Fetal Circulations and changes at birth Flashcards
What are the functions of the placenta?
- fetal homeostasis
- gas exchange
- acid base balance
- nutrient absorption to foetus
- waste product transport from foetus
- hormone production
- transport of IgG
- PGE2
What is different about the foetal circulation?
Lungs are fluid filled and unexpanded
Liver has little role in nutrition and waste management
The gut is not in use
Where does the foetal heart pump to?
Pumps to the placenta via the umbilical veins
What vessels are present in the umibilical cord?
Two arteries and a vein
How does blood return to the foetus from the placenta?
Returns to the foetus via the umbilical vein
What is the challenge of the foetal circulation?
Oxygenated, nutrient rich blood returns from the placenta to the right side of the heart needs to be distributed to the growing foetus
What are the three shunts present in the foetal circulation?
Ductus venosus
Foramen ovale
Ductus arteriosus
What is the role of the ductus venosus?
Connects the umbilical vein to the inferior vena cava, it carries the majority of the placental blood straight to the IVC by bypassing the portal circulation
What is the the foramen ovale?
Opening in the atrial septum connecting RA to LA
What does the foramen ovale allow?
Allows blood to flow from the right to left atrium, allowing the best oxygenated bloos to enter the LA then on to LV, ascending aorta…
Where is the membrane flap of the foramen ovale?
On the left atrium side
What is the ductus arteriosus?
Connection of pulmonary bifurcation to the descending aorta
What maintains the patency of the ductus arteriosus?
Flowing blood
Prostaglandin E2 produced by placents
What are the circulatory changes immediately after birth?
PVR falls
- breath in, lungs physically expand
- increasing circulating O2
SVR increased
- cord clamped and cut
More cardiac output to lungs
When does the foramen ovale close?
As PVR falls and SVR rises the LA pressure exceeds the RA pressure and the flap is pushed closed
What is associated with patent foramen ovale?
Stroke, migraine
What causes duct constriction?
- rising O2 concentration acts as vasoconstrictor
- placenta no longer produced PGE2
- decreased flow due to decreased PVR
When does the duct close?
Physiological closure within hours/days
Anatomical closure within 7-10 days
When might the duct fail to close?
Preterm infants
What may a patent duct cause?
Preterm complications
What are the treatments for failure of duct closure?
Wait and see
NSAIDs (reduce PGE2)
Surgery (ligation)
What can cause a duct dependant circulation?
Congenital heart disease
What is often done in duct dependant circulations until resolved?
IV PGE2 to keep duct open
When does pulmonary resistance reach normal adult levels?
by 2-3 months
What can result from failure of adaptation?
persistent pulmonary hypertension of the newborn
What happens in PPHN?
Lung vascular resistance fails to fall
Shunts remain
- right to left flow at PFO
- right to left flow at PDA
When is PPHN more likely?
Sick babies
- sepsis
- hypoxic ischaemic insult
- meconium aspiration syndrome
- cold stress
Can be related to anatomical abnormalities such as a congenital diaphragmatic hernia
How would PPHN present?
Blue baby
Large difference between pre and post ductal O2 sats
What is the treatment involved in PPHN?
- ventilation
- oxygenation
- high systemic BP
- inhaled NO
- ECLS
