Mechanical ventilation can cause damage to the lung parenchyma, this is known as ventilatory induce lung injury (VILI).To avoid this damage, ventilatory strategies have been created, focused on the reduction of tidal volume, airway pressures and use of PEEP (positive end-expiratory pressure), which together are called "protective ventilation".

Although ventilation with protective parameters seems to reduce VILI in one-lung ventilation, the optimal parameters are not clear.

This research aims to describe the ventilation, perfusion and pulmonary mechanics on one-lung ventilation with different levels of tidal volume and PEEP.

An extreme situation of VILI occurs in thoracic surgery, where the atelectasis of a lung is required, ventilating throughout the surgery only the contralateral one. This generates an inflammatory state, with the release of alveolar cytokines from both the non-ventilated and ventilated lungs, which potentiates the development of damage in the lung parenchyma. In addition, one lung ventilation has traditionally been performed with high tidal volume (Vt) values and low PEEP. In this context, the development of VILI is even more probable, so extreme measures of protection in this kind of ventilation are necessary.

The electrical impedance tomography will allow the investigators to obtain a visual and quantitative representation of the areas of ventilation and perfusion of the lung. By relating the tidal volume and PEEP with the tomographic results, it is expected to define mechanical ventilation parameters that achieve the best ventilation/perfusion ratio for patients in one-lung ventilation. Specifically, analyze the distribution and deformation of the ventilated areas in the different lung regions and its correlation with respiratory mechanics and volumetric capnography. This will allow the investigators to make a better definition of the tidal volume and PEEP in patients undergoing one-lung ventilation.

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Inclusion Criteria:

• ASA (American Society of Anesthesiologists) classification I-III
• Age 18-75 Years
• Elective thoracic surgery
• One-Lung Ventilation
• Healthy non ventilated lung

Exclusion Criteria:

• ASA classification > III
• BMI (Body mass index) > 30
• Emergency surgery
• Pregnancy
• Patients includes in other protocols

Adult patients between 18 and 75 years old. With pulmonary diseases that require thoracic surgery with one-lung ventilation.