Neonatal Physiology Flashcards
When does the CVS begin to develop and when does the heart start to beat?
Begins to develop towards end of third week
Heart starts to beat at beginning of fourth week
Critical period of heart development is from day 20-50 after fertilisation
Features of the foetal circulation
Oxygenated blood via umbilical vein into ductus venosus
Some blood via foramen ovale to left atrium -> left ventricle -> aorta
Some blood to right ventricle -> pulmonary artery -> patent ductus arteriosus and aorta
SaO2 in foetal bosy is 60-70%
Features of ductus arteriosus
Protects lungs against circulatory overload
Allows right ventricle to strengthen
Carries low oxygen saturated blood
Features of ductus venosus
Foetal blood vessel connecting the umbilical vein to the IVC
Blood flow regulated via sphincter
Carries mostly oxygenated blood
Liver gets the most oxygenated blood so is the largest organ in the foetus
Thermoregulation in babies
Maternal thermoregulation in the womb
Newborn babies lack shivering thermogenesis so need a metabolic production of heat
Brown fat is well innervated by sympathetic neurons
Cold stress leads to lipolysis and heat production
How is heat lost in babies?
Radiation - heat dissipated to colder objects
Convection - heat loss by moving air
Evaporation - if baby is wet and not dried
Conduction - heat loss to surface on which baby lies
What happens when a baby takes its first breath?
Ductus arteriosus becomes a ligament Foramen ovale closes and leaves a depression Ductus venosus becomes a ligament Umbilical vein becomes a ligament Umbilical arteries become ligaments
What is foetal circulation characterised by?
Foetal circulation is characterised by a connection to the placenta via umbilical cord and several bypasses around organs that do not yet perform their postnatal functions
At birth, the umbilical cord is tied off and cut, leaving the navel
The bypasses close, allowing more blood to reach the now functional organs of the newborn
How do you assess newborn breathing?
Non-invasive
- Blood gas determination
- PaCO2 5-6mmHg, PaO2 8-12mmHg
- Trans-cutaneous pCO2/O2 measurement
Invasive
- Capnography
- Tidal volume 4-6ml/kg
- Minute ventilation - tidal volume ml/kg x respiratory rate
- Flow-volume loop
Normal vital signs of full term newborns
BP
- 70 systolic 44 diastolic at 1 hour old
- 70 +/- 9 systolic 42 +/- 12 diastolic at 1 day old
- 77 +/- 12 systolic 49 +/- 10 diastolic at 3 days old
RR
- 30-60/min
HR
- 120-160bpm
What is new-born tachycardia and bradycardia?
Tachycardia > 160bpm
Bradycardia < 100bpm
Physiology of fluid balance in the full term newborn
Full-term infant is able to maintain fluid/electrolyte balance
Weight loss up to 10% is normal
Loss is due to shift of interstitial fluid to intravascular and diuresis
It is normal not to pass urine for the first 24 hours
Physiology of fluid balance in the premature infant
Less fat in body composition
Increased loss through kidney
- Slower GFR
- Reduced Na reabsorption
- Decreased ability to concentrate or dilute urine
Increased insensible water loss
- Via immature skin and breathing
- Physiological IWL is 20-40ml/kg/day but could be up to 82ml/kg/day in 750-1000g babies
Physiology of anaemia in the newborn
At day 7 of life, RBC production is 10% of what it was in uterus Born with Hb 15-20g/l By week 10 Hb is 11.4g/l Increased production of erythropoietin Week 20 Hb is 12.0g/l
Anaemia of prematurity
- Reduced erythropoiesis
- Blood letting (most important cause)
When does physiological jaundice appear?
Appears on day 2-3 of life
Disappears within 7-10 days of life in term infants and up to 21 days of life in premature infants
