compensatory adaptive possibility of fetus
TRANSCRIPT
COMPENSATORY ADAPTIVE POSSIBILITY
OF FETUS DURING LABOR AND IN EARLY
NEONATAL PERIOD
Author: Hoo Jun TingEditor: Jayatheeswaran. Vijayakumar
Introduction■ The transition from a fetus to a newborn is the most complex physiologic
adaptation that occurs in human experience.■ The transition had to occur quickly for survival of the newborn.■ The neonatal period – First 28th day of life ■ Involves various physiologic and behavioral adaptations. Many of these occur
within the first few hours and even minutes or seconds of the newborn’s birth.
■ During this time, the newborn must successfully adapt in order to survive in the extrauterine environment.
Adaptation to Extrauterine Life
■ How is it achieved ?■ Successful transition from fetal to neonatal life includes the following
components :1. Respiratory2. Circulatory3. Thermoregulatory4. Energy Metabolism
Fetal Circulation
Prenatally – we have right to left pressure gradient
After birth
■ Pressure gradient reverse (Left-Right)■ Foramen ovale close IMMEDIATELY■ Ductus arteriosus close gradually■ Ductus venosus close gradually
Ductus Arteriosus
■ Have special smooth muscle cell known as “ductal smooth muscle”■ Ductal sm has the ability to contract a lot – to the point that it will
completely occlude the vessel■ Since sm constricts slowly – this process is gradual (usually 24-48
hours)
How does ductal smooth muscle know when to contract ?1.Increase oxygen tension2.Decrease PGE (approximately 9th
month of gestation)
Foramen ovale
■ Close IMMEDIATELY■ How ?
2 functional requirements when building the septa1. There must always be a communication between right and left atria2. That the communication can be close immediately at birth
Atrial Septation (4th to 6th week)
Endocardial Cushion Migration
Formation of Septum Primum
Formation of Foramen Secundum
Closure of Foramen Primum
Formation of Septum Secundum
RA pressure > LA Pressure
After birth , LA pressure > RA Pressure
Respiration
Some concepts…■ Surface Tension – Property of the surface of a liquid that allows it to
resist external force (by cohesive force between its molecules)■ What exactly does surfactant do ?
It forms a that adheres closely to the alveolar interface and prevents the sac from collapsing once the fluid is removed.■ How then is the fluid removed ?
– Cortisol in association with increasing thyroid hormones activates the sodium pump that clears fetal lung fluid at birth.
– Most of it is expelled by the upper aiways– Rest of it drained by the lymphatics and capillaries
■ What provides the force required to force open the partially collapsed fluid filled alveolar sacs ?– A negative intrathoracic pressure that is created by the first gasp of air
■ What induces this gasp of air ?– Its central nervous system reacts to the sudden change in temperature
and environment.– Clamping the cord asphyxiates the baby, provoking a violent gasp of air
■ With the first breath, there is a fall in pulmonary vascular resistance, and an increase in the surface area available for gas exchange.
■ Over the next 30 seconds the pulmonary blood flow increases and is oxygenated as it flows through the alveoli of the lungs.
■ Oxygenated blood stimulates constriction of the umbilical arteries resulting in a reduction in placental blood flow.
■ As the pulmonary circulation increases there is an equivalent reduction in the placental blood flow which normally ceases completely after about three minutes.
■ These two changes result in a rapid redirection of blood flow into the pulmonary vascular bed
■ Left atrial pressure being slightly higher than right atrial pressure, closes the foramen ovale
Umbilical cord clamps and respiration initiated
Co2 ↑
↑Pa02 Levels
↓Pulmonary vascular resistance
↑Pulmonary Blood Flow
↑Pressure in LA↓Pressure in RA
Closure of foramen ovale
↑Systemic vascular resistance
↓Systemic venous return
Cessation of umbilical venous return
Closure of ductus venosus
Pulmonary resistance less than systemic ressistance
Left-to-right shunting
Closure of ductus arteriosus
Thermoregulatory
■ Reasons which cause the neonate vulnerable to hypothermia Inability to shiver Vasculature close to the skin surface Small amount of subcutaneous fat
Physiologic Mechanisms for Preserving Core Temperature■ Increasing muscle activity: Cold neonates are restless and will cry
■ Flexed positioning: Decreases the surface ratio of exposed skin to environment
■ Brown fat metabolism: which is specialized adipose tissue with a high concentration of mitochondria designed to rapidly oxidize fatty acids in order to generate metabolic heat
■ Increased metabolic activity of heart, brain, and liver■ Prioritization: Feet and hands will become cool to the touch (vasoconstriction)
as heat is conserved for organs, most essential to survival
CRECCConvection: the flow of heat from body surface to cooler air. Keep room at 24 degrees Celsius
RRadiation: loss of heat from body surface to cooler solid surface not in direct contact, but in relative proximityPlace cribs away from windows.
EEvaporation: loss of heat that occurs when a liquid is converted to vapor.Make sure to dry infant after birth.
CConduction: loss of heat from body surface to cooler surfaces in direct contact.Pre-warm crib to prevent heat loss.
Energy Metabolism■ Energy metabolism in the fetus must be converted from a continuous
placental supply of glucose to intermittent feeding.■ Glycogen synthesis in the liver and muscle begins in the late second
trimester of pregnancy, and storage is completed in the third trimester. ■ Glycogen stores are maximal at term, but even then, the fetus only has
enough glycogen available to meet energy needs for 8–10 hours, which can be depleted even more quickly if demand is high.
■ Newborns will then rely on gluconeogenesis for energy, which requires integration, and is normal at 2–4 days of life.
■ Fat stores are the largest storage source of energy. At 27 weeks gestation, only 1% of a fetus' body weight is fat. At 40 weeks, that number increases to 16%.
■ Anticipating potential problems is the key to managing most neonatal problems of energy metabolism. For example, early feeding in the delivery room or as soon as possible may prevent hypoglycemia. If the blood glucose is still low, then an intravenous (IV) bolus of glucose may be delivered, with continuous infusion if necessary.
THANK YOU