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TAS Perinatal Medicine ✅ > Fetal Circulation ✅ > Flashcards

Fetal Circulation ✅ Flashcards

1
Q

How is oxygenated blood carried to the foetus?

A

Via the umbilical vein

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2
Q

What organ does oxygenated blood in the umbilical vein bypass in foetal circulation?

A

The liver

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3
Q

How does oxygenated blood bypass the liver?

A

Via the ductus venous

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4
Q

Where does oxygenated blood travel after bypassing the liver?

A

The inferior vena cava

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5
Q

Where does oxygenated blood pass after reaching the inferior vena cava?

A

Enters the right atrium

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6
Q

What happens to oxygenated blood entering the right atrium?

A

It is shunted to the left atrium

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7
Q

How is oxygenated blood shunted from the right atrium to left atrium?

A

Via the foramen ovale

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8
Q

Where does oxygenated blood travel from the left atrium?

A

Into the left ventricle then aorta

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9
Q

What does the aorta supply in the foetal circulation?

A
  • Coronary arterys

- Cerebral vessels

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10
Q

What is the result of the aorta supplying the coronary artery and cerebral vessels?

A

The foetal brain and heart get the most oxygenated blood

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11
Q

How does deoxygenated blood from the cerebral and coronary vessels return to the heart?

A

Via the superior vena cava into the right atrium

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12
Q

Where does deoxygenated blood pumped by the right ventricle go?

A

Some goes into the pulmonary artery, but the majority bypasses the lungs via the ductus arteriosus

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13
Q

Where does blood bypassing the lungs via the ductus arteriosus go?

A

Into the aorta

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14
Q

What happens to deoxygenated blood entering the aorta?

A

It it carried back to the placenta via two umbilical arteries

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15
Q

What % of the combined ventricular output of the fetal heart passes into the lungs?

A

7%

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16
Q

Which is the dominant ventricle in the fetal circulation?

A

Right ventricle

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17
Q

What % of the combined ventricular output is provided by the right ventricle?

A

66%

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18
Q

What is the fetal pO2?

A

2-4kPa

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19
Q

Is the foetus able to metabolise aerobically with a pO2 of 2-4kPa?

A

Yes

20
Q

What is required for a foetus to metabolise aerobically?

A

Adequate delivery of oxygen to the tissues

21
Q

What factors ensure adequate delivery of oxygen to peripheral tissues?

A
  • Layout of the circulation system
  • High levels of foetal haemoglobin
  • High perfusion rates of the organs
  • Decreased oxygen requirements
22
Q

How does foetal haemoglobin differ to that of adults?

A
  • Higher percentage of haemoglobin F

- High haemoglobin concentration

23
Q

What % of fetal haemoglobin is HbF?

A

75%

24
Q

What is the haemoglobin concentration in a foetus?

A

18g/dl

25
Q

How does HbF differ from adult haemoglobin?

A

Lower affinity for 2,3-diphosphoglycerate (2,3 DPG)

26
Q

What is the result of HbF having a lower affinity for 2,3 DPG?

A

It allows for increased binding of oxygen with greater affinity and better oxygen extraction in the placenta

27
Q

What is the importance of the greater affinity and better oxygen extraction of HbF?

A

It compensates for the relatively lower oxygen tension of the maternal blood supplying the chorion

28
Q

Is is meant by the P50 value?

A

The partial pressure of oxygen at which the protein is 50% saturated

29
Q

What does a lower P50 value mean?

A

Greater affinity

30
Q

What is the P50 value for fetal haemoglobin?

A

2.4kPa

31
Q

What is the P50 value for adult haemoglobin?

A

3.5kPa

32
Q

How does the oxygen saturation curve of fetal haemoglobin compare to that of adult haemoglobin?

A

It is left-shifted

33
Q

When should the cord be clamped after birth in uncompromised babies?

A

1-3 minute from complete delivery, or until cord stops pulsating

34
Q

When should the cord be clamped after birth in babies requiring resuscitation?

A

Insufficient evidence to recommend a time, but resuscitation is the priority

35
Q

Is there any additional benefit of delaying cord clamping beyond 5 minutes?

A

No

36
Q

What are the advantages of delayed cord clamping?

A
  • Neonates continue to receive oxygen from placenta

- Haemoglobin increased immediately after delivery

37
Q

How long do neonates continue to receive oxygen from the placenta for?

A

For as long as the cord os pulsating

38
Q

When is it particularly advantageous for the neonate to continue to receive oxygen from the placenta?

A

If there was fetal hypoxia during labour

39
Q

Is the haemoglobin increase seen after birth with delayed cord clamping sustained?

A

No - there is no significant difference in haemoglobin at 2-6 months of age

40
Q

What advantage of delayed cord clamping is seen at 2-6 months?

A

Increased iron stores

41
Q

What is the disadvantage of delayed cord clamping?

A

Increased risk of neonatal jaundice

42
Q

What does delayed cord clamping have no impact on?

A
  • Risk of polycythaemia needing treatment
  • Maternal outcomes in terms of postpartum haemorrhage or maternal mortality
  • Neonatal mortality
  • Long-term neurodevelopment outcomes
43
Q

What are the advantages of delayed cord clamping in preterm infants?

A
  • Reduction in blood transfusions
  • Lower incidence of NEC
  • Lower incidence of intraventricular haemorrhage
44
Q

What are the disadvantages of delayed cord clamping in preterm infants?

A

Peak bilirubin concentration is increased

45
Q

What does delayed cord clamping have no effect on in preterm infants?

A
  • Severe intraventricular haemorrhage (grade 3 or 4)
  • Periventricular leukomalacia
  • Mortality
  • Neurodevelopmental outcomes

TAS Perinatal Medicine ✅ (16 decks)

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