• Thomas Luecke, Harry Roth, Peter Herrmann, Alf Joachim, Gerald Weisser, Paolo Pelosi, and Michael Quintel.
• Department of Anesthesiology and Critical Care Medicine, Faculty of Clinical Medicine, University Hospital, Theodor-Kutzer-Ufer, 68167, Mannheim, Germany. thomas.Luecke@anaes.ma.uni-heidelberg.de
• Intensive Care Med. 2003 Nov 1;29(11):2026-33.

ObjectiveTo examine the effects of positive end-expiratory pressure (PEEP) on extravascular lung water (EVLW), lung tissue, and lung volume.Design And SettingExperimental animal study at a university research facility.SubjectsFifteen adult sheep.InterventionsAll animals were studied before and after saline washout-induced lung injury while ventilated with sequentially increasing PEEP (0, 7, 14, or 21 cmH(2)O).Measurements And ResultsLung volume was determined by computed tomography and EVLW by the thermal dye dilution technique. Saline washout significantly increased lung tissue volume (21+/-3 to 37+/-5 ml/kg) and EVLW (9+/-2 to 36+/-9 ml/kg). While increasing levels of PEEP reduced EVLW (30+/-7, 24+/-8, and 18+/-4 ml/kg), lung tissue volume remained constant. Total lung volume significantly increased (50+/-8 ml/kg at PEEP 0 to 77+/-12 ml/kg at PEEP 21). Nonaerated lung volume significantly decreased and was closely correlated with the changes in EVLW ( r=0.67). In addition, a highly significant correlation was found between PEEP-induced decrease in nonaerated lung volume and decrease in transpulmonary shunt ( r=0.83).ConclusionsThe main findings are as follows: (a) PEEP effectively decreases EVLW. (b) The decrease in EVLW is closely correlated with the PEEP-induced decrease in nonaerated lung volume, making EVLW a valuable bedside parameter indicating alveolar recruitment, similar to measurements of transpulmonary shunt. (c) As excess tissue volume remained constant, however, EVLW may not be suitable to reflect overall severity of lung disease

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