Combining "open-lung" ventilation and arteriovenous extracorporeal lung assist: influence of different tidal volumes on gas exchange in experimental lung failure
Ralf M Muellenbach, Markus Kredel, Julian Kuestermann, Michael Klingelhoefer, Frank Schuster, Christian Wunder, Peter Kranke, Norbert Roewer, Joerg Brederlau
Med Sci Monit 2009; 15(8): BR213-220
Although low-tidal ventilation may reduce mortality in acute respiratory distress syndrome (ARDS), it can also result in severe respiratory acidosis and lung derecruitment. This study tested the hypothesis that combining "open-lung" ventilation and arteriovenous extracorporeal lung assist (av-ECLA) allows for maximal tidal volume (VT) reduction without the development of decompensated respiratory acidosis and impairment of oxygenation.
Material and Method: After induction of ARDS in eight female pigs (56.1+/-3.2 kg), lung recruitment was performed and positive end-expiratory pressure was set 3 cmH2O above the lower inflection point of the pressure-volume curve. All animals were ventilated in the pressure-controlled ventilation mode (PCV) with VTs ranging from 0-8 ml/kg. At each VT, gas exchange and hemodynamic measurements were obtained with the av-ECLA circuit clamped and declamped. With each declamping, the gas flow through the membrane lung was set to 10 l of oxygen/min. The respiratory rate was adjusted to maintain normocapnia, but limited to 40/min.
Results: After lung recruitment, oxygenation remained significantly improved although VTs were minimized to 0 ml/kg (p<0.05). PaO2 was significantly improved during PCV and av-ECLA compared with PCV alone at VTs <4 ml/kg (p<0.05). With VT <6 ml/kg, severe acidosis could only be avoided if PCV was combined with av-ECLA.
Conclusions: Due to sufficient CO2 elimination during av-ECLA, the VTs could be reduced to 0-2 ml/kg without the risk of decompensated respiratory acidosis. It was also shown that the "open-lung" strategy chosen was associated with sustained improvements in oxygenation, even though VTs were minimized.
Keywords: Swine, Tidal Volume - physiology, Respiration, Artificial - methods, Pulmonary Ventilation - physiology, Pulmonary Gas Exchange - physiology, Partial Pressure, Oxygen - metabolism, Lung Diseases - physiopathology, Hemodynamics, Carbon Dioxide - metabolism, Animals, Time Factors