*Paediatrics Flashcards
What is the function of the placenta? (8)
Foetal homeostasis Gas exchange Acid base balance Nutrient transport to foetus Waste product transport from foetus Hormone production Transport of IgG (crosses the placenta from mother to baby protecting the baby while their humoral response is developing) PGE2 (helps to maintain duct potency in utero.)
In utero, what is the state of the baby’s lungs?
Fluid filled and unexpanded (the liver has little role in nutrition and waste management and the gut is not in use)
What blood vessels carry blood to and from the foetal heart to the placenta?
The foetal heart pumps blood to the placenta via the umbilical arteries and blood from the placenta returns to the foetus via the umbilical vein
What are the 3 blood vessels in the umbilical cord?
2 umbilical arteries
1 umbilical vein
(some babies can only have one artery and one vein - this can be normal but can also be a sign that there are other problems)
What are the 3 foetal shunts?
The ductus venosus
The foramen oval
The ductus arteriosus
In the foetal circulation, does the right heart or left heart have higher pressure?
The right heart
Which ventricle is dominant in the foetus?
The right ventricle
What does the ductus venous do?
Connects the umbilical vein to the inferior vena cava
What does the foramen ovale do?
Opening in atrial septum connecting RA to LA
What does the ducts arteriosus do?
Connects pulmonary bifurcation to the descending aorta
Why does the ductus venosus exist?
Nutrients coming from placenta don’t need further processing in the liver
Ductus venosus carries the majority of the placental blood straight into the IVC bypassing portal circulation
What does foramen ovale allow?
Blood to flow from right to left atrium
Allows the best oxygenated blood to enter left atrium then on to LV, ascending aorta, carotids
Membrane flap on left atrium side
Where does the output from the RV go?
Only 7% goes to the lungs
The restless via ductus arteriosus to join descending aorta
What maintains the potency of the ductus arteriosus?
Circulating prostaglandin E2 produced by the placenta
Summary of foetal circulation?
Oxygenated comes from the placenta to the foetus via the umbilical vein.
In the liver, the ductus venosus connects the umbilical vein to the IVC
The blood passes into the right sides of the heart and the oxygenated blood passes through the foramen ovale into the left atrium
The blood then passes into the left ventricle and out the aorta
Blood coming from the body also enter the right atrium
This deoxygenated blood passes to the right ventricle
The blood is pumped via the pulmonary artery
Most of the blood bypasses the lungs and is pumped through the ductus arteriosus where the deoxygenated blood is pumped to the lower half of the foetal body where it leaves via the umbilical arteries
Some blood does pass to the lungs
Why do babies cry when they are first born?
It creates back pressure opening up the alveoli
What are the circulation changes during the first few mins after birth? (3)
First breath = lungs open up, pO2 increases and causes pulmonary vasodilation
Decrease in resistance to flow to lungs
Cord clamping = large, low resistance vascular bed removed from circulation, systemic vascular resistance increases
Baby going pink = more blood circulating to lungs, progressively increasing pO2
What are the O2 sats of the foetus in the womb?
60 - 70%
What causes the foramen ovale flap to close?
As PVR falls and SVR rises, LA pressure exceeds the RA pressure = the flap is pushed closed (stays open in up to 35% of the population = implicated in stroke and migraine)
What causes the ductus arteriosus to close? (3)
Fall in pulmonary vascular resistance reduces blood flow through the duct
Rising oxygen tension has a direct effect on the duct smooth muscle causing constriction
The loss of circulating PGE2 from the placenta and increased PGE2 metabolism in the lung
How long does it take for the ductus arteriosus to functionally close?
To anatomically close?
hours to days
7-10 dats
What does the ductus arteriosus end up as when it closes?
Fibrous ligament called the “ligamentum arteriosum”
What type of babies have a very high incidence of failure of ductus arteriosus closure?
Preterm infants
Treatment options for failure of ductus arteriosus to close?
Wait and see
NSAIDs (cause the duct to close)
Surgery (if NSAIDs don’t work)
How are “duct dependent circulations” managed in babies with congenital heart disease?
IV prostaglandin E2 is used to keep the duct open until an alternative shunt is established or definitive surgery is carried out
What can cause persistent pulmonary hypertension of the newborn? (failure of adaption)
(vascular resistance in the lungs fails to drop when baby is born)
More likely in sick babies e.g. sepsis, hypoxic ischaemic insult, meconium aspiration syndrome, cold stress)
Can be related to underlying anatomical abnormality such as congenital diaphragmatic hernia
What type of circulation will you get in a newborn if there is persistent pulmonary hypertension?
Persistence of foetal circulation = shunts remain
What will the baby look like if they persistent pulmonary hypertension?
Blue
baby will have a large difference between their pre and post ductal oxygen saturation
Treatment of persistent pulmonary hypertension of the newborn?
Ventilation Oxygenation High systemic blood pressure Inhaled NO (potent vasodilators) ECMO
Where is pre and post ductal saturation measurements taken?
Pre = right hand Post = left foot
