Now let's talk about some key differences
between the pediatric and the
adult respiratory system.
We're going to talk through each
of these major differences.
Let's start with the chest
and thoracic shape.
In infants and young children,
the ribs are attached horizontally
to the vertebra and to the sternum,
while an older child or adult
has a more oblique angle.
Here you can see that
the trachea bifurcates
or divides at the level of T3 in children.
While in adults, the trachea
bifurcates lower at a level of T6.
Now the right mainstem bronchus in children
has a steeper slope than in adults,
and this is important
in the setting of intubation.
The shape of the chest wall is
also going to mature gradually
from a relatively round shape in utero,
to a more flattened shape in adulthood.
Here you can see at 3 months,
at 3 and a half years,
and then finally, in adulthood
with full expansion.
The shape of the chest can
be due to genetic factors
or due to external forces that are
going to promote chest deformities.
Scoliosis, which is a sideways
curvature of the spine,
can make it difficult for the lungs
to operate at full capacity.
The curvature can cause an
asymmetric ventilation and perfusion
between the right and left lungs in more
than half of children with scoliosis.
Kyphosis is a spinal disorder in which
an excessive outward curve of the spine
results in an abnormal
rounding of the upper back.
It can occur at any age, but this
is commonly seen in adolescence.
The altered shape of the spine can affect
the heart and the lungs'
ability to function properly.
This is a picture of a patient
with pectus excavatum,
and this is a condition in a child's chest,
that causes it to look sunken or caved in.
And this happens because of
a defect in the cartilage
that's going to hold the bony
parts of the ribs to the sternum.
The cartilage is actually going
to push the sternum inward.
This can be mild, moderate, or severe,
and the sternum can actually
intrude on the space
that's dedicated for the heart and lungs,
causing shortness of breath and
other respiratory compromise.
This can be corrected surgically.
Here's a patient with the opposite
deformity called pectus carinatum.
In this case, the chest wall is going
to jut out into a convex shape.
This happens because of unusual growth
of the rib and sternal cartilage.
This condition usually does not impair
the cardiac and respiratory function,
because it's not really infringing
on any chest wall space.
Now let's talk about the diaphragm
and the muscles of respiration.
The diaphragm is the primary muscle used
for inspiration in pediatric patients
because the other surrounding muscles
are also immature and mostly inactive.
The angle of insertion in
infants is more horizontal
than in older children and adults.
The young child's diaphragm has a lower
content of high endurance muscle fibers,
putting at a higher risk of fatigue.
If the function of the
diaphragm is impaired,
the ventilation is going to be compromised.
Now, air moves in and out of the lungs
due to changes in pressure gradients
created by the movement of the chest wall
and the use of the chest wall muscles.
Inspiration is an active process.
It requires energy.
During inspiration, the diaphragm,
and accessory muscles are used
to bring the air into the body.
When you expire or breathe
out, this is a passive action.
It can involve active use of abdominal
muscles, for example, during a cough.
In infancy, the intercostal muscles
are inactive and poorly developed,
so they aren't much help in the
setting of respiratory distress.
The abdominal muscles are going to mature
and help stabilize the rib cage
around 3 to 4 months of age.
But again, before that age, these
muscles are of little help,
and that's why young babies
can do really poorly
in the setting of respiratory compromise.
Now let's talk about the pediatric
relative internal organ size.
Here, you see the bones
and the bony structures
overlaying the organs in the chest cavity.
Pediatric internal organs
are relatively large
in relation to the infant or child size,
and this can be a real problem.
The increased size of the organs
and proximity to the lungs
leaves little space for
increased chest expansion.
With these limited opportunities for
chest expansion due to their anatomy,
a young pediatric patient can
only attempt to increase
their lung function by increasing
their respiratory rate,
since their anatomy is going to restrict
other compensatory changes
that we see in children and adults.
Now, let's talk about upper
airway structural differences.
We see adults on the left
and children on the right.
So, relative, a child has a
larger head and this is a problem
in the setting of a floppy head
or malpositioning of the baby.
This can really obstruct their airway.
Babies are obligate nose breathers, and
this is fine if their nose is patent,
but let's say they have a cold
and they have a lot of nasal
mucus and it gets plugged up.
Well, they're not able to
breathe through their nose
and then become mouth breathers,
which is less efficient.
They have smaller nares and for the
same reason, this is a problem.
If they're obstructed, or
swollen, or full of mucus,
this can cause a lot of
problems with breathing.
Children also have a smaller mouth
and this allows for a smaller
amount of air to pass through.
It can easily be obstructed by the
larger tongue that is present,
and they also have a larger epiglottis
in the back of their throat
that can further complicate problems.
The larynx and glottis are
found higher in the neck,
and the baby will have
a more flexible trachea.
So this is really important when
you're positioning your patient
and when they're sleeping at home.
The airway is also narrow,
and we'll talk about that.
Now, let's talk about the major
differences in airway diameter.
Respiratory disorders can cause
significant proportional changes
in the pediatric airway size,
and this can further compromise
the pediatric respiratory status.
Here, on the left, you'll see an infant's lumen.
The diameter is patent about 4 mm and on
the bottom, you'll see an adult airway.
The lumen is patent about 8 mm.
Now let's say both of
these patients get a cold.
This is going to increase the wall
thickness by about 1 mm circumferentially,
and the patient will also
develop mucus in the airway.
This is going to cause a 50%
reduction in the diameter
of the pediatric lumen to about 2 mm size.
In the adult patient,
they're going to have the 1 mm of
circumferential increased wall thickness,
and this is still going to allow for a
6 mm diameter in their airway size.
The infant has additional resistance
due to their narrow lumen.
Now let's talk about the bronchial walls.
The bronchial walls are
supported by cartilage.
Pediatric patients have
less muscle tissue present,
and so these are more prone to collapse.
Also, the beta-adrenergic
receptors are immature,
making these patients less
responsive to bronchodilation.
Let's talk about the cilia.
These are the small hair-like structures
that help move mucus and expectorate,
thus, out of your body.
At birth, these are poorly developed.
These babies have ineffective
which means they're unable to fully
propel the mucus out of their body.
They can't really clear their secretions
and this puts kids at risk for
airway obstruction from mucus.
Let's talk about surfactant.
Surfactant is a phospholipid produced by
the type II pneumocytes in the lungs.
It's going to reduce surface tension
and keep the alveoli open.
This is formed about 23 weeks of gestation
and then again at 30-34 weeks.
Premature infants have
thus they have increased surface tension,
they have difficulty
expanding their alveoli.
And this can cause an
increase work of breathing,
and they can develop
atelectasis or lung collapse.
So if a baby is going to be
given surfactant after birth,
the first dose needs to be given as soon as
a diagnosis of respiratory distress is made.
And this is defined as the requirement
of more than 30% oxygen
and an abnormal chest X-ray.
Now prophylactic surfactant
should be considered
in intubated neonates born
at < 26 weeks gestation.
Now let's talk about the alveoli.
These are the tiny air sacs in the
lungs that aid in gaseous exchange.
Their function is to exchange oxygen and
carbon dioxide to and from the bloodstream.
There's very few functioning
alveoli at birth.
And these air sacs are going to increase
in size and numbers as the baby matures.
The majority of development happens
within the first 2 years of life.
Here, you'll see normal alveoli.
They're nice and expanded,
ready to exchange gas.
In the setting of a cold, a baby's
going to develop a mucus plug
and this is going to start
accumulating on the alveoli.
The air is going to be absorbed
from the alveoli and slowly,
the lung segments can collapse.
Because the alveoli are small
and immature in children,
they're more susceptible to
collapse and atelectasis.
Even when they're functioning properly,
these smaller sacs provide a
smaller area for gas exchange.