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Byline: Raffaele L. Dellaca (1), Marie Andersson Olerud (2), Emanuela Zannin (1), Peter Kostic (2), Pasquale P. Pompilio (1), Goran Hedenstierna (3), Antonio Pedotti (1), Peter Frykholm (2) Keywords: Forced oscillation technique; ALI/ARDS; Mechanical ventilation; PEEP; Respiratory mechanics Abstract: Purpose ALI and ARDS are associated with lung volume derecruitment, usually counteracted by PEEP and recruitment maneuvers (RM), which should be accurately tailored to the patient's needs. The aim of this study was to investigate the possibility of monitoring the amount of derecruited lung by the forced oscillation technique (FOT). Methods We studied six piglets (26 +- 2.5 kg) ventilated by a mechanical ventilator connected to a FOT device that produced sinusoidal pressure forcing at 5 Hz. The percentage of non-aerated lung tissue (V tiss.sub.NA%) was measured by whole-body CT scans at end-expiration with zero end-expiratory pressure. Respiratory system oscillatory input reactance (X .sub.rs) was measured simultaneously to CT and used to derive oscillatory compliance (C .sub.X5), which we used as an index of recruited lung. Measurements were performed at baseline and after several interventions in the following sequence: mono-lateral reabsorption atelectasis, RM, bi-lateral derecruitment induced by broncho-alveolar lavage and a second RM. Results By pooling data from all experimental conditions and all pigs, C .sub.X5 was linearly correlated to V tiss.sub.NA% (r .sup.2 = 0.89) regardless of the procedure used to de-recruit the lung (reabsorption atelectasis or pulmonary lavage). Separate correlation analysis on single pigs showed similar regression equations, with an even higher coefficient of determination (r .sup.2 = 0.91 +- 0.07). Conclusion These results suggest that FOT and the measurement of C .sub.X5 could be a useful tool for the non-invasive measurement of lung volume recruitment/derecruitment. Author Affiliation: (1) Dipartimento di Bioingegneria, Politecnico di Milano University, Piazza Leonardo da Vinci 32, 20133, Milan, Italy (2) Department of Surgical Sciences, Anaesthesia and Intensive Care, Uppsala University, Uppsala, Sweden (3) Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden Article History: Registration Date: 10/09/2009 Received Date: 19/01/2009 Accepted Date: 02/09/2009 Online Date: 30/09/2009 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1673-3) contains supplementary material, which is available to authorized users.