Fetal Oxygenation

Question 1

What 4 factors influence placental gas exchange?

Answer 1

Gradients
Affinity
Flow rate
Diffusion

Question 2

Does maternal or fetal hemoglobin have higher affinity for O2?

Answer 2

Fetal hemoglobin

Question 3

Is the fetal O2-Hb dissociation curve to the left or right of the maternal curve?

Answer 3

To the left

Because fetal hemoglobin has higher affinity

Question 4

Bohr effect

Answer 4

Fetal metabolites and CO2 pass from fetus to mother in the intervillous space
IVS becomes more acidic (maternal curve shifts to right to facilitate O2 release)
Fetal pH becomes less acidic (fetal curve shifts further to the left to facilitate O2 uptake)

Question 5

Umbilical cord contains…

Answer 5

1 umbilical vein (placenta to fetus)

2 umbilical arteries (fetus to placenta)

Question 6

Fetal oxygen capacity is influenced by (2)

Answer 6

Fetuses Hb concentration

Fetal Hb’s oxygen affinity

Question 7

3 reasons why fetal blood can deliver O2 to tissues even though there is a low pO2

Answer 7

Higher Hb concentration than adult
Different Hb type with higher O2 carrying capacity than adult
Higher CO (so greater perfusion)

Question 8

Why is the low pO2 helpful in the fetus? (2)

Answer 8

Keeps the ductus arteriosus open

Keeps the pulmonary vascular bed constricted

Question 9

Structure of fetal Hb

Answer 9

2 alpha and 2 gamma chains

Question 10

3 physiologic shunts in the fetus

Answer 10

Ductus arteriosus
Foramen ovale
Ductus venosus

Question 11

Fetus relies on what organ to clear acid and maintain pH

Answer 11

The placenta

Cannot rely on kidneys and lungs like an adult would

Question 12

2 kinds of acids that the fetus produces from 2 different metabolisms

Answer 12

Aerobic: carbonic acid
Anaerobic: organic acids (lactic and ketoacids)

Question 13

Carbonic Acid

Answer 13

Produced by fetus during normal, oxidative metabolism
Dissociated to CO2 and H2O
CO2 rapidly diffuses across placenta

Question 14

Organic Acids

Answer 14

Results from anaerobic metabolism
Produced when fetal oxygenation is impaired (many possible causes)
Organic acids cross placenta more slowly than CO2

Question 15

Respiratory acidosis

Answer 15

When the blood flow is interrupted for a brief period of time
The fetal pH drops and CO2 rises (but metabolic acid-base status is unchanged)

Question 16

Metabolic acidosis

Answer 16

If oxygen lack is sustained
The fetus decreases its O2 consumption, redistributes blood flow (to vital organs), and relies partly on anaerobic metabolism to meet energy needs
Get lactic acid produced
Can overwhelm the buffer system

Question 17

Should pH be higher or lower in venous or arterial blood in the fetus?

Answer 17

Higher in the venous blood

Arterial is more acidic which is opposite to adult