How do you start oral rehydration in a patient with mild to moderate dehydration?

How to Start Oral Rehydration

For patients with mild to moderate dehydration, begin with reduced osmolarity oral rehydration solution (ORS) containing 50-90 mEq/L sodium as first-line therapy, administering 50 mL/kg over 2-4 hours for mild dehydration (3-5% deficit) or 100 mL/kg over 2-4 hours for moderate dehydration (6-9% deficit). 1, 2

Initial Assessment

Before starting ORS, rapidly assess dehydration severity using clinical signs:

• Capillary refill time is the most reliable predictor of dehydration 2
• Examine skin turgor, mucous membranes, mental status, and pulse to categorize severity 1, 2
• Obtain baseline weight to calculate fluid deficit 2
• Classify as:
  • Mild: 3-5% fluid deficit 2
  • Moderate: 6-9% fluid deficit 2
  • Severe: ≥10% fluid deficit with shock signs 2

Starting ORS by Dehydration Severity

Mild Dehydration (3-5% deficit)

• Administer 50 mL/kg of reduced osmolarity ORS over 2-4 hours 1, 2
• Give small, frequent volumes to improve tolerance 2

Moderate Dehydration (6-9% deficit)

• Administer 100 mL/kg of reduced osmolarity ORS over 2-4 hours 1, 2
• If oral intake fails, consider nasogastric administration rather than immediately switching to IV 1, 2

Severe Dehydration (≥10% deficit)

• Do NOT start with ORS - this is a medical emergency 1, 2
• Immediately administer 20 mL/kg boluses of lactated Ringer's or normal saline IV until pulse, perfusion, and mental status normalize 1, 2
• Transition to ORS only after circulation is restored to replace remaining deficit 1

ORS Formulation Specifics

The reduced osmolarity formulation is superior to standard WHO-ORS:

• Use ORS with total osmolarity <250 mmol/L (not the older 311 mmol/L formulation) 1
• Reduced osmolarity ORS decreases unscheduled IV therapy need by 33% compared to standard ORS 3, 4
• Acceptable commercial products include Pedialyte, CeraLyte, and Enfalac Lytren 1
• Do NOT use apple juice, Gatorade, soft drinks, or sports drinks - these have inadequate sodium and excessive osmolality 1, 2

Ongoing Loss Replacement

Once initial rehydration begins:

• Replace each watery stool with 10 mL/kg of ORS 2, 5
• Replace each vomiting episode with 2 mL/kg of ORS 2, 5
• Continue until diarrhea and vomiting resolve 1

Concurrent Feeding

Do not delay feeding - this is a critical pitfall to avoid:

• Continue breastfeeding throughout the entire episode without interruption 1, 2
• Resume age-appropriate normal diet during or immediately after rehydration 1, 2
• There is no justification for "bowel rest" 2
• For formula-fed infants, use full-strength lactose-containing formula in most cases 1

Monitoring Response

• Reassess hydration status after 2-4 hours of ORS therapy 2, 5
• Monitor for normalization of skin turgor, mucous membranes, mental status, and urine output 5, 6
• If rehydration fails despite adequate trial, switch to IV therapy 1, 2

Critical Contraindications

• Never give antimotility drugs (loperamide) to children <18 years - risk of respiratory depression and cardiac adverse reactions 2, 6
• Avoid loperamide in any patient with fever or bloody diarrhea regardless of age 1, 6

Special Considerations

• In patients with ketonemia, initial IV hydration may be needed before ORS tolerance is possible 1
• Ondansetron may facilitate ORS tolerance in children >4 years with significant vomiting 1
• Hyponatremia risk is not increased with reduced osmolarity ORS compared to standard formulations 3, 4