0.45% Normal Saline: Clinical Indications
0.45% normal saline (half-normal saline) has extremely limited clinical indications and is generally not recommended in modern fluid resuscitation or maintenance therapy due to its hypotonic nature and associated risks.
Primary Contraindications and Safety Concerns
Hypotonic solutions like 0.45% NS should be avoided in patients with severe head trauma or traumatic brain injury, as they can cause fluid shift into damaged cerebral tissue and worsen cerebral edema 1. The European guideline on trauma management explicitly recommends against hypotonic solutions in this population 1.
In hemorrhagic shock and trauma resuscitation, balanced crystalloids (such as Lactated Ringer's or Plasma-Lyte) or 0.9% saline should be used instead of hypotonic solutions 1. If 0.9% saline is used, it should be limited to 1-1.5 L maximum to avoid hyperchloremic acidosis 1.
Rare Appropriate Uses
The only clinical scenario where 0.45% NS may be considered is as a maintenance fluid in specific pediatric or adult patients who require free water replacement without significant sodium needs, though even this indication has been largely replaced by more physiologic solutions 1.
For hypernatremia correction, D5W (5% dextrose in water) is the preferred hypotonic solution rather than 0.45% NS, as it delivers pure free water without additional sodium burden 2. The American Diabetes Association recommends D5W for controlled correction of water deficits in hypernatremic states 2.
Modern Fluid Therapy Recommendations
Balanced crystalloids should be used in preference to 0.9% normal saline for resuscitation and maintenance of intravascular volume 1. The ERAS Society and European trauma guidelines both recommend balanced crystalloids over saline-based solutions due to superior outcomes including reduced acute kidney injury and lower mortality 1.
In emergency laparotomy and critically ill patients, balanced crystalloids (such as Lactated Ringer's or Plasma-Lyte) result in improved patient outcomes compared to 0.9% saline, with lower rates of major adverse kidney events (15.4% vs 14.3%) 1. The SMART trial demonstrated this benefit in 15,802 ICU patients 1.
Critical Pitfalls to Avoid
- Never use 0.45% NS for volume resuscitation in shock states - it provides inadequate sodium replacement and can worsen hyponatremia 1
- Avoid in traumatic brain injury or any patient at risk for cerebral edema - hypotonic solutions exacerbate intracranial pressure 1
- Do not use for diabetic ketoacidosis - these patients require isotonic fluids (0.9% NS or balanced crystalloids) with potassium supplementation once K+ <5.5 mEq/L 3
- Hypotonic solutions like 0.45% NS can cause hyponatremia and cellular swelling in vulnerable populations 1, 2
Evidence-Based Alternatives
For maintenance fluids requiring free water: Consider D5W with appropriate electrolyte supplementation based on patient needs 2.
For volume resuscitation: Use balanced crystalloids (Lactated Ringer's, Plasma-Lyte) as first-line 1.
For hypernatremia correction: Use D5W at controlled rates (not exceeding 8-10 mEq/L sodium correction per day) 2.
For anaphylaxis fluid resuscitation: Normal saline (0.9%) is recommended, with 1-2 L administered rapidly to adults at 5-10 mL/kg in the first 5 minutes 1.