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

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 CO(2)-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 cmH(2)O 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 cmH(2)O. 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