Newborn Physiology: First 28 Days

• The newborn period extends from birth through the first 28 days of life
• Significant physiological and behavioral changes occur as the newborn adapts to extrauterine life
• Nurses play a vital role in assessing these changes and providing appropriate care

Initial Physiological Adjustments

• The most critical adaptations involve establishing respiratory function and circulatory changes
• Prior to birth, the fetus receives oxygen and nutrients via the placenta
• The first breath triggers a cascade of events leading to lung expansion and pulmonary circulation
• The foramen ovale, ductus arteriosus, and ductus venosus close, transitioning to independent circulation
• Body temperature regulation is another immediate challenge
• Newborns have a large surface area-to-body mass ratio, making them susceptible to heat loss
• Non-shivering thermogenesis, using brown adipose tissue (BAT), generates heat
• Glucose homeostasis must be achieved as the maternal glucose supply is cut off
• The newborn relies on glycogen stores until feeding is established

Respiratory System Adaptation

• Initiation of breathing is stimulated by chemical, mechanical, thermal, and sensory factors
• Chemical factors include decreased blood oxygen and increased carbon dioxide levels
• Mechanical factors involve chest compression during vaginal delivery, which helps expel fluid from the lungs
• Thermal and sensory stimuli at birth also stimulate the respiratory center in the brain
• Normal respiratory rate is 30 to 60 breaths per minute and is often irregular
• Periodic breathing, with short pauses of less than 20 seconds, can be normal
• Signs of respiratory distress include nasal flaring, retractions, grunting, and cyanosis

Cardiovascular System Adaptation

• At birth, the foramen ovale functionally closes due to increased pressure in the left atrium
• The ductus arteriosus constricts in response to increased oxygen levels and decreased prostaglandins
• The ductus venosus closes when the umbilical cord is clamped
• A heart rate of 110 to 160 beats per minute is considered normal in the newborn period
• Blood pressure varies with gestational age; typical range is 60-80 mmHg systolic and 40-50 mmHg diastolic
• Murmurs may be present but are often transient and resolve within the first few days

Thermoregulation

• Newborns are prone to heat loss through four mechanisms: conduction, convection, evaporation, and radiation
• Conduction is heat loss through direct contact with a cold surface
• Convection is heat loss through air currents
• Evaporation is heat loss as surface moisture converts to vapor
• Radiation is heat loss to nearby cold objects
• Methods to prevent heat loss include drying the newborn immediately after birth, using a radiant warmer, and skin-to-skin contact
• Signs of cold stress include increased respiratory rate, mottling, and hypoglycemia

Hepatic System Adaptation

• The liver plays a crucial role in glucose homeostasis and bilirubin conjugation
• Newborns are at risk for hypoglycemia due to limited glycogen stores
• Early and frequent feeding helps stabilize blood glucose levels
• Physiologic jaundice occurs in many newborns due to the immature liver's inability to conjugate bilirubin efficiently
• High levels of unconjugated bilirubin can lead to kernicterus, a form of brain damage
• Breast milk jaundice can occur due to factors in breast milk that inhibit bilirubin breakdown

Gastrointestinal System Adaptation

• The newborn's digestive system is initially sterile
• Meconium, the first stool, is a thick, tarry substance
• Transitional stools are greenish-brown and less sticky
• Breastfed infants typically have more frequent, seedy, yellow stools
• Formula-fed infants have fewer, more formed, pale yellow stools
• Regurgitation is common due to the immature cardiac sphincter

Genitourinary System Adaptation

• Newborns typically void within the first 24 hours
• Uric acid crystals may be present in the urine, causing a reddish stain ("brick dust")
• Pseudomenstruation may occur in female infants due to maternal hormones
• The ability to concentrate urine is limited in the first few weeks

Immune System Adaptation

• Newborns have limited immunity, primarily relying on passive immunity from maternal antibodies
• IgG crosses the placenta, providing protection against bacterial and viral infections
• IgA is present in breast milk, providing localized protection in the gastrointestinal tract
• IgM is produced by the newborn but levels are low in early life
• Newborns are at increased risk for infection

Behavioral Adaptations

• The newborn's behavior is influenced by gestational age, sleep-wake states, and temperament
• Sleep-wake states include deep sleep, light sleep, drowsy, quiet alert, and active alert
• The Brazelton Neonatal Behavioral Assessment Scale (NBAS) evaluates newborn reflexes, motor abilities, and responses to stimuli

Reflexes

• Reflexes are automatic responses to stimuli and indicate neurological function
• The rooting reflex helps the newborn find the nipple
• The sucking reflex allows the newborn to ingest milk
• The Moro reflex (startle reflex) is a response to sudden noise or change in position
• The grasp reflex involves the newborn grasping objects placed in the palm
• The Babinski reflex involves extension of the toes when the sole of the foot is stroked
• The stepping reflex involves the newborn making stepping motions when held upright
• The tonic neck reflex involves the newborn extending the arm and leg on the side to which the head is turned

Sensory Capacities

• Newborns can see, hear, smell, taste, and feel
• Vision is clearest at a distance of 8 to 12 inches
• Newborns prefer human faces and high-contrast patterns
• Hearing is well-developed; newborns respond to sounds, especially the human voice
• Newborns can distinguish different tastes and prefer sweet flavors
• The sense of smell is present, and newborns can recognize their mother's scent
• Touch is important for comfort and bonding

Nursing Care

• Nursing care focuses on supporting the newborn's physiological and behavioral adaptations
• Monitoring vital signs, including temperature, heart rate, and respiratory rate, is essential
• Assessing the newborn's skin color, activity level, and feeding patterns is important
• Preventing heat loss, ensuring adequate hydration and nutrition, and promoting bonding are key interventions
• Educating parents about newborn care, including feeding, bathing, and safety, is crucial
• Newborn screening tests are performed to identify certain genetic or metabolic disorders
• Administering Vitamin K is vital as newborns are born with low levels, and it helps with blood clotting
• Eye prophylaxis prevents ophthalmia neonatorum from maternal gonorrhea or chlamydia
• Maintaining a safe environment and preventing infection are priorities
• Supporting breastfeeding or formula feeding according to the parents' choice is essential
• Addressing parental concerns and providing emotional support is an important aspect of nursing care