9.2 Pediatric Airway and Ventilatory Management

Pediatric Airway and Ventilatory Management

Pediatric Airway Anatomy

Securing and managing the airway of a pediatric patient during flight requires an understanding of distinct anatomical differences compared to adults. These differences make the airway prone to obstruction and complicate visualization during intubation:

• Large Occiput: Infants and young children have a relatively large occiput. When the child is placed supine on a flat stretcher, the head is forced into flexion, which can easily occlude the highly compliant airway. To maintain a neutral "sniffing position," a towel or pad must be placed under the shoulders (shoulder roll) to align the external auditory canal with the sternal notch.
• Large Tongue: The tongue is large relative to the oral cavity, making it the most common cause of airway obstruction in obtunded pediatric patients. It also makes laryngoscopy more difficult, as the tongue is harder to sweep and control.
• Epiglottis: The epiglottis is long, narrow, floppy, and U-shaped (or omega-shaped). It projects at a more acute angle over the glottis. A straight laryngoscope blade (Miller) is typically preferred in infants and young children to lift the epiglottis directly off the glottic opening.
• Larynx Location: The pediatric larynx is located higher and more anterior in the neck, typically at the level of the C3-C4 vertebrae (compared to C5-C6 in adults). This anterior position makes direct visualization during laryngoscopy more challenging.
• Funnel-Shaped Airway: In infants and young children, the airway is funnel-shaped, narrowing at the level of the cricoid ring, which is the only complete ring of cartilage in the trachea. Because of this non-distensible ring, uncuffed endotracheal tubes (ETTs) were historically used to prevent pressure necrosis of the subglottic mucosa. However, modern guidelines (PALS and CAMTS) strongly recommend cuffed ETTs for almost all ages, as they allow for reliable ventilation, accurate tidal volume delivery, and protection against microaspiration. Cuff pressures must be monitored and maintained below 20-25 cm H2O.
• Short Trachea: The trachea is extremely short (4-5 cm in neonates, 7-8 cm in toddlers). This leaves a very narrow margin of safety. Simple movement of the child's head can cause displacement of the ETT: head extension pulls the tube out (accidental extubation), while head flexion pushes the tube down (right mainstem intubation). The rule "the tube follows the nose" applies.

Endotracheal Tube Sizing and Insertion

Calculating the correct ETT size and depth of insertion is critical to prevent airway damage or inadequate ventilation.

ETT Sizing Formulas

• Uncuffed ETT Size (for children > 2 years): $\text{ETT Size (ID mm)} = \frac{\text{Age in years}}{4} + 4$
• Cuffed ETT Size (for children > 2 years): $\text{ETT Size (ID mm)} = \frac{\text{Age in years}}{4} + 3.5$
• Alternative sizing: The diameter of the child's pinky finger or the size of the nares can serve as a rough physical guide in emergencies.

ETT Insertion Depth Formula

Once the ETT size is determined, the depth of insertion at the lip can be estimated using the following formula: $\text{Depth at lip (cm)} = \text{ETT Size} \times 3$ $\text{Alternative Formula (for children > 1 year)}: \text{Depth at lip (cm)} = \frac{\text{Age in years}}{2} + 12$

Rapid Sequence Intubation (RSI) in Pediatrics

RSI is utilized in critical care transport to secure the airway while minimizing the risks of aspiration, intracranial pressure spikes, and cardiovascular collapse.

Pre-oxygenation and Apneic Oxygenation

Due to the child's high metabolic rate and low FRC, rapid desaturation is common. Pre-oxygenation with 100% oxygen is mandatory. Apneic oxygenation via high-flow nasal cannula should be maintained during the intubation attempt to prolong the safe apnea time.

Pre-treatment

• Atropine (0.02 mg/kg IV/IO, minimum dose 0.1 mg, max single dose 0.5 mg): Historically administered to prevent reflex bradycardia caused by vagal stimulation during direct laryngoscopy or secondary to succinylcholine administration. While no longer routinely mandatory for all pediatric intubations under current guidelines, it remains indicated for infants $< 1$ year of age, patients receiving succinylcholine, or those who are already bradycardic.

Induction Agents

• Ketamine (1 - 2 mg/kg IV/IO): The preferred induction agent for hemodynamically unstable patients or those with reactive airway disease (bronchoconstrictive pathology like status asthmaticus). Ketamine preserves respiratory drive, induces bronchodilation, and stimulates endogenous catecholamine release, maintaining blood pressure. Use caution in catecholamine-depleted patients in shock, as it can cause profound myocardial depression.
• Etomidate (0.3 mg/kg IV/IO): A hemodynamically neutral agent suitable for patients with head trauma or shock. Note that it causes transient adrenal suppression, which is a consideration in septic shock.
• Fentanyl (1 - 2 mcg/kg IV/IO): Excellent for cardiovascular blunting in head injuries or cardiogenic shock, but can cause chest wall rigidity if pushed too rapidly.

Neuromuscular Blockers (Paralytics)

• Succinylcholine (2.0 mg/kg IV/IO for infants; 1.5 mg/kg for older children): A depolarizing agent with rapid onset (30-45 seconds) and short duration (4-10 minutes). Infants require a higher mg/kg dose of succinylcholine than adults due to their larger volume of distribution. Contraindicated in crush injuries, major burns $> 24$ hours old, history of malignant hyperthermia, or pre-existing neuromuscular disease.
• Rocuronium (1.0 - 1.2 mg/kg IV/IO): A non-depolarizing paralytic with an onset of 60 seconds and a duration of 45-60 minutes. It is the agent of choice when succinylcholine is contraindicated.

Mechanical Ventilation

Ventilation strategies in pediatrics must focus on lung protection to prevent ventilator-induced lung injury (VILI).

• Ventilation Mode: Pressure Control (PC) or Pressure-Regulated Volume Control (PRVC) is favored in infants and neonates. PC allows gas to flow at a constant pressure, accommodating leaks around the ETT and preventing high peak inspiratory pressures (PIP) that cause barotrauma.
• Tidal Volume ($V_t$): Target 6-8 mL/kg based on ideal body weight.
• Positive End-Expiratory Pressure (PEEP): Start at 5 cm H2O to maintain functional residual capacity and prevent micro-atelectasis. Titrate upward in severe hypoxic respiratory failure (e.g., pediatric ARDS) while monitoring hemodynamics.
• Respiratory Rate: Set to match the normal physiologic range for the child's age:
  • Infants (< 1 year): 25 - 30 breaths/min
  • Toddlers (1-3 years): 20 - 24 breaths/min
  • School-age (4-12 years): 16 - 20 breaths/min
  • Adolescents (> 12 years): 12 - 16 breaths/min
• Troubleshooting Deterioration (DOPE Mnemonic): If a ventilated child suddenly desaturates, becomes bradycardic, or exhibits high airway pressures, immediately systematically apply the DOPE mnemonic:
  1. Displacement: Verify ETT tube placement using end-tidal CO2 (ETCO2), chest rise, and breath sounds. Check if the tube has migrated into the right mainstem bronchus or has been extubated.
  2. Obstruction: Suction the ETT to clear secretions, mucus plugs, or blood. Check for tube kinking.
  3. Pneumothorax: Listen for asymmetric breath sounds, inspect for tracheal deviation or subcutaneous emphysema, and assess for hemodynamic collapse. Perform immediate needle decompression if tension pneumothorax is suspected.
  4. Equipment Failure: Disconnect the ETT from the ventilator and manually ventilate using a bag-valve-mask with 100% oxygen. This isolates the patient from the machine and allows the clinician to feel the compliance of the lungs.