Background and aim of study We hypothesized that continuous high airway pressure without ventilatory movements (apneic oxygenation), using an open lung approach, combined with extracorporeal, pumpless, arterio-venous, carbon dioxide (CO2) removal would provide adequate gas exchange in acute lung injury. The aim of this study was to test this hypothesis in a lung injury model using pigs of human adult size, to mimic the O2 consumption and the CO2 production of adult patients. Materials and methods In eight anesthetized, tracheally intubated and mechanically ventilated pigs (85-95 kg), lung injury was induced by repeated lung lavage. Thereafter the tracheal tube was, after a lung recruitment maneuver, connected to 20 cmH2O continuous positive airway pressure (FiO2 = 1.0) for oxygenation of the blood. A pumpless membrane lung (Interventional Lung Assist, NovaLung, Germany) was connected in an arteriovenous shunt for CO2 removal. Cardiac output (CO), mean arterial blood pressure (MAP), and the arteriovenous shunt flow were continuously monitored. PaO2, PaCO2 and pH were obtained every 30 minutes for 3.5 hours. Results and discussion PaO2 was 61 (53-66) kPa (median and IQR) throughout the experiment. The O2 uptake via the lungs was 185 (164-212) mL/min, whereas the O2 uptake via the Novalung was 4 (0-11) mL/min. PaCO2 increased exponentially towards a maximum value just below 8 kPa. The CO2 removal via the Novalung was 178 (148-178) mL/min and pH was 7.35 (7.33-7.37) during the experiment. CO was 8.9 (7.2-10.5) L/min and MAP was 85 (79-89) mmHg. The high, stable PaO2 suggests that 20 cmH2O airway pressure was sufficient to prevent alveolar collapse and the stabilization of PaCO2 and pH at physiological levels indicate that the membrane lung provided sufficient CO2 elimination. Conclusion In this porcine lung injury model, apneic oxygenation with arteriovenous CO2 removal provided sufficient gas exchange and stable hemodynamics, indicating that the method might have a potential in the treatment of severe ARDS. Acknowledgements The membrane lungs were kindly provided by Novalung GmbH, Germany.
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The 14<sup>th</sup> World Congress of Anaesthesiologists, 2008