Infant anatomy and physiology Flashcards
define the memory aid to remember the vertebral level of spinal cord and dural sac termination in adults and infants
By 2 (years) L2 (spinal cord) and S2 (dural sac) –> Adult
“Before” (B4) (at birth) L4 (spinal cord) and S4 (dural sac)
Summarise the the anatomical and mechanical differences between adult and neonatal breathing
Neonate
1. Ribs already elevated and horizontal. No assistance from rib elevation during inspiration (diaphragm only)
2. Highly compliant (non-ossified) chest wall (highly amenable to distortion)
3. Flattened (not dome shaped diaphragm - decreased range of displacement
4. Posterior limb of diaphragm moves dorsally –> subcostal recession (Adult diaphragm contracts caudally like a piston).
5. Neonate diaphragm has fewer fatigue-resistant slow twitch (type-I) fibres with decreased oxidative capacity - fatiguable with increased wOB.
6. Grunting = post-inspiratory diaphragm activation + Laryngeal breaking –> autoPEEP –> Increased FRC and improved gas exchange
Why does the dose of sux differ in infants vs children/adults
Infants have a much larger total body water (80% versus 60% adults)
Also, infants have relatively mre ECF vs ICF
Infant ECF:ICF > 1
Adult ECF:ICF < 1
This means that water soluble drugs (like sux) have a larger volume of distribution and higher doses are required to obtain the same plasma concentration
E.g. Sux (infant) 3mg/kg
Sux adult 1 - 1.5 mg/kg
Summarise the airway differences in a child
- Large head, occiput
- Short neck
- Large tongue
- Superior larynx (C4)
- Funnel shaped larynx
- Cricoid narrowest
- Neutral postion NOT sniffing
- Epiglottis long, narrow, large, stiff, omega
- Preferential nasal breathers
- Minimal oedema –> significant obstruction (radius^4)
Summarise the respiratory differences in a child
- Dominant diaphragmatic breathing
- Horizontal ribs (no bucket handle): Vt cannot change
- MV is rate dependent (Vt can’t change)
- Bulky abdo organs/gas filled stomach (impairs vent.)
- Chest wall high compliance –> low FRC
- Closing Vol. > FRC –> airway close end expiration
- Work of breathing = 15% VO2
- Diaphragm fatiguable - low % type 1 fibers (1yr = adult)
- Alveoli: thick walled + 10% adult numbers (8 yrs = adult)
When is apnoea significant
> 15 seconds or associated with hypoxia or bradycardia
What is the expected respiratory rate in children
24 - Age/2
What is the Vt in spont. ventilation vs IPPV
Spont: 6 - 8 ml/kg
IPPV: 7 - 10 ml/kg
Summarise the cardiovascular differences in children vs adults
- CO is HR dependent (SV fixed d/t decrease ventricle compliance and contractility)
- Immature SNS. Dominant PSNS –> Bradycardias
- CO: Birth 400ml/kg/min–> at 2 months 200ml/kg/min.
- Sinus arrhythmia common. Other arrhythmia all abN
- DA closes 2 - 4 days and fibrosis 2 - 4 weeks
- FO closes Day 1 but may open up until 5yrs (Pressure)
- Hypoxia and acidosis –> ^PVR –> return to transitional circ.
What are the normal blood volumes of neonatal / 6 wks - 2yrs / 2 - 12 yrs
Neonate 90 ml/kg
6 wks - 2 yrs 85 ml/kg
2yrs - 12 yrs 80 ml/kg
Summarise the neurological differences in paediatrics
- Pain = ^HR + ^BP + neuroendocrine response (hgt)
- Narcotics depress Vent response to PaCO2
- BBB immature: Prolonged and variable drug action
- Thin + fragile cerebral vessels + impaired CBF autoregulation (prems) –> Intraventricular bleeds
What are the physiological factors that contribute to the risk of intracranial haemorrhage increase the risk for intraventricular haemorrhage
- Fragile germinal matrix (microvascular)
- Immature autoregulation cerebral blood flow
- Instability of cerebral blood flow (pressure-passive circ.)
—-> Anaemia
—-> Acidaemia
—-> Hypercarbia
—-> Hypoglycaemia
—-> Asphyxia
—-> Abrupt elevations in blood pressure
———> Pain
———> Seizures
———> Rapid volume expansion - Coagulopathy
Summarise the renal differences in paediatric patients
Increased renal vascular resistance
1. RBF low until 2 yr
2. GFR low until 2 yr
3. Tubular function low until 8 months (cant excrete Na load)
Increased insensible losses (surface area to volume)
- Dehydration is poorly tolerated
Increased TBW (and larger ECF volume)
Urine output 1 - 2 ml/kg/hr
Summarise the differences in the hepatic system
Liver function immature
- E.g. barbiturates and opiates have longer duration of action
