• M van Heerde, K Roubik, V Kopelent, M C J Kneyber, and D G Markhorst.
• Department of Pediatric Intensive Care, VU University Medical Center, Amsterdam, The Netherlands. m.vanheerde@vumc.nl
• Acta Anaesthesiol Scand. 2010 Nov 1;54(10):1248-56.

BackgroundMaintenance of spontaneous breathing is advocated in mechanical ventilation. This study evaluates the effect of spontaneous breathing on regional lung characteristics during high-frequency oscillatory (HFO) ventilation in an animal model of mild lung injury.MethodsLung injury was induced by lavage with normal saline in eight pigs (weight range 47-64 kg). HFO ventilation was applied, in runs of 30 min on paralyzed animals or on spontaneous breathing animals with a continuous fresh gas flow (CF) or a custom-made demand flow (DF) system. Electrical impedance tomography (EIT) was used to assess lung aeration and ventilation and the occurrence of hyperinflation.ResultsEnd expiratory lung volume (EELV) decreased in all different HFO modalities. HFO, with spontaneous breathing maintained, showed preservation in lung volume in the dependent lung regions compared with paralyzed conditions. Comparing DF with paralyzed conditions, the center of ventilation was located at 50% and 51% (median, left and right lung) from anterior to posterior and at 45% and 46% respectively, P<0.05. Polynomial coefficients using a continuous flow were -0.02 (range -0.35 to 0.32) and -0.01 (-0.17 to 0.23) for CF and DF, respectively, P=0.01.ConclusionsThis animal study demonstrates that spontaneous breathing during HFO ventilation preserves lung volume, and when combined with DF, improves ventilation of the dependent lung areas. No significant hyperinflation occurred on account of spontaneous breathing. These results underline the importance of maintaining spontaneous breathing during HFO ventilation and support efforts to optimize HFO ventilators to facilitate patients' spontaneous breathing.© 2010 The Authors. Journal compilation © 2010 The Acta Anaesthesiologica Scandinavica Foundation.

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