Neonatal A

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Neonatal A P

• RC 290

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Neonate Compared to Adult

• More compliant and flexible thorax
• Large tongue
• Large U-shaped epiglottis
• Narrowest part of upper airway is at cricoid
  cartilage (where is an adults?)

• Larynx is higher up
• Carina is higher up
• Both right and left main stem bronchi are at 45
  degree angle to trachea
• Neonate is an obligate nose breather

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Neonatal PFTs(for a normal 3 kilogram infant)

• Vt 20-30 ml
• Respiratory rate 30-40
• VC 70-130 ml
• Vd/Vt 4.4 ml 9.2 ml (25-40)
• FRC (24 hours after birth) 80 ml

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Thermal regulation

• Neonate prone to heat loss because of
• Increased surface area to mass ratio
• Decreased amounts of sub-Q fat

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Two Types of Heat Loss

• Internal gradient from body core to skin
• Normally 1 degree C
• External gradient from skin surface to
  environment

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Mechanisms of Heat Transfer
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Methods of Heat Production

• Voluntary Muscle Activity
• Involuntary Muscle Activity, ie, Shivering
• Non-shivering Thermogenesis
• Brown Fat metabolism
• Main method of heat production in the neonate

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Brown Fat

• 2-6 of neonates body weight
• Located around vital organs
• Innervated by sympathetic nerves
• Usually present until 2 months after birth

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Causes of Moderate Cold Stress and Hypothermia

• The following impair thermogenesis. Either
  the infant cant metabolize brown fat or he cant
  metabolize it fast enough to keep up with the
  heat loss.
• Asphyxia/Hypoxia
• Sepsis
• Intra-cranial pathology
• Hypoglycemia
• Environmental cooling (usually through the four
  mechanisms of heat transfer)

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Effects of Moderate Cold Stress and Hypothermia

• Increased O2 consumption and hypoxemia
• Hyperthermia also increases O2 consumption
• O2 consumption is lowest in a NTE (neutral
  thermal environment) as well as in severe
  hypothermia
• Hypoglycemia
• Metabolic acidosis
• Inhibition of Surfactant production

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Clinical Signs of Hypothermia(Moderate Cold
Stress)

• Lethargy
• Cold skin
• Bright red color
• Slow shallow respirations

• Bradycardia
• Depressed CNS
• Physiologic effects
• Hypoxemia (due to increased O2 consumption)
• Hypoglycemia
• Metabolic acidosis
• Lung dysfunction due to decreased surfactant

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Hypothermia Treatment

• Prevention is best maintain NTE
• Warm slowly otherwise O2 consumption may
  increase!
• Heated and humidified O2
• May need NaHCO3 for metabolic acidosis
• Dextrose for hypoglycemia

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Maintaining NTE

• Equipment

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Isolettes

• Maintain NTE by convection
• Usually have double layered plexiglass walls to
  prevent heat loss due to radiation

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Overhead Radiant Warmers

• Warm by radiant heat
• Used in L D
• Also used in NICU when neonate needs procedures
  performed outside of isolette

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Mechanics of Neonatal Respiration

• Because of the flexible thorax, most of the
  resistance to breathing in the neonate is airway
  resistance

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Inspiration

• Airway resistance is lowest because of negative
  pressure generated when intrathoracic pressure
  drops

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Expiration

• Airway resistance is at its highest because of
  the increase in intrathoracic pressure. The
  increased airway resistance during expiration
  helps maintain FRC

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Time Constant

• TC Cstat X Raw
• Represents amount of time it takes for the
  proximal airway and alveolar pressure to
  equilibrate
• TC is variable throughout the lung and during
  inspiration and expiration!
• Expiratory TC is greater than inspiratory TC
  because airway resistance is highest during
  expiration
• Normal averages Adult .66 seconds, neonate
  .33 seconds
• Knowing how pathology affects TC is crucial in
  ventilator management!

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Decreased TC

• Decreased Cstat or decreased Raw
• Decreased Cstat more common in neonate
• RDS, atelectasis, pneumonia
• Decreased Cstat increased elastic resistance
• Proximal airway and alveolar pressure equilibrate
  more quickly when TC is decreased
• May use high ventilator rates and narrow (or
  inverse) IE ratios

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Increased TC

• Increased Raw or increased Cstat
• Increased Raw more common in neonate
• Mucus plugs, aspirations, upper airway
  obstructions
• Proximal airway and alveolar pressure take longer
  to equilibrate when TC is increased
• Increased TC makes infant prone to gas-trapping
  so must use lower ventilator rates and wide IE
  ratios to prevent lung damage and hemodynamic
  compromise

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Neonatal Breathing Patterns

• Periodic Breathing
• Apnea periods lasting less than 20 seconds
• Heart rate and temperature not affected
• Common in premature infants
• Usually only need monitoring possibly O2 therapy

• Apneic Breathing
• Apnea periods last longer than 20 seconds
• Heart rate and temperature decrease
• Need monitoring, O2, and possibly ventilation
• Sometimes methylxanthines help