Module 2-Caitlyn Flashcards
The fetus exists in a state of hypoxemia.
The fetus exists in a state of hypoxemia because the fetal pO2 is lower (17-19mmhg). This means when the blood oxygen levels are low, tissue oxygen levels are sufficient to meet the fetus’ low oxygen needs.
Right to left shunting, through the foramen ovale and ductus arteriosus, is a feature of fetal circulation.
Right to left shunting is normal and, in fact, desired characteristic of fetal circulation. Right to let shunting means that blood is normally headed for the lungs via the pulmonary artery is shunted through the ductus arteriosus to the aorta, thereby bypassing the lungs. Further, blood in the right atrium headed for the right ventricle is shunted through the foramen ovale to the left atrium, bypassing the lungs. Right to left shunting occurs due to patent shunts (foramen ovale + ductus arteriosus) and pressure gradients. Fetal pressure gradients are..pressure in the right heart is higher than the left; blood flows from path of least resistance –> flowing from high pressure areas to low pressure area.
Fetal lungs are high pressure, low volume organs.
The high pressure in the fetal lungs is due to pulmonary vasoconstriction, low blood oxygen and to the collapsed and fluid-filled nature of fetal lungs.
Fetal circulation functions to provide vital organs with sufficient oxygen.
Vital organs–> brain + heart
receive blood that is preductal.
Preductal blood:
is well oxygenated blood because it is blood through the foramen ovale rather than the ductus arteriosus.
Preductul blood is better oxygenated and the brain and the heart, due to the anatomic location, receive blood that arises from the coronary arteries and the carotid arteries. The coronary and carotid arteries are both preductal arteries. This is due the arteries being located on the aorta prior to the location of the ductus arteriosus.
What two perinatal events initiate transition?
The first breath:
The first breath causes the lungs to fill with air and expand, this helps to reduce pulmonary vascular resistance, allowing more blood to flow to the lungs.
Therefore more blood, in combination with the first few breaths means the lungs begin to function as organs of gas exchange.
Cutting the umbilical cord:
This eliminates the placenta as a reservoir for blood, causing a rise in bp and systemic vascular resistance.
What effect does rising pO2 have on transition?
Closure of the DA:
When the pO2 rises, it closes the Ductus Arteriosus which then also increases pulmonary perfusion.
What causes the DA to close?
- rising P02
- decreasing levels of prostaglandin, this occurs during labour and delivery.
What must happen for the infant to make a successful transition from fetal to newborn circulation?
- infant must breathe –> spontaneous or mechanically
- lungs must inflate
- cord must be cut
- blood oxygen levels must rise
- pulmonary vascular resistance must fall
- fetal shunts (ductus arteriosus and foramen ovale must close)
- pressure gradient must change
- infant must be warm (cold stress uses lots of oxygen)
What can impede transition?
- apnea at birth ( if not remedied will lead to asphyxia and PPHN)
- lung diseases such as diaphragmatic hernia and pulmonary hypoplasia can prevent gas exchange from adequately occurring in the lungs immediately after birth.
- Central nervous system depression can interfere with breathing at birth and this can be due to drugs, intrauterine hypoxia and congenital defects.
- Mec. aspiration can block airways and can interfere with gas exchange at birth.
- Hypothermia can lead to high oxygen utilization and, while hypothermia does not cause asphyxia, it does worsen it.
What does meconium consist of?
- viscous dark green
- water
- intestinal epithelial cells
- lanugo
- mucous
- intestinal secretions
How does meconium passage happen in utero?
in utero passage results from neural stimulation of the mature GI tract and usually results from fetal hypoxic stress.
as fetus approaches term , GI tract matures, and vagal stimulation from head or cord compression may cause peristalsis and relaxation of rectal sphincter leading to meconium passage.
Meconium stained amniotic fluid can be aspirated…
before or during labour and delivery.
Meconium aspiration chiefly affects which type of neonate?
term or post term infants.
meconium is rarely found in amniotic fluid prior to 34 weeks.
What are the effects of meconium in utero?
- meconium directly alter the amniotic fluid, reducing antibacterial activity therefore increasing the risk of perinatal bacterial infection
- meconium is irritating to fetal skin
Meconium aspiration effects pulmonary function in three ways:
- airway obstruction
- surfactant dysfunction
- chemical pneumonitis
Meconium aspiration: airway obstruction effects
- complete obstruction of the airways by meconium results in atelectasis
- partial obstruction causes air trapping and hyperdistention of the alveoli, communly termed the ball valve effect.
- hyperdistention of the alveoli occurs from airway expansion during inhalation and airway collapse around meconium in the airway, causing increased resistance during exhalation.
- the gas that is trapped (hyperinflating the lung) may rupture into the pleura (pneumothorax), mediastinum (pneumomediastinum), or pericardium (pneumopericardium).
Meconium aspiration: Surfactant dysfunction effects
meconium deactivates the surfactant and results in diffuse atelectasis.
Meconium aspiration: Chemical pneumonitis effects
enzymes, bile salts and fats in meconium irritate the airways and parenchyma, causing a release of cytokines and resulting in a diffuse pneumonitis.
What is does PPHN stand for?
Persistent Pulmonary Hyptertension of the newborn.
What is PPHN?
It is a serious life threatening complication of perinatal asphyxia.
However not all babes with perinatal asphyxia will develop PPHN, they are at a higher risk.
It is defined as the failure of normal circulatory transition that occurs after birth. It is a syndrome characterized by marked pulmonary hypertension that causes hypoxemia and right-to-left shunting of blood through the ductus arteriosus and foramen ovale.
