Pediatrics (System-Integrated)

Pediatric gastroenteritis: dehydration assessment and rehydration

Clinical Overview and When to Suspect Pediatric Gastroenteritis

— Leading cause of pediatric ED visits and outpatient morbidity in the US; ~1.5 million outpatient visits/year.

— Norovirus is now the #1 cause in US children post-rotavirus vaccine rollout (2006); rotavirus still important in unvaccinated.

— Bacterial (Salmonella, Campylobacter, Shigella, STEC, C. difficile) ~10–20%; parasitic (Giardia, Cryptosporidium) more chronic.

— Sudden onset vomiting → diarrhea sequence in a child with sick contacts, daycare exposure, or recent travel.

— Low-grade fever, no peritoneal signs, urine output preserved early.

— Bilious or bloody vomiting → obstruction, malrotation with volvulus, intussusception.

— Bloody diarrhea + pallor + oliguria → suspect STEC/HUS; avoid antibiotics and antimotility agents.

— Diarrhea >14 days → chronic causes (post-infectious, IBD, celiac, lactose intolerance, Giardia).

— Severe focal abdominal pain, rigid abdomen → appendicitis, surgical abdomen.

— Altered mental status, seizures → severe hyponatremia/hypernatremia, sepsis, DKA mimicking AGE.

Definition: Acute gastroenteritis (AGE) = diarrhea (≥3 loose stools/24h) ± vomiting, ± fever, ± abdominal pain, typically <14 days duration in a previously well child.

Epidemiology:

When to suspect AGE:

When NOT just AGE — red flags that should redirect workup:

Step 3 management: The pivotal early decision is dehydration severity assessment, because it drives route (PO vs IV), disposition (home vs ED vs admit), and fluid choice — not the etiologic workup, which is usually unnecessary in uncomplicated cases.

Board pearl: A toddler with "vomiting and diarrhea" who has isolated vomiting without diarrhea, especially with lethargy or abdominal distension, is not AGE until proven otherwise — think DKA, increased ICP, pyloric stenosis (infant), intussusception, or UTI/pyelonephritis. AGE almost always evolves to include diarrhea within 24 hours.

Presentation Patterns and Key History

— Day 1: abrupt vomiting + low-grade fever.

— Days 2–4: watery, non-bloody diarrhea predominates as vomiting subsides.

— Self-limited, typically 5–7 days total.

— Bloody/mucoid stools, high fever, tenesmus, severe cramping.

— Shigella → seizures (even without high fever, due to neurotoxin); Salmonella → recent reptile/poultry exposure; Campylobacter → undercooked poultry, raw milk; STEC O157:H7 → undercooked ground beef, petting zoo, → HUS risk 5–10 days post-onset.

— Giardia: prolonged greasy, foul-smelling diarrhea, bloating, weight loss; daycare, well water, camping.

— Cryptosporidium: pool/waterpark outbreaks; severe/prolonged in immunocompromised.

— Intake/output diary: number of vomits, stool volume/frequency, last wet diaper or void (>8 hours dry = concerning).

— Weight: pre-illness vs current — gold standard for quantifying dehydration (% loss).

— Oral intake tolerated (sips, ORS).

— Tears, mental status, activity level reported by caregiver.

— Sick contacts, daycare, recent travel, antibiotic exposure (C. difficile), well water, animal contact.

— Immunization status (rotavirus, MMR for measles enteritis).

— Underlying conditions: prematurity, short gut, immunodeficiency, metabolic disorders, age <6 months.

— Projectile non-bilious vomiting in 3–6 week-old infant → pyloric stenosis.

— Bilious vomiting at any age → surgical emergency (malrotation/volvulus until ruled out).

Classic viral AGE pattern:

Bacterial clues (dysentery pattern):

Parasitic clues:

Key history points to elicit:

Vomiting timing pearl:

Key distinction: Diarrhea-predominant illness with mild vomiting suggests true AGE; vomiting-predominant illness with minimal/no diarrhea should broaden differential to include CNS, metabolic, surgical, and urologic causes.

Board pearl: Always quantify time since last urination — this single data point correlates best with caregiver-reported dehydration severity and helps triage phone calls.

Physical Exam Findings and Hemodynamic Assessment

— Minimal/none (<3%): normal exam, alert, moist mucosa, brisk cap refill, normal HR/BP, tears present, normal urine output.

— Mild–moderate (3–9%): restless/irritable, slightly sunken eyes, dry mucosa, decreased tears, cap refill 2–3 sec, mild tachycardia, decreased urine output, skin turgor slightly decreased.

— Severe (≥10%): lethargic/obtunded, deeply sunken eyes and fontanelle, parched mucosa, no tears, cap refill >3 sec, tachycardia, weak/thready pulses, cool mottled extremities, hypotension (late, ominous), anuria.

— Prolonged capillary refill >2 sec, abnormal skin turgor, and abnormal respiratory pattern (deep/tachypneic from metabolic acidosis) are the three most predictive findings.

— Sunken fontanelle helpful only in infants.

— Tachycardia is the earliest sign; hypotension is a late, pre-arrest sign in children due to robust compensatory vasoconstriction.

— Tachypnea without lung findings → Kussmaul-like compensation for metabolic acidosis (lactic from hypoperfusion, or bicarb loss from diarrhea).

— % dehydration = (pre-illness weight − current weight) / pre-illness weight × 100.

— Each 1% = ~10 mL/kg fluid deficit.

— Soft, mildly diffusely tender, hyperactive bowel sounds in AGE.

— Localized tenderness, guarding, rebound, or mass → reconsider diagnosis (appendicitis, intussusception "sausage-shaped" RUQ mass).

Dehydration severity (CDC/AAP/WHO synthesis): estimated by % body weight loss.

Best single signs (evidence-based, Gorelick/Steiner studies):

Vitals interpretation:

Weight-based quantification (gold standard when pre-illness weight known):

Abdominal exam:

CCS pearl: In the simulated case, order vital signs, weight, capillary refill, mental status assessment, and mucous membrane exam before committing to a rehydration route. Document urine output as a downstream monitoring parameter.

Board pearl: A child who is alert, drinking eagerly, and making tears is almost never severely dehydrated regardless of caregiver concern.

Diagnostic Workup — Initial Labs and Studies

— No labs needed. Diagnosis is clinical; testing does not change management and adds cost.

— Send home with oral rehydration solution (ORS) instructions.

— Basic metabolic panel (BMP):

· Na+: hyponatremia (free water > Na loss, or hypotonic fluid replacement) vs hypernatremia (water loss > Na, classically in breastfed infants with poor intake).

· K+: typically low (GI losses); occasionally high if AKI/acidosis.

· HCO3⁻: low → non-anion-gap metabolic acidosis from stool bicarb loss, or anion-gap if lactic from hypoperfusion.

· BUN/Cr: prerenal AKI; BUN/Cr ratio >20 suggests volume depletion.

· Glucose: hypoglycemia common in young children with poor PO intake — always check.

— Venous blood gas if severe acidosis suspected (tachypnea, lethargy).

— Urinalysis: specific gravity >1.020 supports dehydration; ketones expected; exclude UTI if fever without source.

— Indications: bloody/mucoid diarrhea, severe/prolonged (>7 days), immunocompromised, recent antibiotics (C. diff), travel, outbreak investigation, public health needs (daycare worker).

— Stool culture (Salmonella, Shigella, Campylobacter), Shiga toxin EIA or STEC PCR if bloody, C. difficile PCR if antibiotic exposure (only in children >1 year; colonization common <1 yr makes testing unreliable), O&P or Giardia antigen if prolonged.

— Multiplex GI PCR panels increasingly used; interpret cautiously (detects colonization).

— Not routine. Abdominal US for suspected intussusception; upright/decubitus films if obstruction or perforation suspected.

Uncomplicated AGE with mild–moderate dehydration:

When to obtain labs (severe dehydration, atypical features, prolonged illness, or considering IV therapy):

Stool studies — selective, not routine:

Imaging:

Key distinction: Routine electrolytes are not indicated in mild AGE managed with PO rehydration — overtesting drives unnecessary IV fluids and admissions.

Board pearl: A child with AGE + lethargy + hypoglycemia should prompt consideration of an underlying fatty acid oxidation defect (e.g., MCAD) unmasked by fasting.

Diagnostic Workup — Advanced or Confirmatory Studies

— Persistent diarrhea (>14 days):

· Stool for O&P × 3, Giardia/Cryptosporidium antigen.

· Stool calprotectin (elevated → IBD).

· Celiac serology (tTG-IgA + total IgA) if growth faltering, post-viral lactose intolerance picture, or family history.

· Stool reducing substances, pH <5.5 → carbohydrate malabsorption (post-viral disaccharidase deficiency).

· Fecal fat / elastase if steatorrhea suspected (CF, pancreatic insufficiency).

— Bloody diarrhea workup:

· STEC PCR + Shiga toxin assay.

· CBC with smear, BUN/Cr, LDH, haptoglobin, urinalysis → screen for HUS (MAHA, thrombocytopenia, AKI).

· If HUS suspected → avoid antibiotics and antimotility agents (may worsen STEC-HUS).

— Intussusception: abdominal ultrasound = first-line (target/donut sign); air or contrast enema is both diagnostic and therapeutic.

— Appendicitis: US first in children; CT if non-diagnostic and high suspicion.

— Malrotation/volvulus: upper GI series is gold standard — bilious vomiting demands urgent imaging.

— Hirschsprung enterocolitis: contrast enema, rectal biopsy; consider in neonates/infants with chronic constipation now presenting with explosive diarrhea + sepsis.

— Coordinate with local health department for cluster cases (daycare, school, restaurant).

— Norovirus PCR, hepatitis A serology if jaundice + GI symptoms.

When initial workup is non-diagnostic or course atypical:

Imaging in selected scenarios:

Endoscopy: reserved for suspected IBD, chronic refractory diarrhea, or eosinophilic GI disease — typically after GI consult.

Outbreak/public health testing:

Step 3 management: For the persistently sick or bloody-stool child, the workup pivot is CBC + BMP + stool studies + urinalysis to detect HUS or evolving sepsis early — repeat at 48–72 hours if initial labs were normal but bloody diarrhea continues.

Board pearl: STEC-HUS classically appears 5–10 days after onset of bloody diarrhea, often as the diarrhea is improving — counsel families to return for decreased urination, pallor, or petechiae.

Risk Stratification and Rehydration Route Logic

— Minimal/no dehydration (<3%): Home management. Continue age-appropriate diet, offer ORS 10 mL/kg per loose stool and 2 mL/kg per emesis as replacement.

— Mild–moderate dehydration (3–9%): Oral rehydration therapy (ORT) in clinic/ED is first-line per AAP and CDC. Goal: replace deficit over 4 hours, then maintenance + ongoing losses.

— Severe dehydration (≥10%) or shock: IV/IO bolus resuscitation, admit.

— Age <6 months or weight <8 kg.

— Prematurity, chronic illness, immunocompromise.

— Persistent vomiting despite ondansetron.

— Caregiver unable to administer ORT or unreliable follow-up.

— Bloody diarrhea with HUS concern.

— Significant electrolyte derangement (Na <130 or >150, HCO3 <13, glucose <60).

— Altered mental status, signs of shock.

— Multiple RCTs and Cochrane reviews show ORT is equivalent to IV fluids for mild–moderate dehydration, with fewer adverse events, shorter LOS, and lower cost.

— Failure rate ~4%; failure usually due to intractable vomiting (mitigated by ondansetron) or caregiver inability.

— Single PO dose 0.15 mg/kg (max 8 mg) or weight-banded ODT (2 mg for 8–15 kg, 4 mg for 15–30 kg, 8 mg >30 kg) reduces vomiting, ORT failure, IV use, and admission.

— Avoid in children with prolonged QT or on QT-prolonging meds.

Three-tier triage based on dehydration severity:

High-risk features warranting lower threshold for IV/admission:

ORT first principle:

Ondansetron use:

Step 3 management: For mild–moderate dehydration, the correct order set is: ondansetron ODT × 1 → ORS 50–100 mL/kg over 4 hours via syringe or teaspoon every 2–5 minutes → reassess at 1, 2, and 4 hours → discharge with ORS plan if tolerating and improving.

Board pearl: "Failed PO trial" requires a real attempt — small, frequent volumes (5 mL every 2–5 min), not "tried sips and vomited once."

Pharmacotherapy and Fluid Composition — First-Line Regimens

— Na+ 75 mEq/L, K+ 20 mEq/L, glucose 75 mmol/L, citrate 10 mmol/L, osmolarity 245 mOsm/L.

— Glucose-Na cotransport in small bowel epithelium drives water absorption even during active secretory diarrhea — this is the physiologic basis of ORT.

— Commercial products: Pedialyte, Enfalyte, generic equivalents.

— Avoid: plain water (hyponatremia, seizures), juice/soda/sports drinks (high osmolarity → osmotic diarrhea, low Na), broth (hypernatremia).

— Mild dehydration (3–5%): 50 mL/kg ORS over 4 hours + replace ongoing losses (10 mL/kg per stool, 2 mL/kg per emesis).

— Moderate dehydration (6–9%): 100 mL/kg ORS over 4 hours + ongoing losses.

— Administer in small frequent aliquots (5 mL every 2–5 min) — large volumes trigger vomiting.

— Bolus: 20 mL/kg isotonic crystalloid (NS or LR) over 10–20 min; repeat up to 60 mL/kg total while reassessing perfusion.

— After hemodynamic stabilization: deficit + maintenance + ongoing losses.

— Maintenance fluid: AAP 2018 recommends isotonic fluids (D5NS or D5½NS with KCl 20 mEq/L once urinating) for most hospitalized children to prevent iatrogenic hyponatremia from hypotonic fluids + ADH release.

— Holliday-Segar maintenance: 100 mL/kg/day for first 10 kg, +50 mL/kg/day for next 10 kg, +20 mL/kg/day thereafter.

— Ondansetron is first-line; avoid promethazine and metoclopramide in young children (extrapyramidal effects, black box for promethazine <2 yr).

— Loperamide, diphenoxylate contraindicated in young children with AGE — risk of ileus, toxic megacolon, masking dehydration; absolute contraindication in dysentery/STEC.

— Bismuth subsalicylate not recommended (Reye syndrome risk).

Oral Rehydration Solution (ORS) composition (WHO reduced-osmolarity formula):

Dosing protocols:

IV rehydration (severe or failed ORT):

Antiemetics:

Antidiarrheals:

Probiotics: Lactobacillus GG and Saccharomyces boulardii may modestly reduce diarrhea duration; 2018 AAP/NEJM trials show no significant benefit — not routinely recommended.

Zinc: WHO recommends 10–20 mg/day × 10–14 days in children <5 yr in low-resource settings; not standard in US.

Board pearl: The single most common iatrogenic harm in pediatric AGE is hyponatremic seizure from hypotonic maintenance IV fluids — always use isotonic.

Antibiotic Use and Special Pharmacology

— Shigella: treat to shorten illness and reduce transmission → azithromycin 10 mg/kg/day × 3 days (first-line for resistance); ceftriaxone if severe.

— Cholera (Vibrio cholerae): azithromycin or doxycycline (yes, even in young children for cholera per WHO).

— Giardia: metronidazole, tinidazole, or nitazoxanide.

— Entamoeba histolytica: metronidazole + luminal agent (paromomycin).

— C. difficile: PO vancomycin or fidaxomicin (metronidazole now second-line per IDSA 2018).

— Severe Campylobacter (high fever, bloody, prolonged, immunocompromised): azithromycin.

— Salmonella (non-typhoidal): treat only if <3 months, immunocompromised, hemoglobinopathy, bacteremia, or severe disease — otherwise antibiotics prolong carriage.

— Typhoid Salmonella: ceftriaxone or azithromycin.

— Do NOT give antibiotics — increases Shiga toxin release and risk of HUS (especially fluoroquinolones, TMP-SMX, beta-lactams in some studies).

— Avoid antimotility agents.

— Supportive care + monitor for HUS.

— Generally avoided pending stool culture/STEC testing because of HUS risk.

— Exception: toxic-appearing child with suspected invasive bacterial enteritis pending workup → empiric ceftriaxone is reasonable while awaiting cultures.

— Ondansetron: weight-based; ECG concerns mainly with IV doses in adults.

— Azithromycin: extended QT consideration; preferred over fluoroquinolones in children.

— Fluoroquinolones: relative caution in children (cartilage, tendinopathy) but acceptable when first-line agents fail or for resistant pathogens.

Antibiotics are NOT indicated for most pediatric AGE (viral etiology, self-limited bacterial cases).

Specific bacterial scenarios where antibiotics ARE indicated:

Critical contraindication — STEC (E. coli O157:H7):

Empiric antibiotics for bloody diarrhea?

Drug-specific pediatric pearls:

Step 3 management: For the febrile child with bloody diarrhea, the correct sequence is: stool culture + Shiga toxin/STEC PCR + CBC/BMP → withhold antibiotics → supportive IV fluids → reassess at 48–72 hours and tailor therapy by pathogen.

CCS pearl: Ordering "empiric ciprofloxacin" for bloody pediatric diarrhea will be penalized — the safer move is supportive care and targeted testing.

Special Populations — Renal Impairment, Hyper/Hyponatremia

— Cause: free water replacement (plain water, juice) or hypotonic IV fluids during illness with high ADH.

— Risk: cerebral edema, seizures (especially Na <125 or rapid drop).

— Correction: isotonic saline; if symptomatic seizure, 3% hypertonic saline 3–5 mL/kg over 15–30 min.

— Do not correct >10–12 mEq/L per 24 hours — risk of osmotic demyelination (rare in acute hyponatremia but cautious correction still standard).

— Cause: pure water loss > Na loss; classic in young breastfed infants with poor intake, or after high-Na rehydration attempts.

— Brain shrinks → intracellular osmoles ("idiogenic osmoles") accumulate to defend cell volume → rapid correction causes cerebral edema and seizures.

— Correct slowly: decrease Na by ≤0.5 mEq/L/hour, max 10–12 mEq/L per 24 hours.

— Use isotonic saline for initial resuscitation; then D5½NS over 48–72 hours to replace deficit gradually.

— Lethargy, doughy skin, irritability with high-pitched cry are clinical clues.

— Prerenal from hypovolemia: responds to fluid resuscitation.

— Intrinsic AKI suggests HUS (STEC), ATN from prolonged shock, or pre-existing renal disease.

— Monitor urine output goal ≥1 mL/kg/hr in children, ≥0.5 mL/kg/hr in adolescents.

— Hypoglycemia risk increased with limited glycogen stores in young children; add dextrose (D5) to maintenance IVF.

— Underlying metabolic disease (urea cycle, fatty acid oxidation, organic acidemias) can decompensate with fasting/AGE — order ammonia, lactate, glucose if AMS persists despite rehydration.

Hyponatremic dehydration (Na <130):

Hypernatremic dehydration (Na >150):

Acute kidney injury:

Hepatic considerations:

Key distinction: Hypotonic dehydration (Na <130) and hypertonic dehydration (Na >150) both need isotonic crystalloid for initial resuscitation; the difference is in the rate and tonicity of the maintenance/deficit replacement phase.

Board pearl: Sudden-onset seizure in a dehydrated infant rehydrated with tap water at home → hyponatremic seizure — give 3% saline, not antiepileptics first.

Special Populations — Infants, Neonates, and Immunocompromised

— AGE is uncommon and concerning — broaden differential to sepsis, NEC, inborn errors of metabolism, congenital adrenal hyperplasia (salt-wasting CAH presents with vomiting, hyponatremia, hyperkalemia, hypoglycemia in 1–2 week old).

— Low threshold for full sepsis workup (CBC, blood/urine/CSF cultures, empiric antibiotics).

— Admit; ORT generally inadequate in this age group.

— Limited physiologic reserve; dehydrate faster.

— Breastfed infants: continue breastfeeding through illness — do not interrupt; supplement with ORS for ongoing losses.

— Formula-fed: continue full-strength formula; diluted formula is no longer recommended.

— Avoid juice, water, broth as primary rehydration.

— Current recommendation: resume age-appropriate regular diet as soon as rehydrated (within 4–6 hours).

— Early refeeding shortens illness, reduces stool output, prevents malnutrition.

— Brief (1–2 weeks) lactose avoidance only if clear post-viral lactose intolerance with persistent watery diarrhea on reintroduction.

— Lower threshold for stool studies including viral PCR panel (norovirus, rotavirus, adenovirus, CMV).

— Consider opportunistic infections (Cryptosporidium, CMV colitis).

— Earlier admission for IV hydration and monitoring.

— Short bowel syndrome, ostomies, IBD on immunosuppression — higher dehydration risk, may need scheduled ORS at home.

— Coordinate with primary GI team.

— Confirm rotavirus vaccine (RV1 or RV5) completion — first dose by 15 weeks, completed by 8 months.

— Counsel on vaccine benefits at well visits; rotavirus vaccination has dramatically reduced US hospitalizations.

Neonates (<1 month):

Young infants (1–6 months):

The "BRAT diet" is outdated:

Immunocompromised children (oncology, transplant, primary immunodeficiency, HIV):

Children with chronic GI disease:

Vaccination status:

Step 3 management: For the <3-month-old with AGE-like illness, the default disposition is ED evaluation with labs and observation, not phone triage to home ORT — physiologic reserve is too limited and differential too broad.

Board pearl: A 2-week-old with vomiting, hyponatremia, and hyperkalemia is salt-wasting CAH, not AGE — check 17-OH-progesterone and give hydrocortisone + saline.

Complications and Adverse Outcomes

— Hypovolemic shock: tachycardia, prolonged cap refill, cool extremities, altered mental status → may progress to cardiac arrest.

— Acute kidney injury: prerenal initially; ATN if prolonged.

— Electrolyte derangements: hyponatremia (seizures), hypernatremia (seizures, cerebral hemorrhage on rapid correction), hypokalemia (arrhythmia, ileus), metabolic acidosis.

— Hypoglycemia: especially in young children and metabolic disease — AMS, seizures.

— STEC → HUS: triad of microangiopathic hemolytic anemia, thrombocytopenia, AKI. Peak 5–10 days after diarrhea onset. Management: supportive, transfusions, dialysis as needed; avoid platelets unless bleeding (may worsen thrombosis); avoid antibiotics and antimotility agents.

— Shigella → seizures, hemolytic uremic syndrome (S. dysenteriae type 1), Reiter syndrome (older children).

— Salmonella → bacteremia, osteomyelitis (especially in sickle cell disease), endovascular infection.

— Campylobacter → Guillain-Barré syndrome, reactive arthritis.

— Yersinia → pseudoappendicitis (terminal ileitis/mesenteric adenitis mimicking appendicitis).

— C. difficile → toxic megacolon, perforation (less common in children than adults).

— Hyponatremic seizures from hypotonic IVF — use isotonic maintenance fluids.

— Cerebral edema from rapid correction of hypernatremia — correct slowly.

— Inappropriate antibiotic use → C. difficile, prolonged Salmonella carriage, increased HUS risk in STEC.

— Transient lactose intolerance (most common, self-limited 1–2 weeks).

— Post-infectious IBS.

— Failure to thrive if prolonged or recurrent infections.

— Reactive arthritis (HLA-B27 associated) after Shigella, Salmonella, Campylobacter, Yersinia.

Acute complications of dehydration:

Disease-specific complications:

Iatrogenic complications:

Post-infectious complications:

Key distinction: A child with bloody diarrhea improving clinically but newly pale, oliguric, with bruising has HUS until proven otherwise — get CBC, smear, BUN/Cr, urinalysis immediately.

Board pearl: Sickle cell + Salmonella enteritis + bone pain = Salmonella osteomyelitis — get blood cultures, MRI, empiric ceftriaxone.

When to Escalate Care — ICU, Consult, or Admit

— Minimal-to-mild dehydration, tolerating ORT, reliable caregiver, follow-up available within 24 hours, no red flags.

— Mild–moderate dehydration → ORT trial in ED ± single ondansetron dose → discharge if tolerating after 4-hour reassessment.

— Severe dehydration requiring ongoing IV fluids.

— Failed ORT despite ondansetron.

— Significant electrolyte abnormalities (Na <130 or >150, K <3.0, HCO3 <13, glucose <60).

— Age <2 months with significant dehydration.

— Concerning underlying condition (short gut, metabolic disease, immunocompromise).

— Suspected HUS, sepsis, surgical abdomen.

— Inadequate caregiver capacity or unsafe discharge environment.

— Bilious or bloody vomiting.

— Persistent altered mental status.

— Refractory shock despite 60 mL/kg crystalloid → vasopressor support, central access.

— Severe metabolic acidosis (pH <7.1, HCO3 <10) not correcting with resuscitation.

— Active seizures, status epilepticus from electrolyte disturbance.

— Evolving HUS with severe AKI requiring dialysis, severe anemia requiring transfusion, neurologic involvement.

— Need for continuous vasoactive infusions, mechanical ventilation, CRRT.

— Nephrology: HUS, AKI requiring renal replacement.

— GI: prolonged/refractory diarrhea, suspected IBD, persistent bloody diarrhea without infectious cause.

— Surgery: suspected appendicitis, intussusception (often pediatric surgery + IR), volvulus, perforation.

— Infectious disease: unusual pathogens, immunocompromised host, outbreak.

— Public health: reportable infections (Salmonella, Shigella, STEC, cholera, hepatitis A, typhoid).

Outpatient (home) management criteria:

ED observation / short-stay criteria:

Admission criteria:

ICU/PICU criteria:

Subspecialty consultations:

CCS pearl: When a CCS pediatric AGE case fails to improve in the ED with two crystalloid boluses, the next correct moves are admit, recheck electrolytes, consider PICU consult, and broaden differential (sepsis, surgical, metabolic) — not a third bolus alone.

Board pearl: The triage question "outpatient ORT vs admit" is the single most tested decision in pediatric AGE on Step 3.

Key Differentials — Other GI/Infectious Causes

— Appendicitis: RLQ pain, fever, anorexia, may have diarrhea (especially retrocecal); classic Rovsing, psoas, obturator signs; elevated WBC; US/CT confirms.

— Intussusception: infants 6–36 months, intermittent severe colicky pain (drawing knees to chest), "currant jelly" stool (late), sausage-shaped mass, lethargy may dominate; US first-line (target sign), air enema reduction.

— Malrotation with midgut volvulus: bilious vomiting in any child = surgical emergency; UGI series; can present at any age but classically <1 year.

— Pyloric stenosis: 3–6 weeks old, projectile non-bilious vomiting, hungry after vomiting, "olive" mass, hypochloremic hypokalemic metabolic alkalosis; US shows pyloric thickening; pyloromyotomy after fluid/electrolyte correction.

— Hirschsprung enterocolitis: neonate/infant with history of delayed meconium, chronic constipation now with explosive bloody diarrhea + sepsis; contrast enema, rectal biopsy.

— NEC (neonates, especially preterm): abdominal distension, bloody stools, pneumatosis intestinalis on KUB.

— Inflammatory bowel disease: older child/adolescent with chronic bloody diarrhea, weight loss, growth failure, perianal disease (Crohn), extraintestinal manifestations; elevated calprotectin, CRP, ESR.

— Celiac disease: chronic diarrhea, failure to thrive, abdominal distension; tTG-IgA + total IgA; duodenal biopsy.

— Lactose intolerance (post-viral or primary): watery diarrhea after dairy, bloating, flatulence; resolves with dairy elimination.

— Food allergy / FPIES: infant with profuse vomiting 1–4 hours after specific food (milk, soy, rice, oat), pallor, lethargy, can mimic sepsis.

— Cyclic vomiting syndrome: stereotyped episodes, well between, family history of migraine.

Same-category mimics within GI/infectious:

Key distinction: AGE = diarrhea-dominant febrile illness; isolated vomiting without diarrhea, especially with bilious content, bloody stools without diarrhea, or focal abdominal findings should redirect workup toward surgical/structural causes.

Board pearl: Toddler with intermittent inconsolable crying + lethargy + currant jelly stool = intussusception — US, then air enema; surgical reduction if enema fails or perforation suspected.

Key Differentials — Non-GI Mimics

— Diabetic ketoacidosis: polyuria, polydipsia, weight loss, Kussmaul breathing, fruity breath, abdominal pain, vomiting; hyperglycemia, anion-gap acidosis, ketonuria. Every vomiting child should have a glucose checked.

— Congenital adrenal hyperplasia (salt-wasting): neonate at 1–3 weeks with vomiting, weight loss, hyponatremia, hyperkalemia, hypoglycemia; ambiguous genitalia in girls; 17-OH-progesterone elevated; treat with hydrocortisone + IV saline.

— Inborn errors of metabolism: vomiting + lethargy + acidosis or hyperammonemia, especially after fasting (MCAD, urea cycle defects, organic acidemias).

— Increased intracranial pressure (tumor, hydrocephalus, abuse): morning vomiting, headache, papilledema, focal deficits, change in personality, sun-setting eyes (infants).

— Migraine equivalents: cyclic vomiting, abdominal migraine.

— Meningitis/encephalitis: fever, vomiting, AMS, neck stiffness, photophobia, bulging fontanelle (infants).

— UTI/pyelonephritis in young children: may present with vomiting, fever without localizing signs; always check urinalysis in febrile infants and toddlers with vomiting.

— Testicular/ovarian torsion: sudden severe pain, vomiting; exam reveals scrotal/lower abdominal findings.

— Iron, acetaminophen, salicylates, lead, caustic, mushrooms — vomiting ± diarrhea ± AMS; toxidromes; history of access to medications/substances.

— Infant heart failure (myocarditis, coarctation, ALCAPA): poor feeding, vomiting, diaphoresis with feeds, tachypnea, hepatomegaly — easily mistaken for AGE.

— Myocarditis post-viral: tachycardia out of proportion to dehydration, hepatomegaly, gallop.

— Henoch-Schönlein purpura (IgA vasculitis): palpable purpura on legs/buttocks + colicky abdominal pain ± intussusception + arthritis + hematuria.

Metabolic/endocrine mimics:

Neurologic mimics:

Urologic/GU:

Toxic ingestions:

Cardiac:

Hematologic:

Step 3 management: When a "gastroenteritis" case isn't improving as expected with rehydration, broaden the differential systematically: glucose, electrolytes, urinalysis, abdominal exam, neuro exam, cardiac exam — and reconsider the diagnosis.

Board pearl: A "vomiting" child with Kussmaul respirations and fruity breath is DKA — fingerstick glucose + UA ketones immediately.

Discharge Planning and Anticipatory Guidance

— Tolerating PO fluids without vomiting × 2–4 hours.

— Urine output documented (wet diaper, void).

— Normal mental status, vital signs at baseline.

— Electrolytes corrected or trending appropriately.

— Reliable caregiver, transportation, follow-up arranged.

— ORS plan: specific product (Pedialyte/generic), amount (10 mL/kg per loose stool, 2 mL/kg per emesis), administration technique (5 mL every 2–5 min if vomiting).

— Diet: resume age-appropriate regular diet within hours; continue breastfeeding/formula; avoid juice, soda, sports drinks, BRAT-only restriction.

— Avoid: loperamide, antidiarrheal OTC products, bismuth, herbal remedies.

— Hand hygiene: soap and water (alcohol gel less effective against norovirus, C. difficile, Cryptosporidium); disinfect surfaces with bleach for norovirus.

— Return precautions (clear written list):

· Persistent vomiting >24 hours or inability to keep fluids down.

· No urination >8 hours.

· Bloody stools, severe abdominal pain, bilious vomiting.

· Lethargy, irritability, decreased responsiveness.

· High persistent fever, especially >5 days.

· Pallor, bruising, decreased urine output (HUS warning).

— Most policies: return when no vomiting/diarrhea for 24 hours and able to participate.

— Shigella, STEC, Salmonella typhi: may require two negative stool cultures before return (state-dependent).

— Reportable infections: notify local public health.

— Rotavirus vaccination completion (RV1 by 24 weeks, RV5 by 32 weeks; first dose must be by 15 weeks).

— Hand hygiene education, especially in daycare settings.

— Safe food preparation (cook ground beef thoroughly, avoid unpasteurized dairy, wash produce).

— Travel counseling for older children: bottled water, hand hygiene, hepatitis A vaccine.

Discharge criteria from ED/inpatient:

Discharge instructions for caregivers:

Daycare/school return:

Secondary prevention:

Step 3 management: Discharge packet includes written ORS plan, return precautions, primary care follow-up within 24–48 hours, and verbal teach-back from caregiver to confirm understanding.

Board pearl: A child discharged after bloody diarrhea needs a scheduled 48-hour follow-up CBC/BMP/UA to screen for evolving HUS, not just symptomatic recheck.

Follow-Up, Monitoring, and Longitudinal Care

— Phone or in-person check at 24–48 hours for moderate dehydration or bloody diarrhea.

— Office visit at 48–72 hours if symptoms persist, with weight check and exam.

— Weekly check if diarrhea >7 days; transition to chronic diarrhea workup at 14 days.

— Weight: compare to pre-illness; flag if >5% deficit persists.

— Hydration status: mucous membranes, cap refill, urine output, activity.

— Stool pattern: frequency, consistency, blood/mucus presence.

— Feeding tolerance and dietary return to baseline.

— For bloody diarrhea cases: CBC, BUN/Cr, UA at 48–72 hours and 7 days to monitor for HUS.

— Workup: stool O&P × 3, Giardia/Cryptosporidium antigen, calprotectin, celiac serology, stool reducing substances/pH, fecal elastase.

— Empiric lactose-free trial 1–2 weeks if post-viral pattern.

— Refer to GI if no resolution by 3–4 weeks or if growth faltering.

— If weight loss persists >2 weeks, consider caloric supplementation, dietitian referral.

— Catch-up growth typically achieved within 2–4 weeks of recovery.

— Reinforce hand hygiene, food safety, vaccination.

— Discuss daycare hygiene practices, sick policies.

— For families with recurrent AGE episodes: review water source, food handling, daycare exposure.

— Investigate underlying immunodeficiency (CVID, IgA deficiency), CF, IBD, immune dysregulation.

— Consider primary immunodeficiency workup if multiple severe/prolonged infections.

— Reducing unnecessary ED visits via clear caregiver education and accessible ORT instructions is a quality measure.

— Avoid unnecessary labs and IV fluids in mild AGE — overutilization marker.

Outpatient follow-up cadence:

Monitoring parameters at follow-up:

Persistent/post-infectious diarrhea (>14 days):

Nutritional rehabilitation:

Counseling and prevention:

Recurrent or unusually severe AGE:

Health systems / value-based pearls:

Step 3 management: For a child seen for AGE in clinic, schedule a 48-hour telephone follow-up as part of the visit — proactive contact reduces ED bounce-backs and catches deteriorating courses early.

Board pearl: Persistent watery diarrhea on dairy reintroduction post-AGE = transient secondary lactase deficiency — trial lactose-free formula/diet for 2 weeks before deeper workup.

Ethical, Legal, and Patient Safety Considerations

— Reportable enteric infections (varies by state but generally includes Salmonella, Shigella, STEC, Campylobacter, Vibrio cholerae, Listeria, hepatitis A, typhoid, giardiasis, cryptosporidiosis). Notify local/state health department promptly.

— Outbreak suspicion in daycare, school, restaurant — public health investigation can identify common source and prevent further cases.

— Severe dehydration in a child with multiple missed appointments, inconsistent caregiver history, or evidence of poor caregiving → mandated reporting to Child Protective Services.

— Failure to thrive with recurrent presentations may indicate neglect.

— Munchausen syndrome by proxy (factitious disorder imposed on another): consider in atypical, recurrent, witness-only symptoms.

— Parental refusal of IV fluids or admission for clearly severe dehydration → engage in shared decision-making, document discussion of risks (shock, seizures, death), offer ORT alternatives, involve social work/ethics/legal as needed; emergency exception to consent applies if child is in imminent danger.

— Adolescent confidentiality: in older adolescents with AGE plus pregnancy or STI risk, navigate state-specific minor consent laws.

— Isotonic IV maintenance fluids to prevent iatrogenic hyponatremic seizure (AAP 2018, joint commission priority).

— Weight-based dosing for all medications and fluids — use kg, not lbs; double-check ondansetron and antibiotic doses.

— Avoid loperamide in pediatric AGE and antibiotics in STEC — both cause documented harm.

— Glucose check in any lethargic vomiting child to catch hypoglycemia and DKA.

— ED-to-home transition: closed-loop follow-up call within 24–48 hours, written discharge instructions, clear return precautions, ORS access (consider providing a sample bottle if SDOH barriers).

— Inpatient-to-outpatient: medication reconciliation, weight at discharge, primary care follow-up within 1 week.

— Language-concordant materials; use certified interpreters, not family members.

— Food/water insecurity, daycare crowding, and limited primary care access increase AGE morbidity. Connect families to WIC, food assistance, and care coordination.

Mandatory reporting:

Suspected child neglect/abuse:

Informed consent edge cases:

Patient safety priorities:

Transitions of care risks:

Health equity:

CCS pearl: Reporting Salmonella or STEC to public health is an expected order in the simulated case — omitting it may cost points.

Board pearl: A child with severe dehydration whose caregivers refuse IV access does not automatically end care — engage shared decision-making, document, and treat under emergency exception if life-threatening.

High-Yield Associations and Rapid-Fire Clinical Facts

— Reptiles, turtles, poultry → Salmonella.

— Undercooked ground beef, petting zoo, unpasteurized juice/milk → STEC O157:H7 → HUS.

— Raw/undercooked poultry, puppies, unpasteurized milk → Campylobacter → Guillain-Barré.

— Daycare, well water, camping streams → Giardia.

— Pools, water parks → Cryptosporidium (chlorine-resistant).

— Fried rice left at room temperature → Bacillus cereus emetic toxin.

— Mayonnaise-based salads, custards → Staph aureus preformed toxin (rapid <6 hr vomiting).

— Raw shellfish, gulf coast → Vibrio parahaemolyticus / vulnificus.

— Recent antibiotics → C. difficile.

— Cruise ship, nursing home, daycare outbreaks → Norovirus.

— STEC + bloody diarrhea + pallor + AKI + thrombocytopenia = HUS.

— Shigella + seizure = neurotoxin effect; can occur with low fever.

— Salmonella + sickle cell + bone pain = osteomyelitis.

— Campylobacter + ascending weakness 1–3 weeks later = GBS (Miller Fisher variant possible).

— Yersinia + RLQ pain = pseudoappendicitis (terminal ileitis, mesenteric adenitis).

— Rotavirus + winter + unvaccinated infant = profuse watery diarrhea + dehydration.

— Hypochloremic hypokalemic metabolic alkalosis → pyloric stenosis (vomiting).

— Non-anion-gap metabolic acidosis → diarrhea (stool bicarbonate loss).

— Anion-gap acidosis in AGE → hypoperfusion (lactic) or DKA mimic.

— Eosinophilia + diarrhea → parasites (Strongyloides, schistosomiasis), allergic enteritis.

— Rotavirus vaccine: first dose by 15 weeks, series complete by 8 months; live oral; rare intussusception risk; contraindicated in SCID.

— 1% dehydration = 10 mL/kg deficit.

— Maintenance Holliday-Segar: 4-2-1 mL/kg/hr (≤10 kg, 10–20 kg, >20 kg).

— Isotonic maintenance fluids prevent hyponatremia.

Pathogen ↔ exposure pairings:

Classic syndromes:

Lab patterns:

Vaccine facts:

Fluid facts:

Board pearl: "Bloody diarrhea + petting zoo + thrombocytopenia + AKI" is a near-100% pathognomonic Step 3 stem for STEC-HUS — no antibiotics.

Board Question Stem Patterns

— 2-year-old with 2 days of vomiting and diarrhea, sunken eyes, dry mucosa, cap refill 3 sec, alert.

— Best next step: Oral rehydration with ORS + single-dose ondansetron, not IV fluids. Tests recognition that ORT is first-line.

— Lethargic infant with cool extremities, weak pulses, cap refill >4 sec.

— Best next step: 20 mL/kg isotonic crystalloid IV bolus (NS or LR), repeat as needed. Then check labs, glucose, ongoing reassessment.

— Child with bloody diarrhea after picnic with hamburgers, now pallor, decreased urination, petechiae.

— Labs: anemia, schistocytes, thrombocytopenia, elevated Cr.

— Best next step: Supportive care, transfusion as needed, avoid antibiotics and antimotility agents, monitor for dialysis need. Diagnosis: HUS.

— Hospitalized child on D5¼NS develops seizure; Na 122.

— Best next step: 3% hypertonic saline for symptomatic hyponatremia; switch to isotonic maintenance fluids going forward.

— Breastfed neonate with poor feeding, weight loss, Na 162, doughy skin.

— Best next step: Initial isotonic bolus for perfusion, then slow correction with D5½NS; decrease Na by ≤10–12 mEq/L per 24 hr to prevent cerebral edema.

— 4-week-old with projectile non-bilious vomiting, hungry after feeds, palpable olive, hypochloremic alkalosis.

— Best next step: US, then fluid/electrolyte correction → pyloromyotomy. Not AGE.

— Any age with bilious emesis → upper GI series urgently to rule out malrotation/volvulus.

— Vomiting child with weight loss, Kussmaul breathing, fruity breath, glucose 480.

— Best next step: IV fluids + insulin protocol for DKA, not AGE workup.

— Sickle cell patient with diarrhea now with bone pain, fever.

— Best next step: Blood cultures, MRI, empiric ceftriaxone for Salmonella osteomyelitis.

— Several daycare children with watery diarrhea; norovirus most likely; report to public health, hand hygiene with soap and water.

Stem 1 — Mild–moderate dehydration in toddler:

Stem 2 — Severe dehydration / shock:

Stem 3 — STEC and HUS:

Stem 4 — Hypotonic IVF iatrogenic harm:

Stem 5 — Hypernatremic dehydration:

Stem 6 — Pyloric stenosis vs AGE:

Stem 7 — Bilious vomiting:

Stem 8 — DKA masquerading:

Stem 9 — Salmonella + sickle cell:

Stem 10 — Daycare outbreak:

Step 3 management: Match the dehydration severity to the rehydration route — this binary is the most-tested concept.

One-Line Recap

High-yield rapid recaps:

Core teaching point: Pediatric gastroenteritis management hinges on clinical assessment of dehydration severity (which drives the choice between oral rehydration therapy with ORS for mild–moderate and IV isotonic crystalloid boluses for severe dehydration), with strict avoidance of antibiotics in STEC, antimotility agents in any pediatric AGE, and hypotonic maintenance fluids in hospitalized children.

Assessment: Capillary refill, skin turgor, and respiratory pattern are the three best clinical signs of dehydration; weight loss percentage is the gold-standard quantitative metric (1% = 10 mL/kg deficit). Always check glucose in lethargic vomiting children.

Rehydration: ORS (75 mEq Na, 75 mmol glucose, 245 mOsm) given in small frequent aliquots with ondansetron 0.15 mg/kg PO is first-line for mild–moderate dehydration; deliver 50–100 mL/kg over 4 hours plus ongoing losses. Severe dehydration: 20 mL/kg NS/LR IV bolus, repeat to 60 mL/kg, then isotonic maintenance.

Avoid: Loperamide in any pediatric AGE, antibiotics in STEC (HUS risk), hypotonic maintenance IVF (hyponatremic seizures), rapid correction of hypernatremia (cerebral edema), diluted formula, juice/soda/sports drinks as rehydration, prolonged BRAT diet.

Red flags redirecting workup: Bilious vomiting (malrotation/volvulus), bloody diarrhea + pallor + oliguria (HUS), projectile non-bilious in 3–6 week-old (pyloric stenosis), isolated vomiting with AMS (DKA, ICP, metabolic), neonate with hyponatremia + hyperkalemia (CAH).

Board pearl: When in doubt, assess dehydration → choose route → reassess in 4 hours; this single algorithm answers the majority of Step 3 pediatric AGE questions and should anchor your CCS order set from triage through discharge with 24–48 hour follow-up.