Non-invasive respiratory function measurements of changes in functional residual capacity and adequacy of tidal volumes in preterm infants at birth

The transition to air-breathing at birth is vital for infant survival. To
establish gas exchange at birth, the liquid-filled airways must be cleared and
air has to remain in the lungs at end of expiration (functional residual
capacity (FRC)). Preterm infants often fail to create FRC because they have an
impaired ability to clear airway liquid and their lungs are surfactant
deficient. In the Netherlands, ~2500 infants are born very preterm (<32 weeks
gestation) annually and 60% of them need resuscitation. Although research is
evolving, current resuscitation guidelines are based on very little data and
our knowledge of neonatal transition is largely based on observations,
assumptions and extrapolation rather than sound scientific studies.

There is consensus that the key to successful resuscitation is adequate
positive pressure ventilation (PPV). The adequacy of PPV is traditional
assessed by adequate chest rise, which is very subjective and inaccurate, and
increased heart rate. However, we are unaware of the effect of our ventilation
approaches on lung volume changes and FRC. To understand the effect and
adequacy of our interventions, more knowledge in this field is essential as the
immature lung is highly vulnerable to injury, ventilation immediately after
birth may affect long-term morbidity and survival. Animal studies have
demonstrated that lung injury can occur during resuscitation with just a few
large manual inflations.

Although we have learned from observational studies that preterm infants at
birth use specific mechanism for recruit and defend their FRC, the exact
mechanisms remain speculative. With the measurements we currently use in the
delivery room we are not informed what effect ventilation has on improving FRC.
In addition, for adequate ventilation (gas exchange) we currently aim for tidal
volumes of 4-6 mL/kg, but this range is extrapolated from data collected later
in the Neonatal Intensive Care Unit (NICU).

Recent animal studies have demonstrated that, during lung aeration, the
concentration of CO2 in exhaled air increases as the proportion of
aerated distal gas exchange regions of the lung gradually increases. The
explanation for this finding is simply explained by the fact that when the gas
exchange regions of the lung are liquid-filled, no CO2 is exchanged and so no
CO2 will appear in the expired air. Gradually, as more and more of the gas
exchange regions aerate, the concentration of CO2 in the expired air increases.
At this early stage of initiating ventilation, the proportion of aerated gas
exchange units is the greatest determinant of CO2 concentration in exhaled air.

To improve our respiratory support in preterm infants at birth, we need to be
better informed on the effect of respiratory support on FRC and the adequacy of
delivered tidal ventilation.

1) To investigate whether our current respiratory support improves/recruits FRC
in preterm infants at birth by measuring changes in FRC in a non-invasive
manner.
2) To investigate the adequacy of tidal ventilation during respiratory support
in preterm infants at birth by measuring non-invasive capnography.

Prospective observational study performed in the Leiden University Medical
Center (LUMC).

Recording end-tidal CO2 and RIP bands are not cumbersome, and are not contrary
to the interests of the infant and the recording are and will not interfere
with the standard treatment procedure that is followed. When the state of the
infant is in such a way that the attending neonatologist or resident, who is
treating the patient, finds it necessary the recoridng will not be commenced or
will be stopped.