The foetal circulation and adaption at Birth Flashcards
Function of placenta?
Fetal homeostasis Gas exchange Acid base balance Nutrient transport to fetus Waste product transport from fetus Hormone production Transport of IgG Prostaglandin E2
How fetal circulation differs from adult circulation? (4)
- Placenta is included in fetus fro - gas exchange, nutrition, waste excretion and homeostasis
- Lungs are fluid filled and unexpanded
- Liver has little role in nutrition and waste management
- Gut is not in use
What do the umbilical arteries do?
Take deoxygenated blood to placenta
What does umbilical vein do?
Take oxygenated blood from the placenta back to foetus
Where does the placenta sit?
End of the umbilical cord
What are the 3 shunts specific to foetal life?
Ductus venosus
Foramen Ovale
Ductus arteriosus
Where does blood go when returning from the placenta?
Right side of the heart- then distributed to growing foetus
Anatomy of the ductus venosus?
Connects the umbilical vein to the inferior vena cava
Anatomy of the foreman ovale?
Opening in the atrial septum connecting RA to LA
Anatomy of ductus arteriosus?
Connects pulmonary bifurcation to descending aorta
What does the ductus venous do?
Carries majority of blood from the placenta into the inferior vena cava bypassing portal circulation (liver)
What does the ductus venous do?
Carries majority of blood from the placenta into the inferior vena cava bypassing portal circulation (liver)
Function of the foreman ovale?
Allows blood to flow from RA to LA
Allows best oxygenated blood to enter LA then go into LV, to ascending aorta and then carotids
What is the foreman ovale physically?
Membrane flap on left atrium side
How is the ductus arteriosus kept open?
Circulating prostaglandin E2 produced by the placenta
How much of the RV output in a fetus goes to the lungs?
7%
Where does majority of the RV output go in a fetus?
Ductus arteriosus to join the descending aorta
What happens to a baby in the few minutes following birth?
Baby inflates lung and cries
Goes from blue to pink
Cord is clamped and cut
Changes in pulmonary vascular resistance when a baby is born?
Decreases
Breath in- lungs can physically expand
Increased circulating oxygen
Changes in systemic vascular resistance when a baby is born?
Increases
Cord clamped and cut
General circulation changes when a baby is born?
More of cardiac output goes to lungs
How does the foreman ovale close?
As PVR falls and SVR rises- the left atriall pressure exceeds the right atrial pressure
- Flap is pushed closed
- Once the cord has been clamped the pressure in the left side becomes higher than the pressure in the right
Explain duct constriction?
Decreased PVR cause a decrease in flow
Decreased circulating PGE2 due to increased lung metabolism
Increased PO2= oxygen sensitive muscular layer
Shunt becomes bidirectional than left to right
Physiologically it closes withing first 24 hours, anatomically closes withing 7-10 days
In what types of patients is a patent ductus arteriosus common?
Preterm infants
Treatment options for failure of duct closure?
Wait and see
Surgery
NSAIDS (Nonsteroidal anti-inflammatory drugs)
What can be used to keep a duct open?
PGE2
Prostaglandin E2
Until an alternative shunt is established or a definitive surgery carried out
Duct dependent circulation?
Some congenital heart diseases cause this where the duct must be kept open with PGE2
What happens to pulmonary resistance when a baby is born?
Continues to drop until it reaches adult level about 2-3 months later
When is persistent pulmonary hypertension of the newborn more likely?
Sick babies- Sepsis Hypoxic ischaemic insult Meconium aspiration syndrome Cold stress
Can be related to underlying anatomical abnormality = congenital diaphragmatic hernia
When does PPHN occur?
Lung vascular resistance fails to fall after birth
Anatomically and physiologically what happens in PPHN?
Shunts remain - R-L blood flow in PFO and PDA
Large difference between pre and post ductal oxygen saturation
Signs of PPHN?
Blue baby
What does PPHN mean?
persistent pulmonary hypertension of the newborn
Treatment for PPHN?
Ventilation Oxygenation High systemic blood pressure - more difficult for blood to go from left to right Inhaled nitric oxide ECLS- extracorporeal life support
What is important in congenital heart disease
Ductus arteriosus
How we treat PPHN?
2 Aims- reduce PVR, increase SVR
How we increase SVR when treating HHPN?
Oxygen Ventilation Sedation Thermoregulation Correction of acidosis Treatment of sepsis Inhaled NO
How we reduce PVR? Peripheral when treating HHPN?
Maintain higher than adequate BP
Inotropes Support other organ function
In severe cases ECLS
