations

Traumatic brain injury patients:

• Use 0.9% saline as the initial fluid choice 1, 7
• The benefit appears related to tonicity and salt load, though more research is needed 1

Patients with pre-existing hyperchloremia or metabolic acidosis:

• Strongly prefer balanced crystalloids over any saline-based solution 1, 8