Identifying optimal lung volume in paediatric high-frequency oscillatory ventilation: a pilot study

Lung volume is the main determinant of oxygenation in diffuse alveolar disease
(DAD) during HFOV. This suggests that an open lung strategy (i.e. opening up
the lung and keeping it open) in diffuse alveolar disease by (repeated)
recruitment manoeuvres (RM) should be considered when switching to HFOV. But at
the same time, not all lung diseases are recruitable and in general the
potential for lung recruitability is highly variable. This signifies that
individual titration of the mean airway pressure generated by the oscillator is
indicated when using HFOV. Unfortunately, at present physicians have the SpO2,
blood gas analysis, *P and chest radiography at their disposal for evaluating
the response of a patient to HFOV. Developments are being made with respect to
respiratory inductive plethysmography (RIP) as tools for the determination of
the optimal mean airway pressure. Recently, we have completed a study in N = 20
children (NL32761.042.10, METc 2010/091) in whom we have explored if RIP would
be a useful tool for monitoring lung recruitment during titration of the mean
airway pressure, and if there was a correlation between an increase in RIP
signal and the SpO2. Sixteen children showed an increase in RIP signal,
suggestive for an increase in end-expiratory lung volume (EELV). However, this
increase in RIP signal coincided only in 9 patients with an increase in SpO2.
This raises the question what the association is between the increase in RIP
signal and a) the increase in EELV, b) the delivered tidal volume, and c) the
elimination of CO2.

The primary objective is to asses the association between the EELV measured
with RIP and EELV volume measured with electrical impedance tomography (EIT).
Secondary objectives include a) studying the association between the EELV
measured with RIP and the delivered tidal volume generated by the oscillator,
and b) studying the association between the EELV measured with RIP and the
transcutaneously measured pCO2.

Prospective, observational study without invasive measurements.

There are a priori no specific benefits for the patients who participate in the
study. We consider the risks associated with this non-therapeutic study
acceptable and the burden minimal, based upon the following arguments:
• Blood sample drawing is done via the already present indwelling arterial
line, so that no additional venous or arterial punctures are necessary.
• All parameters collected in this study are displayed real-time on either the
ventilator or the pulmonary function monitor; only the EIT en RIP analyses are
performed off-line. For the EIT measurements 16 electrodes must be placed
circumferentially around the chest; for the RIP measurements two elastic bands
are placed circumferentially around the patient*s chest and abdomen. The
electrodes are fully comparable with the electrodes routinely used for ECG
monitoring; hence they pose minimal burden.
• The sensor that is used for the continuous PTCCO2 measurement is the same
that is routinely used in the neonatal intensive care unit, hence they are
clinically accepted
• The flowsensor used for the continuous measurement of the tidal volume can be
used safely and has a small dead space (0.9 mL) that does not affect gas
exchange during HFOV.
• There is no interference with clinical management of the patients for this
study.