What is the appropriate evaluation and initial management for a patient presenting with vomiting, diarrhea, and abdominal pain?

Evaluation and Management of Acute Gastroenteritis with Vomiting, Diarrhea, and Abdominal Pain

Begin immediate oral rehydration with 8–10 large glasses of clear fluids per day while simultaneously assessing for dehydration severity and red-flag features that require urgent diagnostic workup or hospitalization. 1

Immediate Assessment Priorities

Dehydration Status (First Priority)

• Check for tachycardia, orthostatic blood pressure changes (drop >20 mmHg systolic or pulse increase >20 bpm when standing), decreased skin turgor, dry mucous membranes, decreased urine output, and altered mental status 2, 1
• Document vital signs including temperature—fever ≥38.5°C suggests invasive bacterial infection requiring different management 2, 1
• Assess volume depletion severity: thirst, lethargy, absent jugular venous pulsations 2

Red-Flag Clinical Features Requiring Urgent Evaluation

• High fever (≥38.5°C) 2, 1
• Bloody or mucoid stools 2, 1
• Severe abdominal pain or tenderness (especially if out of proportion to exam findings, suggesting mesenteric ischemia) 3
• Signs of shock (hypotension, persistent tachycardia, altered mental status) 3
• Bilious or feculent vomiting (suggests mechanical obstruction) 3
• Severe dehydration despite oral intake attempts 1

Essential History Elements

• Stool characteristics: frequency, volume, presence of blood/mucus/pus, watery vs. greasy 2
• Duration of symptoms—illness >48–72 hours without improvement warrants stool testing 2, 1
• Recent antibiotic use (raises C. difficile risk) 2, 1
• Epidemiological factors: travel history, food consumption (especially raw oysters, undercooked meat, shrimp/crab), contact with ill persons, daycare attendance, recent hospitalization 2, 4
• Immunocompromised status (HIV/AIDS, immunosuppressive medications) 2
• Medication history: antacids (increase gastroenteritis risk 4-fold), recent antibiotics 4

Immediate Treatment—Start Before Diagnostic Results

Rehydration (Highest Priority)

• Initiate oral rehydration solution (ORS) immediately: target 8–10 large glasses per day, plus 200–400 mL after each loose stool 1
• Use WHO-recommended ORS composition: sodium 90 mM, potassium 20 mM, chloride 80 mM, bicarbonate 30 mM, glucose 111 mM 1
• Half-strength apple juice followed by preferred liquids is equally effective for mild dehydration in children and can be extrapolated to adults 5
• Reserve IV fluids for severe dehydration, shock, altered mental status, or inability to tolerate oral intake 1, 5

Antiemetic Therapy

• Ondansetron (oral or IV) improves oral fluid tolerance, reduces vomiting frequency, and decreases need for IV hydration 5, 6
• Use cautiously in elderly patients with other antiemetics (promethazine, prochlorperazine) due to anticholinergic effects 3

Dietary Management

• Immediately eliminate lactose-containing products, caffeine, alcohol, and spicy foods 1, 7
• Initiate BRAT diet (bananas, rice, applesauce, toast) with frequent small meals 7
• Resume age-appropriate diet once rehydration achieved 1

Loperamide—Use with Extreme Caution

• Absolutely contraindicated if fever ≥38.5°C or bloody stools present due to toxic megacolon risk 1
• May use for uncomplicated watery diarrhea without red flags: 4 mg initially, then 2 mg after each unformed stool (maximum 16 mg/day) 1
• Avoid in elderly patients on QT-prolonging medications 7

Diagnostic Testing Algorithm

When to Order Stool Studies

Obtain stool culture, fecal leukocytes/lactoferrin, and C. difficile toxin if ANY of the following: 2, 1

• Fever ≥38.5°C
• Bloody or mucoid stools
• Symptoms persisting >48–72 hours
• Severe dehydration or systemic illness
• Recent antibiotic exposure (within 3 months)
• Immunocompromised status
• Recent hospitalization
• Daycare attendance or known outbreak exposure

When to Order Blood Tests

• Complete blood count: leukocytosis >15,000 cells/µL suggests bacterial infection; eosinophilia suggests parasitic infection 1
• Serum electrolytes, creatinine, lactate, blood gas: essential for severe dehydration or suspected bowel ischemia 3
• Liver enzymes: if systemic illness or right upper quadrant pain 3

When to Order Imaging

• Plain abdominal radiograph is initial test but has limited sensitivity—negative films do NOT exclude serious pathology 3
• CT abdomen/pelvis with IV contrast is definitive test if: 3
  • Bilious vomiting or suspected obstruction
  • Severe abdominal pain out of proportion to exam
  • Peritoneal signs (rebound, guarding, rigidity)
  • Abdominal distension with diminished bowel sounds
  • Suspected mesenteric ischemia (pain out of proportion + elevated lactate)

Antibiotic Decision Algorithm

Do NOT Give Antibiotics If:

• Uncomplicated watery diarrhea without fever or blood 1
• Viral gastroenteritis suspected (most common cause in developed countries) 8
• Inappropriate antibiotic use increases C. difficile risk and antimicrobial resistance 1

Consider Empiric Antibiotics If:

• Fever >38.5°C PLUS bloody diarrhea 1
• Signs of sepsis or systemic toxicity 1
• Severe immunocompromise 2
• First-line agents: azithromycin or fluoroquinolone (ciprofloxacin) based on local resistance patterns 1

Specific Pathogen-Directed Therapy:

• C. difficile suspected (recent antibiotics, healthcare exposure, leukocytosis): start oral vancomycin or fidaxomicin immediately 1
• Parasitic infection suspected (eosinophilia, travel history, pruritic rash): obtain parasite-specific stool microscopy and serology 1

Hospitalization Criteria—Admit If ANY Present:

• Persistent severe dehydration despite oral rehydration attempts 1, 7
• Hemodynamic instability (hypotension, ongoing tachycardia despite fluids) 3, 7
• Altered mental status 3, 7
• Inability to maintain oral hydration 1, 7
• Leukocytosis >30,000 cells/mm³ 7
• Suspected toxic megacolon, bowel obstruction, or mesenteric ischemia 3
• Signs of peritonitis (rebound, guarding, rigidity) 3

Expected Course and Warning Signs

Normal Recovery Timeline

• Complete resolution expected within 5–7 days with supportive care alone 1
• If symptoms persist ≥7 days, obtain stool studies for bacterial pathogens, parasites, and C. difficile 1

Instruct Patient to Return Immediately If:

• Development of high fever (>38.5°C) 1
• Appearance of blood or mucus in stool 1
• Onset of severe abdominal pain or distension 1
• Signs of worsening dehydration: orthostatic dizziness, oliguria, confusion, persistent tachycardia 1
• Inability to keep down any fluids 7

Common Pitfalls to Avoid

• Do not use loperamide before excluding fever and bloody stools—risk of toxic megacolon with invasive pathogens 1
• Do not prescribe empiric antibiotics for uncomplicated watery diarrhea—increases C. difficile risk without benefit 1
• Do not rely on plain radiographs alone—negative films do not exclude mesenteric ischemia or early obstruction 3
• Do not overlook parasitic causes in travelers—eosinophilia is the critical diagnostic clue 1
• Do not dismiss new rash as incidental—may signal systemic infection (rickettsial disease) or drug toxicity requiring specific therapy 1
• Do not assume absence of peritonitis excludes bowel ischemia—lactate and blood gas are essential 3