Monitoring lung fluid clearance and aeration during pulmonary transition after birth

During intra-uterine life, the lungs of the human fetus is fluid filled. This
fluid is necessary for normal lung development. Clearance of carbon dioxide and
delivery of oxygen is governed by the placenta connected to the fetus by the
umbilical cord. At the time of birth these conditions change dramatically. The
umbilical cord is clamped, thereby stopping gas exchange via the placenta. This
means that normal lung function is now necessary for normal gas exchange. This
process is called pulmonary transition. To make pulmonary transition a success,
the fluid that is still present at the time of birth needs be to cleared from
the lungs. Furthermore, the lungs need to be aerated and perfused in order to
start normal gas exchange. Based om studies in lambs and rabbit pups, it is
assumed that the postnatal breaths taken in the first minutes after birth are
most important in clearing the lung fluid and aerating the lungs. During each
inspiration air enters the lungs and the fluid is pushed distally via the
airways. This latter process is supported by so-called expiratory breaking.
During expiratory breaking, the infants builds up high airway pressure by
grunting or crying. This facilitates distal movement of the fluid. At that
level the fluid enters the interstitial space and is taken up by the lymphatic
vessels. If the infant is not spontaneously breathing at the time of birth, the
physician needs to support lung fluid clearance and aeration by applying
positive pressure breaths via a mask and bag. To mimic expiratory breaking,
pressure also needs to be applied during the expiratory phase of positive
pressure ventilation (positive end-expiratory pressure (PEEP)). It is clear
that the process of pulmonary transition takes time and that it is perfectly
normal that during this transition infants slowly turn pink as the lung gets
aerated. Under physiological conditions this may take up to 10 minutes.
Studies animal models and human infants have suggested that pulmonary
transition differs between infants born via the vaginal route and via caesarian
section. Furthermore, it has been suggested that fluid clearance and aeration
of the lungs is compromised in preterm infants due to immaturity of the lungs.
As previously mentioned the physiology of normal pulmonary transition is mainly
based on animal models. The most important reason for the lack of human data is
the absence of a tool to non-invasively measure changes in (regional) lung
aeration at the bedside. This has recently changed with the introduction of a
new technique called electrical impedance tomography (EIT). EIT uses 32
electrodes circumferentially placed around the chest wall. A small current is
injected between a pair of adjacent electrodes and all other electrodes measure
the voltage change. The pair of electrodes used for current injection changes
in a rotating manner. One full circle is an EIT scan and all measured voltage
changes are used to reconstruct the regional changes in lung impedance
(=resistivity to an alternating current). Aeration will have, by far, the
largest impact on impedance. EIT has a high temporal resolution (real-time
continues imaging of dynamic lung function), is radiation free and can be used
at the bedside. EIT has been studied in (preterm) neonates, infants and
children. These studies have shown that EIT imaging is feasible in this
population and that it provides reliable imaging of regional lung aeration. The
two most important parameters obtained with EIT are regional changes in
end-expiratory lung volume (EELV) and changes in the distribution of tidal
volume (tidal ventilation). Previous studies have reported no adverse effects,
making EIT use safe in this vulnerable population. Part of these studies have
been conducted in the Neonatal Intensive Care Unit (NICU) of the Emma
Children*s Hospital AMC (METC 05/069, METC 2012/079). More recently EIT has
taken another important step that allows it to be used the delivery room. The
electrodes have been integrated in a belt and no longer need to placed one by
one and stick to the skin of the patient. This means that these non-adhesive
electrodes can be place completely non-invasively and vary rapidly provide
real-time data on lung aeration.
This makes EIT the first monitoring tool that, in theory, should be ably to
monitor normal physiological pulmonary transition after birth. Knowledge on
pulmonary transition will be extremely valuable for several reasons. First,
understanding normal physiology is essential to define abnormal or compromised
pulmonary transition. Second, it also allows to identify possible interventions
to support pulmonary transition. Studies have suggested that supporting a
compromised pulmonary transition may impact the pulmonary outcome of preterm
infants.
As a first step this study aims to monitor pulmonary transition in both term
and preterm infants born either via the vaginal route or caesarian section.

The objective of this study is to obtain physiological data on lung aeration
during pulmonary transition in newborn infants.

This is a prospective observational study conducted in the neonatal intensive
care unit of the Emma Children*s Hospital, Academic Medical Center, Amsterdam
over a period of 24 months

The burden for the included patients are as minimal as possible as it is a
observational study with interventions. The improved non-adhesive EIT belt with
sutured in electrodes has made the risk of side effects minimal. In literature
no side effects have been reported.