Fetal-newborn transition Flashcards
Requirements for cardiorespiratory transition
structural maturity of lung replacement of fetal lung fluid --> air adequate pulmonary surfactant onset of breathing incrase in pulmonary blood flow
Embryonic maturity of lung
less than 5 weeks
trachea and bronchi
evidence of 5 lobes
Pseudoglandular lung
5-16 wks
airway branching x 15 generations
cuboidal cell lining
Canalicular lung
16-25 wks
airways enlarge
thinned epithelium
capillary development
Saccular lung
24-36 wks
basement membranes fuse –> future blood-gas barrier
type II cells –> surfactant
Alveolar lung
36 weeks to 2-8 years
capillaries bulge into terminal sacs
formation of septae, crests
increasing surface area
Immature lung histology
canalicular
thick blood-gas barrier
small area for gas exchange
poorly vascularized
Mature lung histology
thin blood-gas barrier
large area for gas exchange
highly vascular
In utero lung fluid
ultrafiltrate of pulmonary capillary blood
actively secrete (Cl ion transport)
250-300 ml/day
essential for fetal respiration and maintenance of FRC
Lung fluid in transition
fluid secretions slows in late pregnancy
absorption begins in labour (active transport of Na ions)
vaginal squeeze forces fluid out of lungs (not extremely significant)
cleared by capillaries and lymphatics postnatally
aided by lung distension driving fluid into interstitium
Transient tachypnea of the newborn
Retained fetal lung fluid increased central vascular markings hyperaeration evidence of interstitial/pleural fluid prominent interlobar fissures flat diaphragm - hyperinflated lungs
Embryonic maturity of lung
less than 5 weeks
5 lobules
trachea and bronchi
Canalicular lung
16-25 wks
airways enlarge
thinned epithelium
capillary development
Saccular lung
24-36 wks
basement membranes fuse –> future blood-gas barrier
type II cells –> surfactant
Fetal channels
umbilical vein ductus venosus foramen ovale ductus arteriosus umbilical arteries
Breathing after birth
Onset
Reduction in pulmonary vascular resistance: crying
increased lung blood flow
increased pO2 in blood
increased blood to the LA
functional closure of foramen ovale due to LA pressure> RA
Cord clamped - increased SVR, close umbilical vessels
closed DA: usually 24-48h in term infants
Mature lung histology
thin blood-gas barrier
large area for gas exchange
highly vascular
In utero lung fluid
ultrafiltrate of pulmonary capillary blood
actively secrete (Cl ion transport)
250-300 ml/day
essential for fetal respiration and maintenance of FRC
Lung fluid in transition
fluid secretions slows in late pregnancy
absorption begins in labour (active transport of Na ions)
vaginal squeeze forces fluid out of lungs (not extremely significant)
cleared by capillaries and lymphatics postnatally
aided by lung distension driving fluid into interstitium
Cord clamping time
Effects on infant from delayed (1-2 min) cord clamping
Higher Hb at 24-48 h
Reduced Fe deficiency at 3-6 mo
increase in phototherapy for neonatal jaundice (more blood, more jaundice)
Preterm infants: reduction in rates of interventricular hemorrhage
Transient tachypnea of the newborn
Retained fetal lung fluid increased central vascular markings hyperaeration evidence of interstitial/pleural fluid prominent interlobar fissures flat diaphragm - hyperinflated lungs
Surfactant production
by alveolar type II cell
stored in Lamellar body, secreted and then adsorped to alveolar space
Surfactant composition
70-80% phospholipids
10% proteins - apoproteins AD immunity, BC hydrophobic membrane proteins that increase the rate at which surfactant spreads over surface
10% neutral lipids - cholesterol
Respiratory distress syndrome
preterm infant
tachypnea, retractions, grunting, cyanosis
hypoxia
hypercapnia
Fetal breathing movements
rhythmic contarctions of diaphragm associated with movement of small volumes of fluid in fetal airway
1-60 min episodes
increase after each maternal meal
circadian rhythm, increasing at night
related to maternal melatonin concentration
inhibited by acute, severe hypoxia, sedatives, alcohol, PGE2
Onset of breathing at birth
breathing becomes regular
mechanisms: sensory/chemical stimuli, removal of placental inhibitor peptide
Baby must overcome:
- viscosity of lung fluid
- resistance of lung tissue
- surface tension at air-liquid interface
Newborn thermal properties
Cooler environment
heat loss via conduction, convection, radiation, evaporation
Breathing after birth
Onset breathing
Reduction in pulmonary vascular resistance: crying
increased lung blood flow
increased pO2 in blood
increased blood to the LA
functional closure of foramen ovale due to LA pressure> RA
Cord clamped - increased SVR, close umbilical vessels
closed DA: usually 24-48h in term infants
Newborn arterial gases
pO2: 1 h 60 , 24 h 90 O2 sat: 1 h 90, 24 h 98 O2 content, 18 then 20 pCO2 35-45 pH 7.3-7.4transition
Time course of cardiorespiratory transition
Seconds: first breath, high transpulmonary pressure, not pink
Minutes: pink, regular breathing, pulmonary blood flow increases, absorption of lung fluid
Hours: rising pO2, FRC established, absorption of FLF, increasing lung compliance, RR40-60
Days: remodelling of pulmonary arteries, further increase in lung compliance