What is the difference between half normal saline (0.45% sodium chloride solution) and D5 half normal (5% dextrose in 0.45% sodium chloride solution)?

Difference Between Half Normal Saline and D5 Half Normal

Half normal saline (0.45% NaCl) contains only sodium and chloride at half the concentration of normal saline, while D5 half normal (5% dextrose in 0.45% NaCl) adds 5 grams of glucose per 100 mL to the same electrolyte solution.

Composition and Osmolality

Half Normal Saline (0.45% NaCl):

• Contains 77 mEq/L of sodium and 77 mEq/L of chloride 1
• Hypotonic solution with osmolality approximately 154 mOsm/L 1
• No caloric content 2

D5 Half Normal (5% Dextrose in 0.45% NaCl):

• Contains the same 77 mEq/L sodium and 77 mEq/L chloride 3
• Plus 50 grams of dextrose per liter (5% dextrose) 2
• Initially isotonic (approximately 406 mOsm/L) but becomes hypotonic after glucose metabolism 4
• Provides approximately 170 kcal per liter 2

Clinical Behavior and Distribution

The critical difference is that D5 half normal behaves as a hypotonic solution once the glucose is metabolized, effectively becoming free water plus electrolytes 4. After glucose metabolism:

• The dextrose distributes primarily into intracellular spaces 4
• The remaining electrolyte solution distributes into extracellular spaces (both interstitial and intravascular) 4
• This dual distribution pattern makes it less effective for intravascular volume expansion compared to isotonic solutions 4

Volume Expansion Capacity

Neither solution is appropriate for intravascular volume expansion 4. The American Journal of Kidney Diseases explicitly recommends against using D5W (and by extension, dextrose-containing hypotonic solutions) for volume expansion because they distribute primarily to intracellular spaces after glucose metabolism 4. For volume expansion, isotonic crystalloids such as 0.9% saline should be used as first-line fluids 4.

Glucose Effects

D5 half normal causes significant hyperglycemia even with modest volumes 2. In non-diabetic surgical patients, 500 mL of 5% dextrose in 0.9% normal saline caused plasma glucose to exceed 10 mmol/L in 72% of patients within 15 minutes of infusion completion 2. This hyperglycemia was transient but significant 2.

Plain half normal saline maintains normoglycemia 2. Patients receiving lactated Ringer's or normal saline remained normoglycemic throughout study periods despite fasting times averaging 13 hours 2.

Electrolyte Considerations

Both solutions can contribute to electrolyte abnormalities, but in different ways:

• Half normal saline alone carries risk of hyponatremia, particularly in children and when used as maintenance fluid 3
• In pediatric studies, half normal saline showed a trend toward increased hyponatremia (14.3% vs 6%) compared to normal saline, though not statistically significant 3
• D5 half normal provides the same sodium load as plain half normal saline but with added glucose-related metabolic effects 2, 3

When saline-based solutions are used as drug diluents in ICU patients, they increase risk of hypernatremia and hyperchloremia 5. Changing from D5W to saline as a drug diluent increased hypernatremia incidence (27.3% vs 14.6%) and hyperchloremia (36.9% vs 20.4%) 5.

Appropriate Clinical Uses

Half Normal Saline:

• May be used for maintenance fluid in specific clinical contexts 1
• Historically used as a "gold standard" for hydration before contrast procedures 1
• Not recommended for volume expansion 4

D5 Half Normal:

• Can be used for subcutaneous rehydration in geriatric patients when combined with appropriate dextrose concentrations 1
• May be appropriate for treating hypernatremia in hemodynamically stable patients 4
• Serves as a vehicle for medication administration when glucose supplementation is needed 4
• Used to prevent hypoglycemia while providing some electrolyte replacement 4

Critical Safety Considerations

Avoid D5 half normal in patients with:

• Acute ischemic stroke or risk of cerebral edema, as hypotonic solutions can exacerbate brain edema 4
• Need for intravascular volume expansion, as it distributes primarily intracellularly after glucose metabolism 4
• Hyperglycemia or poor glucose control, as even 500 mL causes significant glucose elevation 2

Avoid half normal saline in patients with:

• Severe hyponatremia requiring careful sodium correction 6
• Hemodynamic instability requiring volume expansion 4

Practical Algorithm for Selection

For volume expansion or resuscitation: Use isotonic crystalloids (0.9% saline or balanced crystalloids), not half normal saline or D5 half normal 4.

For maintenance fluid in stable patients: Consider clinical context including sodium status, glucose control, and underlying conditions 3. Half normal saline may be reasonable in general pediatric ward patients under 5 years, though isotonic solutions are increasingly preferred 3.

For hypernatremia correction: D5 half normal or D5W may be appropriate in hemodynamically stable patients 4, 6.

For medication diluent: Consider that D5W-based diluents reduce risk of hypernatremia and hyperchloremia compared to saline-based diluents, though this must be balanced against glucose control needs 5.