What are the indications and precautions for administering D5 (dextrose 5%) half normal saline in patients with dehydration?

D5 Half Normal Saline: Indications and Precautions

D5 half normal saline (5% dextrose in 0.45% NaCl) is indicated for maintenance fluid therapy in patients unable to drink who have ongoing losses from diarrhea or vomiting, and for treating low-intake dehydration (hypotonic dehydration) in older adults, but should NOT be used for initial rehydration of severe dehydration where isotonic fluids are required. 1

Primary Indications

Maintenance Therapy After Initial Rehydration

• Use D5 0.25 normal saline (with 20 mEq/L potassium chloride) intravenously for maintenance when patients cannot drink and have ongoing diarrheal or vomiting losses after initial rehydration is complete. 1
• This formulation replaces ongoing fluid losses while providing dextrose to prevent hypoglycemia and less sodium to avoid fluid overload. 1

Low-Intake Dehydration in Older Adults

• For older adults with measured serum osmolality >300 mOsm/kg who appear unwell or cannot drink, subcutaneous or intravenous hypotonic dextrose solutions (including half-normal saline with 5% glucose) are appropriate for treating low-intake dehydration. 1
• These hypotonic fluids help correct the fluid deficit while diluting down the raised osmolality characteristic of low-intake dehydration. 1

Specific Clinical Scenarios

• In cerebral malaria with volume depletion, D5 half normal saline is the IV fluid of choice because it provides dextrose to prevent hypoglycemia while minimizing sodium that could leak into pulmonary and cerebral tissues. 1
• Hypoglycemia is a complicating factor and risk factor for fatal outcome in cerebral malaria, making the dextrose component essential. 1

Critical Contraindications and Precautions

NOT for Initial Severe Dehydration

• Never use D5 half normal saline for initial rehydration of severe dehydration (≥10% fluid deficit) or shock—isotonic crystalloids (normal saline or lactated Ringer's) must be used first. 1
• Isotonic fluids should be administered as 20 mL/kg boluses until pulse, perfusion, and mental status normalize. 1

NOT for Volume Depletion

• Volume depletion (from blood loss, vomiting, diarrhea with electrolyte losses) requires isotonic fluids, not hypotonic solutions like D5 half normal saline. 1
• Isotonic fluids should be given orally, nasogastrically, subcutaneously, or intravenously depending on severity. 1

Ileus is an Absolute Contraindication to Oral Intake

• When ileus is present, isotonic IV fluids (lactated Ringer's or normal saline) must be used; oral rehydration and maintenance oral fluids are contraindicated. 2
• Continue IV rehydration until there is no evidence of ileus and bowel function returns. 2

Important Clinical Considerations

Risk of Hyperglycemia

• Even modest volumes (500 mL) of dextrose-containing solutions can cause significant transient hyperglycemia, with 72% of patients exceeding 10 mmol/L glucose after infusion. 3
• This is particularly relevant in non-diabetic patients undergoing elective procedures, though the effect is transient. 3

Preventing Hypoglycemia

• The dextrose component (typically 25-50 gm/L or 139-278 mmol/L) prevents hypoglycemia during rehydration without producing osmotic diuresis. 4
• Hypoglycemia risk is highest in patients with prolonged fasting, severe illness, or cerebral malaria. 1, 4

Fluid Overload Risk

• Exercise caution with fluid administration as overload can precipitate pulmonary edema or ARDS, which can worsen cerebral edema. 1
• The lower sodium content (0.45% vs 0.9%) helps minimize this risk compared to normal saline. 1

Subcutaneous Administration Option

• In older adults, subcutaneous administration of hypotonic dextrose solutions (including half-normal saline with 5% glucose) is effective with similar adverse effect rates to IV infusion. 1
• Approximately 3 L can be given in 24 hours at two separate sites, with mild subcutaneous edema being the most common adverse effect. 5

Monitoring Requirements

Electrolyte Monitoring

• Monitor serum sodium, potassium, chloride, and glucose levels, particularly when administering hypotonic solutions to avoid hyponatremia or electrolyte imbalances. 1, 4
• Adjust electrolytes and add potassium chloride (typically 20 mEq/L) based on chemistry values. 1

Hydration Status Assessment

• Reassess hydration status regularly using serum osmolality (target <300 mOsm/kg) until corrected, then monitor periodically. 1
• Clinical signs alone are insufficient; laboratory confirmation is essential. 1