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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oxygen) has usually been replaced by adult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?