Airway Compression - Pediatric vs Adult: MD Anaesthesia PG Exam Answer

PART 1: ANATOMICAL DIFFERENCES - PEDIATRIC vs ADULT AIRWAY

Shape and Narrowest Point

Key Implication of Funnel Shape

• Uncuffed tubes have traditionally been used in neonates (to avoid circumferential mucosal pressure at the cricoid)
• Cuffed, small-volume, high-compliance tubes are increasingly used now, but uncuffed tubes still remain common in neonates

Other Pediatric Airway Peculiarities

1. Obligate/preferential nasal breathing - neonates and young infants; any nasal obstruction (bilateral choanal atresia = life-threatening)
2. Large tongue - relatively larger in oropharynx; promotes soft-tissue upper airway obstruction and makes direct laryngoscopy harder
3. Cephalad larynx - the larynx appears "anterior" but is actually positioned higher (cephalad); the tip of the epiglottis at C1 allows simultaneous suckling and breathing
4. Large occiput - causes spontaneous neck flexion when supine; optimal position is neutral with slight extension (may need a roll under shoulders, not head)
5. Submandibular soft tissue - must NOT be compressed during mask ventilation, as this pushes the tongue back and obstructs the airway

PART 2: AIRWAY COMPRESSION - ANTERIOR MEDIASTINAL MASS

Pathophysiology: Why Does GA Make it Worse?

1. Reduced lung volume - FRC falls under GA; tracheobronchial diameters decrease proportionally with lung volume
2. Bronchial smooth muscle relaxation - GA relaxes bronchial smooth muscle, making large airways more compressible
3. Loss of spontaneous ventilation/diaphragmatic tone - Neuromuscular blockade eliminates the caudal diaphragmatic movement of spontaneous breathing; this abolishes the normal transpleural pressure gradient that dilates intrathoracic airways during inspiration

Why Are Children at Higher Risk Than Adults?

• More compressible cartilage - the cartilaginous airway structure is more pliable in children
• Inability to report positional symptoms - adults can describe orthopnea or supine cough; young children cannot, so warning signs are missed
• Life-threatening complications can occur even in asymptomatic children with anterior mediastinal masses

Critical Threshold

• CT scan: >50% tracheal or tracheobronchial compression = unsafe for routine general anesthesia in children
• In the absence of this threshold, tracheal cross-sectional area and peak expiratory flow rates at least 50% of predicted have been used as a guide for safer induction

Anesthetic Management of Airway Compression

Preoperative Assessment

• CT chest (most important test): defines location, extent, degree of compression
• Flow-volume loops (upright + supine): variable intrathoracic obstructive pattern (expiratory plateau) when supine
• Transthoracic echocardiography: if vascular compression symptoms present
• Ask specifically: Can the patient lie flat? Supine dyspnea or cough = high risk
• Seek extrathoracic biopsy source first (pleural fluid, supraclavicular node)

Induction Principles (High-Risk/Symptomatic Patient)

Specific Drug Choices for Induction (Morgan & Mikhail 7e)

1. IV ketamine - greater hemodynamic stability in patients with reduced cardiac output from vascular compression
2. Inhalational sevoflurane - maintains spontaneous ventilation
3. Small incremental propofol or etomidate - carefully titrated

Intraoperative Airway Collapse - Rescue

1. Reposition the patient (must have determined safest position preoperatively)
2. Rigid bronchoscopy - pass distal to obstruction; can oxygenate even if into one main bronchus only
3. Mount an ETT over a small rigid bronchoscope (e.g. 6 mm) and deliver it distal to the obstruction
4. Femoro-femoral ECMO instituted beforehand for "unsafe" adult patients - CPB "standby" alone is inadequate because there is not enough time after sudden collapse to establish bypass before hypoxic brain injury

Extubation

• Keep intubated until airway obstruction has resolved
• Confirm by flexible bronchoscopy or presence of an air leak around the cuff when it is deflated

PART 3: MASK VENTILATION COMPRESSION POINTS

• Submandibular soft-tissue compression must be avoided - pressing the mask firmly against the face pushes the soft tissue under the mandible into the oropharynx, causing upper airway obstruction
• Oral airways displace the oversized tongue; nasal airways used with caution in children (can traumatize small nares or adenoids)
• In the neonate: slight neck extension in neutral position is optimal; avoid both flexion (large occiput causes this spontaneously) and hyperextension

SUMMARY TABLE: PEDIATRIC vs ADULT AIRWAY COMPRESSION

• Functionally narrowest point in neonate = cricoid ring (not vocal cords as in adults)
• GA worsens airway compression by 3 mechanisms: reduced lung volume + bronchial relaxation + loss of diaphragmatic traction
• Children are at higher risk from anterior mediastinal masses due to more compressible cartilage AND inability to report symptoms
• Management priority: maintain spontaneous ventilation, secure airway beyond stenosis, rigid bronchoscope available
• Point of tracheobronchial compression from a mass may be distal to the ETT tip - always consider this