Research article

Arteriovenous extracorporeal lung assist allows for maximization of oscillatory frequencies: a large-animal model of respiratory distress

Ralf M Muellenbach , Julian Kuestermann , Markus Kredel , Amélie Johannes , Ulrike Wolfsteiner , Frank Schuster , Christian Wunder , Peter Kranke , Norbert Roewer and Jörg Brederlau

University of Wuerzburg, Department of Anaesthesiology; University hospital Wuerzburg; Oberduerrbacherstr. 6; 97080 Wuerzburg, Germany

author email corresponding author email

BMC Anesthesiology 2008, 8:7doi:10.1186/1471-2253-8-7

Published:	14 November 2008

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.

Conclusion

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