Why is D5 (Dextrose 5%) 0.45% NaCl (Sodium Chloride) recommended for a patient with moderate dehydration?

Why D5 0.45% NaCl for Moderate Dehydration?

D5 0.45% NaCl should NOT be routinely used for moderate dehydration in most clinical scenarios—oral rehydration solution (ORS) is first-line for moderate dehydration, and when IV therapy is required, isotonic fluids (0.9% NaCl or lactated Ringer's) are preferred to avoid hyponatremia and provide adequate sodium replacement. 1

First-Line Treatment: Oral Rehydration

• Reduced osmolarity ORS is the recommended first-line therapy for mild to moderate dehydration in infants, children, and adults with acute diarrhea from any cause 1
• ORS should be administered at 50-100 mL/kg over 2-4 hours for moderate dehydration 2, 3
• Nasogastric administration at 15 mL/kg/hour may be considered if the patient cannot tolerate oral intake but is not in shock 1, 2

When IV Therapy Is Necessary

Isotonic intravenous fluids (lactated Ringer's or 0.9% normal saline) should be administered when there is severe dehydration, shock, altered mental status, or failure of ORS therapy 1

Why Isotonic Fluids Are Preferred

• Recent evidence demonstrates significant risk of hyponatremia with hypotonic fluids (0.45% NaCl) at 12 and 24 hours compared to isotonic solutions 4
• Multiple randomized controlled trials show that 0.9% saline maintains serum sodium levels more effectively than 0.45% saline, with mean sodium levels of 138.3 mEq/L versus 135.1 mEq/L at 24 hours 5
• The incidence of mild and moderate hyponatremia is significantly higher with 0.45% saline at both 12 hours (P < 0.001) and 24 hours (P < 0.001) 4

The Problem With D5 0.45% NaCl

Insufficient Sodium Content

• Hypotonic solutions like 0.45% NaCl contain only 77 mEq/L of sodium, which is inadequate for replacing losses in most diarrheal illnesses where stool sodium losses are substantial 6
• Standard ORS contains 50-90 mEq/L sodium, making 0.45% saline only marginally better than oral solutions while carrying IV risks 1

Special Contraindication in Hypernatremic Dehydration

• In hypernatremic dehydration (common with severe diarrhea), salt-containing solutions like 0.45% NaCl should be avoided because their tonicity (~154 mOsm/kg for the NaCl component) can worsen hypernatremia 1
• For hypernatremic states, 5% dextrose alone (without saline) is recommended to provide free water without additional osmotic load 1, 7

Appropriate Clinical Algorithm

Step 1: Assess Dehydration Severity

• Mild dehydration (3-5% deficit): ORS at 50 mL/kg over 2-4 hours 2
• Moderate dehydration (6-9% deficit): ORS at 100 mL/kg over 2-4 hours 2
• Severe dehydration (≥10% deficit): IV isotonic fluids immediately 1, 2

Step 2: Choose Appropriate IV Fluid When Needed

• For isonatremic or hyponatremic dehydration: 0.9% NaCl or lactated Ringer's at 20 mL/kg boluses 1, 3, 6
• For hypernatremic dehydration: 5% dextrose alone (D5W) to avoid additional sodium load 1, 7
• Add potassium (20-40 mEq/L) once urine output is established 7, 3

Step 3: Replace Ongoing Losses

• 10 mL/kg of ORS for each diarrheal stool and 2 mL/kg for each vomiting episode 2
• For hypernatremic patients, replace ongoing losses with isotonic fluids (0.9% NaCl) at 10 mL/kg per stool 7

Critical Pitfalls to Avoid

• Do not use hypotonic fluids (0.45% NaCl) as routine maintenance in hospitalized children due to hyponatremia risk 5, 4
• Do not use 0.9% NaCl in hypernatremic dehydration as it provides excessive osmotic load requiring 3 liters of urine to excrete the solute from 1 liter of fluid 1
• Do not delay ORS in favor of IV therapy for moderate dehydration—ORS is equally effective and safer 1, 8
• Reassess hydration status after 2-4 hours and adjust therapy accordingly; if dehydration persists, reestimate deficit and restart 1, 2

The Limited Role of D5 0.45% NaCl

The combination of D5 0.45% NaCl may have been used historically based on older maintenance fluid calculations, but current evidence supports isotonic fluids for safety and efficacy 6, 4. If D5 0.45% NaCl is being considered, it should only be after successful rehydration with isotonic fluids and transition to maintenance therapy in carefully selected patients without ongoing significant losses 9.