18. Neonatal Development

Question 1

Is the placenta efficient or inefficient compared to the lung at gas exchange?

Answer 1

inefficient

Question 2

fetal blood distribution max’s what?

Answer 2

02 delivery to vital tissues (heart, brain)

Question 3

what % of cardiac output do cardiac lungs receive? why?

Answer 3

5-8%. because of high pulm vascular resistance.

Question 4

in the fetus, the umbilical vein is ox or deox?

Answer 4

ox from placenta

Question 5

regulation of pulm vascular resistance: what causes vasoconstriction?

Answer 5

generally: mechanical means, 02, hormones from arachodonic acid.
- low 02 and low pH (remember this is pulm so it is backwards in terms of pH)
- leukotrienes
- thromboxane A2

Question 6

regulation of pulm vascular resistance: what causes vasodilation?

Answer 6

mostly endothelial-derived.

• NO
• incr 02, high pH
• PGI2 prostacyclin

Question 7

what structures does the ductus arteriosus connect?

Answer 7

connects pulm artery and aorta. allows oxygenated blood from the placenta to pass directly into systemic circ.

Question 8

what keeps the ductus open?

Answer 8

prostaglandin E2 keeeeeeeps the ductus open!

Question 9

what makes the ductus close? think about where it is produced.

Answer 9

the absence of PGE2 allows the ductus to close… PGE2 is made in the placenta, cleared by the fetal lung

Question 10

what is ET1? what does it do?

Answer 10

endothelin 1, major constrictor of the ductus arteriosus.

Question 11

for term infants, how does the ductus close?

Answer 11

functional closure with smooth muscle vasoconstriction within hours of birth. local action.
anatomic occlusion over days with intimal thickening and loss of smooth muscle cells from inner muscle media

Question 12

what are the molecules responsible for closing the ductus?

Answer 12

02 appears to be ultimately responsible.
incr in P02 increases for formation of ET-1.
ET-1 promotes constriction, overcomes the dilating effects of PGE2/NO
also, removal of the placenta decreases the concentration of PGE2

Question 13

what are some physiological changes that cause changes in pulmonary vasc at birth?

Answer 13

• rapid decr in pulm vasc resistance with lung inflation
• additional vasodilator effects of oxygen
• adaptive changes in the heart (closure of shunts)

Question 14

fetal circulation pattern turns into what? which turns into what?

Answer 14

fetal –> transitional –> neonatal

Question 15

what are characteristics of the transition from fetal to transitional circ?

Answer 15

• placenta: has been part of circuit, now removed.
• FO and DA have been open; now FO closes and flow through the DA reverses
• there has been high PVR; now it decreases
• RA pressure has been higher than LA pressure; now LA pressure rises and LA pressure falls
• pulm blood flow overall increases.

Question 16

what forces characterize the transition from transitional to neonatal circulation?

Answer 16

• with neonatal circ, both the FO and the DA are closed
• PVR is lowered further
• LA pressure is consistently higher than RA pressure

Question 17

what are 2 categories of failure to transition?

Answer 17

persistence of fetal circulation, and a patent ductus arteriosus

Question 18

what can cause a delay in the decrease in pulm vascular resistance?

Answer 18

• perinatal asphyxia: low 02 during delivery, causes baby to try to maintain fetal breathing style
• sepsis
• undergrowth of pulm vasculature
• idiopathic PFC (persistence of fetal circ): we don’t know

Question 19

definition of asphyxia?

Answer 19

failure of gas exchange: low Pa02, high PaC02

Question 20

what happens during perinatal asphyxia (leading to persistence of fetal circ?)?

Answer 20

• blood flow to the lungs remains decr as it was in utero.
• in the fetus, blood flow to the placenta is maintained unless there is cord obstruction
• flow to vital organs is maintained
• blood to liver, kidneys, GI, skin decreases

Question 21

clinical presentation of a neonate with hypoxia due to a decr in pulm blood flow?

Answer 21

cyanosis, low 02 sat, incomplete correction in Pa02 when breathing 100% 02. (basically due to a shunt)

Question 22

describe the hyperoxia test

Answer 22

allows you to tell is a problem in pa02 is due to a shunt (persistence of fetal circ) or due to a problem with gas exchange in the lung.
if due to PFC, giving 100% 02 won’t help. if due to a problem of incomplete gas exchange in the lung, it will raise Pa02.

Question 23

why might a pulm vasc bed not develop properly?

Answer 23

congenital pulm hypoplasia, secondary pulm hypoplasia (diaphragmatic hernia, neuro causes of decr fetal breathing)

Question 24

why might there be functional obstruction to neonate lungs?

Answer 24

polycythemia with incr viscosity decr pulm blood flow.

polycythemia is high levels of RBCs in blood, seen w mothers with gestational diabetes

Question 25

why might there be pulm vascular constriction with a neonate?

Answer 25

perinatal asphyxia, pulm parenchymal disease (RDS, pneumonia), PFC

Question 26

what might cause neonatal pulm venous hypertension?

Answer 26

pulm venous obstruction, LA, or mitral obstruction

Question 27

a word about pulm venous outflow obstruction: what does it resemble, what is the treatment?

Answer 27

looks like severe non responsive hypoxia. CXR looks like severe pneumonia. only chance for survival is urgent surgery.

Question 28

a very low Pa02 from birth that does not increase with 100% 02 and pos pressure ventilation is what?

Answer 28

cardiac disease until proven otherwise.

Question 29

most infants with pulm causes of PFC respond to 100% 02 or not?

Answer 29

yes

Question 30

treatment for a diaphragmatic hernia?

Answer 30

gentle ventilation, surgery after delay if low risk. if high risk, ECMO and then surgical repair.

Question 31

treatment for left atrial obstruction?

Answer 31

create shunt across atria.

Question 32

how do we treat PFC?

Answer 32

disease is hyperoxia, hypercapnia, acidosis. so give 02, hypocapnia, alkalosis. sedation, ventilation, iNO

Question 33

how does iNO help in the setting of PFC?

Answer 33

decr pulm vascular resistance

Question 34

why does the ductus remain patent in premature infants?

Answer 34

ductus of a preterm infant is less sensitive to 02 constriction. ductus of a preterm infant is more sensitive to dilating effects of PGE2 and NO than that of a term infant.

Question 35

treatment of a PDA?

Answer 35

- steroids to mom before birth - give porstaglandin synthetase inhibitors (indomethacin, ibuprofen) - surgery