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.

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