This document discusses the numerous anatomical and physiological differences between paediatric patients and adults that are relevant to anaesthesia. It covers differences in the airway, respiratory system, cardiovascular system, central nervous system, hepatic and renal systems, thermoregulation, pharmacology, and psychological considerations. The key differences include proportionally larger heads, smaller airways, incomplete organ system development and immaturity of various physiological systems in paediatric patients compared to adults. These differences require special considerations for anaesthesia management in children.

1. ANATOMICAL AND PHYSIOLOGICAL
DIFFERENCES IN PAEDIATRICS;
ANAESTHETIC RELEVANCE
DR IRAYA

2. INTRODUCTION
• ‘Children not small Adults’
• Numerous anatomical and physiological differences btw paediatric and
adult pts
• Similarly many differences between various paediatric ages
• Paediatric pt> Birth till 18yrs: Inclusive;
 Newborn> preterm(<37/40), term
 Neonate> 1/12
 Infant> 1/12 till 1yr, former prematures
 Child> toddler(1-3yrs), young child(3-7), older child(7-12), Adolescence

3. AIRWAY
ANATOMY
• Large head relative to body, prominent occiput
• Face smaller relative to head size, small mandible
• Short neck
 Airway not naturally aligned, especially with deteriorating
neurostatus or induction anaesthesia
 Need for shoulder roll, airway maneuvers to align and open upper
airways. Neutral position neonate/Infant, Sniffing position older child

4. • Large tongue relative size oral cavity, absent teeth
Nasopharyngeal/Oropharyngeal airway to maintain patency
• Epiglottis> narrow, omega shaped, angled away from trachea.
• Adult> flat, broad, angled same axis as trachea
• Cephalad position Larynx, C3-4 neonate Vs. C5-6 Adults
 Difficult laryngoscopy/intubation especially with micrognathia,
macroglosia. Base of tongue nearer more superior larynx(Glosoptosis)
 Straight blade(lifts tongue from base) Vs. curved laryngoscope
blades

5. • Cords> anterior insertion more caudad than posterior insertion
 Difficult intubation as ETT may impinge anterior commissure that is
more caudad. May need rotate ETT posteriorly to enter glottis
• Cricoid cartilage/Subglottic functionally narrowest part, funnel
shaped infant larynx vs. cylindrical adult larynx
 Tracheal tube may pass glottis but fail pass subglottic +/- pressure
injury
• Short trachea
 High risk endo bronchial intubation
 Correct depth ETT placement, confirm after every maneuver

6. PHYSIOLOGY
• Neonates/Young Infants Obligate nasal breathers
• Epiglottis nearer Uvula allowing breastfeeding and breathing
simultaneously
• Immature coordination between respiratory and pharyngeal muscles
 Obstruction of anterior or posterior nares( nasal congestion,
stenosis, choanal atresia) can cause asphyxia

7. • Small airways, loose fitting pseudo stratified columnar epithelium
 Minimize airway trauma to avoid mucosal injury
 Correct size Tracheal tube, adequate cuff pressure, <25mmHg
 Leak test to avoid risk post extubation croup
 Paediatric micro cuff tubes> high volume low pressure, cuff lower away
from cricoid cartilage
• Poiselleau formulae; Resistance to flow prop 1/r4
 Higher degree resistance to air flow with same degree edema. Increased
work breathing, respiratory distress
 1mm circumferential edema causes X16 increase Resistance flow in
infants, compared X3 adults

8. RESPIRATORY SYSTEM
• Compliant Larynx, trachea and bronchi, subject to distention and
compression forces
• Inspiration> negative intrathoracic pressure dilates intrathoracic
trachea & bronchi.
• Expiration> dilatation extrathoracic trachea
 Upper airway/ Extrathoracic obstruction> Inspiratory stridor
 Intrathoracic/Lower airway obstruction> Expiratory stridor

9. • Paediatric Chest wall more compliant than adult’s
• Weak intercoastal muscles
• Ribs more horizontal, prevents ‘bucket handle’ chest wall movement like
adults, upward and outward
 Limited lung volumes, tidal volume, Functional residual capacity
 Less oxygen reserve, reduced apneic time to desaturation
• Higher metabolic rate and oxygen consumption X3 times adult contributes
to quicker desaturation with apnea, ventilation compromise
• Diaphragm major muscle of ventilation
 Less type 1 fatigue resistant fibers, increased WOB leads to fatigue faster
 Easily splinted by abdominal distention such as gastric air insufflation

10. • Poor Ventilatory mechanics; Lungs poorly compliant, chest wall
compliant
• Immature parenchyma, fewer number alveoli, less amount surfactant
 Relatively fixed Tidal volume
 Minute ventilation increased by RR
 Atelectasis occurs easier
• Respiratory center not fully mature at birth and immature ventilatory
control
 Term neonate> Biphasic response to hypoxia, initial
hyperventilation(peripheral chemoreceptors), then apnea after
ventilator depression
 Preterm> respond to hypoxia with apnea

11. CARDIOVASCULAR SYSTEM
• Myocardium Poorly compliant; less contractile
• Higher cardiac output 200-300ml/kg/min Vs. Adult 70mls/kg/min
• Maintain high C.O with faster HR
• Limited stroke volume, 1.5mls/kg
 Cardiac output increase dependent on Heart rate
 Fluid overload easier due to poorly developed starlings forces; check s/s
fluid overload after fluid boluses
• Dominant vagal tone
• Sympathetic innervation incomplete at birth, adrenaline stores inadequate
 More prone to bradycardia

12.  Bradycardia causes reduced cardiac output, progresses to asystolic
cardiac arrest
 Hypoxia commonest cause of bradycardia, managed with adequate
ventilation with 100% oxygen
 CPR commenced with HR <60

13. CENTRAL AND PERIPHERAL NERVOUS SYSTEM
• Blood brain barrier not fully developed at birth
 Drugs (opioids, barbiturates, antibiotics, bilirubin)easily cross
causing prolonged and varied duration action
 Narcotics alter respiratory response to hypercapnia
• Nueronal connection not fully developed and formed at birth
• Paediatric age has rapid brain development and growth
 Effect on anaesthetic on developing brain still under research
 Negative anaesthetic effect noted on animal research

14. • Cerebral vessels thin walled and fragile in preterms
 Risk IVH increase with hypoxia, hypercapnia, hypernatremia, low
haematocrit, awake airway manipulation, fluctuating Bp and cerebral
blood flow and rapid bicarbonate administration
• Spinal cord terminates at L3 at birth, moves to L1 by 1yr
 Intercristal line passes L4 at birth, so used as landmark for spinal
 CSF vol higher % of body water, hence need higher doses/body
weight LA for spinal in neonates>infants>children>adults
 CSF turnover higher, hence SAB shorter duration in paeds, 60-90min

15. • Peripheral nerves smaller and not fully myelinated at birth
 Lower concentrated LA effective
• Pain perception present at birth
 Pain associated with tachycardia, increased Bp and neuro-endocrine
response

16. HEPATIC
• Enzymatic systems to metabolize drugs not fully mature at birth
 Delayed drug metabolism and prolonged effect vs. higher risk drug
toxicity at higher doses
• Protein production not fully developed
 Coagulation factor deficient. Need Vit K at birth
 Reduced protein bidding of blood circulation meds e.g. LAs by Alpha
1 glycoprotein, risk toxicity by unbound drug
• Reduced Hepatic glycogen stores in prematures and infants
 Risk hypoglycemia peri-operatively

17. RENAL SYSTEM
• GFR, renal blood flow not fully mature till 2yrs. GFR 20ml/min at
birth, 125ml/min adult
• Tubular function immature, infants unable excrete large sodium load
and free water
 Dehydration poorly tolerated, with higher risk of dehydration
 Prolonged excretion of medicine, longer half life

18. THERMOREGULATION
• Larger surface area to weight ratio
• Minimal subcutaneous fat, thin skin
• Poorly developed shivering mechanics, depend on brown fat
metabolism to generate heat
• Poor vasoconstriction mechanics, sympathetic system not well
developed
 Heat loss via radiation, convection, evaporation and conduction
 Mechanisms to prevent heat loss essential during anaesthesia
 Ambient temp at 34deg premature, 32deg neonate, 28 deg older
child
 Forced air warming, bair hugger, warming mattress, warm fluids

19. • Hypothermia effects
 Respiratory depression
 CNS depression
 Increased duration action drugs, delayed reversal anaesthesia
 Coagulopathy, decreased platelet function
 Increased risk infection

20. PHARMACOLOGICAL
• Pharmacokinetic and pharmacodynamic differences exist between
paediatric and adult populations
• Mainly depend on;
 Volume of distribution higher in neonates and infants due to higher
percentage body water
 Higher cardiac output, mainly to vessel rich organs
 Immature physiological barriers e.g. BBB
 Varied sensitivity of receptors to medicines
 Protein binding effect of reduced levels albumin, Alpha 1 glycoprotein
 Effect of immature liver and kidney on drug metabolism and excretion

21. PSYCHOLOGICAL
• Experience of anaesthesia affects different aged paediatric patients differently
• This best recognized by level of anxiety before anaesthesia induction;
 Infants <6/12; no parental separation anxiety, accept strangers
 Children up to 4yrs; separation anxiety, skeptical of strangers, unpredictable
behavior, hard to rationalize with
 School age; upset by surgical procedure, its mutilating effects and possibility of
pain
 Adolescents; Fear pain, loss of control, loss of privacy and not being able cope
with the illness. Worsened by long periods of hospitalization/ chronic illness
 Cognitive impairment; Anxiety marked but not able to express it
• PTSD post anaesthesia and surgery recognized phenomenon

22. • Various techniques available for anxiolysis preoperatively;
 Preparation programs
 Music, Hypnosis, distraction
 Councelling to reassure parents and Patients
 Spiritual motivation
 Medication
 Parental presence at induction