Physiologic Adaptation to Extrauterine Life

Question 1

What are the three phases of lung development?

Answer 1

• Canalicular phase: 17 - 27 weeks; capillary network begins; type II cells begin to differentiate
• Saccular phase: 27 weeks to 36 weeks; type I cells and endothelial cells associate
• Alveolar phase: 36 weeks to 3 years; presence of true alveoli

Question 2

Prior to about _________, the alveoli are not close enough to the endothelium for gas exchange to occurs.

Answer 2

22 weeks

Question 3

Why is it important to prevent the alveoli from completely closing?

Answer 3

If the alveoli close, then the force to open them is much higher than if they remain open. (Think of how hard it is to blow up a balloon that has totally deflated.)

Question 4

Surfactant is secreted by _______________.

Answer 4

type II pneumocytes

Recall that type I pneumocytes are the long, flat, epithelial cells (like the number I).

Question 5

Surfactant deficiency presents with what radiologic sign?

Answer 5

“Whiteout” in the lungs – that is, a diffuse opacity without enough air to create a heart shadow

Question 6

Surfactant deficiency is also called ______________.

Answer 6

hyaline membrane disease (because proteinaceous fluid leaks into the alveolar spaces as in RDS)

Question 7

What are physical signs of hyaline membrane disease?

Answer 7

Belly breathing that leads to pectus excavatum (because the ribcage is mostly cartilage at birth and can be sucked in by the negative pressure generated by forceful inspiration)

Question 8

Why do babies grunt when they have respiratory insufficiency?

Answer 8

Grunting is expiration against a partially closed epiglottis. That closure generates positive end-expiratory pressure (PEEP) that prevents the bronchioles from closing.

Question 9

What three treatments can be administered to babies with HMD?

Answer 9

• Surfactant
• Nasal CPAP
• Intubation with mechanical ventilation

Question 10

During gestation, the lungs actually produce ______________.

Answer 10

amniotic fluid

Question 11

In all babies, the first few breaths push fluid _____________. Without sufficient breathing, however, the fluid can _________________.

Answer 11

into the interstitial spaces; seep back into the alveoli

Question 12

Differentiate primary and secondary apnea.

Answer 12

• Primary apnea: HR and BP maintained; stimulation elicits a cry
• Secondary apnea: HR and BP drop; ventilation required

Question 13

What is the APGAR range?

Answer 13

0 (dead) to 10

Question 14

How is APGAR scoring usually done?

Answer 14

• 1 min
• 5 min
• 10 min
• 15 min
• 20 min

(or until a score of 7 or more is reached)

Question 15

What are the five categories in APGAR scoring?

Answer 15

• HR: absent; less than 100, or greater than 100
• Respiration: absent, irregular, or regular/crying
• Motion: limp, some flexion, or actively moving
• Response to suction: none, grimace, or coughing/sneezing
• Color: pale blue, acrocyanotic, or pink

Question 16

What happens to the pulmonary circulation after birth?

Answer 16

Two things: (1) the larger chest volume decreases pulmonary vascular resistance, leading to increased pulmonary flow, and (2) the increased arterial PO2 leads to closure of the ductus arteriosus.

Question 17

The umbilical arteries arise from the _____________.

Answer 17

common iliac arteries (remember the vestigal umbilical artery in adults)

Question 18

What are normal pulmonary responses to extrauterine life?

Answer 18

• Tachypnea (sometimes greater than 60/min) for the first hour
• Pauses of several seconds without hypoxia, cyanosis, or bradycardia
• No retractions and RR 40-60 after the first hour

Question 19

What are normal cardiac responses to extrauterine life?

Answer 19

• Tachycardia up to 180 BPM during the first hour; decreasing to 110-140 BPM after the first hour
• Murmurs (50%)
• BP (60 - 90) / (30 - 60) mm Hg

Question 20

Signs of neonatal hypoglycemia include __________________.

Answer 20

jitteriness, irritability, apnea, and seizures

Question 21

In which stage of lung development does the capillary network form?

Answer 21

Canalicular (17 - 27 weeks)

“The canalicular phase forms canals for blood.”

Question 22

The umbilical vein enters the circulation through the ______________.

Answer 22

ductus arteriosus (which itself becomes the ligamentum venosus)

Question 23

Why do obstetricians often wait until the newborn is breathing strongly to clamp the umbilical cord?

Answer 23

The umbilical artery (away from the baby) constricts with increasing oxygenation. As such, the baby is receiving a net influx of blood during the first couple minutes of life, because the artery is constricting while the vein remains patent. Delaying the clamping can improve neonatal blood volume.

Question 24

Lengthening and sprouting of the alveolar network occurs during the ____________ stage.

Answer 24

alveolar

Question 25

Surfactant is stored as _____________ bodies in type II pneumocytes.

Answer 25

lamellar

Question 26

How does surfactant prevent alveoli from closing?

Answer 26

Its hydrophobic tails repel one another when forced into close contact by contracting alveoli.

Question 27

Why does C-section lead to more lung disease in infants?

Answer 27

Labor helps expel fluid from the lungs. Without labor, a disorder called transient tachypnea of the newborn develops.

Question 28

What is Apgar scoring NOT used for?

Answer 28

• Diagnosis of asphyxia
• Determine need to resuscitate
• Gauge long-term outcome

Question 29

How does lung transition also determine cardiac transition?

Answer 29

Oxygenation of the alveoli leads to pulmonary vasodilation. This directs blood through the adult circuit in the heart and increases left atrial pressure, thereby closing the foramen ovale and ductus arteriosus.

Question 30

Closing of the _____________ is reversible.

Answer 30

DA and FO

Question 31

How do prostacyclin and pO2 affect the pulmonary vascular resistance?

Answer 31

They decrease it.