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During fetal life the alveoli make fetal lung fluid that expands the alveoli and helps in developing the lungs.
In labor the fluid starts to move to the interstitial spaces where it is absorbed. Absorption is started by the labor process and might be delayed in c-sections.
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What is surfactant and what does it do?
Slippery detergent like combo of lipoproteins. It reduces surface tension in the alveoli, without surfactant the alveoli collapse as the infant exhales.
Surfactant secretion increases during labor and immediately after birth to enhance the transition from fetal to neonatal life.
Steroids can be given to women in preterm labor to help increase surfactant production and help mature lungs.
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The baby's first breath at birth must force the remaining fetal lung fluid out of the alveoli and into the interstitial space to allow air to enter the lungs.
Breathing can be started by different ways, chemical, mechanical, thermal, and sensory factors that stimulate the respiratory center in the medulla of the brain and trigger respirations.
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Chemical Factors:
chemoreceptors in the carotid arteries and aorta respond to changes in he blood chemistry brought about by the hypoxia that occurs with normal birth
Mechanical Factors:
Fetal lung fluid being forced out during the compression of narrow birth canal. When the pressure against the chest is released at birth, recoil of the chest draws a small amount of air into the lungs.
Thermal Factors:
Temperature change that occurs with birth stimulates the start of respirations.
Sensory Factors:
Tactile stimuli that occur during birth stimulate skin sensory. Nurses hold, dry and place infants skin to skin with mother or wrap them in blankets, providing further stimulation to skin sensors.
Stimulation of the sound, light, smell, and pain at delivery also aid in initiating respirations.
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Most fluid is absorbed within a few hours, complete absorption may take as long as 24 hours, so lungs may sound moist when first auscultated and become clear a short time later.
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During fetal life there are three shunts that carry much of the blood away from the lungs and some blood away from the liver.
- Ductus Venosus
- Foramen ovale
- Ductus arteriosus
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Thermoregulation: the maintenance of body temperature
The fetus makes heat in the uterus by the warm temp of the amniotic fluid and the mother's body, so when the neonate moves from the warm uterus to the cooler outside environment it must produce and maintain heat to prevent the serious effects of cold stress.
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Newborns have easy heat loss because their skin is thin, blood vessels are close to the surface and they have little subcutaneous (white) fat to provide a barrier to loss of heat.
Newborns have three times more surface area to body mass than the adult and the rate of heat loss if four times greater than in adults!
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There are four methods of heat loss:
Evaporation
Conduction
Convection
Radiation
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Evaporation:
- Air drying of the skin that results in cooling!
- Drying the baby immediately when wet helps prevent loss of heat by evaporation.
- Evaporation can occur during birth or bathing from moisture on skin, as a result of wet linens or clothes and from insensible water loss.
- Wet diaper
- Throw up milk on shirt
- Wet hair after bath
- Insensible water loss from lungs
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Conduction:
- Movement of heat AWAY from the body
- Occurs when newborns come in direct contact with objects that are cooler than their skin!
- Cold hands
- Metal scale with thin paper liner
- Stethoscope
- Warming objects that will touch the infant or placing the unclothed infant against the mother's skin helps prevent conductive heat loss.
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Convection:
- Transfer of heat from the infant to cooler surrounding air
- Occurs when drafts come from open doors, air conditioning, or even air currents created by people moving
- Blanket being loose or off
- When infnats are in incubators the circulating warm air helps keep them warm by convection
- Provide a warm, draft free place
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Radiation:
- The transfer of heat to cooler objects that are not in direct contact with the infant
- Like when the infant is near cold surfaces, heat is lost from the infants body to the sides of the crib or incubator and to the outside walls and windows.
- Place cribs and incubators away from windows and outside walls minimizes this type of heat loss
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When babies are cold they cry and get restless moving alot so they can help maintain heat.
Vasoconstriction occurs to decrease heat loss and ACROCYANOSIS may result (bluish discoloration of hands and feet)
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The primary method of heat production is....
Nonshivering thermogenesis (NST)
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Nonshivering thermogenesis is the metabolism of brown fat to produce heat. They can increase heat production by 100% using NST
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What is brown fat and where does it show up on the baby?
- Brown adipose tissue, is vascular specialized fat that provides heat when metabolized.
- Located around the back of the neck, axillae, kidneys, adrenals, and sternum
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NST may begin in an infant when skin temp has been cooled, even though a temp taken rectally shows a normal reading.
A decreased core temp will not occur until NST is no longer effective.
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Effects of Cold Stress:
An increase in metabolic rate and metabolism of brown fat can lead to a significant rise in the need for oxygen.
If a baby is having even a little bit of resp distress the problem may be increased as oxygen is used for heat production
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Cold stress also causes decreased production of surfactant impeding lung expansion and leading to more resp distress.
Glucose is needed in larger amounts when the metabolic rate rises to produce heat.
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Metabolism of brown fat also releases fatty acids and can cause metabolic acidosis.
Elevated fatty acids in the blood also can interfere with transport of bilirubin increasing the risk of jaundice.
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