The Foetal Circulation and Adaptation at Birth

Question 1

what is the placental function?

Answer 1

• fetal homeostasis
• gas exchange
• acid base balance
• nutrient transport to fetus
• waste product transport from fetus
• hormone production
• transport of IgG
• PGE2

Question 2

what are the key differences in the fetus compared to a baby?

Answer 2

the placenta is included in the circulation
the lungs are fluid filled and unexpanded
the liver has little role in nutrition and waste management
the gut is not in use

Question 3

describe the role of the placenta in the circulation

Answer 3

foetal heart pumps blood to the placenta via the umbilical arteries
blood from the placenta returns to the foetus via the umbilical vein

Question 4

what are the 3 shunts specific to foetal life?

Answer 4

• ductus venosus
• foramen ovale
• ductus arteriosus

Question 5

what is the role of the ductus venosus?

Answer 5

connects the umbilical vein to the inferior vena cava
nutrients come from placenta, dont need further processing in liver
it carries the majority of the placental blood straight into IVC bypassing portal circulation

Question 6

what is the role of the foramen ovale?

Answer 6

opening in atrial septum connecting right atrium to left atrium
allows blood to flow from right to left atrium
allows the best oxygenated blood to enter the left atrium then onto LV, ascending aorta, carotids
membrane flap on left atrium side

Question 7

what is the role of the ductus arteriosus?

Answer 7

connects pulmonary bifurcation to the descending aorta
only a very small amount of RV output goes to the lungs
the rest goes to join the descending aorta

Question 8

what maintains patency in the ductus arteriosus?

Answer 8

circulating prostaglandin E2 produced by the placenta

Question 9

describe the circulatory changes following birth

Answer 9

decrease in PVR
- breath in- lungs physically expanded
- increasing circulating oxygen 
increase in SVR
- cord clamped and cut
more of cardiac output to lungs
foramen ovale closes

Question 10

describe duct constriction

Answer 10

functional closure within hours to days

anatomical closure within 7-10 days

Question 11

what does the ductus arteriosus end up as in humans?

Answer 11

ligamentum arteriosum

Question 12

what happens if the duct fails to close?

Answer 12

may contribute to other preterm complications

treatment options include wait and see, NSAIDs and surgery

Question 13

what happens if a baby has a ‘duct dependant circulation’?

Answer 13

IV prostaglandin E2 can be used to keep the duct open until an alternative or definitive surgery can be carried out

Question 14

describe what happens to pulmonary resistance

Answer 14

continues to drop

reaches normal adult type levels by 2-3 months

Question 15

when is pulmonary resistant hypertension most likely?

Answer 15

• sepsis
• hypoxic ischaemic insult
• meconium aspiration syndrome
• cold stress
• can be related to underlying anatomical abnormality such as congenital diaphragmatic hernia

Question 16

what is persistent hypertension of the newborn?

Answer 16

persistence of the fetal circulation

Question 17

what happens in persistent pulmonary hypertension of the newborn?

Answer 17

lung vascular resistance fails to fall
shunts remain
- right to left flow at PFO
- right to left flow at PDA
- blue baby
- large difference between pre and post ductal oxygen saturation
- ventilation, oxygenation, high systemic blood pressure, inhaled nitric oxide, ECLS