2006 OPEN FORUM Abstracts
THE DIFFERENT EFFECTS OF CMV AND HFOV IN A MODEL OF EXTRAPULMONARY ARDS
Roubik, PhD MSc, Petr Waldauf*,
MD, Jan Pachl*, PhD MD,
Martin Rozanek, MSc, Michal Fric*, MD, Tomas Jursa, MSc.
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: The target group for HFOV therapy has not been identified yet. The aim of the study was to determine the impact of CMV and HFOV on lung compliance (CL) and oxygenation (expressed as P/F index = PaO2/FiO2 ratio) in animals with the oleic acid and/or the chest and abdominal wall injuries (CAWI), i.e. a lesion similar to extrapulmonary form of ARDS.
Methods: Ten laboratory rabbits were instrumented under general anesthesia. Lung lesion was induced by intravenous oleic acid administration (0.1 ml/kg B.W.) to reach P/F index below 200 Torr. CAWI was induced by a pressure cuff (inflated to 2 kPa) placed around the chest and abdomen. All animals underwent a four-step protocol with normocapnic CMV (f=100/min, Vt=7 ml/kg) and normocapnic HFOV (f=8 Hz, Vt=2.5 ml/kg). The variable parameters were PEEP, MAP (during HFOV referred to as CDP), type of the lung lesion and presence of CAWI. Step1―CMV (with two levels of PEEP: PEEP=0.8 and 1.2 kPa). Step 2―CMV (the same setting) + pressure cuff at 2 kPa. Step 3―HFOV (with three levels of CDP: CDP=1.5, 2.0 and 2.5 kPa). Step 4―HFOV (the same setting) + pressure cuff at 2 kPa. A special system for CMV and HFOV monitoring  was used for airway pressure, esophageal pressure, airflow, Vt, Crs, Ccw and CL continuous measurement. Parameters: CL, Ccw, blood gases and acid base balance during the experiment were evaluated using the Wilcoxon test.
Results: Step 1: Increasing PEEP during CMV increased P/F from 126 to 210 Torr (p<0.05), CL remained constant. Step 2: CMV failed to increase P/F and CL. Step 3: The improvement of P/F from 121 to 301 and 189 Torr (p<0.01) occurred with increasing CDP in spite of a sustained CL decrease (19, 15 and 11 ml/kPa, p<0.01). Step 4: Improvement of P/F (52, 61 and 269 Torr (p<0.05)) occurred at the highest CDP level while CL changed to 14, 20 and 17 ml/kPa (NS).
Conclusion: In the lung lesion without CAWI, there is no significant difference in oxygenation effect between CMV and HFOV (NS). The best oxygenation during HFOV was reached at high CDP levels when CL was reduced, i.e. significantly behind the maximum value of CL. When CAWI is present, HFOV is more efficient in oxygenation compared to CMV (p<0.05).
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.