2006 OPEN FORUM Abstracts
imposed work of breathing REDUCTION during high-frequency OSCILLATORY ventilation
Karel Roubik1 PhD MSc, Marc van Heerde2 MD, Vit
Kopelent1 MSc,
Daniel Pachner3 MSc
PhD, Frans B Plötz2 MD, Dick G Markhorst2 MD
1Czech
Technical University in Prague, Faculty of Biomedical Engineering, Kladno, Czech Republic; 2VU University Medical
Center,
Dept. of Pediatric Intensive Care, Amsterdam, The Netherlands; 3Czech
Technical University in Prague, Faculty of Electrical Engineering, Prague,
Czech Republic
Introduction: Maintenance of
spontaneous breathing in mechanically ventilated patients augments ventilation
perfusion matching and cardiopulmonary function, reduces sedative requirement
and shortens intensive care stay. In larger children and adults, spontaneous breathing
during high-frequency oscillatory ventilation (HFOV) is currently advocated but
usually not well tolerated because of patient discomfort. A special demand flow
system (DFS) was constructed in order to help patients to overcome resistances
of the HFOV ventilator and its circuit, i.e. to reduce imposed work of
breathing (iWOB). Furthermore, DFS eliminates
fluctuations in MAP caused by patient's spontaneous breathing and consequently
allows functioning of HFOV ventilator by prevention of exceeding pressure
alarms. The aim of the study is to evaluate the effect of DFS on iWOB reduction in settings simulating typical situations.
Methods: A custom made DFS was assembled
with the use of an electrically-driven computer-controlled flow valve, an
airway pressure sensor with a measuring circuit and a multichannel
AD/DA converter. The device is controlled by real-time computer software that
separates the patient-generated pressure changes from the HFOV ventilator
pressure swings. The patient-generated signal is used for DFS control with the aim to minimize these
pressure changes. An ASL 5000 (IngMar Medical,
Pittsburgh, PA)―a digitally controlled real-time breathing simulator
allowing generation of various breath types including spontaneous ventilation―was connected to a modified HFOV
ventilator (3100B SensorMedics, Yorba Linda, CA) via a standard breathing
circuit and endotracheal tubes of various sizes. Inspiratory and expiratory
airway flow and pressure at several places were sampled. Spontaneous breath
rate and volume, tube size and ventilator settings were adjusted to represent
the pediatric to adult range. Values of iWOB were
calculated using the Campbell diagram.
Results: For simulations of an adult
subject (VT = 500 ml) the level of iWOB
was 1.2 J/l
without DFS and 0.5 J/l with DFS. For simulations of shallow breathing of an
adult subject (VT = 300 ml), iWOB was 0.85
J/l without DFS and 0.37 J/l with DFS. Overall, DFS
reduces iWOB by 30-56%. The lowest
possible iWOB that could be accomplished with DFS was
0.3 J/l in adult simulations. Fluctuations in mean airway
pressure on account of spontaneous breathing were markedly reduced.
Conclusion: The use of the demand-flow system
during HFOV results in a reduction of both iWOB and fluctuations in MAP. Our
initial goal was to reduce the level of iWOB to the physiologic range of WOB. This
was realized. DFS makes maintenance of spontaneous breathing during HFOV
possible and easier in a clinical setting.
Supported by grant MSM 6840770012.