9.3 Dehydration, Gastroenteritis, Intussusception & Pyloric Stenosis

Pediatric Gastroenterology and Hydration Management

Gastrointestinal complaints in children range from self-limiting viral illnesses to acute surgical emergencies. A thorough history detailing the onset, type of vomiting (bilious vs. non-bilious), stool characteristics, and an assessment of volume status are paramount for accurate diagnosis.

Dehydration and Gastroenteritis

Acute gastroenteritis is characterized by the rapid onset of diarrhea, often accompanied by nausea, vomiting, and fever. In children, viruses (Rotavirus, Norovirus, Adenovirus) are the most common culprits. The most significant and potentially life-threatening complication is dehydration.

Assessment of Dehydration: Accurate assessment directs therapy. Clinical signs guide the estimation of volume deficit:

• Mild (<5%): Normal mental status, slight thirst, normal heart rate, normal tears, slightly dry mucous membranes.
• Moderate (5-10%): Irritable/restless, thirsty, tachycardia, decreased tears, dry mucous membranes, delayed capillary refill (2-3 seconds), decreased urine output.
• Severe (>10%): Lethargic/unconscious, unable to drink, tachycardia or bradycardia, absent tears, parched mucous membranes, sunken eyes/fontanelle, capillary refill >3 seconds, oliguria/anuria.

Management:

• Mild to Moderate: Oral Rehydration Therapy (ORT) is the preferred treatment. Use commercially available oral rehydration solutions (ORS) administered frequently in small amounts (e.g., 50-100 mL/kg over 3-4 hours, plus replacement for ongoing losses). Avoid sugary drinks like juice or soda, which can worsen osmotic diarrhea.
• Severe: A medical emergency requiring immediate intravenous (IV) access. Administer an isotonic crystalloid fluid bolus (Normal Saline or Lactated Ringer's) at 20 mL/kg over 20-30 minutes. Repeat as necessary until perfusion improves, then transition to maintenance and deficit replacement fluids.

Hypertrophic Pyloric Stenosis (HPS)

HPS is an acquired hypertrophy of the pyloric muscle leading to gastric outlet obstruction. It is more common in first-born males and typically presents between 3 and 6 weeks of age.

Clinical Presentation:

• Progressively worsening, non-bilious, projectile vomiting immediately after feeding. The infant remains hungry and eagerly feeds again ("hungry vomiter").
• Physical examination may reveal a palpable, firm, "olive-like" mass in the right upper quadrant, especially post-emesis, and visible gastric peristaltic waves moving from left to right.

Pathophysiology & Labs: Persistent vomiting of gastric acid (HCl) leads to the classic laboratory derangement: hypochloremic, hypokalemic metabolic alkalosis. The kidneys excrete potassium to conserve hydrogen ions in response to the alkalosis.

Diagnosis & Management:

• Ultrasound is the imaging modality of choice, showing an elongated and thickened pyloric muscle (muscle thickness >3 mm, length >14 mm, often described as the "target sign" in cross-section).
• Treatment: Initial management MUST focus on correcting fluid and electrolyte imbalances (IV hydration with 0.45% NS + D5 + Potassium chloride) before surgical intervention. Once the alkalosis is corrected and the patient is stable, a definitive surgical pyloromyotomy (Ramstedt procedure) is performed.

Intussusception

Intussusception is the invagination (telescoping) of a proximal segment of the bowel into a distal segment, most commonly at the ileocecal junction. It is the most common cause of intestinal obstruction in children aged 6 to 36 months.

Clinical Presentation:

• Sudden onset of severe, intermittent, colicky abdominal pain. The child typically draws their legs up to the abdomen and cries uncontrollably, with periods of normal behavior or extreme lethargy between episodes.
• Associated with non-bilious vomiting that may progress to bilious vomiting as obstruction worsens.
• Classic late finding: Passage of "currant jelly" stools (a mixture of blood and mucus from ischemic bowel mucosa).
• A sausage-shaped mass may be palpated in the right upper or middle abdomen, while the right lower quadrant feels empty (Dance sign).

Diagnosis & Management:

• Ultrasound: The initial test of choice; demonstrates a "target sign" or "donut sign" (concentric rings of bowel) in the transverse view, or a "pseudokidney sign" in the longitudinal view.
• Treatment: Non-operative reduction using an air or contrast enema under fluoroscopic or ultrasound guidance is both diagnostic and therapeutic. It is successful in the majority of cases and is the standard of care in stable patients without signs of peritonitis or bowel perforation. If non-operative reduction fails or if there is evidence of necrosis/perforation, surgical exploration and manual reduction or resection is required.

Hirschsprung Disease

A congenital disorder characterized by the absence of ganglion cells (aganglionosis) in the myenteric and submucosal plexuses of the distal colon and rectum, leading to functional obstruction due to failure of relaxation.

Clinical Presentation:

• Neonates: Failure to pass meconium within the first 48 hours of life, bilious vomiting, and abdominal distension.
• Older infants/children: Chronic, severe treatment-resistant constipation and failure to thrive.
• Digital rectal examination reveals a tight anal sphincter and an empty rectal vault; withdrawal of the finger may result in a forceful expulsion of retained stool and flatus (the "squirt sign" or "blast sign").

Diagnosis & Management:

• Contrast enema shows a transition zone between the narrow aganglionic distal segment and the dilated normal proximal bowel.
• Rectal suction biopsy is the gold standard for diagnosis, demonstrating an absence of ganglion cells and hypertrophied nerve trunks.
• Treatment is surgical resection of the aganglionic segment with an anastomosis of the normal innervated bowel to the anus.

Key Differentiating Signs in Pediatric GI Obstruction

Identifying the type of emesis (bilious vs. non-bilious) is a critical branching point in pediatric surgical emergencies.