The aim of this project is to evaluate the effects of positional changes in mechanically ventilated patients.

In critically ill patients undergoing invasive mechanical ventilation (IMV), several negative effects converge, promoting the development of collapse in the dorsal areas of the lung. These among others include deep sedation, relaxation, prolonged immobility and the supine position. This results of an added impairment in lung function both in the mechanical and gas exchange. In addition lung collapse contributes to a significant increase in the heterogeneity the distribution of alveolar ventilation and perfusion that may increase the risk of ventilator-induced lung injury (VILI).

Postural therapy is widely recommended as prevention/treatment of pressure ulcers, whose presence, according to the Spanish Society of Intensive Care Medicine (SEMICYUC), is a quality criterion for intensive care units (ICUs), with a prevalence of 18% in these units compared to 7.8% in adult hospitalization. However, how postural changes may affect lung function is an aspect that has been scarcely studied. Given the strong influence of gravity on lung function, positional changes can produce significant alterations in the distribution of trans-pulmonary pressures (a decrease along the vertical gravitational axis of approximately 0.25 cmH2O per cm). Depending on the severity, distribution and location of the respiratory pathology, positional changes may have a significant effect either benefiting or impairing the patient's condition.

The investigators will dynamically assess the effects of routine lateral positioning up to 30-40º by means of electrical impedance tomography (EIT), a non-invasive, radiation-free functional bedside imaging technique that allows to monitor the regional distribution of ventilation and perfusion.

Inclusion Criteria:

• Patients undergoing IMV under sedation, in a controlled ventilatory modality in passive conditions (i.e. without any spontaneous inspiratory efforts by the patient).
• Signature of the informed consent by family member or legal representative.

Exclusion Criteria:

• Presence of any clinical contraindication for postural therapy, including patient haemodynamic instability, traumatism, pathology or any other cause.
• Contraindication for the placement of the EIT electrode belt due to unstable spinal cord injury or other skin injuries or wounds in the thoracic region (surgical, traumatic, etc.)
• Assisted ventilatory modes in a non-passive breathing patient.
• Hypernatremia
• Patients with pacemakers or implantable automatic defibrillators (IAD).

Critically ill patients admitted in the ICU of La Princesa University Hospital, Madrid, Spain.