Induction Techniques in Pediatric Anesthesia

Overview

1. Inhalational (Mask) Induction

Agent: Sevoflurane

• Sevoflurane is the agent of choice due to its non-pungent odour, rapid onset, and haemodynamic stability.
• Desflurane and isoflurane are avoided for inhalational induction because they are pungent and cause coughing, breath-holding, and laryngospasm - Morgan & Mikhail's Clinical Anesthesiology, p. 1697.
• Nitrous oxide (N2O, 60-70%) was historically added to speed induction via the second-gas effect, but use has declined; N2O should be avoided where air trapping is a concern (e.g., foreign body aspiration, bowel obstruction).

Technique - Gradual (Tidal Volume) Method

• Child may sit in parent's lap or lie on the table - accommodate the child's preference.
• A pulse oximeter is placed first (with other monitors applied after loss of consciousness).
• A flavoured face mask (e.g., lip balm, oil of orange on mask interior) is used to reduce anxiety and mask the smell.
• The mask is initially held near (not pressed against) the face - gentle insufflation of O2, then sevoflurane concentration is gradually increased.
• Fresh gas flow should NOT exceed the patient's minute ventilation - higher flows do not speed induction but waste agent. When flow exceeds minute ventilation, an open circuit is effectively created.
• The APL valve should be fully open to avoid resistance to exhalation.
• Distraction techniques: songs, stories, videos, virtual reality, smartphone apps, games - Barash Clinical Anesthesia 9e, p. 3751.
• "Troposmia" induction: the child is instructed to imagine the mask will emit their favourite smell.

Technique - Single/Two-Breath (Vital Capacity) Method

• Best for cooperative older children who can follow instructions.
• Circuit pre-filled with 7-8% sevoflurane in 60% N2O (or high-concentration sevoflurane in O2).
• Child takes a single maximal breath (vital capacity breath) and holds it - loss of consciousness typically in one to two breaths.
• Speeds induction significantly in cooperative patients - Morgan & Mikhail's Clinical Anesthesiology, p. 1697.

Technique - "Steal" Induction

• Used in very young, sedated, or sleeping children (often after oral midazolam premedication).
• Child falls asleep in parent's lap; the mask is gently placed over the face without waking them.
• The child is "stolen" into anaesthesia without awareness - Morgan & Mikhail's Clinical Anesthesiology, p. 1697.

IV placement after induction

• IV access is secured after loss of consciousness in inhalational induction, allowing subsequent IV drugs, fluids, and emergency agents to be administered.

2. Intravenous (IV) Induction

• IV access is already in place (older cooperative child, critically ill patient)
• Full stomach / aspiration risk (Rapid Sequence Induction - RSI)
• Contraindication to inhaled agents (e.g., MH susceptibility)
• Speed is essential

Standard IV Induction

• Propofol 2-3 mg/kg (higher dose than adults due to larger volume of distribution and faster clearance in children) followed by a muscle relaxant or opioid.
• Alternatively: propofol + lidocaine + an opioid (without a paralytic) is very commonly used in pediatric practice to facilitate intubation or LMA placement - Morgan & Mikhail's, p. 1696.
• Lidocaine reduces the pain of propofol injection.
• Paralytic agents are not needed for LMA insertion, which is common in pediatric anaesthesia.

IV Agent Options

3. Intramuscular (IM) Induction

• Used in uncooperative children who refuse mask or oral premedication, or in children with severe intellectual/behavioral disability.
• Ketamine 4-6 mg/kg IM is the standard agent - produces dissociative anaesthesia with preservation of airway reflexes and haemodynamic stability.
• Onset within 3-5 minutes IM.
• Atropine (0.02 mg/kg) often co-administered to reduce hypersalivation.
• IV access is then established after the child is sedated.

4. Rapid Sequence Induction (RSI) in Children

Key Steps:

1. Preoxygenation - target exhaled O2 >90% or SpO2 >97%; may be challenging in uncooperative children; premedication (midazolam/dexmedetomidine) helps with mask acceptance.
2. Cricoid pressure - may be applied, but avoid excessive pressure in infants/children as the cricoid ring is softer and more compressible than in adults; too much pressure can obstruct the trachea.
3. Rapid hypnotic (propofol or ketamine) followed by:
   • Rocuronium 1.2 mg/kg (paralysis within 60-75 sec), or
   • Succinylcholine 2 mg/kg (fastest onset, ~30 sec) - note higher dose than adults due to larger Vd.

Succinylcholine Caution in Children:

• Avoid in known or suspected myopathies and MH susceptibility - risk of rhabdomyolysis and hyperkalemic cardiac arrest.
• If full stomach risk outweighs myopathy risk: keep atropine and IV calcium immediately available.
• Atropine (0.02 mg/kg) routinely given before succinylcholine to prevent bradycardia (children are more prone to bradycardia with succinylcholine) - Barash Clinical Anesthesia 9e, p. 3749.

Modified RSI in Infants/Neonates:

• Neonates and infants have shorter apnoeic oxygenation times due to lower FRC and higher O2 consumption - they desaturate much faster than older children and adults.
• Modified RSI with gentle positive pressure ventilation (10-20 cmH2O) while waiting for muscle relaxant to work reduces the risk of severe desaturation.
• Trans-nasal Humidified Rapid Insufflation Ventilatory Exchange (THRIVE) can be used in the ultra-modified RSI technique.
• Classical RSI (no ventilation between induction and intubation) carries significant risk of desaturation in this age group.

5. Rectal Induction (Historical/Special Circumstances)

• Rectal thiopental or methohexital was historically used in young toddlers who refused mask or IV.
• Largely replaced by modern inhalational agents (sevoflurane) and intranasal dexmedetomidine/ketamine combinations.
• Still occasionally used in resource-limited settings.

Pre-induction Anxiolysis and Premedication

• Non-pharmacological methods: parental presence, child life specialist, video games, music, virtual reality - though evidence does not clearly show parental presence reduces anxiety better than midazolam.
• A quiet environment and adequate preparation remain important.

Choosing the Induction Technique

Key Pharmacological Differences from Adults

• Children have a larger volume of distribution for most drugs - higher mg/kg doses required.
• MAC of volatile agents is higher in infants and young children (e.g., MAC of sevoflurane peaks at ~3.3% in infants 1-6 months) then decreases with age.
• Faster inhalational induction than adults due to: higher alveolar ventilation:FRC ratio, higher cardiac output:muscle ratio, and lower blood-gas solubility.
• Neonates and infants are obligate nasal breathers and obstruct easily - oral airways helpful once deeply anaesthetized.