Clinical Indications for 0.45% Normal Saline
The use of 0.45% (half-normal) saline in modern clinical practice is extremely limited and essentially restricted to one specific indication: hyperglycemic crises (DKA/HHS) with normal or elevated corrected sodium after initial resuscitation with isotonic fluids. 1
Primary Indication: Hyperglycemic Crisis Management
The American Diabetes Association recommends 0.45% NaCl at 4-14 ml/kg/h specifically when corrected sodium is normal or elevated in patients with diabetic ketoacidosis or hyperosmolar hyperglycemic state, but only after initial resuscitation with 0.9% saline. 1
Calculate corrected sodium using the formula: Corrected [Na+] = Measured [Na+] + 1.6 × ([Glucose in mg/dL - 100]/100). 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 to prevent hypoglycemia while continuing insulin therapy. 1
Absolute Contraindications
The American Academy of Pediatrics strongly recommends against using 0.45% saline for maintenance fluids in children aged 28 days to 18 years due to the risk of hyponatremia and neurologic complications. Isotonic solutions should be used instead. 1
0.45% saline is absolutely contraindicated in patients with severe head trauma or increased intracranial pressure, as it can worsen cerebral edema. The Brain Injury Foundation recommends avoiding all hypotonic solutions in traumatic brain injury. 2, 1
In patients with existing hyponatremia, 0.45% NaCl is contraindicated. The Endocrine Society recommends isotonic solutions instead. 1
Never use 0.45% saline for acute resuscitation or volume expansion, as it distributes primarily to the intracellular compartment and provides inadequate intravascular volume support. 3
Why 0.45% Saline Has Fallen Out of Favor
Balanced crystalloids (lactated Ringer's, Plasma-Lyte) have superseded both normal saline and hypotonic solutions for nearly all clinical scenarios. Large randomized trials (SMART, n=15,802; SALT) demonstrate reduced mortality (OR 0.84,95% CI 0.74-0.95) and fewer major adverse kidney events compared to normal saline. 2, 3
The Society of Critical Care Medicine recommends balanced crystalloids over both normal saline and hypotonic solutions for any acute resuscitation needs. 2
Hypotonic saline markedly increases the risk of perioperative hyponatremia, especially when antidiuretic hormone levels are elevated by surgical stress. 3
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. 2
Do not use 0.45% saline based on outdated teaching about "free water replacement" in stable NPO patients. Modern guidelines recommend isotonic maintenance fluids (approximately 25-30 mL/kg/day) with appropriate electrolyte supplementation. 3
Avoid using 0.45% NS in neurosurgical patients or those with increased intracranial pressure due to risk of cerebral edema from hypotonic fluid administration. 2
Do not use 0.45% NS as the primary fluid in perioperative settings. The American Society of Anesthesiologists recommends buffered crystalloid solutions over both 0.9% saline and hypotonic solutions, with 98% agreement in 2024 guidelines. 1
Clinical Decision Algorithm
Step 1: Identify the clinical scenario
- Hyperglycemic crisis? → Proceed to Step 2
- Any other scenario (trauma, surgery, sepsis, maintenance fluids)? → Use balanced crystalloids; 0.45% saline has no role 2, 1, 3
Step 2: For hyperglycemic crisis only
- Initial resuscitation: Use 0.9% saline first 1
- Calculate corrected sodium 1
- If corrected sodium normal/elevated: Use 0.45% NaCl at 4-14 ml/kg/h 1
- If corrected sodium low: Continue 0.9% saline 1
- When glucose reaches 250 mg/dL: Switch to 5% dextrose with 0.45% NaCl 1
Step 3: Monitor closely