Adaptation to extrauterine life
Encyclopedia
At the end of pregnancy
, the fetus
must take the journey of childbirth
to leave the reproductive female
mother.
Upon its entry to the air-breathing world, the newborn must begin to adjust to life outside the uterus
.
l oxygen
is the first challenge of a newborn. At birth, the baby's lungs are filled with amniotic fluid and are not inflated. The newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment. This triggers it to take the first breath, within about 10 seconds after delivery. With the first breaths, 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 now reaches the left atrium and ventricle, and through the descending aorta reaches the umbilical arteries. Oxygenated blood now 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, from approximately 4% to 100% of cardiac output
. The increase in pulmonary venous
return results in left atrial
pressure being slightly higher than right atrial pressure, which closes the foramen ovale
. The flow pattern changes results in a drop in blood flow across the ductus arteriosus
and the higher blood oxygen content of blood within the aorta stimulates the constriction and ultimately the closure of this fetal circulatory shunt.
All of these cardiovascular system changes result in the adaptation from fetal circulation patterns to an adult
circulation
pattern. During this transition, some types of congenital heart disease that were not symptomatic in utero
during fetal circulation will present with cyanosis
or respiratory
signs.
It is common obstetric practice to intervene in these changes by applying a clamp to the umbilical cord, often within 20 seconds of birth, before transition has taken place.
Following birth, the expression and re-uptake of surfactant
, which begins to be produced by the fetus at 20 weeks gestation, is accelerated. Expression of surfactant into the alveoli is necessary to prevent alveolar closure (atelectasis
). At this point, rhythmic breathing movements also commence. If there are any problems with breathing, management can include stimulation, bag and mask ventilation, intubation
and ventilation
. Cardiorespiratory monitoring is essential to keeping track of potential problems.
Pharmacological therapy such as caffeine
can also be given to treat apnea
in premature newborns. A positive airway pressure should be maintained, and neonatal sepsis
must be ruled out.
Potential neonatal respiratory problems include apnea
, transient tachypnea of the newborn
(TTNB), respiratory distress syndrome
(RDS), meconium aspiration syndrome
(MAS), airway obstruction
, and pneumonia
.
must be converted from a continuous placenta
l supply of glucose
to intermittent feeding.
While the fetus is dependent on maternal glucose as the main source of energy, it can use lactate
, free-fatty acids, and ketone bodies under some conditions.
Plasma glucose is maintained by glycogenolysis
.
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%.
Inadequate available glucose
substrate can lead to hypoglycemia
, fetal growth restriction, preterm delivery, or other problems.
Similarly, excess substrate can lead to problems, such as infant of a diabetic mother (IDM), hypothermia
or neonatal sepsis
.
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.
Rarely, steroid
s or glucagon
may have to be employed.
They are naked, wet, and have a large surface area to mass ratio, with variable amounts of insulation
, limited metabolic reserves, and a decreased ability to shiver. Physiologic mechanisms for preserving core temperature include vasoconstriction (decrease blood flow to the skin), maintaining the fetal position (decrease the surface area exposed to the environment), jittery large muscle activity (generate muscular heat), and "non-shivering thermogenesis". The latter occurs in "brown fat"
which is specialized adipose tissue with a high concentration of mitochondria designed to rapidly oxidize fatty acids in order to generate metabolic heat. The newborn capacity to maintain these mechanisms is limited, especially in premature infants. As such, it is not surprising that some newborns may have problems regulating their temperature
.
As early as the 1880s, infant incubators were used to help newborns maintain warmth, with humidified incubators being used as early as the 1930s.
Basic techniques for keeping newborns warm include keeping them dry, wrapping them in blankets, giving them hats and clothing, or increasing the ambient temperature.
More advanced techniques include incubators (at 36.5°C), humidity
, heat shields, thermal blankets, double-walled incubators, and radiant warmers.
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
must take the journey of childbirth
Childbirth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
to leave the reproductive female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
mother.
Upon its entry to the air-breathing world, the newborn must begin to adjust to life outside the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
.
Breathing and circulation
Perfusing its body by breathing independently instead of utilizing placentaPlacenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
is the first challenge of a newborn. At birth, the baby's lungs are filled with amniotic fluid and are not inflated. The newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment. This triggers it to take the first breath, within about 10 seconds after delivery. With the first breaths, there is a fall in pulmonary vascular resistance, and an increase in the surface area available for gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
. Over the next 30 seconds the pulmonary blood flow increases and is oxygenated as it flows through the alveoli of the lungs. Oxygenated blood now reaches the left atrium and ventricle, and through the descending aorta reaches the umbilical arteries. Oxygenated blood now 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, from approximately 4% to 100% of cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
. The increase in pulmonary venous
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
return results in left atrial
Left atrium
The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...
pressure being slightly higher than right atrial pressure, which closes the foramen ovale
Foramen ovale (heart)
In the fetal heart, the foramen ovale , also ostium secundum of Born or falx septi, allows blood to enter the left atrium from the right atrium. It is one of two fetal cardiac shunts, the other being the ductus arteriosus...
. The flow pattern changes results in a drop in blood flow across the ductus arteriosus
Ductus arteriosus
In the developing fetus, the ductus arteriosus , also called the ductus Botalli, is a shunt connecting the pulmonary artery to the aortic arch. It allows most of the blood from the right ventricle to bypass the fetus's fluid-filled lungs. Upon closure at birth, it becomes the ligamentum arteriosum...
and the higher blood oxygen content of blood within the aorta stimulates the constriction and ultimately the closure of this fetal circulatory shunt.
All of these cardiovascular system changes result in the adaptation from fetal circulation patterns to an adult
Adult
An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age....
circulation
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
pattern. During this transition, some types of congenital heart disease that were not symptomatic in utero
In utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
during fetal circulation will present with cyanosis
Cyanosis
Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...
or respiratory
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
signs.
It is common obstetric practice to intervene in these changes by applying a clamp to the umbilical cord, often within 20 seconds of birth, before transition has taken place.
Following birth, the expression and re-uptake of surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
, which begins to be produced by the fetus at 20 weeks gestation, is accelerated. Expression of surfactant into the alveoli is necessary to prevent alveolar closure (atelectasis
Atelectasis
Atelectasis is defined as the collapse or closure of alveoli resulting in reduced or absent gas exchange. It may affect part or all of one lung. It is a condition where the alveoli are deflated, as distinct from pulmonary consolidation.It is a very common finding in chest x-rays and other...
). At this point, rhythmic breathing movements also commence. If there are any problems with breathing, management can include stimulation, bag and mask ventilation, intubation
Intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...
and ventilation
Ventilation (physiology)
In respiratory physiology, ventilation is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:-Sample values:...
. Cardiorespiratory monitoring is essential to keeping track of potential problems.
Pharmacological therapy such as caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
can also be given to treat apnea
Apnea
Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...
in premature newborns. A positive airway pressure should be maintained, and neonatal sepsis
Neonatal sepsis
In common clinical usage, neonatal sepsis specifically refers to the presence of a bacterial blood stream infection in the setting of fever...
must be ruled out.
Potential neonatal respiratory problems include apnea
Apnea
Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...
, transient tachypnea of the newborn
Transient tachypnea of the newborn
Transient tachypnea of the newborn is a respiratory problem that can be seen in the newborn shortly after delivery. Amongst causes of respiratory distress in term neonates, it is the commonest . It consists of a period of rapid breathing...
(TTNB), respiratory distress syndrome
Respiratory distress syndrome
There are two forms of respiratory distress syndrome:* ARDS, which is acute respiratory distress syndrome* Infant respiratory distress syndrome , which is a complication of premature birth, also known as hyaline membrane disease Also, respiratory distress can mean:* Shortness of breath*...
(RDS), meconium aspiration syndrome
Meconium aspiration syndrome
Meconium aspiration syndrome is a medical condition affecting newborn infants. It occurs when meconium is present in their lungs during or before delivery...
(MAS), airway obstruction
Airway obstruction
Airway obstruction is a respiratory problem caused by increased resistance in the bronchioles that reduces the amount of air inhaled in each breath and the oxygen that reaches the pulmonary arteries...
, and pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
.
Energy metabolism
Energy metabolism in the fetusFetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
must be converted from a continuous placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l supply of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
to intermittent feeding.
While the fetus is dependent on maternal glucose as the main source of energy, it can use lactate
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
, free-fatty acids, and ketone bodies under some conditions.
Plasma glucose is maintained by glycogenolysis
Glycogenolysis
Glycogenolysis is the conversion of glycogen polymers to glucose monomers. Glycogen is catabolized by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate...
.
Glycogen synthesis in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
begins in the late second trimester of pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, and storage is completed in the third trimester.
Glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
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
Gluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....
for energy, which requires integration, and is normal at 2–4 days of life.
Fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
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%.
Inadequate available glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
substrate can lead to hypoglycemia
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
, fetal growth restriction, preterm delivery, or other problems.
Similarly, excess substrate can lead to problems, such as infant of a diabetic mother (IDM), hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
or neonatal sepsis
Neonatal sepsis
In common clinical usage, neonatal sepsis specifically refers to the presence of a bacterial blood stream infection in the setting of fever...
.
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
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
.
If the blood glucose is still low, then an intravenous (IV) bolus of glucose may be delivered, with continuous infusion if necessary.
Rarely, steroid
Steroid
A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
s or glucagon
Glucagon
Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...
may have to be employed.
Temperature regulation
Newborns come from a warm environment to the cold and fluctuating temperatures of this world.They are naked, wet, and have a large surface area to mass ratio, with variable amounts of insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
, limited metabolic reserves, and a decreased ability to shiver. Physiologic mechanisms for preserving core temperature include vasoconstriction (decrease blood flow to the skin), maintaining the fetal position (decrease the surface area exposed to the environment), jittery large muscle activity (generate muscular heat), and "non-shivering thermogenesis". The latter occurs in "brown fat"
Brown adipose tissue
Brown adipose tissue or brown fat is one of two types of fat or adipose tissue found in mammals....
which is specialized adipose tissue with a high concentration of mitochondria designed to rapidly oxidize fatty acids in order to generate metabolic heat. The newborn capacity to maintain these mechanisms is limited, especially in premature infants. As such, it is not surprising that some newborns may have problems regulating their temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
.
As early as the 1880s, infant incubators were used to help newborns maintain warmth, with humidified incubators being used as early as the 1930s.
Basic techniques for keeping newborns warm include keeping them dry, wrapping them in blankets, giving them hats and clothing, or increasing the ambient temperature.
More advanced techniques include incubators (at 36.5°C), humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
, heat shields, thermal blankets, double-walled incubators, and radiant warmers.