Intussusception and dehydration

Intussusception

Intussusception is the invagination or telescoping of a proximal segment of intestine (the intussusceptum) into the lumen of an immediately adjacent distal segment (the intussuscipiens). As peristalsis draws the bowel segment forward, the mesentery is dragged into the lumen, causing venous compression, mucosal oedema, arterial compromise, bowel necrosis, and perforation.

Epidemiology and Anatomical Location

• Peak Age: Most common between 6 and 36 months of age (peak incidence at 6 to 9 months). It is the leading cause of intestinal obstruction in infants and young children.
• Anatomical Site: Over 90% of cases are ileocolic, where the terminal ileum invaginates through the ileocaecal valve into the ascending or transverse colon.

Aetiological Classification

• Idiopathic (~90% of cases): Hypertrophy of lymphoid tissue in the terminal ileum (Peyer patches) acts as a physiological lead point. Frequently triggered by an antecedent viral infection, such as adenovirus (mesenteric adenitis) or rotavirus.
• Pathological Lead Points (~10% of cases): Strongly suspected in children older than 2 to 3 years, children with recurrent intussusceptions, or infants under 3 months. Specific lead points include:
  • Meckel diverticulum (most common pathological lead point).
  • Intestinal polyps (e.g., Peutz-Jeghers syndrome).
  • Submucosal bowel haematoma in Henoch-Schönlein purpura (IgA vasculitis).
  • Intestinal duplication cyst or non-Hodgkin lymphoma.

Classical Clinical Presentation

• The Classical Triad (present in fewer than 30% to 50% of presentations):
  1. Paroxysmal Severe Colicky Abdominal Pain: The infant suddenly screams, draws the knees and legs up to the chest, and turns pale. Episodes last 2 to 5 minutes, recur every 15 to 20 minutes, and are separated by intervals where the infant appears deceptively calm, comfortable, or unusually lethargic.
  2. Vomiting: Initially non-bilious gastric contents; becomes bilious (dark green) as complete mechanical intestinal obstruction develops.
  3. "Red Currant Jelly" Stools: Stool containing a mixture of sloughed, ischaemic intestinal mucosa, blood, and mucus. This is a late finding indicating advanced mucosal ischaemia and impending bowel infarction; clinicians must not wait for red currant jelly stools to make the diagnosis.
• Physical Examination:
  • Sausage-Shaped Mass: Palpation of a tubular, sausage-shaped mass in the right upper quadrant or epigastrium, oriented along the axis of the colon.
  • Dance Sign: An empty feeling or emptiness in the right lower quadrant (right iliac fossa) due to the migration of the caecum into the upper abdomen.
  • Systemic lethargy: A subgroup of infants presents predominantly with profound lethargy, hypotonia, and somnolence (often mistaken for sepsis, intoxication, or encephalitis) driven by endogenous opioid/endorphin release.

Diagnostic Imaging

• Abdominal Ultrasonography: The imaging modality of choice, with sensitivity and specificity approaching 100% in experienced hands.
  • Transverse view: "Target sign" or "Doughnut sign" consisting of concentric alternating hyperechoic and hypoechoic rings formed by the edematous layers of the intussusceptum and intussuscipiens.
  • Longitudinal view: "Pseudokidney sign" (curved bowel layers mimicking renal parenchyma).

Emergency Management & Non-Operative Reduction

1. Initial Stabilization: Cease oral intake, insert a nasogastric tube on free drainage, secure intravenous access, administer fluid resuscitation with $0.9\%$ sodium chloride, and consult paediatric surgery.
2. Pneumatic (Air) Enema Reduction: The definitive first-line procedure of choice under fluoroscopic control. Air is insufflated via a large-bore Foley catheter placed in the rectum at controlled pressures (maximum pressure limit $80\text{ to }120\text{ mmHg}$). Complete reduction is confirmed by the abrupt disappearance of the soft-tissue mass and free, extensive reflux of air into multiple loops of the terminal ileum. Non-operative air reduction achieves success in over 80% to 90% of uncomplicated cases.
3. Contraindications to Air Enema Reduction:
   • Clinical signs of peritonitis or generalised abdominal rigidity.
   • Evidence of bowel perforation or pneumoperitoneum on plain radiography (e.g., Rigler sign, free gas under the diaphragm).
   • Prolonged irreversible shock.
4. Operative Intervention: Indicated when pneumatic enema is contraindicated, fails after 2 to 3 careful attempts, or when a pathological lead point is identified. Involves open or laparoscopic manual reduction via gentle retrograde milking (never pulling); segmental bowel resection and end-to-end anastomosis are performed if the bowel is gangrenous or perforated.

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Assessment and Management of Paediatric Dehydration

Infants and young children have a high ratio of body surface area to body weight, higher metabolic rates, and higher total body water turnover, rendering them exceptionally vulnerable to rapid dehydration during acute gastroenteritis or febrile illnesses.

Clinical Dehydration Staging (Australian Clinical Practice Guidelines)

• Mental State: Mild Dehydration ($< 5\%$ Weight Loss): Alert, active, responsive; Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Irritable, restless, thirsty; Severe Dehydration ($\ge 10\%$ Loss / Shock): Lethargic, somnolent, comatose, limp
• Mucous Membranes: Mild Dehydration ($< 5\%$ Weight Loss): Moist; Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Dry; Severe Dehydration ($\ge 10\%$ Loss / Shock): Parched, cracked
• Eyes & Tears: Mild Dehydration ($< 5\%$ Weight Loss): Normal eyes; tears present; Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Sunken eyes; reduced tears; Severe Dehydration ($\ge 10\%$ Loss / Shock): Deeply sunken eyes; absent tears
• Anterior Fontanelle: Mild Dehydration ($< 5\%$ Weight Loss): Normal, flat; Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Sunken; Severe Dehydration ($\ge 10\%$ Loss / Shock): Deeply depressed
• Skin Turgor: Mild Dehydration ($< 5\%$ Weight Loss): Instant recoil ($< 1\text{ s}$); Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Mild delay (recoil $1\text{ to }2\text{ s}$); Severe Dehydration ($\ge 10\%$ Loss / Shock): Marked tenting (recoil $> 2\text{ seconds}$)
• Capillary Refill: Mild Dehydration ($< 5\%$ Weight Loss): Normal ($< 2\text{ seconds}$); Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Prolonged ($2\text{ to }3\text{ seconds}$); Severe Dehydration ($\ge 10\%$ Loss / Shock): Markedly prolonged ($> 3\text{ to }4\text{ seconds}$)
• Circulatory Signs: Mild Dehydration ($< 5\%$ Weight Loss): Normal pulse, normal BP; Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Tachycardia; normal blood pressure; Severe Dehydration ($\ge 10\%$ Loss / Shock): Marked tachycardia; weak thready pulses; hypotension
• Urine Output: Mild Dehydration ($< 5\%$ Weight Loss): Normal or slightly decreased; Moderate Dehydration ($5\%\text{ to }9\%$ Loss): Oliguria (decreased wet nappies); Severe Dehydration ($\ge 10\%$ Loss / Shock): Anuria

Fluid Resuscitation Protocols

1. Mild to Moderate Dehydration: Oral Rehydration Therapy (ORT)

• First-Line Standard: Oral rehydration therapy is safer, more physiological, and has lower complication rates than intravenous fluids for mild-to-moderate dehydration.
• Physiological Mechanism: Exploit intact sodium-glucose cotransporters (SGLT1) on the brush border membrane of enterocytes. Active equimolar absorption of sodium and glucose generates an osmotic gradient that drives passive water reabsorption into the bloodstream, bypassing intestinal secretory pathways.
• Commercial Solutions: Hypotonic oral rehydration salts (e.g., Gastrolyte, Hydralyte) containing sodium $45\text{ to }60\text{ mmol/L}$ and glucose $2\%\text{ to }2.5\%$.
• Enteral rehydration: Small frequent sips improve tolerance, but a 5-mL sip schedule alone is not a full deficit-replacement plan. Set a weight-based oral/NG volume under the gastroenteritis pathway, replace continuing losses and reassess. Shock or impaired airway protection requires IV/IO resuscitation.
• Breastfeeding Rule: Breastfeeding must never be ceased during rehydration.

2. Severe Dehydration / Hypovolaemic Shock: Intravenous Resuscitation

• Immediate medical emergency. Establish intravenous (or intraosseous) access.
• Paediatric shock fluids: Give a measured 10–20 mL/kg isotonic bolus under the local emergency pathway, reassess perfusion and signs of overload after each bolus, and obtain early senior support. Do not automatically continue to 60 mL/kg before reconsidering the cause or vasoactive support.
• Maintenance Fluid Calculation (Holliday-Segar Formula):
  • First $10\text{ kg}$: $100\text{ mL/kg/day}$ ($4\text{ mL/kg/hr}$)
  • $11\text{ to }20\text{ kg}$: Add $50\text{ mL/kg/day}$ ($2\text{ mL/kg/hr}$ for each $\text{kg} > 10\text{ kg}$)
  • Each $\text{kg} > 20\text{ kg}$: Add $20\text{ mL/kg/day}$ ($1\text{ mL/kg/hr}$ for each $\text{kg} > 20\text{ kg}$)
• Maintenance fluids: Isotonic fluids are standard for most acutely unwell hospitalised children to reduce hyponatraemia risk. Calculate requirements, then adjust for illness and losses; the hourly 4:2:1 rule approximates the daily Holliday–Segar method. Add potassium only after kidney function/urine output assessment, never to a resuscitation bolus. Special circumstances require specialist prescriptions rather than a blanket ban on every non-isotonic fluid.

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Primary references (checked 7 October 2026): RCH pyloric stenosis.