Neonatal A & P
RC 290
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 adult’s?)
 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
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
Thermal regulation
Neonate prone to heat loss because of :
Increased surface area to mass ratio
Decreased amounts of sub-Q fat
Two Types of Heat Loss
 Internal gradient –
from body core to
skin
– Normally 1 degree C
 External gradient –
from skin surface to
environment
Mechanisms of Heat Transfer
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
Brown Fat
 2-6% of neonate’s
body weight
 Located around vital
organs
 Innervated by
sympathetic nerves
 Usually present until
2 months after birth
Causes of Moderate Cold Stress
and Hypothermia
The following impair thermogenesis. Either the
infant can’t metabolize brown fat or he can’t
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)
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
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
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
Maintaining NTE
Equipment
Isolettes
 Maintain NTE by
convection
 Usually have double
layered plexiglass
walls to prevent heat
loss due to radiation
Overhead Radiant Warmers
 Warm by radiant heat
 Used in L & D
 Also used in NICU
when neonate needs
procedures performed
outside of isolette
Mechanics of Neonatal
Respiration
Because of the flexible thorax, most
of the resistance to breathing in the
neonate is airway resistance
Inspiration
Airway resistance is lowest because
of negative pressure generated when
intrathoracic pressure drops
Expiration
Airway resistance is at it’s highest
because of the increase in
intrathoracic pressure. The increased
airway resistance during expiration
helps maintain FRC
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!
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) I:E ratios
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 I:E
ratios to prevent lung damage and hemodynamic
compromise
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