The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts


TRACHEAL GAS INSUFFLATION WITH HFOV-AN EFFICIENT MODE OF UNCONVENTIONAL VENTILATION

Karel Roubik, PhD MSc, Jan Pachl*, PhD MD, Vladimir Zabrodsky*, MD Czech Technical University, Faculty of Biomedical Engineering,
Zikova 4, CZ - 166 36, Prague 6, Czech Republic *Charles University, 3rd School of Medicine, Dep. of Anesthesiology and CCM, Srobarova 50, CZ - 100 34, Prague 10, Czech Republic

Introduction: Combination of tracheal gas insufflation (TGI) with HFOV has not been studied yet. TGI reduces the anatomical dead space volume VD. Considering the strong effect of the anatomic dead space on alveolar ventilation in HFOV, when VD is similar to VT, the combination of TGI and HFOV may offer promising results. Description of dependencies of PaCO2 and PaO2 changes on TGI flow during HFOV and definition of the optimal TGI flow during HFOV are the main aims of the study.

Methods:
A group of 9 healthy rabbits under general anaesthesia and relaxation was evaluated. Endotracheal tube was introduced through tracheostomy. A volume-controlled HFO ventilator with a humidifier has been constructed in order to maintain constant tidal volumes during all experiment, independently on the respiratory mechanics changes, CDP, etc. TGI flow was generated using a source of humidified gas at an adjustable pressure and a TGI catheter (18 cm long with an inner diameter of 0.7 mm) placed into the endotracheal tube 3 cm above its distal end. Three stages of experiment: (1) HFOV without TGI: HFOV with f=10 Hz, CDP=0.8 kPa, Ti/T=0,5. Tidal volume VT was experimentally set to reach normocapnia (PaCO2 = 42 ± 2 Torr). This normocapnic VT (2,2 ± 0.4 ml/kg) was taken as a reference during the next stages. (2) HFOV with TGI: TGI flow 0.5 l/min was introduced. Total tidal volume, comprising the tidal volume generated by the ventilator and the volume generated by the TGI flow, was maintained constant and equal to the reference VT from phase 1. (3) HFOV without TGI: The final control stage, after which the whole sequence of phases was repeated stepwise for TGI flows 1 l/min and 2 l/min.

Results:
During phase 2, decrease in PaCO2: Δ PaCO2= -2.9 (s=2.2), -7.0 (s=3.7) and -11.6 (s=4.8) Torr was reached for TGI= 0.5, 1 and 2 l/min respectively. Increase in oxygenation: Δ PaO2= 5.8 (s=4.0), 18.0 (s=9.0) and 27 (s=9.7) Torr was reached for TGI= 0.5, 1 and 2 l/min respectively. Significant changes were observed for TGI flow around 1 l/min, which represents only 12% of minute ventilation.

Conclusion:
TGI significantly improves oxygenation and CO2 elimination during HFOV while preserving the total tidal volume. The method is prepared for testing in clinical conditions.

Supported by grant MSM 6840770012.

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TRACHEAL GAS INSUFFLATION WITH HFOV-AN EFFICIENT MODE OF UNCONVENTIONAL VENTILATION