What fluid type and volume should be administered for a patient with vomiting and diarrhea?

Fluid Management for Vomiting and Diarrhea

Use reduced osmolarity oral rehydration solution (ORS) as first-line therapy for mild to moderate dehydration, administering 50-100 mL/kg over 2-4 hours depending on dehydration severity, and reserve isotonic intravenous fluids (lactated Ringer's or normal saline) only for severe dehydration, shock, altered mental status, or ORS failure. 1, 2, 3

Initial Assessment and Fluid Type Selection

Oral Rehydration Solution (ORS) is superior to IV fluids for patients who can tolerate oral intake—it is safer, less painful, less costly, and equally effective. 3 The key decision point is dehydration severity:

Mild to Moderate Dehydration (3-9% fluid deficit):

• Use reduced osmolarity ORS (total osmolarity <250 mmol/L) such as Pedialyte, CeraLyte, or Enfalac Lytren 1, 4, 2
• Never use apple juice, Gatorade, or soft drinks 4
• The WHO-recommended formulation contains approximately Na 90 mM, K 20 mM, Cl 80 mM, HCO₃ 30 mM, and glucose 111 mM 3

Severe Dehydration or ORS Failure:

• Switch immediately to isotonic IV fluids (lactated Ringer's or normal saline) 1, 3
• IV therapy is mandatory for: severe dehydration, shock, altered mental status, ileus, or inability to tolerate oral intake 1, 3

Volume Administration Protocol

For Children:

Rehydration Phase:

• Mild dehydration (3-5% deficit): 50 mL/kg ORS over 2-4 hours 2
• Moderate dehydration (6-9% deficit): 100 mL/kg ORS over 2-4 hours 2, 3

Replacement of Ongoing Losses:

• For each watery stool: 10 mL/kg ORS (or 120-240 mL for children >10 kg) 4, 2
• For each vomiting episode: 2 mL/kg ORS 4, 2
• Maximum daily ORS: approximately 1 L/day 4

ORS Tolerance Test: Children who tolerate at least 25 mL/kg of ORS in the emergency department are likely to succeed with home oral rehydration, while those tolerating <11 mL/kg are at higher risk of failure and may need admission. 5

For Adults:

• Administer approximately 100 mL/kg ORS over 2-4 hours for moderate dehydration 3
• Replace ongoing losses with ORS until diarrhea and vomiting resolve 1, 3

Transition Strategy from IV to Oral

If IV fluids are initiated for severe dehydration:

• Continue IV rehydration until pulse, perfusion, and mental status normalize 1, 3
• Transition to ORS as soon as the patient stabilizes to replace the remaining fluid deficit 1, 3
• In patients with ketonemia, an initial IV bolus may be needed before oral rehydration can be tolerated 1, 3

Alternative Route: Nasogastric ORS

Nasogastric administration of ORS may be considered in patients with moderate dehydration who cannot tolerate oral intake, or in children with normal mental status who are too weak or refuse to drink adequately. 1, 3, 6

Maintenance Phase

Once rehydration is achieved:

• Continue ORS to replace ongoing losses until symptoms resolve 1, 3
• Resume age-appropriate normal diet immediately during or right after rehydration—do not withhold food 1, 4, 2, 3
• Continue breastfeeding throughout the illness in infants 1, 2, 3
• Avoid foods high in simple sugars and high-fat foods, as these worsen diarrhea 4

Adjunctive Medications to Facilitate Oral Intake

Ondansetron may be administered to children >4 years and adolescents with vomiting to facilitate ORS tolerance. 1, 4, 3 This can be particularly helpful when vomiting is severe and interfering with oral rehydration. 4

Critical Pitfalls to Avoid

• Never give antimotility drugs (loperamide) to children <18 years with acute diarrhea 1, 2, 3
• Avoid loperamide in any patient with bloody diarrhea, fever, or suspected inflammatory diarrhea due to toxic megacolon risk 1, 3
• Do not use metoclopramide in gastroenteritis management 4
• Never use antimicrobials for STEC O157 or Shiga toxin 2-producing E. coli—they increase hemolytic uremic syndrome risk 1, 3

Reassessment Protocol

Reassess hydration status every 2-4 hours by evaluating skin turgor, mucous membrane moisture, mental status, capillary refill, urine output, and vital signs. 4, 3 Signs requiring return to IV therapy include: worsening dehydration despite ORS, persistent altered mental status, inability to tolerate oral intake, or signs of shock. 4