What is the initial management for a patient presenting with vomiting and dehydration?

Initial Management of Vomiting with Dehydration

Oral rehydration solution (ORS) is the first-line treatment for mild to moderate dehydration from vomiting, with intravenous fluids reserved only for severe dehydration, shock, altered mental status, or failure of oral rehydration. 1

Assess Dehydration Severity

Mild to Moderate Dehydration:

• Signs include decreased skin turgor, dry mucous membranes, decreased urine output, but normal mental status and adequate perfusion 1
• This represents the vast majority of patients presenting with vomiting and dehydration 2

Severe Dehydration:

• Altered mental status, shock, poor perfusion, weak or absent pulse 1
• Requires immediate intravenous intervention 1

Treatment Algorithm

For Mild to Moderate Dehydration (First-Line)

Administer reduced osmolarity ORS (osmolarity <250 mmol/L):

• Infants and children: 50-100 mL/kg over 3-4 hours 1
• Adolescents and adults (≥30 kg): 2-4 liters over 3-4 hours 1
• Commercial formulations include Pedialyte, CeraLyte, and Enfalac Lytren 1
• Do not use apple juice, Gatorade, or soft drinks—these have inappropriate osmolality 1

If patient cannot tolerate oral intake despite vomiting:

• Consider nasogastric administration of ORS at 15 mL/kg/hour in patients with normal mental status who are too weak or refuse to drink 1
• This approach avoids unnecessary IV placement in most cases 2

Reassess after 3-4 hours:

• If still dehydrated, continue ORS 1
• If rehydrated, transition to maintenance therapy 1

For Severe Dehydration (IV Fluids Required)

Immediate intravenous resuscitation is indicated when:

• Severe dehydration with shock or altered mental status is present 1
• ORS therapy has failed 1, 2
• Ileus is present 1
• Ketonemia prevents oral tolerance 1

IV fluid regimen:

• Use isotonic crystalloids: lactated Ringer's or normal saline 1
• Administer boluses of up to 20 mL/kg until pulse, perfusion, and mental status normalize 1
• Exception: Malnourished infants benefit from smaller 10 mL/kg boluses due to reduced cardiac reserve 1

Transition strategy:

• Continue IV fluids until pulse, perfusion, and mental status normalize, patient is awake, has no aspiration risk, and no ileus 1
• Switch to ORS for remaining deficit replacement once patient can tolerate oral intake 1, 2

Maintenance and Ongoing Loss Replacement

After rehydration is complete:

• Infants <10 kg: 60-120 mL ORS per diarrheal stool or vomiting episode (up to ~500 mL/day) 1
• Children >10 kg: 120-240 mL ORS per episode (up to ~1 L/day) 1
• Adolescents and adults: Ad libitum ORS up to ~2 L/day 1
• Continue until vomiting and diarrhea resolve 1

Feeding During Treatment

Resume feeding immediately:

• Continue breastfeeding throughout the illness in infants 1
• Resume age-appropriate normal diet during or immediately after rehydration 1
• Do not dilute formula or delay feeding—there is no benefit to "resting the bowel" 1

Adjunctive Therapy

Antiemetics (ondansetron):

• May facilitate oral rehydration tolerance in children >4 years and adolescents with vomiting 1
• Use only after adequate hydration is initiated, not as substitute for fluid therapy 1

Antimicrobial therapy:

• Not recommended for routine watery diarrhea with vomiting 1
• Exception: immunocompromised patients or ill-appearing young infants may warrant empiric treatment 1

Critical Pitfall to Avoid

The most common error is automatic use of IV fluids for moderate dehydration. 2 This represents overtreatment when ORS is effective in approximately 96% of cases, with only 4% requiring IV therapy due to ORS failure 1. Starting with ORS avoids unnecessary IV placement, reduces phlebitis risk, and is equally effective for rehydration 1, 2.