physiological differences between children and adults
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PHYSIOLOGICAL
DIFFERENCES BETWEEN
CHILDREN AND ADULTSEdward Greenwood
CT1
October 2014
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AIMS
Broadly discuss differences between adults and
children
System by system
Relate these to clinical practiceFurther reading
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AIRWAY (HEAD NECK AND FACE)
Relatively large head
Short neck
Prominent occiput neutral position
Obligate nasal breathers until 6/12 easilyblocked
No teeth/loose teeth
Big tongue
High anterior larynxLong epiglottis - straight blade
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AIRWAY 2
Trachea is shorter and importantly narrower
endobronchial intubation easy
Narrowest point of the airway is at the level of
the cricoid cartilage even minor trauma can
cause oedema and life threatening airway
obstruction remember resistance to flow is
inversely proportional to the 4thpower of the
radius
Irritable airways, prone to laryngospasm
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BREATHING
Limited respiratory reserve reduced FRC,
compensate with tachypnoea rather than
increased tidal volumes
Normal RR in a neonate is 30, 20 aged 1 and 15
as an adolescent
Bulky abdominal organs and a often have gas
filled stomachs - this can make facemask
ventilation difficult
Increased oxygen consumption
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BREATHING 2
Low proportion of type 1 muscle fibres in
diaphragm so easily fatigued
Proportion of dead space is significantly
increased by anaesthetic equipment
Fewer alveoli only 10% of total at birth
complete by aged 8
Spontaneous apnoeas are common, especially in
premature infants
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CIRCULATION
Myocardium less contractile and ventricles less
compliant therefore rate dependant cardiac
output
High vagal tone, prone to bradycardias
Sinus arrhythmia is common in children, other
arrhythmias are all abnormal
Average heart rate for a neonate is 120-130 and
falls to normal by around age 15
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CIRCULATION 2
Mean systolic blood pressure is lower 50-90 in a
new born, 95-105 by aged 2
Foetal haemoglobin HbF (higher affinity for
oxygen) has usually been replaced by adult
haemoglobin by 3-6 months
Hb at birth is usually 18-20g/dl and is 9-12g/dl by
6 months
Venous access sometimes difficult consider IO
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RENAL SYSTEM AND FLUIDS
Urine output should be higher (1-2mls/kg/hr)
Prone to dehydration and poorly tolerated large
surface area to body weight ratio so significant
insensible losses
Renal tubular function immature until approx 8
months so unable to excrete large sodium loads
Remember 4-2-1 rule...
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SKIN
High surface area to body weight ratio so prone
to hypothermia
In addition; poorly developed vasoconstriction,
shivering and sweating so temperature control is
difficult
Thermogenesis is from metabolism of brown fat
Skin is thin and topical medication is absorbed
quickly
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CENTRAL NERVOUS SYSTEM
Cerebral blood flow autoregulation is present
from birth, however cerebral vessels are thin
walled and prone to haemorrhage
Immature blood brain barrier so centrally acting
drugs may have a prolonged effect eg
antibiotics, opiates and barbiturates
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HEPATIC FUNCTION
Immature liver with reduced levels of hepatic
enzymes
Many drugs metabolised by the liver will have a
longer during of action eg opiates and
barbiturates
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GLUCOSE METABOLISM
Neonates are prone to hypoglycaemia when
under physiological stress or when starved
Glycogen is stored in the liver and myocardium
Neurological damage may occur as a result ofhypoglycaemia so great care must be taken to
avoid it
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TAKE HOME MESSAGES
Children are not just small adults
Significant implications to paediatric anaesthesia
Most important things not to forget dont let
them get hypothermic, hypoxic, hypoglycaemic and nothing will go wrong
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FURTHER READING (ESSENTIAL!)
World of anaesthesia tutorial of the week
PAEDIATRIC ANATOMY AND PHYSIOLOGY
AND THE - BASICS OF PAEDIATRIC
ANAESTHESIA Fiona Macfarlane
eLA Paediatrics
Anaesthesia UK
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Questions?