Lecture 55: Neonatal Physiology Flashcards
what is the importance of fetal circulation
- receives oxygenated purified, detoxified blood via placental (maternal) circulation in umbilical veins
- this blood is distributed all around the body and returned to be reoxygenated, supplied via umbilical arteries
why does fetal circulation mostly bypass liver and lungs
maternal circulation via placenta takes on the function of these organs so excess circulation to these organs would be wasted
describe the direction of flow in fetal circulation
- oxygenated blood comes from umbilical vein
- some will pass through liver, then to IVC (50% bypasses liver and goes straight through ductus venosus - links hepatic, portal and umbilical circulations - to IVC)
- IVC also returns deoxygenated blood from lower body so mixed oxygenated blood goes to RA
- this blood flow is divided into 2 streams
- most goes straight across to LA via foramen ovale
- from LA partially oxygenated blood flows to LV where it is pumped to supply head
- blood returning from head arrives at RA where it mainly goes to RV and then pulmonary trunk
- blood to primitive lungs would be wasted circulation so majority of this blood travels to descending aorta via ductus arteriosus
- only then (after being twice denuded of its oxygenated and nutrients) does blood return to placenta via umbilical arteries
where does umbilical vein connect to in fetus
ductus venosus
where do umbilical arteries connect to in fetus
L + R iliac arteries
describe the changes to fetal circulation occur after birth
- shunts in fetal circulation will close over
- at birth umbilical vein and arteries clamped
- this causes ^ in peripheral resistance in infant systemic circulation
- causes BP to increase
- at same time infant lungs are expanding, ^ O2 tensions there cause huge dec. in pulmonary vascular resistance
- pressures in RA, RV and pulmonary trunk all fall
- these changes reverse pressure difference between right and left that were useful in utero
- foramen ovale closed by flap acting as valve preventing reverse flow; hole then fibroses in few months after birth
- ductus arteriosus closes within first few days of life (prob due to ^ O2 tension)
- ductus venosus close 1-3hrs after birth w/ subsequent fibrosis
what are the anatomical shunts present in fetal circulation
- ductus venosus
- ductus arteriosus
- foramen ovale
why might problems arise after birth if left to right shunts persist and don’t close
although no effect on blood oxygenation (blood already passes through pulmonary circulation prior to shunting) they do ^ work of heart so may result in HF if not treated by surgery
outline the resp adjustments that occur at birth
- initial breath requires huge inspiratory intrapleural pressure to be developed to overcome surface tension of fluid that fills alveoli
- this rapidly reduces
- neonatal compliance remains less than that of an adult
- expiration is active rather than passive in newborn, to overcome ^ resistance from fluid in airways
- neonate has appx twice adult ventilation when accounting for body size differences; resp rate 40 breaths per min w/ vol of 650ml/min (compared to adult 12 breath/min vol 6L/min)
why might resp distress syndrome occur
- esp seen in preterm infants
- due to surfactant deficiency ^ work of breathing
describe the change in fetal weight and nutrition that occur after birth
- over first few days of life, neonate often drops in weight (up to 10% dec) mostly due to fluid loss
- this is due to difficulties in breastfeeding; both mother initiating supply and infant mastering art of suckling
- rapidly resolves by day 10
- weight triples in first year of life
- vit D, calcium and iron are in much demand during this period so supplementation for breastfeeding mothers is often indicated
describe the change in temperature of baby after birth
- infant has about 2x metabolic rate of adult so generates more heat
- despite this there is initial drop in temp in newborn of about 1-2C which one resolves after 12hrs
- fluctuations in core temp still occur for first few weeks of life due to immature thermoregulatory mechanisms
- neonate has a lot of SA to body volume so loses heat quicker
describe the change in temperature of baby after birth
- infant has about 2x metabolic rate of adult so generates more heat
- despite this there is initial drop in temp in newborn of about 1-2C which one resolves after 12hrs
- fluctuations in core temp still occur for first few weeks of life due to immature thermoregulatory mechanisms
- neonate has a lot of SA to body volume so loses heat quicker
- this may be countered by brown fat in infant which uncouples ADP phosphorylation from mitochondrial function w/ all of the energy going to heat
- extra heat generated may be vital for infants
describe the change in infant liver function after birth
- liver poorly formed at birth
- ^ in plasma bilirubin which reaches max 5x greater than normal after 1-2 weeks (neonatal jaundice)
- as liver matures, levels fall back to normal over next few months
- glycogen storage and manufacture also compromised
- glucose can drop to 2mmol/L in first day after birth
- necessitates frequent feeding
- plasma protein levels also low (incl. clotting factors, ^ bleeding risk)
describe the change in immunity for the infant after birth
- active acquired immunity poorly developed so must rely on mother’s immunoglobulins (IgGs) absorbed from placenta
- IgAs may be absorbed in colostrum
- passive immunity does decline over first few months slowly being taken over by immunity acquired by infant exposure to pathogens
- generally infant immunisation programs only start after 2-3 months when infant capable of acquired immunity
