Fetal And Newborn Physiology Flashcards
Umbilical vein oxygen saturation
Where does blood flow from the umbilical vein
80%
Half through liver after merging with portal vein
Half through ductus venosus into ivc.
Oxygen Saturation of fetal ivc after joining of ductus venosus
Oxygen saturation of fetal svc
65%
25%
Flow from ivc and svc through the heart
Most ivc blood directed from RA through foramen ovale to LA and LV then pumped into systemic circulation
Most svc blood directed from RA to RV and pulmonary artery. Most of this then passes through ductus arteriosus into aorta
How much of fetal blood passes through the pulmonary circulation? Why?
10% due to very high PVR and patent ductus arteriosus
Oxygen saturation of blood supplying brain in fetus
What about supplying lower body
65% (same as ivc)
55% - mix of ivc blood now in aorta and svc blood through ductus arteriosus
Where do the blood vessels return to the placenta in the fetus? What proportion of fetal cardiac output is to the placenta?
From the internal iliacs
60%
How does fetal circulation change at birth?
Rapid fall in PVR
Blood flows from RV through the lungs
Clamping of the cord results in increased SVR
As a result reversal of flow through ductus arteriosus (aorta to pulmonary artery)
Higher pressure on left closes foramen ovale
Oxygenated blood and reduced prostoglandin E2 causes closure of ductus arteriosus
Ductus venousus closes possibly due to lack of blood flow
When does the ductus arteriosus close and obliterate
Effect of prematurity?
Closes at 24hrs
Obliterates by 3 weeks
Opens longer in prematurity
Drug that closes ductus arteriosus
Drug that keeps it open
Closes - indomethacin
Opens - prostaglandin E2
Effect on fetal cirucation of hypoxia
Very musclar pulmonary vessels
Vasoconstriction to hypoxia with increased PRV
Increased rv pressure
Reversal of shunt through foramen ovale
Difference between newborn and adult heart
Results in?
Poorly organised myofibril
Increased connective tissue
Limited contractility and compliance
Flat starling curve
Responds poorly to both low and high preload
Significantly higher heart rate and lower Bp
Incomplete sympathetic innervation to heart and vessels
Less BP drop in spinal, less response to vasopressors
Why does the developing fetus make breathing movements
Develop muscles
What happens to fluid in fetal lungs as term approaches?
Catecholamines and T3 stimulate reabsorption
Passage down birth canal stimulates further final absorption
When does surfactant production begin?
What stimulates it
26 weeks gestation
Cortisol
What are the differences between a newborn and adult lung
Lack of alveoli
Increased compliance of chest wall
Very compressible chest wall
Horizontal ribs
Less slow twitch muscle - rapid fatigue
Effect of hypoxia and hypercapnia on newborns and breathing during sleep
Less marked effect than in adults
Respond to hypoxia with brief hyperpnoea then depression due to underdeveloped chemoreceptors
Diminished arousal response to hypoxia (sleep instead of agitation)
During sleep intercostal muscle activity inhibited
During sleep many infants breath rapidly alternated with short 10s periods of apnoea
What is renal blood flow at birth? What about at 1 months
5% Co
20% CO
What is GFR at birth
What about at 2 yrs
Effect?
30
110
At birth unable to deal with water and solute loads esp glucose and sodium, also unable to compensate for acidosis
Why is there a rise in bilirubin after birth?
Fetus removes bilirubin over the placenta
At birth liver enzymes immature
Peak bilirubin at day 3-4
What is the risk of high bilirubin in babies
Kernicterus
Damage to basal ganglia and auditory tissues from unconjugated bilirubin entering brain through immature bbb
Definition of neonate
Infant
<28 days
Infant < 1yr
Heart rate of
Neonate
6month
1yr
5yr
12yr
Neonate - 120-150
6month - 120-140
1yr - 110-130
5yr - 90-100
12yr - 80-100
SBP of
Neonate
6month
1yr
5yr
12yr
Neonate - 70-80
6month - 80-90
1yr - 90-100
5yr - 95-100
12yr - 110-120
Differences in neonate hepatic drug metabolism
Immature enzymes reduce metabolism
Blood supply to liver mainly via portal vein rather than hepatic artery thus increased intraabdominal pressure reduced hepatic drug clearance
Why do infants readily loose heat?
High BSA to weight
Poor subcutaneous fat
Thin skin (esp preterm)
Difficulty in heat production
How do neonates produce heat
Non shivering thermogenesis in brown fat
