Newborn Physiology

• Initiation of Breathing

  Mechanical events: squeeze

  Chemical events: mild asphyxia/hypoxia

  Thermal stimuli: chill

  Sensory stimuli: lights, smell, touch
• First birth phenomenon

  Chest compression during labor and birth expels fluid

  Chest re-expansion sucks air into airways causing lung expansion and establishment of lung volume

  Immediate increase in PO2 levels and blood flow through the lungs
• Important markers of fetal lung maturity

  Lecithin & sphinogomyelin

  Phosphatidylglycerol (PG)

  Phosphatidylinositol (PI)
• Surfactant

  Production begins at about 24-25 weeks gestation

  Surfactant coats the inner surfaces of the alveoli, preventing the alveoli from collapsing after each expiration by decreasing surface tension

  Peaks at 34-36 weeks
• Respiratory assessment

  Average rate 30-60

  Irregular respirations are common

  Crackles: newborns may have a lot of mucous first few hours
• Signs of respiratory distress

  Grunting *

  Flaring of the nares *

  Retractions

  Tachypnea

  Cyanosis

  Pallor

  Poor muscle tone

  Apnea: pauses > 20 sec
• Cardiovascular Changes

  Air enters lungs -> increased O2 levels

  Pulmonary vascular resistance (pressure) decreases

  Systemic vascular resistance (pressure) increases
• Cardiovascular changes part two

  Foramen ovale: closes functionally 1-2 hours after birth (permanently after 2-4 months)

  Ductus arteriosus: closes functionally usually within 10-15 hours, up to 24 hours (permanently in 1-2 weeks)

  Ductus venous: closes functionally soon after birth (permanently at about 1-2 weeks)
• Cardiovascular assessment

  HR: 110-160

  Transient murmurs are not uncommon
• Screening for CCHD

  Pulse oximetry screening of all infants at 24-48 hours of age or prior to discharge

  Passing screen:

  1. More than or equal to 95% O2 sat in either the right hand or foot AND
  2. Less than or equal to 3% difference between right hand & foot
• Thermal regulation

  Normal temperatures: axillary (36.5-37.5) (97.7-99.5)

  Newborns have increased surface area to body mass, less fat, thinner skin, and immature thermoregulatory abilities (unable to shiver)

  Heat production:

  Non shivering thermogenesis: brown fat breakdown but increased oxygen and calorie consumption-> cold stress

  Increase in muscle activity, restlessness

  Peripheral vascular constriction: mottling, acrocyanosis
• Methods of heat loss

  Conduction: contact with cold objects

  Convection: cold air draft

  Evaporation: wet or moist skin dried by air resulting in cooling

  Radiation: no direct contact, transfer of heat to a cooler object
• How long do iron stores last?

  4-6 months
• What is the glucose range for newborns?

  45-96 mg/dl
• Vitamin K functions

  Influences the activation of coagulation factors

  Synthesized in intestinal flora

  Intestinal flora is absent in newborn until first feeding introduced

  Levels are low at birth

  Administered to all infants within first hour of life
• Hypoglycemia

  Blood glucose maintained by converting glycogen stores to glucose and glucose to glycogen

  Full term infants have large stores of glycogen in liver

  Less than 40 mg/dl
• Risk factors for significantly elevated bilirubin

  Physiological destruction of RBCs & shorter RBC lifespan of fetal cells with an immature liver

  Newborn has bruising, cephalohematoma

  Pathological destruction of RBCs: ABO and Rh incompatibility

  Exclusive breastfeeding or breast milk issues

  Preterm and late preterm infants
• Unconjugated bilirubin

  Indirect, lipid-soluble, non-excretable

  Crosses blood-brain barrier
• Conjugated

  Direct, water-soluble, excretable

  Does not cross blood-brain barrier
• Physiologic Jaundice

  Does not occur within the first 24 hours

  Jaundice associated with breastfeeding

  Early onset/breastfeeding jaundice: poor breastfeeding

  Late onset/breast milk jaundice: Something in breastmilk interferes with conjugation
• Pathologic Jaundice

  Often occurs within 24 hours of birth

  Common causes: LPT, preterm, ABO incompatibility, bruising, cephalohematoma
• Coombs test

  Indirect: on mother (look for antibodies)

  Direct: on baby (looks for RBCs with antibodies attached)
• Common Screenings done on all newborns

  1. CCHD screening
  2. Hyperbilirubinemia screening (TcB Transcutaneous bilirubin)
  3. Genetic disease screen (GDS)
  4. Hearing screen
• Humoral immunity

  Concerned with immunoglobulin/antibody response that are antigen specific
• Cellular immunity

  Concerned with leukocytes (WBCs)
• IgG

  Passively acquired across placenta during last trimester
• IgA

  Passively acquired in colostrum, produced by newborn at 1 month
• IgM

  Active immunity, produced by fetus in response to infection in utero
• Neonatal infection classification

  1. Acute life-threatening infection of the blood -> sepsis (GBS or E coli infection)
  2. Localized infections (gonorrhea or chlamydia into eyes)
  3. Congenital infections (acquired in utero, TORCH, syphilis, HIV)