Fetal Circulation ✅ Flashcards
How is oxygenated blood carried to the foetus?
Via the umbilical vein
What organ does oxygenated blood in the umbilical vein bypass in foetal circulation?
The liver
How does oxygenated blood bypass the liver?
Via the ductus venous
Where does oxygenated blood travel after bypassing the liver?
The inferior vena cava
Where does oxygenated blood pass after reaching the inferior vena cava?
Enters the right atrium
What happens to oxygenated blood entering the right atrium?
It is shunted to the left atrium
How is oxygenated blood shunted from the right atrium to left atrium?
Via the foramen ovale
Where does oxygenated blood travel from the left atrium?
Into the left ventricle then aorta
What does the aorta supply in the foetal circulation?
- Coronary arterys
- Cerebral vessels
What is the result of the aorta supplying the coronary artery and cerebral vessels?
The foetal brain and heart get the most oxygenated blood
How does deoxygenated blood from the cerebral and coronary vessels return to the heart?
Via the superior vena cava into the right atrium
Where does deoxygenated blood pumped by the right ventricle go?
Some goes into the pulmonary artery, but the majority bypasses the lungs via the ductus arteriosus
Where does blood bypassing the lungs via the ductus arteriosus go?
Into the aorta
What happens to deoxygenated blood entering the aorta?
It it carried back to the placenta via two umbilical arteries
What % of the combined ventricular output of the fetal heart passes into the lungs?
7%
Which is the dominant ventricle in the fetal circulation?
Right ventricle
What % of the combined ventricular output is provided by the right ventricle?
66%
What is the fetal pO2?
2-4kPa
Is the foetus able to metabolise aerobically with a pO2 of 2-4kPa?
Yes
What is required for a foetus to metabolise aerobically?
Adequate delivery of oxygen to the tissues
What factors ensure adequate delivery of oxygen to peripheral tissues?
- Layout of the circulation system
- High levels of foetal haemoglobin
- High perfusion rates of the organs
- Decreased oxygen requirements
How does foetal haemoglobin differ to that of adults?
- Higher percentage of haemoglobin F
- High haemoglobin concentration
What % of fetal haemoglobin is HbF?
75%
What is the haemoglobin concentration in a foetus?
18g/dl
How does HbF differ from adult haemoglobin?
Lower affinity for 2,3-diphosphoglycerate (2,3 DPG)
What is the result of HbF having a lower affinity for 2,3 DPG?
It allows for increased binding of oxygen with greater affinity and better oxygen extraction in the placenta
What is the importance of the greater affinity and better oxygen extraction of HbF?
It compensates for the relatively lower oxygen tension of the maternal blood supplying the chorion
Is is meant by the P50 value?
The partial pressure of oxygen at which the protein is 50% saturated
What does a lower P50 value mean?
Greater affinity
What is the P50 value for fetal haemoglobin?
2.4kPa
What is the P50 value for adult haemoglobin?
3.5kPa
How does the oxygen saturation curve of fetal haemoglobin compare to that of adult haemoglobin?
It is left-shifted
When should the cord be clamped after birth in uncompromised babies?
1-3 minute from complete delivery, or until cord stops pulsating
When should the cord be clamped after birth in babies requiring resuscitation?
Insufficient evidence to recommend a time, but resuscitation is the priority
Is there any additional benefit of delaying cord clamping beyond 5 minutes?
No
What are the advantages of delayed cord clamping?
- Neonates continue to receive oxygen from placenta
- Haemoglobin increased immediately after delivery
How long do neonates continue to receive oxygen from the placenta for?
For as long as the cord os pulsating
When is it particularly advantageous for the neonate to continue to receive oxygen from the placenta?
If there was fetal hypoxia during labour
Is the haemoglobin increase seen after birth with delayed cord clamping sustained?
No - there is no significant difference in haemoglobin at 2-6 months of age
What advantage of delayed cord clamping is seen at 2-6 months?
Increased iron stores
What is the disadvantage of delayed cord clamping?
Increased risk of neonatal jaundice
What does delayed cord clamping have no impact on?
- Risk of polycythaemia needing treatment
- Maternal outcomes in terms of postpartum haemorrhage or maternal mortality
- Neonatal mortality
- Long-term neurodevelopment outcomes
What are the advantages of delayed cord clamping in preterm infants?
- Reduction in blood transfusions
- Lower incidence of NEC
- Lower incidence of intraventricular haemorrhage
What are the disadvantages of delayed cord clamping in preterm infants?
Peak bilirubin concentration is increased
What does delayed cord clamping have no effect on in preterm infants?
- Severe intraventricular haemorrhage (grade 3 or 4)
- Periventricular leukomalacia
- Mortality
- Neurodevelopmental outcomes
