title: Arteriovenous Extracorporeal Lung Assist Allows For Maximization Of Oscillatory Frequencies: A Large-animal Model Of Respiratory Distress.
abstract: BACKGROUND
  Although the minimization of the applied tidal volume (VT) during high-frequency oscillatory ventilation (HFOV) reduces the risk of alveolar shear stress, it can also result in insufficient CO₂-elimination with severe respiratory acidosis. We hypothesized that in a model of acute respiratory distress (ARDS) the application of high oscillatory frequencies requires the combination of HFOV with arteriovenous extracorporeal lung assist (av-ECLA) in order to maintain or reestablish normocapnia.
  
  
  METHODS
  After induction of ARDS in eight female pigs (56.5 ± 4.4 kg), a recruitment manoeuvre was performed and intratracheal mean airway pressure (mPaw) was adjusted 3 cmH₂O above the lower inflection point (Plow) of the pressure-volume curve. All animals were ventilated with oscillatory frequencies ranging from 3-15 Hz. The pressure amplitude was fixed at 60 cmH₂O. At each frequency gas exchange and hemodynamic measurements were obtained with a clamped and de-clamped av-ECLA. Whenever the av-ECLA was de-clamped, the oxygen sweep gas flow through the membrane lung was adjusted aiming at normocapnia.
  
  
  RESULTS
  Lung recruitment and adjustment of the mPaw above Plow resulted in a significant improvement of oxygenation (p < 0.05). Compared to lung injury, oxygenation remained significantly improved with rising frequencies (p < 0.05). Normocapnia during HFOV was only maintained with the addition of av-ECLA during frequencies of 9 Hz and above.
  
  
  CONCLUSIONS
  In this animal model of ARDS, maximization of oscillatory frequencies with subsequent minimization of VT leads to hypercapnia that can only be reversed by adding av-ECLA. When combined with a recruitment strategy, these high frequencies do not impair oxygenation.
authors.affiliation: University of Wuerzburg, Department of Anaesthesiology; University hospital Wuerzburg; Oberduerrbacherstr, 6; 97080 Wuerzburg, Germany. muellenbac_r@klinik.uni-wuerzburg.de.
authors.forename: Ralf M
authors.initials: RM
authors.lastname: Muellenbach
authors.forename: Julian
authors.initials: J
authors.lastname: Kuestermann
authors.forename: Markus
authors.initials: M
authors.lastname: Kredel
authors.forename: Amélie
authors.initials: A
authors.lastname: Johannes
authors.forename: Ulrike
authors.initials: U
authors.lastname: Wolfsteiner
authors.forename: Frank
authors.initials: F
authors.lastname: Schuster
authors.forename: Christian
authors.initials: C
authors.lastname: Wunder
authors.forename: Peter
authors.initials: P
authors.lastname: Kranke
authors.forename: Norbert
authors.initials: N
authors.lastname: Roewer
authors.forename: Jörg
authors.initials: J
authors.lastname: Brederlau