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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Acute gastroenteritis and oral rehydration

Paediatrics and child health · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Shock or surgical vomiting

Reduced consciousness, weak pulses, prolonged capillary refill, hypotension, severe tachycardia, mottling, anuria or bilious vomiting is not suitable for routine home oral rehydration.

Action: Use ABCDE, check glucose, obtain urgent paediatric help and give intravenous isotonic crystalloid in weight-based boluses for shock while investigating sepsis, obstruction or another critical cause.

Overview

Recognise dehydration and serious alternatives in a vomiting or diarrhoeal child, then restore fluid safely with age-appropriate oral rehydration while limiting unnecessary tests, antibiotics and dietary restriction.

Establish onset, stool frequency and character, vomiting colour and force, oral intake, urine, fever, pain, travel, water, food and affected contacts. Record age, birth weight, breastfeeding, comorbidity, immunisation and recent antibiotics. Weigh the child where possible and compare with a recent reliable weight. A young infant can have substantial proportional loss before hypotension appears, so behaviour, perfusion and urine matter.

Classify as no clinical dehydration, clinical dehydration or shock using the whole pattern. A child with clinical dehydration may appear unwell or irritable, have sunken eyes, dry mucosa, tachycardia, tachypnoea, reduced urine and altered skin elasticity. Shock adds depressed consciousness, weak pulses, prolonged capillary refill, cold extremities and hypotension. Hypernatraemic dehydration may preserve skin turgor and produce jitteriness or increased tone; rehydration needs expert monitoring.

Practice

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Paediatrics and child healthOriginal SBA

Oral deficit replacement

A 10 kg toddler with gastroenteritis has clinical dehydration but no shock and can tolerate small sips. What initial rehydration regimen does NICE recommend?

Choose one answer, then submit
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Sources and review status3 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE CG84 Gastroenteritis RecommendationsDehydration risk, ORS regimen, feeding, stool testing and antibiotic indications.
  • NICE NG29 Intravenous Fluids in ChildrenWeight-based paediatric fluid resuscitation and monitoring.
  • UKHSA Managing Specific Infectious DiseasesExclusion, outbreak and infection-control advice for diarrhoea and vomiting.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Use low-osmolarity ORS mixed exactly as directed. For clinical dehydration, NICE recommends 50 ml/kg over four hours plus maintenance, using small frequent volumes and continuing breastfeeds. Replace ongoing large watery stool losses in higher-risk children. If oral intake repeatedly fails but the gut is usable, nasogastric ORS can avoid intravenous therapy. Use IV fluid for shock, deterioration despite oral therapy or persistent inability to tolerate oral or nasogastric replacement.

Once rehydrated, resume usual full-strength milk, feeds and solid food. Water or milk may supplement ORS in a child without red-flag deterioration, but juice and carbonated drinks can worsen osmotic diarrhoea. Do not dilute formula or impose a prolonged BRAT-style diet. Paracetamol may improve comfort when appropriate, but nephrotoxic NSAIDs are unsafe during dehydration and symptom relief must not obscure worsening perfusion or abdominal signs.

Stool microbiology is indicated when blood or mucus is present, the child is immunocompromised, there has been recent foreign travel, diarrhoea has not improved by day seven, diagnosis is uncertain or public-health investigation is needed. Antibiotics are not routine and can harm in some infections; use only for defined pathogens, septicaemia or extra-intestinal spread with microbiology or infectious-disease advice. Give handwashing, nappy handling, food preparation and return guidance.

Key points

  • Assess hydration from appearance, responsiveness, urine, eyes, mucosa, heart rate, breathing, pulses, capillary refill, skin and peripheral temperature; no single sign is sufficient.
  • First-line treatment for clinical dehydration without shock is low-osmolarity ORS: give 50 ml/kg over 4 hours in addition to maintenance, frequently in small amounts.
  • Continue breastfeeding throughout; if vomiting persists, try 5 ml ORS every 1 to 2 minutes and consider nasogastric delivery before intravenous fluid when safe.
  • During rehydration, consider 5 ml/kg ORS after each large watery stool for children at increased risk of recurrent dehydration.
  • Shock needs urgent isotonic intravenous fluid under a paediatric resuscitation protocol; reassess after every bolus and reconsider sepsis or haemorrhage if response is poor.
  • After rehydration, restart full-strength milk and usual age-appropriate food; avoid fruit juice and fizzy drinks until diarrhoea has stopped.
  • Do not routinely use antibiotics, antidiarrhoeal medicines, probiotics or routine stool tests; select treatment and testing from pathogen risk and severity.
  • Give families explicit return advice and infection-control guidance, including exclusion from school or childcare until at least 48 hours after the last diarrhoea or vomiting episode.

Aetiology

01

Viral infection

Rotavirus, norovirus, adenovirus and other enteric viruses cause most childhood episodes, spreading efficiently through hands, surfaces, food and close household contact.

02

Bacterial enteritis

Campylobacter, Salmonella, Shigella, pathogenic Escherichia coli and toxin-mediated foodborne disease are more likely with blood, travel, outbreaks or systemic toxicity.

03

Protozoal infection

Giardia and Cryptosporidium can produce longer diarrhoeal illness, especially after travel, unsafe water, nursery outbreaks or in an immunocompromised child.

04

Non-infectious mimic

Urinary infection, sepsis, appendicitis, intussusception, diabetic ketoacidosis, raised intracranial pressure and inborn metabolic disease may initially present with vomiting.

Pathophysiology

  1. 1
    Secretory and osmotic loss

    Enterocyte injury, toxins and unabsorbed solute drive water and electrolyte into bowel, while vomiting further removes chloride, sodium and potassium.

  2. 2
    Small circulating reserve

    Infants have high water turnover and limited renal concentrating ability, so a similar proportional loss produces faster physiological compromise than in older children.

  3. 3
    Sodium glucose cotransport

    Intestinal sodium-glucose transport remains functional during most enteritis, allowing correctly mixed low-osmolarity oral rehydration solution to pull sodium and water into circulation.

  4. 4
    Starvation and ketosis

    Reduced carbohydrate intake rapidly produces ketosis in young children, worsening nausea and lethargy even before severe intravascular depletion develops.

Clinical features and red flags

No clinical dehydration

The child is alert, drinks, passes urine and has normal eyes, mucosa, pulses and peripheral perfusion despite gastrointestinal symptoms.

Clinical dehydration

Reduced urine, altered appearance, sunken eyes, dry mucosa, tachycardia and decreased skin elasticity combine without shock features.

Shock physiology

Reduced consciousness, weak pulses, prolonged refill, cold mottled skin and hypotension signal critically impaired circulation.

Hypernatraemic pattern

Doughy skin, irritability, jitteriness or increased tone can accompany high sodium and deceptively preserved intravascular signs.

Dysenteric illness

Visible blood and mucus with fever or abdominal pain increases likelihood of invasive bacterial disease and need for stool investigation.

Red flags requiring action

  • Bilious green vomit, abdominal distension, focal guarding or bloody stool with severe pain suggests obstruction, volvulus, intussusception or surgical inflammation.
  • Lethargy, altered responsiveness, sunken eyes, weak pulses, prolonged capillary refill, cold mottled limbs or reduced urine indicates important dehydration or shock.
  • Infants under 6 months, low-birth-weight children and those with malnutrition, immunodeficiency or major comorbidity can deteriorate quickly.

Investigations

  1. 01
    First-line clinical hydration assessmentFirst stepFirst line
    Why
    Classify severity and choose home, oral, nasogastric or intravenous management.
    Interpretation and limitations
    Use serial whole-child findings and response; isolated capillary refill or skin turgor cannot determine deficit accurately.
  2. 02
    Bedside glucose
    Why
    Detect hypoglycaemia or hyperglycaemic metabolic illness in a lethargic, young or significantly dehydrated child.
    Interpretation and limitations
    Treat low glucose immediately and investigate diabetic ketoacidosis when hyperglycaemia, ketones and acidosis fit.
  3. 03
    Electrolytes, urea, creatinine and acid base
    Why
    Guide intravenous therapy in shock, severe dehydration or suspected hypernatraemia and detect renal injury.
    Interpretation and limitations
    Routine blood tests are unnecessary in a stable orally rehydrating child; abnormal sodium requires controlled specialist correction.
  4. 04
    Stool microbiology when indicated
    Why
    Identify bacterial or protozoal pathogens when blood, travel, immune compromise, prolonged illness or outbreak risk changes care.
    Interpretation and limitations
    Interpret PCR or culture with symptoms and public-health advice because carriage does not always prove causation.

Differential diagnosis

01

Surgical obstruction

Bilious vomiting, distension, focal tenderness or episodic severe pain requires urgent imaging and surgery rather than continued oral rehydration alone.

02

Sepsis or urinary infection

Fever, poor perfusion, respiratory change, irritability or urinary features can accompany vomiting with little diarrhoea, especially in infants.

03

Diabetic ketoacidosis

Polyuria, polydipsia, weight loss, deep breathing and hyperglycaemia distinguish metabolic dehydration requiring insulin and carefully controlled fluids.

04

Food allergy or inflammatory disease

Repeated blood or mucus, eczema, faltering growth, nocturnal stool and chronic symptoms make a brief self-limiting infection less likely.

Management

01No dehydrationSupport safe home intakeFirst stepThe child is clinically hydrated and has no surgical or systemic red flag.+
  1. 1Continue breast or usual milk feeds and offer ORS after losses in higher-risk children.
  2. 2Avoid juice and fizzy drinks and restart ordinary food as appetite permits.
  3. 3Provide infection-control and explicit urine, behaviour, vomiting and pain return criteria.
02Clinical dehydrationRehydrate through the gutClinical dehydration is present without shock.+
  1. 1Give low-osmolarity ORS 50 ml/kg over four hours plus maintenance in frequent small amounts.
  2. 2Continue breastfeeding and replace significant ongoing stool loss in high-risk children.
  3. 3Use nasogastric ORS if repeated vomiting prevents adequate oral delivery but there is no obstruction.

Complications

01

Hypovolaemic shock

Continued gastrointestinal loss reduces circulating volume, renal perfusion and tissue oxygen delivery, progressing to altered consciousness and cardiovascular collapse.

02

Electrolyte and glucose disturbance

Hypernatraemia, hyponatraemia, hypokalaemia, acidosis and hypoglycaemia may complicate severe loss or incorrectly mixed replacement fluids in children.

03

Acute kidney injury

Renal hypoperfusion and sepsis can reduce urine output and filtration, with risk increased by nephrotoxic medicines during dehydration.

04

Transmission and outbreak

Persistent viral shedding, inadequate hand hygiene and premature return to childcare can infect vulnerable household or nursery contacts.

Monitoring and follow-up

  • Reassess mental state, drinking, vomiting, urine, pulse quality, capillary refill and peripheral temperature during rehydration.
  • Measure weight and fluid input and output in hospital, recognising stool-volume estimates are imprecise.
  • Check sodium and glucose serially when hypernatraemia, shock or intravenous replacement is present.
  • Review after four hours of ORS and classify hydration again before discharge or further fluid.
  • Track diarrhoea duration, blood, fever and public-health features that would trigger stool testing.
  • Confirm caregivers can mix ORS, recognise red flags and obtain urgent help before leaving.

Special situations

Vomiting does not equal ORS failure

Tiny frequent volumes or nasogastric delivery can succeed even when a cup or bottle triggers vomiting.

Hypotension is late

Children compensate with tachycardia and vasoconstriction, so normal blood pressure cannot exclude important depletion.

ORS is precisely formulated

Homemade concentration errors can worsen sodium and osmotic disturbance; commercial sachets require exact dilution.

Feeding aids recovery

Early full-strength milk and ordinary food supports enterocyte repair and avoids unnecessary nutritional deficit.

Common pitfalls

  1. 01

    Missing bilious vomiting because the child also has diarrhoea.

  2. 02

    Using juice, fizzy drink or inaccurately mixed formula as the main rehydration fluid.

  3. 03

    Giving a large ORS volume quickly and declaring failure after vomiting.

  4. 04

    Prescribing antibiotics for uncomplicated watery gastroenteritis.

  5. 05

    Using ibuprofen during dehydration or kidney hypoperfusion.

  6. 06

    Discharging without urine, behaviour and return-to-childcare advice.

  • More than five diarrhoeal stools or more than two vomits in 24 hours, inability to keep fluids down or stopping breastfeeding increases dehydration risk.
  • Non-blanching rash, neck stiffness, bulging fontanelle, respiratory distress or toxic appearance suggests sepsis or another systemic diagnosis.
  • Blood or mucus in stool, recent foreign travel, persistent diarrhoea beyond day 7 or diagnostic uncertainty supports microbiological investigation.
    • 4
    Reassess regularly and move to IV therapy for deterioration or failed enteral rehydration.
    03ShockRestore circulation and diagnose causeShock features or rapid deterioration develops.+
    1. 1Use ABCDE, check glucose, gain IV or intraosseous access and summon senior paediatric help.
    2. 2Give isotonic crystalloid boluses under the current paediatric resuscitation protocol with reassessment after each.
    3. 3Investigate sepsis, surgical disease and metabolic causes and monitor urine and electrolytes.
    4. 4Transition to controlled deficit and maintenance replacement once perfusion is restored.
    Key medicines and prescribing safety1 treatment · regimens, roles and cautions+
    Replaces water, sodium and glucose through preserved intestinal cotransport and is preferred before intravenous fluid when there is no shock or obstruction.

    Low-osmolarity oral rehydration solution

    For a child with clinical dehydration, give 50 ml/kg enterally over 4 hours in addition to maintenance, frequently in small amounts; consider 5 ml/kg after each large watery stool in higher-risk children.

    Mix with the exact stated water volume and do not add sugar or salt; use specialist monitoring for hypernatraemia and stop enteral therapy if bilious vomiting or obstruction is suspected.