0.45% Sodium Chloride (Half Normal Saline)

• Core dose: NOT for resuscitation; maintenance 50–125 mL/h (adult); for hypernatremia correction, calculate free-water deficit and target gradual Na⁺ reduction ≤10–12 mEq/L per 24 h
• Onset/duration: Immediate vascular distribution; ongoing effects depend on fluid-electrolyte shifts and renal regulation
• Key danger: Hypotonic solution can cause or worsen hyponatremia and cerebral edema—absolutely avoid in TBI, elevated ICP, stroke, and SIADH
• Special: Contains only 77 mEq/L Na⁺ and Cl⁻ (half of normal saline); indicated for hypernatremia correction or select DKA cases after initial isotonic resuscitation; NOT for shock or volume resuscitation

Hypotonic crystalloid; fluid and electrolyte replenisher

Mechanism of Action (Pharmacodynamics):

• Expands extracellular fluid with a greater proportion of free water relative to plasma, lowering serum tonicity compared with isotonic crystalloids
• Provides sodium and chloride at half the concentration of normal saline
• Distributes across the extracellular space and, via water movement, partially into the intracellular compartment depending on serum tonicity

Disposition (Pharmacokinetics/Physiology):

• Rapid distribution from intravascular to interstitial space
• ~25–30% of an isotonic bolus remains intravascular at equilibrium—hypotonic solutions provide more free water and a smaller sustained intravascular expansion
• Sodium/chloride are renally regulated under RAAS/ADH
• Clinical effects governed by ongoing fluid and solute shifts

• Hypernatremia with hypovolemia or euvolemia — gradual free-water replacement when D5W alone is not ideal (e.g., need for some sodium)
• Diabetic ketoacidosis (DKA)/hyperosmolar states — after initial isotonic resuscitation, consider 0.45% NS if corrected serum Na⁺ is normal or high (institutional protocol)
• Maintenance fluids in select adult inpatients when risk of hypernatremia exists and close monitoring is possible (many guidelines now prefer isotonic maintenance to reduce hyponatremia risk)
• Medication carrier for specific drugs when hypotonic diluent is acceptable per labeling

Contraindications:

• Hyponatremia or states of non-osmotic vasopressin excess (SIADH, pain, nausea, CNS injury) — hypotonic solutions can worsen hyponatremia
• Elevated intracranial pressure, traumatic brain injury, or acute ischemic stroke — avoid hypotonic fluids
• Severe symptomatic hypovolemia/shock — use isotonic fluids for resuscitation

Cautions:

• Edematous states (HF, cirrhosis, nephrotic syndrome) — risk of fluid overload/hyponatremia; use cautiously with close monitoring

Metabolic:

• Hyponatremia (dilutional)
• Cerebral edema in vulnerable patients
• Hyperchloremic metabolic acidosis is uncommon compared with 0.9% NS but acid-base shifts depend on overall fluid strategy and patient condition

Volume:

• Fluid overload (peripheral/pulmonary edema)

Local IV:

• Phlebitis
• Infiltration
• Infection/air embolism risks relate to IV access rather than solution

Blood Products:

• Avoid hypotonic solutions with PRBCs (hemolysis risk)
• Use 0.9% NS for priming and co-infusion

Medication Compatibility:

• Check Y-site/admixture compatibility per drug
• Hypotonic diluents may be unsuitable for some medications

Concomitant Medications:

• Desmopressin/antidepressants/antiepileptics (↑vasopressin effect) increase hyponatremia risk with hypotonic fluids
• Monitor Na⁺ closely

Electrolytes:

• Serum sodium and chloride, osmolality
• Frequency q2–6 h during active correction, then daily or per status

Neurologic Status:

• During hyponatremia/hypernatremia therapy (headache, confusion, seizure)

Renal Function:

• SCr, BUN and urine output
• Fluid balance, weights, and signs of pulmonary edema

Acid-Base Status:

• ABG/VBG, bicarbonate/base excess if large volumes or metabolic derangements are present

• Generic/Official: Sodium Chloride Injection, USP — 0.45% (half-normal, hypotonic)
• Common Names: 0.45% NS, "half-normal saline" (HNS)

• Infuse via pump when used for sodium correction
• Dedicated line preferred when multiple infusions are running
• Avoid co-infusion with blood products
• Do not use for line priming with PRBCs (hypotonic hemolysis risk)

Adults:

• Not recommended for initial resuscitation of shock/trauma/sepsis (use isotonic balanced crystalloid or 0.9% NS)
• Hypernatremia correction: Calculate free-water deficit (FWD) and replace with 0.45% NS and/or D5W; target ↓Na⁺ ≤10–12 mEq/L per 24 h (≤8 mEq/L/24 h in high-risk)
• DKA/HHS: After initial 0.9% NS boluses, infuse 0.45% NS (e.g., 250–500 mL/h) if corrected Na⁺ is normal/high; continue 0.9% NS if corrected Na⁺ is low (per protocol)
• Maintenance examples (institution-specific): 50–125 mL/h, adjusted to electrolytes, osmolality, and clinical status

Pediatrics:

• Current pediatric guidance: Favors isotonic maintenance fluids to reduce hyponatremia risk
• Reserve 0.45% NS for specific indications (e.g., hypernatremia correction) under close monitoring
• Shock/dehydration boluses should be isotonic (LR/0.9% NS). Avoid hypotonic boluses
• Hyponatremia risk is higher with hypotonic maintenance; if used, monitor Na⁺ frequently (q4–6 h initially)

• DailyMed/FDA. (2024). Sodium Chloride Injection, USP (0.45%) — Prescribing Information (composition, pH, osmolarity).
• Evans, L., et al. (2021). Surviving Sepsis Campaign: International guidelines for management of sepsis and septic shock 2021. Intensive Care Medicine, 47, 1181–1247.
• StatPearls. (2024). Sodium Chloride. StatPearls Publishing.