Adaptation to extrauterine life

At the end of pregnancy, the fetusmust take the journey of childbirthto leave the reproductivefemalemother. Upon its exit into the oxygen-consuming world, the newbornmust begin to adjust to life outside the uterus.

Breathing and circulation

Perfusing its body by breathing independently instead of utilizing placentaloxygenis the first challenge of a newborn. With the first breaths, there is a fall in pulmonary vascular resistance, and an increase in the surface area available for gas exchangedue to the loss of low-resistance placentalcirculation. Overall, there is an increase in total peripheral resistance(TPR). There is a rapid subsequent increase in oxygenation due to the cardiovascular systemchanges. The decrease in venousreturn results in left atrialpressure being slightly higher than right atrial pressure, which closes the ductus arteriosus and foramen ovale fetal circulationshunts, and another increase in pulmonary blood flowfrom approximately 4% to 100% of cardiac output.

All of these changes result in the adaptation of the cardiovascular system from fetal circulation patterns to an adultcirculationpattern. At this point, most congenital heart disease –which was not symptomatic in utero – starts to cause cyanosisor other symptoms. Usually, these problems are caused by cardiac or respiratoryproblems, though other causes may rarely contribute.

At birth, there is a maturation of the alveoliand capillarynetworks of the lungs, as well as the deployment of surfactantsto keep the alveoli open. At this point, a baby's rhythmic breathingalso commences. If there are any problems with breathing, management can include stimulation, bag and mask ventilation, intubationand ventilation. Cardiorespiratory monitoring is essential to keeping track of potential problems. Pharmacologicaltherapy such as caffeinecan also be given to increase heart rate. A positive airway pressure should be maintained, and neonatal sepsismust 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.

Energy metabolism

Energy metabolism in the fetusmust be converted from a continuous placentalsupply of glucoseto 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 synthesisin the liverand musclebegins in the late second trimesterof pregnancy, and storage is completed in the third trimester. Glycogenstores 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. Newbornswill then rely on gluconeogenesisfor energy, which requires integration, and is normal at 2-4 days of life.

Fatstores 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 glucosesubstrate 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), hypothermiaor 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 glucoseis still low, then an intravenous(IV) bolus of glucose may be delivered, with continuous infusion if necessary. Rarely, steroidsor glucagonmay have to be employed.

Temperature regulation

Newborns come from a warm environment to the cold and fluctuating temperatures of this world. They are usually naked, wet, have a larger surface area than in the womb(on account of not being curled up), with variable amounts of insulation, limited metabolic reserves, and an inability to shiver. As such, it is not surprising that some newborns may have problems regulating their temperature. As early as the 1880s, infant incubatorswere 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.

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It uses material from the Wikipedia article Adaptation to extrauterine life.