Pediatric Diarrhea: MCCQE1 Preparation Guide

Introduction

Pediatric diarrhea is a frequent presentation in Canadian emergency departments and family practice clinics. For the MCCQE1, candidates must demonstrate competence in distinguishing between self-limiting acute gastroenteritis and serious pathology requiring intervention. The focus is heavily placed on the Medical Expert CanMEDS role, specifically in the assessment of dehydration and the application of evidence-based rehydration therapies.

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Canadian Context: In Canada, rotavirus vaccination programs have significantly altered the epidemiology of severe pediatric diarrhea. However, outbreaks of Norovirus and seasonal viral gastroenteritis remain common.

Definitions

Acute Diarrhea: Decrease in consistency and increase in frequency of bowel movements lasting < 14 days.
Chronic Diarrhea: Symptoms persisting > 14 days.
Dysentery: Diarrhea with visible blood or mucus, often associated with fever and abdominal pain.

Etiology and Epidemiology

Understanding the cause is vital for management. The MCCQE1 often tests the ability to differentiate between viral, bacterial, and parasitic causes based on history.

Acute Causes

Viral (Most Common):
- Rotavirus: Less common now due to Canadian immunization schedules.
- Norovirus: Common in outbreaks (schools, cruise ships).
- Adenovirus: Respiratory symptoms may coexist.
Bacterial:
- Campylobacter jejuni: Most common bacterial cause in many Canadian provinces.
- Salmonella: Associated with poultry, reptiles.
- E. coli (STEC): Risk of Hemolytic Uremic Syndrome (HUS).
- C. difficile: Recent antibiotic use.
Parasitic:
- Giardia lamblia: “Beaver Fever” (common in Canadian hikers/campers drinking from streams).

Clinical Assessment

The primary goal during the physical exam for the MCCQE1 is to assess hydration status.

History Taking Checklist

Onset and Duration: Acute vs. Chronic.
Stool Characteristics: Watery, bloody, mucous, greasy, foul-smelling.
Hydration Intake: What are they drinking? (Juice/soda can worsen osmotic diarrhea).
Urine Output: Wet diapers (normal is >4/day), frequency of voiding.
Associated Symptoms: Vomiting, fever, abdominal pain, rash.
Epidemiology: Travel history, sick contacts, daycare attendance, water source (well water).

Physical Examination: Dehydration Severity

The Canadian Paediatric Society (CPS) recommends using a clinical dehydration scale.

Clinical Sign	Mild Dehydration (<5%)	Moderate Dehydration (5-10%)	Severe Dehydration (>10%)
General Appearance	Well, alert	Restless, irritable	Lethargic, floppy, comatose
Eyes	Normal	Sunken	Deeply sunken
Mucous Membranes	Moist	Sticky/Dry	Parched
Tears	Present	Decreased	Absent
Skin Turgor	Instant recoil	Slow recoil (<2 sec)	Tenting (>2 sec)
Capillary Refill	<2 sec	2–3 sec	>3 sec
Heart Rate	Normal	Increased	Tachycardic/Bradycardic (late)
Blood Pressure	Normal	Normal	Hypotensive (Shock)

🚩 Red Flags (Requires Urgent Evaluation)

Bilious vomiting (Volvulus until proven otherwise)
Bloody stool in an infant (Intussusception, allergic colitis)
Severe abdominal pain or peritoneal signs
Signs of shock (Hypotension, cool extremities)
Young age (< 2 months)

Investigations

For uncomplicated acute gastroenteritis (AGE), no investigations are required.

Indications for Testing

Stool Culture/Microscopy:
- Bloody diarrhea (dysentery).
- History of travel to endemic areas.
- Immunocompromised host.
- Prolonged diarrhea (>7 days).
- Outbreak situations.
Electrolytes & Glucose:
- Severe dehydration requiring IV fluids.
- Altered mental status.
- History suggestive of hypernatremia (doughy skin) or hyponatremia.

Management

Management focuses on rehydration and nutrition.

1. Rehydration Strategy (Canadian Guidelines)

Step 1: Assess Severity

Determine if the child has mild, moderate, or severe dehydration based on the table above.

Step 2: Oral Rehydration Therapy (ORT)

For mild to moderate dehydration, ORT is the gold standard.

Solution: Use commercially available solutions (e.g., Pedialyte). Avoid juice, soda, or sports drinks (high osmolarity).
Dosing: 50–100 mL/kg over 4 hours.
Small frequent amounts: 5 mL every 2–5 minutes if vomiting.

Step 3: Antiemetics

Ondansetron (Zofran): A single oral dose is recommended by CPS for children (6 months to 12 years) with vomiting related to AGE to facilitate ORT.

Dose: Based on weight (e.g., 2 mg for 8-15 kg).

Step 4: Intravenous Fluids (IVF)

Indicated for severe dehydration (shock) or failure of ORT (intractable vomiting).

Bolus: 20 mL/kg of Normal Saline or Ringer’s Lactate. Repeat as needed for shock.
Maintenance: D5W + 0.9% NaCl (or 0.45% NaCl depending on age/guidelines) once stable.

2. Nutrition

Early Refeeding: Resume age-appropriate diet as soon as rehydration is achieved.
Breastfeeding: Continue breastfeeding throughout rehydration.
BRAT Diet: The BRAT diet (Bananas, Rice, Applesauce, Toast) is no longer recommended as it is low in energy and protein.

3. Pharmacotherapy

Antibiotics: Generally not indicated for routine AGE.
- Exceptions: Proven Shigella, Campylobacter (if severe/early), Giardia, or C. difficile.
Antidiarrheals (Loperamide): Contraindicated in children due to risk of ileus and toxicity.

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Critical MCCQE1 Concept: Never give antibiotics or antimotility agents if E. coli O157:H7 (STEC) is suspected (bloody diarrhea). Antibiotics increase the release of Shiga toxin, significantly increasing the risk of Hemolytic Uremic Syndrome (HUS).

Canadian Guidelines (Key Summaries)

CPS Statement on Acute Gastroenteritis:
- Focus on ORT over IV.
- Use of Ondansetron to prevent IV insertion.
- Rapid return to normal diet.
Public Health:
- Reportable diseases: Salmonella, Shigella, Campylobacter, E. coli O157:H7, Giardia.
- Exclusion from daycare/school until symptom-free for 24–48 hours (varies by province).

Key Points to Remember for MCCQE1

Hypovolemic Shock: The most immediate threat to life in diarrhea. Recognize tachycardia and prolonged capillary refill.
Hypernatremic Dehydration: Classically presents with “doughy” skin and irritability. Rehydrate slowly to prevent cerebral edema.
Toddler’s Diarrhea: A diagnosis of exclusion. Look for the “peas and carrots” description in the stem. Management is dietary modification (more fat/fiber, less fruit juice).
Celiac Disease: Screen with Tissue Transglutaminase IgA (tTG-IgA) if chronic diarrhea + failure to thrive.
Formula Intolerance: Consider switching to hydrolyzed formula if bloody stools are seen in a well-appearing infant (allergic colitis).

Sample Question

Clinical Scenario

A 2-year-old girl is brought to the Emergency Department by her parents with a 2-day history of vomiting and watery diarrhea. She has had 6 episodes of diarrhea and 4 episodes of vomiting today. She is alert but irritable. On examination, her eyes appear slightly sunken, mucous membranes are sticky, and capillary refill is 2.5 seconds. Her heart rate is 130 bpm, and blood pressure is 90/60 mmHg. She weighs 12 kg.

Question

Which one of the following is the most appropriate initial management step?

A. Administer 20 mL/kg bolus of 0.9% saline IV
B. Prescribe loperamide and discharge home
C. Administer a single dose of oral ondansetron and initiate oral rehydration therapy
D. Keep NPO (nothing by mouth) for 4 hours to rest the gut
E. Start empirical antibiotics with oral azithromycin

Explanation

The correct answer is:

C. Administer a single dose of oral ondansetron and initiate oral rehydration therapy

Detailed Explanation:

Assessment: The child presents with signs of moderate dehydration (irritable, sunken eyes, sticky mucosa, prolonged cap refill, tachycardia). She is not in shock (blood pressure is maintained, alert).
Guideline Application: According to Canadian Paediatric Society guidelines, the first-line treatment for mild to moderate dehydration is Oral Rehydration Therapy (ORT).
Role of Ondansetron: Since the child has active vomiting which may hinder ORT, a single dose of oral ondansetron is recommended to reduce vomiting and increase the success rate of oral rehydration, thereby preventing the need for IV fluids.

Why other options are incorrect:

A. IV Bolus: This is reserved for severe dehydration or shock (decompensated state). This child is hemodynamically stable. IV placement is invasive and unnecessary at this stage.
B. Loperamide: Antidiarrheal agents are contraindicated in children due to safety concerns (ileus, sedation) and lack of efficacy in treating the underlying cause.
D. NPO: “Gut rest” is outdated. Continued feeding supports gut mucosal recovery. Starvation can prolong diarrhea and lead to malnutrition.
E. Antibiotics: Most cases of pediatric diarrhea are viral. Antibiotics are not indicated empirically and can be harmful (e.g., increasing HUS risk in STEC).

References

Canadian Paediatric Society. (2021). Oral rehydration therapy and early refeeding in the management of childhood gastroenteritis. Link to CPS
Medical Council of Canada. (2023). MCCQE Part I Objectives: Gastrointestinal System.
Cheng, A. (2011). Emergency management of the paediatric patient with generalized dehydration. Canadian Paediatric Society Position Statement.
Freedman, S. B., et al. (2006). Ondansetron for the treatment of gastroenteritis in children. N Engl J Med.

Study Tip 💡

For the MCCQE1 CDM (Clinical Decision Making) section, always prioritize least invasive measures first. If a child is moderately dehydrated, choose ORT before IV fluids unless there are specific contraindications.