On the crucial ventilatory setting adjustment from two- to one-lung ventilation

► Tidal volumes calculated on the basis of two healthy lungs are twice as great in their impact when delivered to a single lung. ► A tidal volume that would be appropriate to two-lung ventilation should be avoided when changing into one-lung ventilation. ► During one-lung ventilation with tidal volume appropriately calculated for such condition, the use of 5cm H2O PEEP could be useful to maintain arterial oxygenation without inducing a possible inflammatory/remodeling response. Lung mechanics, histology, oxygenation and type-III procollagen (PCIII) mRNA were studied aiming to evaluate the need to readjust ventilatory pattern when going from two- to one-lung ventilation (OLV). Wistar rats were assigned to three groups: the left lung was not ventilated while the right lung received: (1) tidal volume (VT)=5ml/kg and positive end-expiratory pressure (PEEP)=2cm H2O (V5P2), (2) VT=10ml/kg and PEEP=2cm H2O (V10P2), and (3) VT=5ml/kg and PEEP=5cm H2O (V5P5). At 1-h ventilation, V5P2 showed hypoxemia, alveolar collapse and impaired lung function. Higher PEEP minimized these changes and prevented hypoxemia. Although high VT prevented hypoxemia and maintained a higher specific compliance than V5P2, a morphologically inhomogeneous parenchyma and higher PCIII expression resulted. In conclusion, the association of low VT and an adequate PEEP level could be useful to maintain arterial oxygenation without inducing a possible inflammatory/remodeling response