FRCA Notes

Inhalational Induction in Paediatrics

This page falls under the curriculum item 'Describes how anaesthesia can be induced for children aged 1 year and above'.

It has yet to be the subject of a CRQ/SAQ although a recent BJA Education article could make this a potential question in the near future.

Resources

  • Inhalational induction will be familiar to most anaesthetists
  • It carries a number of benefits:
Benefits of inhalational induction in paediatrics
Painless (vs. IV cannulation)
Can be performed incrementally
Generally well-tolerated
Maintenance of spontaneous ventilation
Allows concurrent oxygenation
May be preferable in some settings e.g. inhaled foreign body

Physiology

  • The pulmonary phase of a gas induction is influenced by alveolar minute ventilation, V/Q matching and diffusion across the alveolar capillary membranes
  • As tidal volume is relatively fixed (6-10ml/kg) regardless of age, factors affecting ventilatory frequency will have the greatest effect on speed of induction
  • Factors increasing speed of onset include:
    • Smaller FRC relative to alveolar minute ventilation (concentrates the alveolar partial pressure of the volatile agent)
    • Crying or shouting (increases alveolar minute ventilation)
  • Higher airway resistance and higher oxygen consumption (i.e. neonates) will lead to more rapid fatigue and desaturation during gas induction

  • The circulatory phase consists of transport of volatile agent from the pulmonary capillaries to the brain
  • Influenced by cardiac output, cerebral perfusion and distribution to other (non-cerebral) tissues
  • Cardiac output in paediatric patients is largely a function of heart rate, owing to relatively fixed stroke volumes
  • A higher cardiac output increases delivery to the brain, but paradoxically overall slows the onset of inhalational induction by preventing a build up of alveolar partial pressure of the volatile agent

Pharmacology

  • Relevant Primary FRCA Pharmacology:
    • Speed of onset of inhaled anaesthetic agents
    • Partition coefficients
    • Sevoflurane
    • Nitrous oxide

Anatomy

  • Relevant Primary FRCA Anatomy:
    • The paediatric airway
    • Physiological differences in children

Indications

Indications
Difficult IV access
Uncooperative child
Potentially difficult airway
Other patient factors
Need to maintain SV at induction
(Patient or parent request)

Contraindications

Absolute Relative
Malignant hyperpyrexia Susceptibility to volatiles
E.g. familial MH but patient untested
Certain neuromuscular disorders
Refusal in a capacitous child Inadequately fasted
Severe restrictive or obstructive respiratory disease
Severe low cardiac output state


  • Assessment of child to ascertain need for and/or feasibility of gas induction
  • Build rapport with child and carer
  • Communicate benefits and risks to carer and (in an age-appropriate way) to the child
  • Explain agitation during the process is a normal feature e.g. tense struggling, tearing, lack of voluntary ocular control during stage 2 plane of anaesthesia
  • Consider sedative premedication

Equipment, staff and setting

  • Ensure standard paediatric monitoring and equipment available
  • Suxamethonium 4mg/kg drawn up for IM use in case of laryngospasm
  • Atropine 20mcg/kg may be drawn up although time to onset of IM dose is impractical for bradycardia associated with high-dose volatile agents

  • Ensure team familiar with paediatric anaesthesia inc. ODP
  • Plan for presence of carer/parent as benefit often outweighs risk in most circumstances
  • Presence of play specialist to help provide distraction and reassurance

  • Use dedicated paediatric anaesthetic room or theatre where possible inc. distracting wall decorations, easy access to equipment, team familiarity

  • Full monitoring may be impractical and a saturations probe alone may be the most pragmatic way forward
  • Circle system or Jackson-Rees modification of the T-piece (Mapleson F)

Reduce distress

  • Pre-medication
  • Distraction (particularly in younger children) inc. use of play specialists
  • Familiarise child with anaesthetic mask and breathing system before starting
  • Flavoured lip balm to inside of mask to disguise odour of sevoflurane, or facilitate a 'guess the smell' game
  • Active participation in the process
  • Game-ifying the process by asking the child to use the mask to blow up the bag ('green balloon')

Positioning

  • Maximise child comfort i.e. cuddled by parent or parent in view
  • Minimise risk i.e. parent has a secure but sympathetic wrap around the child's limbs
  • Ergonomics e.g. parent on stool next to operating table to facilitate easy transfer once induced
  • Positioned to facilitate holding gas mask securely but firmly over face
  • Anaesthetic machine within reach or second anaesthetist to manage the anaesthetic

Conduct

  • Sevoflurane is the standard volatile owing to the pungent smell and bronchial irritation from isoflurane and/or desflurane
  • Carrier gas may be medical air (to reduce hyperoxia in neonates), nitrous oxide/oxygen mix or 100% oxygen
  • Use of nitrous oxide is debateable; theoretically increases speed of onset via concentration and second gas effects, but the clinical effect of this may be negligible
  • 'Low and slow' i.e. incremental increases in volatile concentration may be appropriate in cooperative and/or older children
  • 'Smash and grab' 8% sevoflurane may be more appropriate in the upset, young or otherwise non-cooperative child

  • Apply full monitoring once child is anaesthetised
  • Maintain moderately high inspired volatile concentrations until IV access is obtained so as not to invoke laryngospasm during cannulation

  • Laryngospasm (1.2% as per APRICOT study)

  • Loss of airway
    • Often fixed with simple airway manoeuvres or positioning (e.g. shoulder roll in infants, neutral position in younger children)
    • CPAP may help splint open pharyngeal structures and maintain airway patency

  • Uncooperative child ± failure
    • Can lead to temporary maladaptive behavioural responses such as enuresis and night crying

  • Use of restraint only justified if the intention is to prevent greater harm compared to not intervening
    • This could be justified for (say) preventing harm during the excitatory phase of gas induction
    • If greater degrees of restraint are necessary, return to the ward for anxiolytic premedication or rescheduling with advanced planning may be preferable

  • Environmental concerns
    • Nitrous oxide is the most detrimental of the anaesthetic gases with respect to the environment
    • A nitrous oxide-free technique can reduced the environmental impact of gas inductions