CONGENITAL DIAPHRAGMATIC HERNIA (CDH) AND ANORECTAL MALFORMATION (ARM) WITH ANOVESTIBULAR FISTULA (AVF)

A Detailed Review Based on Miller's Anesthesia (10e), Morgan & Mikhail's Clinical Anesthesiology (7e), and Barash's Clinical Anesthesia (9e)

PART I: CONGENITAL DIAPHRAGMATIC HERNIA

1. Introduction and Embryology

• Bochdalek hernia (posterolateral) - 70-75% of CDH cases; occurs predominantly on the left (85%), right (13%), or rarely bilateral (2%)
• Morgagni hernia (anterior) - 23-28%
• Central hernia - 2-7% (Sabiston, p. 2675)

• Pulmonary hypoplasia (bilateral, ipsilateral > contralateral)
• Pulmonary hypertension (reactive, hyperreactive vasculature)
• Potential persistence of fetal circulation with right-to-left shunting

2. Diagnosis

Antenatal Diagnosis

• Mediastinal shift
• Juxta-cardiac gastric dilatation
• Polyhydramnios
• Associated congenital anomalies
• In right-sided CDH, the liver may be seen in the right chest

• Coexistent congenital anomalies (cardiac, chromosomal)
• Degree of lung hypoplasia
• Intrathoracic liver herniation
• Lung-to-Head Ratio (LHR): A sonographic measure comparing contralateral lung area to head circumference. The observed-to-expected LHR (o/e LHR) is a key predictor - fetuses with o/e LHR < 25% have the worst prognosis and lowest survival. (Sabiston, p. 2675-2676)

Postnatal Clinical Presentation

• Respiratory distress immediately or within a few hours of birth
• Scaphoid abdomen (absent intra-abdominal contents, which have herniated into the chest)
• Reduced or absent breath sounds on the affected side
• Bowel sounds audible in the thorax
• Cardiac displacement to the contralateral side
• Hypoxemia, cyanosis

• Chest radiograph is confirmatory - showing multiple gas-filled bowel loops in the hemithorax, mediastinal shift to the contralateral side, and ipsilateral lung opacification. This is the classic and immediate investigation.
• Associated anomalies: More than half of CDH cases are associated with pulmonary hypoplasia and other congenital anomalies including cardiac defects, chromosomal abnormalities, and GI malformations. A full organ system evaluation is required. (Miller's Anesthesia, p. 10640)

3. Treatment

Immediate Stabilization (Preoperative)

1. Airway management: Immediate tracheal intubation and ventilatory support. Bag-mask ventilation must be avoided prior to intubation to minimize gastric distention within the chest, which can further compress the lungs.
2. Nasogastric decompression to reduce bowel distension within the thorax.
3. Ventilation strategy - "Gentilation"/Permissive Hypercapnia:
   • Aggressive hyperventilation to induce respiratory alkalosis has been abandoned due to high iatrogenic lung injury
   • Conventional ventilation with permissive hypercapnia is now favored
   • Goals: preductal SpO2 >85%, peak inspiratory pressures (PIP) <25 cm H2O (Barash) / <30 cm H2O (Morgan), PaCO2 45-55 mmHg (Barash), postductal PaCO2 <65 mmHg (Morgan)
   • High-frequency oscillatory ventilation (HFOV) in place of conventional ventilation to reduce barotrauma - demonstrated beneficial outcomes
   • Pressure-limited ventilation is used (Barash, p. 3653; Morgan & Mikhail, p. 1713)
4. Pulmonary hypertension management (multimodal):
   • Inhaled nitric oxide (iNO): Reduces pulmonary artery pressures but does not appear to improve survival
   • Sildenafil (PDE-5 inhibitor)
   • Milrinone (PDE-3 inhibitor)
   • Epoprostenol/iloprost (PGI2 analogues)
   • Bosentan (endothelin receptor antagonist)
   • Avoid hypoxemia and excessive hypercapnia (both increase pulmonary vascular resistance) (Barash, p. 3655)
5. Surfactant: Neonates with CDH may have surfactant deficiency; surfactant prophylaxis has shown improvement in oxygenation in animal models.
6. ECMO (Extracorporeal Membrane Oxygenation):
   • Venoarterial ECMO is used for the most severe, unstable cases
   • Initiated in the mid-1980s; has improved survival compared to historical data
   • The CDH Study Group demonstrated ECMO improves survival in those with predicted mortality ≥80% based on birth weight and 5-minute Apgar score
   • Right-sided CDH carries higher mortality even with ECMO
   • There is ongoing debate whether repair should occur during, at weaning from, or after ECMO decannulation
   • Bleeding complications are higher in patients repaired while on ECMO (Barash, p. 3653-3654)
7. Avoid hypothermia: Increases oxygen demand and precipitates pulmonary hypertension.

Fetal Surgery

Surgical Repair

• Open: Via an ipsilateral subcostal abdominal incision (most common) - bowel reduced into abdomen and diaphragm closed. Also transthoracic approaches used.
• Thoracoscopic/laparoscopic repair is feasible but no clear data supports superiority over open approach for outcomes.

• Excision of hernia sac if present
• Reduction of intrathoracic visceral contents into the abdomen
• Primary repair with interrupted nonabsorbable sutures (with Teflon pledgets for large defects)
• For large defects: prosthetic patch (Gore-Tex most common), or muscle flaps (rectus abdominis/latissimus dorsi)
• Thoracostomy tube placement is generally not routinely needed post-repair
• Aggressive lung expansion of the ipsilateral lung is detrimental - the hypoplastic lung must not be forcibly inflated
• Abdominal silo may be required if loss of abdominal domain leads to compartment syndrome (Sabiston, p. 2676-2677)

4. Anaesthetic Management

Preoperative Assessment

• Most neonates with CDH will already be intubated and on ventilatory support when they present for surgery
• Assess degree of pulmonary hypertension and hypoplasia
• Review all congenital anomalies (cardiac, GI, renal, chromosomal)
• Document current ventilatory parameters; replicate or improve upon them intraoperatively
• Note pre-existing vasopressor/pulmonary vasodilator support

Induction of Anaesthesia

• Bag-and-mask ventilation must be avoided prior to intubation to prevent gastric distention within the thorax
• The neonate should have a nasogastric tube in place for gastric decompression
• If not already intubated: awake intubation or preoxygenation with intubation without muscle relaxants is preferred (Morgan & Mikhail, p. 1713-1714). This avoids the risk of distending intrathoracic bowel with positive pressure.
• Rapid sequence induction if muscle relaxants are used, with cricoid pressure consideration
• Nitrous oxide is absolutely contraindicated - it expands bowel gas within the chest, worsens hypoxia, and increases pulmonary vascular resistance

Monitoring

• Preductal pulse oximeter (right hand or right ear) - to detect ductal right-to-left shunting
• Postductal pulse oximeter (lower limb) - comparison with preductal value quantifies shunting
• Arterial line for continuous blood pressure and arterial blood gas monitoring (preductal artery preferred - right radial or temporal; umbilical artery catheter if in place)
• Central venous access for vasoactive drug administration
• Temperature monitoring - neonates are highly vulnerable to hypothermia

Maintenance of Anaesthesia

• Volatile agents at low concentrations with or without opioids (Morgan & Mikhail, p. 1714)
• Oxygen-enriched air (avoid 100% oxygen as this may worsen oxidative injury)
• Muscle relaxants to facilitate abdominal closure and control ventilation
• Nitrous oxide strictly avoided due to bowel gas expansion and pulmonary vasoconstriction
• In patients expected to remain intubated postoperatively (majority), opioid-based anesthesia is appropriate
• In patients with small defects where extubation is anticipated, regional/neuraxial analgesia (e.g., caudal epidural) is preferred to minimize opioid use (Barash, p. 3655)

Intraoperative Ventilation Goals (replicate preoperative settings)

• PIP < 25-30 cm H2O
• PEEP: low
• Permissive hypercapnia (PaCO2 45-65 mmHg)
• Preductal SpO2 > 85%
• Avoid high PEEP (risks pneumothorax)

Critical Intraoperative Events

• Sudden fall in lung compliance, blood pressure, or oxygenation must raise immediate suspicion of contralateral (usually right-sided) pneumothorax - requires urgent chest tube placement (Morgan & Mikhail, p. 1714)
• Pulmonary hypertension can be precipitated by: hypoxia, hypercarbia, acidosis, hypothermia, pain/stress (light anaesthesia)
• Blunting the stress response with deep anesthesia helps control pulmonary hypertension
• Blood loss and fluid shifts are usually not major problems but maintaining intravascular volume is essential to avoid acidosis
• Do NOT aggressively attempt to expand the ipsilateral hypoplastic lung following surgical decompression - this is harmful

Postoperative Management

• Continue mechanical ventilation in the NICU (most cases)
• Monitor for and manage pulmonary hypertension with continued nitric oxide, vasodilators
• Extubation: delayed until pulmonary hypertension has resolved and the infant is hemodynamically stable
• Recovery depends on the degree of pulmonary hypoplasia and pulmonary hypertension
• Evidence suggests that potentially reversible pulmonary hypertension may account for up to 25% of reported deaths (not just fixed pulmonary hypoplasia)
• Relative left ventricular hypoplasia may be present - cardiac function must be monitored
• The prognosis is determined by the extent of pulmonary hypoplasia and associated congenital defects (Barash, p. 3655-3656; Morgan & Mikhail, p. 1714)

PART II: ANORECTAL MALFORMATION (ARM) AND ANOVESTIBULAR FISTULA (AVF)

1. Introduction and Embryology

• The anterior urogenital sinus
• The posterior anorectal canal

• Failure of the urorectal septum to form results in a fistula between the bowel and urinary tract (in males) or introitus (in females)
• Complete or partial failure of the anal membrane to resorb results in anal membrane or stenosis
• The perineum also contributes through cloacal fold formation; breakdown anywhere along the cloacal membrane course results in an anterior ectopic anal opening (imperforate anus with perineal fistula)
• A common anatomic feature is incomplete rectal descent to the perineum - the rectum does not fully reach the perineal surface and is not completely within the striated muscle complex (Sabiston, p. 2688)

2. Classification

Classic Classification (Wingspread/Krickenbeck)

Modern Anatomic Classification (Peña)

VACTERL Association

• V ertebral defects
• A norectal malformations
• C ardiac defects
• T racheo-E sophageal fistula
• R enal abnormalities
• L imb abnormalities

3. Diagnosis

Clinical Examination

• 95% of low malformations: thin anal membrane OR fistula to perineum/scrotal raphe

• "Bucket-handle" skin deformity at presumptive anal dimple = diagnostic of low lesion
• High malformations: absent anal skin dimpling, flat gluteal contour, absent contraction of external sphincter with cutaneous stimulation, meconium/gas per urethra

• 90-95% of low malformations have a perineal or vestibular fistula
• Anovestibular fistula is readily visible as a fistulous opening in the vestibule
• A single perineal orifice in a female = cloaca
• Two perineal orifices = urogenital sinus with normal anus, or urethra + vagina without rectal fistula

• Low lesions (including AVF): meconium passes through perineal/vestibular fistula within 24 hours - may not be diagnosed until progressive constipation appears weeks/months after birth if fistula is large
• High lesions (undetected): signs of complete bowel obstruction develop within 1-7 days - abdominal distension, feeding intolerance, bilious vomiting (Mulholland Surgery, p. 5490-5491)

Radiological Investigations

1. Wangensteen-Rice Invertogram: Classic lateral pelvic radiograph taken 12-24 hours after birth with infant in head-down position - used to determine the most distal point of the rectal pouch. Now largely replaced by ultrasound. Requires 12-24 hours to allow gas to migrate distally.
2. Perineal/transperineal Ultrasound: Currently well-accepted as accurate for determining the distal extent of the rectal pouch. Non-invasive, real-time assessment.
3. Distal Colostogram: Loop colostomy with distal colostogram is now the standard to delineate fistula location.
4. CT/MRI: Useful in evaluating the pelvic striated muscle complex in difficult cases, especially cloacal malformations. MRI is also essential for evaluating the distal spinal cord in these infants (tethered cord, sacral agenesis).
5. Associated anomaly workup:
   • Spinal/sacral X-rays (sacral agenesis, hemivertebrae)
   • Echocardiogram (cardiac anomalies)
   • Renal ultrasound (renal anomalies)
   • Spinal MRI (tethered cord) (Mulholland Surgery, p. 5491-5492)

Diagnostic Goal

4. Treatment

Immediate Management (Neonatal Period)

• Once intestinal obstruction is diagnosed in the newborn, it is a surgical emergency - these patients deteriorate rapidly
• Insert nasogastric tube, correct fluid and electrolyte abnormalities, treat sepsis
• Adequate IV access, broad-spectrum antibiotics if needed
• Target serum sodium ≥ 130 mEq/L and urine output 1-2 mL/kg/hr before surgery (Barash, p. 3669)

Low Lesions (including Anovestibular Fistula - AVF)

• Minimal posterior sagittal anorectoplasty (PSARP) or cutback procedure can be performed in the neonatal period
• Perineal anoplasty for cutaneous fistulas
• Many surgeons prefer a limited posterior sagittal approach without colostomy for low lesions
• Primary repair can often be performed in the neonatal period without a diverting colostomy
• Anal dilatations post-procedure to prevent stricture

High and Intermediate Lesions

1. Stage 1 - Newborn Period: Divided loop colostomy with mucus fistula (usually sigmoid or left transverse colon). The colostomy provides fecal diversion, decompresses the bowel, allows distal colostogram to delineate anatomy, and prepares the infant for definitive surgery at 1-3 months of age or when weight >4-5 kg.
2. Stage 2 - Definitive Repair (1-3 months): Posterior Sagittal Anorectoplasty (PSARP) as described by Peña and DeVries. The patient is placed prone. A posterior sagittal midline incision is made from the coccyx to the anal dimple. The rectum is mobilized, fistula is divided, and the rectum is pulled through within the striated muscle complex and skin. This approach provides excellent visualization of the muscle complex.
   • For high lesions: may require a combined abdominal/laparoscopic approach (Laparoscopic Assisted Anorectal Pull-Through - LAARP)
3. Stage 3 - Colostomy Closure (6-8 weeks after PSARP): Colostomy is reversed after confirming adequate healing of the anastomosis and initiating anal dilation program.

Prognostic Factors for Fecal Continence

• Low lesions (including AVF): favorable prognosis - most achieve continence
• High lesions: lower rates of continence, dependent on degree of striated muscle complex hypoplasia
• Good sacral development = better prognosis
• Complete or partial failure of striated muscle development = poorer continence

5. Anaesthetic Management

The Condition as a Neonatal Surgical Emergency

• Full stomach / aspiration risk (bowel obstruction)
• Fluid and electrolyte disturbances
• Potential associated congenital anomalies (cardiac, renal, vertebral - VACTERL)
• Prematurity/low birth weight
• Hemodynamic instability (if septic)

Preoperative Assessment and Optimization

1. Full assessment for VACTERL anomalies - particularly cardiac (echocardiogram if not done)
2. Fluid resuscitation: Sequestration of fluid within the intestinal tract (essentially ECF with high sodium) can be enormous. Correct dehydration and electrolyte disturbances. Target serum Na ≥ 130 mEq/L, urine output 1-2 mL/kg/hr.
3. Antibiotics for sepsis or peritonitis
4. Abdominal distension can push the diaphragm up, causing respiratory failure - ensure adequate oxygenation and ventilation preoperatively
5. NPO status - consider nasogastric tube to decompress the obstructed bowel
6. Review all laboratory results: electrolytes, glucose (risk of hypoglycemia in neonates), CBC, coagulation

Monitoring

• Standard ASA monitoring (SpO2, ECG, NIBP, temperature, ETCO2)
• Temperature monitoring and active warming - neonates are highly susceptible to hypothermia
• Arterial line: Indicated for hemodynamically unstable patients or prolonged complex repairs (e.g., cloaca repair)
• Central venous access: For septic, severely dehydrated, or complex cases requiring vasoactive infusions
• Urine output monitoring via Foley catheter (especially important for cloaca repairs involving urinary tract reconstruction)

Induction of Anaesthesia

• Aspiration risk is high due to bowel obstruction, abdominal distension, and delayed gastric emptying
• Rapid Sequence Induction (RSI) is the standard of care:
  • Preoxygenation
  • Succinylcholine (or rocuronium if succinylcholine contraindicated) for rapid sequence
  • Cricoid pressure
  • Avoid positive pressure ventilation before securing the airway
• Awake intubation remains an option if the patient is severely hemodynamically compromised or a difficult airway is anticipated
• Induction agents: Ketamine or etomidate preferred in hemodynamically unstable patients (cardiovascular stability); thiopentone or propofol in stable patients (Barash, p. 3589-3590)

Maintenance of Anaesthesia

• Volatile anesthetic agents (sevoflurane, isoflurane) - titrated to hemodynamic status
• Muscle relaxants: Essential for:
  • Abdominal closure (especially after pull-through procedures)
  • Surgical exposure in prone position
  • Facilitation of controlled ventilation
• Opioids: Fentanyl or morphine; remifentanil sometimes used for its titrability and short duration - may allow earlier extubation in some patients
• Nitrous oxide is contraindicated in any infant with intestinal distension or obstruction (will worsen gaseous distension - clearly demonstrated on preoperative radiograph)
• Fluid management: Ongoing fluid resuscitation with isotonic crystalloid (normal saline or Ringer's lactate); colloid or blood products if significant blood loss

• Caudal block: Highly effective for anorectal and perineal surgery. Provides excellent intraoperative and postoperative analgesia, reduces opioid requirements, and may allow earlier extubation. Bupivacaine 0.25% 0.5-1 mL/kg or ropivacaine.
• Epidural analgesia: For more extensive procedures (colostomy formation, PSARP, cloaca repairs), continuous epidural infusion provides superior pain control and reduces the neuroendocrine stress response.
• Contraindication: Sacral agenesis (common associated anomaly in ARM) - should be excluded before neuraxial blockade; check spinal X-rays/MRI first.

• Colostomy formation: Supine or slight left lateral
• PSARP (definitive repair): Prone position with pelvis elevated. Ensure:
  • Adequate padding of pressure points
  • Eyes protected and free from pressure
  • Airway secured and tube well-fixed (accidental extubation in prone is catastrophic)
  • Abdominal contents not compressed (impairs ventilation and venous return)
  • Upper limbs padded and protected

Key Anesthetic Concerns Specific to ARM

1. Full stomach/aspiration: Always treat as full stomach due to obstruction
2. Associated cardiac anomalies: Particularly important in VACTERL - tailor anesthetic accordingly; may require invasive monitoring; avoid agents that significantly depress cardiac function
3. Renal anomalies: Monitor renal function; adjust drug doses and avoid nephrotoxins
4. Vertebral/spinal anomalies and sacral agenesis: May affect neuraxial technique feasibility; check sacral anatomy before caudal block
5. Prone position (PSARP): Airway management, venous return, ventilation
6. Blood loss: Usually modest for perineal/caudal repairs but can be significant in abdominal/laparoscopic pull-through operations, especially in cloaca
7. Temperature regulation: Active warming in all neonates
8. Hypoglycemia: Monitor glucose frequently in neonates; give glucose-containing maintenance fluids (D5 0.45% NS)

Postoperative Care

• Colostomy formation (Stage 1): Most infants can be extubated at end of surgery if stable; postoperative analgesia with caudal/epidural + regular paracetamol
• PSARP (Stage 2): Usually extubated post-operatively; regional analgesia is mainstay; nasogastric tube until bowel function returns
• Cloaca repair: May require prolonged postoperative ventilation; intensive nursing care; urinary catheter management; stoma care
• Extubation criteria: Awake, adequate spontaneous ventilation, no residual neuromuscular blockade (confirmed by nerve stimulator), normothermia, hemodynamically stable, adequate analgesia achieved
• Criteria for extubation are deferred if the infant is moderately debilitated or if the surgical incision is extensive, particularly if moderate doses of opioids have been given (Barash, p. 3672)

Summary Comparison Table

Key References (Textbook Sources)

• Miller's Anesthesia (10e) - Miller RS et al., CDH: p. 10640; Pediatric anesthesia chapter
• Morgan & Mikhail's Clinical Anesthesiology (7e) - CDH: pp. 1713-1714; Lower GI obstruction: pp. 1714-1715
• Barash Clinical Anesthesia (9e) - CDH: pp. 3652-3656; Lower GI Tract Obstruction/ARM: pp. 3669-3672
• Sabiston Textbook of Surgery - CDH: pp. 2675-2678; ARM: pp. 2688-2695
• Mulholland & Greenfield's Surgery - ARM: pp. 5487-5494

Clinical Pearl (from all three anaesthesia texts): The single most important intraoperative rule in CDH management is: never use nitrous oxide and never aggressively expand the ipsilateral lung. In ARM, the single most important rule is: treat every neonate as a full stomach and use RSI - bowel obstruction makes regurgitation and aspiration highly likely regardless of NPO status.The above is a comprehensive, textbook-referenced discussion. Here is a concise orientation to help navigate the full response:

What's Covered Above

Congenital Diaphragmatic Hernia (CDH)

Anorectal Malformation (ARM) and Anovestibular Fistula (AVF)