AWABS - Foetal Circulation

Question 1

Foetal circulation:
Include passage, foetal variants and rough oxygen sats at each point

Answer 1

Umbilical vein carries oxygenated blood
Bypasses liver via ductus venosus to go into IVC
Right atrium with right to left shunt via PFO (encouraged by eustachian valve)
Mixing of blood between pulmonary artery and aorta via Ductus arteriosus

Rough guide of O2 sats at each point are illustrated on diagram

Question 2

Extra cardiac shunts

Answer 2

Ductus venosus allows oxygenated blood to bypass the liver

Ductus arteriosus contains O2 sensitive muscle

Question 3

Foetal Hb (HbF)

Answer 3

2 alpha subunits and 2 gamma subunits
Has lower content of 2,3 DPG (diphosphoglycerate)

In adults Hb has 2 alpha and 2 beta subunits (HbA)

Question 4

Foetal Hb oxygen dissociation curve

Answer 4

Question 5

Double Bohr effect

Answer 5

In placenta:
More CO2 from foetal blood moves down concentration gradient to maternal Hb

Question 6

Transition to adult circulation

Answer 6

Transfer from placental to pulmonary oxygenation

Umbilical vessels clamped (or stretched)

Increase in SVR

Foramen ovale closes

Increased pulmonary blood flow

Ductus venosus closes passively in 3-10 days post birth due to low flow

Acidosis and hypercapnia stimulate first breath

Expansion of lungs and fall in pulmonary vascular resistance

Question 7

Ductus arteriosus in adult transition

Answer 7

Ductus arteriosus flow initially becomes bidirectional

Increase PaO2 causes direct vasoconstriction

PGE2 made by placenta rapidly falls adding to ductal vasoconstriction

Functional closure of ductus arteriosus

Question 8

Persistent foetal circulation

Answer 8

Question 9

Tetralogy of Fallot

Answer 9

Overriding aorta
Pulmonary stenosis
Right ventricular hypertrophy
VSD

Question 10

Initial issue and management of Tetralogy of Fallot

Answer 10

Duct dependence to maintain pulmonary blood flow

Managed with prostaglandin infusion to maintain patent ductus arteriosus

Question 11

Foetal circulation diagram with O2 saturations

Answer 11

Question 12

Table of differences between Adult and Foetal circulation

Answer 12

Question 13

Combined ventricular output vs Cardiac output in foetal circulation

Answer 13

Question 14

Control of foetal circulation

Answer 14

Not well understood
Changes depending on gestational age
Influenced by catecholamines

Question 15

Placental anatomy

Answer 15

Need good development of spiral arteries to prevent pre-eclampsia

Question 16

Cross sectional anatomy of placenta

Answer 16

Question 17

Functions of the placenta

Answer 17

Gas exchange
Nutrients / Metabolic transfer
Hormones
Immunological

Question 18

Gas exchange in placenta

Answer 18

Question 19

Metabolic transfer in placenta of glucose, amino acids, fatty acids and electrolytes / water / vitamins

Answer 19

Question 20

Endocrine function of the placenta

Answer 20

Question 21

Immunological function of placenta

Answer 21

Question 22

Drug transfer across placenta

Answer 22

Can be beneficial or harmful

Similar barrier to blood brain barrier

Question 23

Fick principle

Answer 23

Determines factors which affect rate of drug transfer across placenta

Question 24

Drug properties which relate to Fick principle

Answer 24

Question 25

Methods of drug transport (other than simple diffusion)

Answer 25

Pinocytosis is method of immunoglobulin transfer

Question 26

Common induction anaesthetic drugs and transfer across placenta

Answer 26

Remifentanil and Alfentanil less lipid soluble and cross placenta less

Question 27

Other common anaesthetic drugs and transfer across placenta

Answer 27