The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

HIGH-FREQUENCY NORMOCAPNIC HYPERVENTILATION-A POSSIBILITY OF OXYGENATION IMPROVEMENT DURING HFOV

Karel Roubik, PhD MSc, Jan Pachl*, PhD 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: Small changes of tidal volume (VT) during HFOV may cause high changes in alveolar ventilation, because VT during HFOV is similar to the anatomical dead space volume. VT increased by 50% is still small compared to the typical values of VT used during CMV. Therefore, HFOV offers a possibility of hyperventilation induced by an increased VT without significant endangering lungs by high tidal volumes. The aim of the study is to evaluate whether hyperventilation during HFOV leads to an increase in oxygenation. Another aim is to test whether the earned oxygen gain may be preserved when the hyperventilation-based hypocapnia is intentionally compensated by a controlled CO2 admixture into the inspiratory gas.

Methods: Laboratory pigs (n=9) under the total intravenous anaesthesia were tested during 3 phases: {Phase 1} Volume controlled HFOV: f=5 Hz, Ti/T= 50%, VT=1.9±0.3 ml/kg (measured by an original measuring system), initial continuous distension pressure CDP=0.8 kPa. Normocapnia (PaCO2=41.1±2.6 Torr, PaO2=84.4±11.9 Torr) was achieved by iterative changes of VT induced by Δ P changes and measured by the designed measuring system. {Phase 2} Hyperventilation: VT was increased by (46±12)% compared to the normocapnic VT measured in phase 1. Blood gases were analyzed after stabilizing. {Phase 3} Normocapnic hyperventilation: Normocapnia during hyperventilation was achieved by a CO2 supplementation, i.e. by an iterative control of CO2 admixture into the inspiratory gas. Samples for arterial blood gases analyses were taken 15 minutes after each change of VT or CO2 admixture.

Results: Increase of PaO2 (by 28.1±3.9 Torr, p< 0.001) and decrease of PaCO2 (by -15.4±2.3 Torr, p< 0.001) were reached in phase 2 against the phase 1 values. It represents an increase in oxygenation by 33%. In phase 3, the statistically significant increase of PaO2 acquired in phase 2 was preserved (28.5±5.5 Torr against the phase 1 value, p< 0.001) while normocapnia was fully re-established by the CO2 administration into the inspiratory gas.

Conclusion: A new ventilatory mode-high-frequency normocapnic hyperventilation-might be introduced. It may serve as a method improving oxygenation during HFOV.

Supported by grant MSM 6840770012.

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