What is Oral Rehydration Solution (ORS) for a child with diarrhea?

What is Oral Rehydration Solution (ORS)?

ORS is a precisely formulated electrolyte-glucose solution designed to treat and prevent dehydration in children with diarrhea by exploiting sodium-glucose cotransport in the intestine, allowing effective rehydration by mouth even when a child is vomiting. 1, 2

Core Composition

ORS contains four essential components that work together to restore fluid balance 3, 4:

• Sodium chloride (3.5 g/L): Replaces sodium lost in diarrheal stool 3
• Potassium chloride (1.5 g/L): Corrects potassium depletion 3
• Glucose (20 g/L or 111 mmol/L): Enables sodium-glucose cotransport for water absorption 3
• Trisodium citrate (2.9 g/L) or sodium bicarbonate (2.5 g/L): Corrects metabolic acidosis and aids sodium absorption 1

The WHO-recommended formulation has a total osmolarity of 311 mOsm/L, which is lower than previous formulations and reduces stool output while maintaining safety 3, 5.

How ORS Works

The scientific basis relies on the sodium-glucose cotransport mechanism in the small intestine 4. Even during diarrhea when the intestine is secreting fluid, glucose facilitates sodium absorption, and water follows passively 1. This allows effective rehydration by mouth without intravenous fluids in most cases 1.

Sodium Concentration: Clinical Context Matters

The American Academy of Pediatrics recommends different sodium concentrations depending on whether you are actively rehydrating a dehydrated child versus maintaining hydration 1:

For Active Rehydration (Moderate-to-Severe Dehydration):

• Use 75-90 mEq/L sodium, especially when purging rates exceed 10 mL/kg/hour 1, 3
• This higher concentration matches the sodium losses in severe secretory diarrhea 1

For Maintenance Therapy (After Rehydration):

• Use 40-60 mEq/L sodium to prevent sodium overload 1
• These lower concentrations approximate stool-sodium losses in typical viral diarrhea 1

Commercially Available Products in the United States

The most widely used solutions are Pedialyte (45 mEq/L sodium) and Ricelyte (50 mEq/L sodium) 1. These products are designed primarily for maintenance therapy and prevention of dehydration 1. While they can be used for rehydration in mild cases, they are suboptimal for moderate-to-severe dehydration where higher sodium concentrations (75-90 mEq/L) are preferable 1, 3.

Critical Caveat:

When using higher-sodium solutions (>60 mEq/L) for maintenance, you must also provide low-sodium fluids like breast milk, formula, or water to prevent sodium overload 1.

Clinical Effectiveness

ORS has proven 90-98% effective for treating dehydration in children, even those with concurrent vomiting 1, 6. The key to success with vomiting children is administering small volumes (5 mL) every 1-2 minutes using a spoon or syringe, gradually increasing as tolerated 2, 6. This approach prevents overwhelming the stomach and triggering more vomiting 6.

Dosing Algorithm

For Mild Dehydration (3-5% fluid deficit):

• Administer 50 mL/kg over 2-4 hours 2, 3

For Moderate Dehydration (6-9% fluid deficit):

• Administer 100 mL/kg over 2-4 hours 2, 3

For Severe Dehydration (≥10% deficit or shock):

• Begin with IV rehydration (20 mL/kg boluses) until vital signs normalize, then transition to ORS 2, 3

Replacing Ongoing Losses:

• Give 10 mL/kg for each watery stool 2, 3
• Give 2 mL/kg for each vomiting episode 2, 3

Alternative Formulations

Rice-based ORS contains cooked rice powder instead of glucose, providing complex carbohydrates that are slowly digested without creating excessive osmotic load 1. Some studies show rice-based solutions reduce stool output in the first 6 hours compared to glucose-based ORS, though the overall duration of diarrhea remains similar 1. Ricelyte (a commercial product with rice-syrup solids) differs from true rice-based ORS by containing only small glucose polymers rather than whole rice 1.

Common Pitfalls to Avoid

• Never allow a thirsty child to drink large volumes of ORS rapidly from a cup or bottle—this worsens vomiting 6
• Do not use inappropriate fluids like apple juice, sports drinks, or soft drinks for rehydration—these lack appropriate sodium and can worsen dehydration 6
• Do not withhold food during or after rehydration—early feeding reduces severity and duration of diarrhea 1, 6
• Do not dilute formula after rehydration—full-strength formula should be resumed immediately 2, 6

When ORS is Inappropriate

ORS should not be used in 6, 3:

• Severe dehydration with shock (requires immediate IV fluids)
• Intestinal ileus (absent bowel sounds)
• Intractable vomiting despite small-volume administration
• Altered mental status preventing safe oral intake