What is the correct composition for preparing an Oral Rehydration Solution (ORS)?

Oral Rehydration Solution (ORS) Preparation

Standard WHO-Recommended Formulation

The correct composition for preparing ORS is: 3.5 g sodium chloride, 2.9 g trisodium citrate (or 2.5 g sodium bicarbonate), 1.5 g potassium chloride, and 20 g glucose (or 40 g sucrose/sugar, or 50-60 g cooked cereal flour) per liter of clean water. 1, 2

This creates a solution with the following electrolyte concentrations 1, 3:

• Sodium: 90 mEq/L (mmol/L)
• Potassium: 20 mEq/L
• Chloride: 80 mEq/L
• Bicarbonate/Citrate: 30 mEq/L
• Glucose: 111 mmol/L
• Total osmolarity: 311 mOsm/L

Simplified Home Preparation Method

For home preparation when pre-packaged ORS is unavailable 1:

• Mix 4 tablespoons of sugar (or equivalent cooked cereal) with half a level teaspoon of salt in 1 liter of clean water 1, 4
• This approximates the WHO formulation, though potassium and citrate are absent 4

Clinical Context Matters: Sodium Concentration Selection

For Active Rehydration (Moderate-to-Severe Dehydration)

Use solutions containing 75-90 mEq/L sodium 1, 5, 3, 6:

• This higher sodium concentration is essential when purging rates exceed 10 mL/kg/hour 1, 5
• Particularly critical for cholera and severe secretory diarrhea 3
• The standard WHO formulation (90 mEq/L) is optimal for rehydration 3

For Maintenance Therapy (After Rehydration Complete)

Use solutions containing 40-60 mEq/L sodium 1, 5, 6:

• Prevents sodium overload during maintenance phase 5, 6
• Commercial products like Pedialyte (45 mEq/L) and Ricelyte (50 mEq/L) are appropriate here 5, 6
• When using higher sodium solutions (>60 mEq/L) for maintenance, provide additional low-sodium fluids 1, 6

Commercial vs. Homemade Solutions

Pre-Packaged Commercial ORS

Most U.S. commercial products contain lower sodium (45-50 mEq/L) than WHO recommendations 5, 6:

• Designed primarily for maintenance and mild dehydration 5
• Can be used for rehydration when the alternative is IV fluids or inappropriate beverages 1
• Offer convenience, sterility, and accurate dosing 5

When Commercial Products Are Suboptimal

For moderate-to-severe dehydration with high stool output, commercial low-sodium products are inadequate 5, 6:

• Pharmacy-prepared WHO-ORS (90 mEq/L sodium) is preferable 1, 3
• If unavailable, use commercial products but monitor closely for inadequate response 1

Critical Formulation Details

Glucose Source Options

The carbohydrate component can be 1, 2:

• 20 g glucose (preferred) 2
• 40 g sucrose (table sugar) 1
• 50-60 g cooked cereal flour (rice, maize, wheat, potato) 1

Base Component

Trisodium citrate (2.9 g) is now preferred over sodium bicarbonate (2.5 g) 3, 2:

• Provides longer shelf life 3
• Equivalent efficacy for sodium-water absorption 3

Common Pitfalls to Avoid

Inappropriate Beverages

Never use these for rehydration 5:

• Apple juice, Gatorade, soft drinks (inappropriate electrolyte content) 5
• Sports drinks lack adequate sodium for diarrheal rehydration 7
• Chicken broth has excessive sodium without glucose cotransport 7

Preparation Errors

Measurement accuracy is critical 8, 4:

• Use level teaspoons, not heaped measures 8
• Half a level teaspoon of salt per liter is the safe home preparation standard 4
• Excessive salt can cause dangerous hypernatremia 1, 4
• Too little salt results in inadequate rehydration 4

Clinical Misapplication

Match the sodium concentration to the clinical scenario 5, 6:

• Using low-sodium maintenance solutions for severe dehydration is inadequate 5
• Using high-sodium rehydration solutions long-term without additional water causes sodium overload 1, 6

Dosing Guidelines

Rehydration Phase

For mild dehydration (3%-5% deficit): 50 mL/kg over 2-4 hours 1

For moderate dehydration (6%-9% deficit): 100 mL/kg over 2-4 hours 1

Ongoing Loss Replacement

Give 10 mL/kg for each watery stool and 2 mL/kg for each vomiting episode 1

Severe Dehydration

Requires immediate IV rehydration with 20 mL/kg boluses until stabilized, then switch to oral 1, 5