Hirschsprung Disease in Neonates

Definition and Epidemiology

• Down syndrome (trisomy 21) - 3-10% of HD cases
• Multiple endocrine neoplasia types 2A and 2B
• Ileal/colonic/anorectal atresias, cleft palate, cardiac septal defects, polydactyly

Pathogenesis

• Meissner's submucosal plexus
• Auerbach's myenteric plexus

Segment Distribution

Clinical Presentation in Neonates

90% of patients present in the neonatal period. Classic triad:

1. Failure to pass meconium within the first 24-48 hours of life (most common presentation; >90% of affected neonates)
2. Abdominal distension - progressive, prominent
3. Bilious vomiting

• Chronic constipation, failure to thrive
• Poor weight gain, irritability
• Alternating diarrhea and obstipation

• Meconium ileus (cystic fibrosis)
• Ileal/colonic atresia
• Meconium plug syndrome / small left colon syndrome
• Anorectal malformations
• Megacystis-microcolon-intestinal hypoperistalsis syndrome
• Paralytic ileus (sepsis, drugs, metabolic)
• Hypothyroidism, infantile botulism

Life-Threatening Complication: Hirschsprung Enterocolitis (HAEC)

• Long-segment disease
• Diagnosis made after the first week of life

Investigations

Imaging

• Narrow caliber aganglionic distal rectum
• Proximal dilation of normally innervated colon
• "Transition zone" - abrupt caliber change
• The rectosigmoid ratio is reversed (normally rectum > sigmoid; in HD, sigmoid > rectum)
• Failure to evacuate contrast within 24 hours is highly suggestive
• Sensitivity ~70%, specificity ~83%
• In TCA, the enema may be entirely normal (difficult to diagnose radiologically)

Barium enema (A) showing constricted rectum with dilated sigmoid colon. Intraoperative specimen (B) demonstrating the grossly dilated proximal colon. - Robbins Basic Pathology

Anorectal Manometry

Rectal Biopsy (Gold Standard)

• Performed at bedside using a suction rectal biopsy kit in neonates
• Must be obtained at least 5 mm to 1 cm above the dentate line (to avoid the normal aganglionic anoderm zone)
• Two or more specimens, 1 cm apart in the posterior rectum, are recommended
• Older children require full-thickness biopsy under general anesthesia

• Absent ganglion cells
• Hypertrophied nerve trunks
• Robust acetylcholinesterase (AChE) immunostaining
• Calretinin immunostaining - a standard adjunct (negative/absent staining in aganglionic segment)

Management

Immediate / Pre-operative

• Daily rectal irrigations with a soft red rubber catheter and warm normal saline - performed 1-2x/day until effluent is clear
• Decompresses the bowel and reduces risk of enterocolitis
• May not be feasible in long-segment disease, certain comorbidities, or poor family circumstances - in these cases, leveling colostomy with intraoperative biopsies is performed

Definitive Surgery: Pull-Through Procedures

Postoperative Issues

• Constipation (common), soiling, incontinence, postoperative enterocolitis
• Intermittent rectal decompression may be needed
• Stool softeners and laxatives for persistent constipation
• Up to 10% of patients eventually require permanent colostomy
• If symptoms persist, histologic re-evaluation to confirm normal ganglionated pull-through and rule out transition zone at anastomosis
• Anastomotic leaks, fistulae, abscesses, stenoses are recognized complications

Summary Table

• Sabiston Textbook of Surgery, block 28 (p. 2687-2688)
• Robbins Basic Pathology, block 6 (p. 563)
• Rosen's Emergency Medicine, block 30
• Grainger & Allison's Diagnostic Radiology, block 13 (p. 1797-1798)

Postoperative Complications of Fentanyl and Atracurium in Neonates

Why Neonates Are Uniquely Vulnerable

FENTANYL - Postoperative Complications in Neonates

1. Respiratory Depression

• μ-receptor activation in the brainstem respiratory center
• Raises the apneic threshold (less sensitive to CO2 rise)
• Blunts the hypoxic ventilatory drive
• Even mild hypocapnia (from anxious or pain-driven hyperventilation pre-op) enhances and prolongs postoperative respiratory depression after fentanyl - because hypocapnia increases un-ionized (brain-penetrant) fentanyl and decreases cerebral blood flow, slowing clearance

• Continuous infusions cause respiratory depression more frequently than bolus doses in neonates
• Postoperative mechanical ventilation is required when high-dose fentanyl (>20 mcg/kg) is used
• Pulse oximetry may fail to detect early respiratory depression during hyperoxia - SpO2 remains normal in the first minutes

2. Chest Wall Rigidity (Fentanyl-Induced Muscle Rigidity / "Wooden Chest")

• Doses as small as 1-2 mcg/kg can cause significant chest wall and glottic rigidity in neonates
• Results in desaturation and inability to ventilate with bag-mask
• May require neuromuscular blocking agent and emergency intubation
• Mechanism: μ-opioid receptor activation causing increased muscle spindle activity; more pronounced with rapid IV bolus administration
• The highly compliant neonatal chest wall makes the rigid thorax particularly difficult to ventilate manually

3. Hemodynamic Instability

• When used with benzodiazepines (e.g., midazolam), fentanyl can cause hypotension in neonates
• In isolation at standard doses, fentanyl maintains good cardiovascular stability
• Causes bradycardia by reducing sympathetic tone and enhancing parasympathetic activity
• Combination of opioids + benzodiazepines for >1 week is associated with worse neurodevelopmental outcomes compared to either agent alone

4. Tolerance and Withdrawal

• Neonates receiving prolonged fentanyl infusions (>5-7 days) develop opioid tolerance and physical dependence
• Abrupt discontinuation causes a neonatal opioid withdrawal syndrome: irritability, tachycardia, diaphoresis, feeding difficulty, tremors, high-pitched cry
• Management requires weaning via methadone (long-acting opioid) in the NICU setting
• Methadone use requires ECG monitoring for QT prolongation

5. Renarcotization After Naloxone

• Fentanyl has a longer plasma half-life than naloxone
• After reversal with naloxone bolus, re-sedation and respiratory depression can recur ("renarcotization") as the naloxone effect wanes
• Requires continuous naloxone infusion or repeated dosing, with careful monitoring

6. Opioid-Induced Pulmonary Vasoconstriction Blunting

• Fentanyl blocks stimulus-induced pulmonary vasoconstriction, which can be beneficial in neonates with reactive pulmonary vascular beds (e.g., after CDH repair, CHD surgery)
• In the postoperative period, loss of this effect upon drug clearance may trigger rebound pulmonary hypertensive crises if fentanyl is weaned too quickly

7. Neurodevelopmental Concerns

• No significant maturational change in brain sensitivity to fentanyl (unlike morphine, where morphine-6-glucuronide sensitivity increases with age)
• Sedation with combined opioids and benzodiazepines >1 week in neonates is associated with worse neurodevelopmental outcomes

ATRACURIUM - Postoperative Complications in Neonates

1. Prolonged Neuromuscular Blockade

• The neonatal NMJ is more sensitive to nondepolarizing agents, meaning a lower dose achieves block
• However, this is counterbalanced by the larger ECF volume (larger volume of distribution), so mg/kg dosing is similar to older children
• Organ maturation has a tremendous impact on clearance - there is considerable variability and unpredictability in duration of action in neonates
• Postoperative residual neuromuscular blockade can cause respiratory failure, upper airway obstruction, and inability to extubate

• Hypothermia - slows Hofmann elimination (requires normal body temperature for reliable degradation)
• Acidosis - also slows Hofmann elimination
• Altered pH - since elimination is pH-dependent, any acid-base disturbance (common postoperatively in sick neonates) can prolong block

2. Histamine Release (Atracurium > Cisatracurium)

• Manifests as: skin flushing, urticaria, hypotension, bronchospasm, tachycardia
• Neonates, especially those with reactive airways or congenital lung disease, are at higher risk
• Cisatracurium, which specifically lacks histamine release, is preferred in neonates for this reason
• Histamine-mediated bronchospasm can lead to severe postoperative respiratory compromise

3. Laudanosine Accumulation (Metabolite Toxicity)

• Laudanosine is a CNS stimulant that can lower the seizure threshold
• Accumulates with prolonged infusions in neonates, particularly in hepatic failure (laudanosine is cleared hepatically)
• Although not clinically significant at typical single doses, prolonged NICU infusions raise concern for seizure activity in neonates
• Cisatracurium produces approximately 5-fold less laudanosine than atracurium at equipotent doses

4. Inadequate Reversal and Postoperative Apnea

• Neostigmine administered without an anticholinergic agent (atropine or glycopyrrolate) is the most common drug error leading to perioperative cardiac arrest in the pediatric population - causes profound bradycardia and bronchospasm
• Neostigmine requires ~10 minutes for 90% reversal at 0.07 mg/kg

5. Cardiovascular Effects

• Unlike pancuronium, atracurium and cisatracurium have minimal to no direct cardiovascular effects on the neonatal myocardium
• However, histamine release from atracurium can cause tachycardia, hypotension, and vasodilation postoperatively
• Cisatracurium has essentially no cardiovascular side effects

6. Temperature and pH Dependence

• Hofmann elimination slows dramatically with hypothermia and acidosis
• A neonate who was blocked intraoperatively and then becomes cold or acidotic postoperatively may have unexpectedly prolonged paralysis
• Active warming and acid-base correction are essential to restore predictable recovery

Summary Comparison Table

Monitoring and Reversal Essentials

• Nerve stimulator monitoring mandatory but technically challenging in neonates
• All nondepolarizing NMBAs must be reversed in neonates given unpredictability
• Neostigmine must always be paired with atropine or glycopyrrolate
• Maintain normothermia and correct acidosis postoperatively to ensure Hofmann elimination proceeds normally
• Fentanyl-treated neonates require continuous SpO2 and respiratory rate monitoring; have naloxone and ventilation equipment at bedside
• In cases of fentanyl chest wall rigidity: succinylcholine 3 mg/kg IV + immediate intubation

• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e (pp. 3594-3599) - Neonatal opioids and NMBAs
• Miller's Anesthesia, 10e (pp. 10765-10768) - Fentanyl in neonatal cardiac surgery; opioid-induced respiratory depression
• Miller's Anesthesia, 10e (Box 22.2) - Factors increasing opioid respiratory depression