Combining "open-lung" ventilation and arteriovenous extracorporeal lung assist: influence of different tidal volumes on gas exchange in experimental lung failure.
BACKGROUND
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.


METHODS
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.
Muellenbach
Ralf M
RM
Department of Anesthesia and Critical Care, University of Wuerzburg, Wuerzburg, Germany. muellenbac_r@klinik.uni-wuerzburg.de
Kredel
Markus
M
Kuestermann
Julian
J
Klingelhoefer
Michael
M
Schuster
Frank
F
Wunder
Christian
C
Kranke
Peter
P
Roewer
Norbert
N
Brederlau
Jörg
J
D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D006439:Hemodynamics; D008171:Lung Diseases / Q000139:chemically induced* / Q000503:physiopathology*; D010100:Oxygen / Q000378:metabolism; D010313:Partial Pressure; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D012121:Respiration, Artificial / Q000379:methods*; D013552:Swine; D013990:Tidal Volume / Q000502:physiology*; D013997:Time Factors
D002245:Carbon Dioxide; D010100:Oxygen