Considerations in Paediatric Anaesthesia

Paediatric anaesthesia:

This section covers various considerations for paediatric anaesthesia. The anaesthetic assessment of a paediatric patient is covered under Paediatric Anaesthetic Assessment.

Age-Independent Factors

Airway:

  • ↓ Airway diameter
    ETT diameter significantly affects airway resistance.

Breathing:

  • Notably similar tidal volume of 7mL/kg
  • Similar dead space volume
    However apparatus dead space becomes proportionally more important.
  • ↑ atelectasis
    PEEP requirement.

Circulation:

  • Absence of coronary disease means children will tolerate significant doses of anaesthesia without circulatory compromise
    Assuming no congenital cardiac disease present.

Neurological:

  • Significant anxiety is common to both children and parents around time of surgery:
    • Parental anxiety is:
      • Common
      • Often exaggerated understanding of risk
    • Child anxiety is common, and exacerbated by:
      • Lack of understanding
      • Lack of cooperation

Extremities:

  • Temperature control
    Surface area to volume ratio ↑ heat flux (usually loss).
    • Minimise exposure
      • Keep dressed in preop hold
      • Wrap in OT
    • Humidification
    • Forced air warmer
      Underbody.
    • Consider warmed fluids
      Only effective if high volumes being given.

Allaying Anxiety

Use of language:

  • Positive language
    Remove words with negative associations, e.g. pain.
    • “You’ll usually wake up pretty comfortable, we’ll give you extra medicine to make you more comfortable, and a nurse will be there to give you more medicine to keep you comfortable.”
  • Emphasis on safety rather than risk
  • Reinforce positive behaviours
  • Don’t downplay pain and anxiety
    Says things will hurt if they will hurt.
  • Reassure that concerns and anxiety is normal, but magnitude of risk is low in well children
  • Project a sense of relaxation
  • Engage in normal conversation with the parents and child

Reducing Intraoperative Heat Loss

Reduce:

  • Unnecessary exposure

↑ warming with:

  • Radiant heaters
  • Warm fluids
    • Intravenous
    • Irrigation
    • Skin preparation
  • Active warmers
  • Adjust operating theatre temperature
    • 20-22°C for children
    • 26-28°C for neonates
  • Humidified ventilators
    • Circle system with HME
    • Inspiratory humidifiers

Key Differences

This section covers key differences from adults relevant to paediatric anaesthesia, broken up by age groups.

Premature, Neonates, and Infants

This group:

  • Present the greatest:
    • Technical challenges
      Both in difficulty, and in difference from adults.
    • Requirement for additional resources
  • Probably has the highest parental anxiety
  • Should have age calculated as post-conceptual age
    \(PCA = Weeks \ of \ Gestation + Weeks \ since \ Birth\).
System Premature Neonate Infant (up to 2 years)
A
  • Very small everything
  • Best lying flat for intubation
  • Consideration of Mac vs. Miller
  • BVM usually straightforward
  • Intubation can be difficult
  • Small ETTs are high resistance
  • As premature
  • Difficult one-hand mask ventilation due to obstructed nasal passages
  • Small ETTs are high resistance
B
  • Surfactant may be inadequate
  • Apnoeas
  • Desaturate very quickly
  • Difficult to preoxygenate
  • As premature
  • Essentially never appropriate for day-case surgery
  • Frequent URTIs
  • Smaller airway diameter
    ↑ Severity of bronchospasm and sputum plugging.
C
  • Foetal shunts may be open/reopen; avoid air bubbles
  • Normal MAP ≈ weeks of gestation
  • HR dependent CO
  • Defend HR
  • Most difficult group for IV access
D
  • BSL management critical; apnoea with hypoglycaemia
  • Cord terminates S1 at 28 weeks
  • BSL management critical
  • Cord terminates at L3 at term
  • Separation anxiety
  • Cord terminates at L2/3 at 1 year
E
  • Temperature management critical
  • Temperature management critical
Other
  • Why are they premature? Foetal/maternal
Requirements
  • NICU
  • Neonatologist
  • NICU
  • Anaesthetic assistant capable of cannulating and ventilating

Key Considerations in Neonates

CATABOLIC:

  • Congenital Associations
    One abnormality suggests presence of another abnormality.
  • Apnoea
    Post-operative.
  • Temperature
    Tendency to hypothermia.
  • Air in stomach
    Significantly impedes ventilation.
  • Bradycardias
    Indicate a low CO.
  • Opioid sensitivity
    ↑ CNS and respiratory effects.
  • Lines
    Avoid air bubbles.
  • Intubation
  • Calcium
    Contractility and blood pressure are dependent on extracellular calcium.
  • Glucose
    Tendency to hypoglycaemia.

Changes in Infants in Detail

Airway Differences:

  • Relatively large:
    • Head
    • Tongue
      • Difficult to negotiate with laryngoscopy
      • ↑ Risk of upper airway obstruction
      • Obligate nasal breathing in first few weeks of life
        • ↑ Risk of obstruction with:
          • Nasal congestion
          • Foreign body
            • Nasal prongs
            • NGT
    • Epiglottis
      May cover laryngeal inlet if laryngoscope is engaged in the vallecula - hence use of straight blades to elevate epiglottis.
  • Relatively small mandible
  • Prominent occiput
  • Short neck and trachea
    • High risk of both endobronchial intubation and inadvertent extubation
      Endobronchial intubation may be eithe left- or right-sided, as both main bronchi divert at the same angle.
  • Higher larynx
    Results in relatively anterior larynx.

Respiratory Differences:

  • ↑ VA:FRC ratio
    Change in inspired gas mixture rapidly alters alveolar (and arterial) gas composition.
    • Rapid uptake of volatile agents
  • Higher closing volume (until 6-12 months) and reduced FRC
    • ↑ Risk of atelectasis
    • ↑ Risk of shunt
    • Rapid desaturation
  • Immature respiratory centres
    • Periodic breathing with apnoeas in neonates
    • Sub-anaesthetic drug concentrations still affect respiration
  • Anatomically inefficient alignment of thoracic bones, and weak respiratory musculature
    • Less efficient ventilation
      Reliant on diaphragm as bucket-handle mechanism not functional.
    • ↓ Respiratory reserve
    • Earlier onset of respiratory failure due to fatigue
    • ↑ Chest wall compliance
      Early appearance of intercostal and sternal recession when work of breathing is ↑.
  • ↓ Number of thick-walled alveoli
    May only be 10% of adult total.

Cardiac Differences:

  • ↓ Myocardial compliance
    Heart failure with ↑ volume due to poor Starling response.
  • ↓ Contractility
    Due to ↓ number of elements.
    • Fixed stroke volume
    • CO is HR dependent
  • Heart rate
    • Bradycardia is poorly tolerated
      HR <60 does not give adequate CO - commence CPR in neonates, or when there are signs of inadequate perfusion in older children.
      • Atropine
        Relative parasympathetic predominance in autonomically stressed child, but not always reliable.
      • Adrenaline
        Better choice when bradycardia must be corrected immediately and reliably (which is usually the case).
        • Consider ~1μg/kg adrenaline for bradycardia in non-arrest situations
          0.1ml/kg of 1:10,000 adrenaline, diluted into a 10ml syringe, will give 1μg/kg/ml.
    • Tachycardia is well tolerated
  • Dominate vagal tone
    Bradycardia common with vagal stimuli, such as laryngoscopy, hypoxia.

CNS Differences:

  • Incomplete blood-brain barrier
    Free passage of:

    • Opioids
    • Barbiturates
    • Bilirubin

  • Open sutures and large anterior fontanelle

    • Can be used to evaluate presence of ↑ ICP
    • Sutures will open and fontanelle expand prior to ↑ in ICP

  • Greater volume of CSF

    • Subarachnoid anaesthesia requires higher doses, and does not last as long

  • Spinal cord occupies entire length of canal
    Canal and cord grow at different rates, so the termination moves cephalad with age:

  • Incomplete ossification of sacral vertebrae
    Neuraxial techniques achievable.

MSK Differences:

  • Sensitivity to hypothermia due to:
    • ↑ Surface area:volume ratio
      ↑ Heat losses to environment, and in respiratory vapour (due to higher MV.
    • ↓ Heat production
      Weaker compensatory mechanisms:
      • Ineffective shivering
      • Poor vasoconstriction
        Ineffective A-V shunts.
      • Non-shivering thermogenesis
        Brown fat metabolism key to heat production.

Renal Differences:

  • ↓ Tubular concentrating ability
  • ↓ Renal bicarbonate levels
  • ↓ GFR
    Reduced ability to cope with volume and electrolyte loads.

Hepatic Differences:

  • Neonate
    • Reduced vitamin K dependent clotting factors in neonate
    • Reduced glucose storage in neonate
      • Hypoglycaemia common if not feeding
  • Infants
    Up to 2-3 months:
    • Immature metabolic pathways
      • Many drugs
        May prolong post-operative effects, and alter dosage intervals or infusion rates.
      • Bilirubin

Pharmacological Differences:

  • Major differences occur in children up to ~6 months
  • Absorption
    • Reduced IM and SC absorption
  • Distribution
    • Rapid distribution due to high CO
    • ↑ TBW and Vd of water-soluble drugs
    • ↑ ECF compartment volume
      ↑ required dosing for drugs distributed to ECF.
    • ↓ Plasma protein level and protein binding
      ↑ free drug fraction.
    • Poorly developed blood-brain barrier
      ↑ CNS distribution of drugs.
  • Metabolism
    • Immature hepatic metabolism
  • Elimination
    • Immature renal function

Young Children

2-4 year old children:

  • Have interactions with adults other than parents
  • Recognise something is up when in hospital, and will be generally suspicious
    • Usually cannot be approached with a needle without significant distress
    • May benefit from premedication
      Difficult to predict which children will require premedication.
      • ~50% of children who are predicted to be well behaved will not be
      • ~50% of children who are given a premedication will still be difficult to manage
    • Tone of language is important
System 2-4 Year Olds
A
  • Laryngospasm
B
  • Frequent URTIs
  • Asthma common
C
  • Assess METs with climbing, crying, and fighting with siblings
D
  • Parental involvement helpful for child anxiety

Primary School-Aged Children

5-10 year old children:

  • Physiology is more similar to adults
  • Primary issue is psychological
    • Word choice is crucial
      Avoid:
      • Needle
      • Mash
      • Pain
      • Separation (from parent)
      • Vomit
      • Nausea
      • Sick
    • Distraction and hyponosis are beneficial
    • In general, believe that the world is fair and adults Do The Right Thing
      Play to this.
    • Ideally, use one voice during induction
      Yours or the parents; but avoid chattering.
System 5-10 Year Olds
A
  • Loose teeth
B
  • Frequent URTIs
  • Asthma
  • Respiratory management
C
  • Assess METs with climbing, crying, and fighting with siblings
D
  • Choose words carefully
  • Distractible
  • Cord terminates at L1/2 at 8

Secondary School-Aged Children

11-18 year old children:

  • Physiology and management almost identical to adults
  • Psychological differences remain the major difference
    Tend to respond in two ways to the stress of hospital and disease. Consult should be tailored appropriately.
    • Child-like response
      • Frustrated, angry, “unfair”
      • Need gentle reassurance
    • Adult-like response
      • Existential fears, uncertainty
      • Honest but fair discussion
System | 5-10 Year Olds |

+——–+——————————————–+ | A | - Nil | | B | - Nil | | C | - Nil | | D | - Tailor discussion to psychological state |

References

  1. von Ungern-Sternberg BS, Boda K, Chambers NA, Rebmann C, Johnson C, Sly PD, et al. Risk assessment for respiratory complications in paediatric anaesthesia: a prospective cohort study. The Lancet. 2010 Sep;376(9743):773–83.