2006 OPEN FORUM Abstracts
THE RELATIONSHIP BETWEEN OXYGENATION AND LUNG COMPLIANCE DURING CMV AND HFOV IN EXPERIMENTAL ARDS
Roubik, PhD MSc, Petr Waldauf*,
MD, Jan Pachl*, PhD MD,
Martin Rozanek, MSc, Michal Fric*, MD
Czech Technical University in Prague, Faculty of Biomedical Engineering,
Nam. Sitna 3105, CZ - 272 01, Kladno, Czech Republic
*Charles University, 3rd School of Medicine, Dep. of Anesthesiology and CCM, Srobarova 50, CZ - 100 34, Prague 10, Czech Republic
Introduction: In clinical practice, pressure parameters (MAP - mean airway pressure and PEEP) are usually set higher during HFOV than during CMV. The aim of the study is to evaluate relationship between oxygenation, lung compliance (CL) and alveolar PEEP (PEEPalv) in oleic acid model of ARDS during CMV and HFOV.
Methods: Five anesthetized and mechanically ventilated rabbits were investigated. ARDS was induced by oleic acid administration (0.08 ml/kg i.v.). Ventilatory parameters for maintaining normocapnia during CMV were: f=100/min, Vt=5-6 ml/kg B.W., PEEPalv was increased stepwise from 0 to 1.6 kPa in steps of 0.2 kPa. A special CMV and FHOV monitoring system  was used allowing also PEEPalv, Vt, CL, Crs and Ccw monitoring. Accuracy of the monitoring system was evaluated using Galileo (Hamilton Medical) ventilator. Normocapnic HFOV parameters were: f=486/min, Vt=3-4 ml/kg B.W., PEEPalv level was set in the same way as during CMV. The following parameters were recorded: Paw, Pes, Vt, CL, PEEPalv and hypoxemic index PaO2/FiO2 (P/F). The results were statistically evaluated using Wilcoxon test. Values are expressed as mean value ± SD.
Results: The curve of CL shows increasing and decreasing arms during increasing PEEPalv level. There is no significant difference in PEEPalv for the highest measured CL and the highest recorded oxygenation (best P/F, respecting circulatory stability) during CMV (the highest value of CL=27±4 ml/kPa was measured when P/F=387±134 Torr vs. the highest P/F=449±146 Torr measured when CL=28±5 ml/kPa, p=0.4, NS). During HFOV, CL at the optimal level of PEEPalv for oxygenation (best P/F, also respecting circulatory stability) was significantly lower (CL=17±2 ml/kPa and P/F 483±61 Torr ) than the best achieved value of CL (CL=26±5 ml/kPa and P/F=141±91 Torr, p<0.05).
Conclusion: The optimal level of PEEPalv for oxygenation during CMV correlates with the best value of PEEPalv for maximum CL. During HFOV, the optimal P/F was found at the decreasing limb of the CL curve in dependency on PEEPalv. The results may also evoke a question about position of PEEPalv (or, during HFOV more suitable parameter MAP, referred to as CDP) on the pressure-volume curve during HFOV with respect to the upper inflection point.
Reference:  Pachl J., Roubik K., Waldauf P. et al.: Normocapnic high-frequency oscillatory ventilation affects differently extrapulmonary and pulmonary forms of acute respiratory distress syndrome in adults. Physiological Research 55 (1): 15-24, 2006.
Supported by MSM 6840770012 and IGA NR 8078-3.