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June
1997
Airway
muscle in preterm infants: Changes during development.
Sward-Comunelli SL, Mabry SM, Truog WE, Thibeault DW;
J Pediatr 1997; 130:570-6.
[ see
abstract below
]
Sward-Comunelli et al have documented with their pathology study of 55
lungs from preterm infants with what we have observed clinically for many
years-- even preterm infants can develop bronchospasm. This is the best
study to date documenting the presence of bronchial muscle at all levels
of the airway, even in infants as young as 23 weeks gestational age. From
25 weeks gestational age until term there was a similar quantity of bronchial
muscle tissue in airways of proportional size.
Preterm infants with chronic lung disease demonstrate an increase over
"normal" in airway musculature particularly in the larger airways. This
also is certainly consistent with clinical experience--the sicker the
patient the more frequent and reactive the airway is to external stimuli.
Clearly this paper documents that even the extremely preterm infant is
capable of developing bronchospasm. The most important clinical implication
of this investigation is that it clearly demonstrates that even the preterm
infant who develops bronchospasm may respond to the administration of
a bronchodilator.
It has been my experience that the very worst case of bronchospasm I have
had the "pleasure" to encounter, was in exactly this type of patient (i.e.
a former preterm infant who had been only briefly ventilated as a neonate
and had not been labeled as having chronic lung disease, but who was now
returning for inguinal hernia repair). Since these infants are generally
not very tolerant of potent anesthetic agents, the availability of a bronchodilator
that can be effectively delivered through the endotracheal tube is an
important part of routine management.
In this population it is particularly valuable to have an adaptor which
allows the administration of a metered dose bronchial inhaler during inspiration,
thus carrying the bronchodilator down to where it might do some good.
Simply giving a puff down the endotracheal tube and then reconnecting
the circuit is very ineffective because most of the inhalant will rain
out in the endotracheal tube. The other question which has yet to be answered
is how much bronchodilator does one administer?
My routine is administer several puffs and if there is no response in
30 seconds, then give several more puffs. If that does not work then I
would give 4 puffs and wait 30 seconds, if no response then give 4 more.
If that does not work, then its time for epinephrine.
Return to the Current Literature Review Front
Page, or read the abstract:
ABSTRACT
Objective: To quantitate airway muscle changes in infants born at
23 to 41 weeks' gestation (control subjects) and to compare the changes
with those in infants with chronic lung disease.
Methods: Fifty-five human lungs (from infants born at 23 to 41 weeks'
gestation) were studied: 46 from infants who died of various diseases within
72 hours of birth, and 9 from infants with CLD (infants born at 26.9 � 0.5
weeks' gestation, who lived 17 � 8 days). All the lungs were perfused via
the trachea and pulmonary artery in a standardized protocol. Formalin-fixed
tissues in paraffin blocks were cut 5 �m thick.
Sections were immunohistochemically stained for alpha-smooth muscle actin.
By using computerized image analysis to quantitate images digitized into
the computer, we measured the area of muscle, epithelium, airway lumen,
and length of basement membrane in 18 airways, from the smallest bronchioles
to bronchi, in each infant.
Results: Muscle was present at 23 weeks' gestation at all levels
of the bronchial tree, and from 25 weeks to term the control lungs had a
similar quantity of muscle at any given airway circumference. Relative to
airway size, there was more muscle in small airways, less than 1000 �m in
circumference, than in larger airways. In airways greater than 1500 �m in
circumference, infants with CLD had significantly more muscle than did control
lungs.
Conclusions: Airway muscle is present at 23 weeks' gestation at all
levels of the conducting airways. The 25-week gestation infants had a quantity
of airway muscle relative to airway circumference similar to that of term
infants. Preterm infants with CLD who were aged 9 to 29 days have increased
airway muscle in airways greater than 1500 �m in circumference. Bronchospasm
in very low birth weight infants is possible within the first days of life.
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