PEEP Levels Selected by PEEP Titration and PEEP Levels Routinely Used in Post-operative Cardiac Patients With Hypoxemic Respiratory Failure

The purpose of this study is to:

* Compare PEEP level selected by individualized PEEP titration by electrical impedance tomography and PEEP level routinely used in post-operative cardiac patients with Hypoxemic Respiratory Failure;
* Evaluate the agreement between the results of a rapid titration (total procedure duration = 5 min) versus an already validated slow titration (total procedure duration = 40 min) of the same patient, sequentially. Specifically, degree of collapse and degree of distention in each PEEP level, estimated by EIT;
* Compare hemodynamics during the two maneuvers of PEEP titration;
* Evaluate the efficacy of the selected PEEP (minimum PEEP preventing lung collapse less than 5%) to maintain stable levels of the following variables: arterial oxygenation, respiratory system compliance, and degree of collapse by EIT;
* Compare these results (evolution of the three variables, along 4 hours) with the control strategy (default strategy currently used in the institution) group.

The acute respiratory distress syndrome (ARDS) increases the morbidity and mortality of patients admitted to the intensive care unit (ICU). In the postoperative period of cardiac surgery, the use of intraoperative extracorporeal circulation is one of the factors triggering the syndrome, its incidence increasing.

Potentially, a protective ventilatory strategy with optimal positive end expiratory pressure (PEEP) could improve the prognosis of those patients with ARDS.

An already validated maneuver to titrate the ideal PEEP to these patients has a longer duration, about 40 minutes. The lung Electrical impedance tomography (EIT) monitors respiratory system mechanics and intrathoracic lung volume changes and provides information about regional behavior and recruitability of lung tissue and thereby allows shortening titration maneuver, reducing its hemodynamic effects.

Patients in the postoperative period of cardiac surgery with a diagnosis of Hypoxemic Respiratory Failure (PaO2/FiO2 \< 250 mmHg, calculated at FiO2 60%, and the presence of bilateral infiltrates on chest radiography), admitted to the surgical ICU from Heart Institute, University of São Paulo.

Recruitment maneuver and PEEP titration maneuver will be monitored by EIT.

All patients will be followed and monitored for 4 hours, with measures of the evolution of alveolar collapse . Hemodynamic and oxygenation data will also be recorded .

Eligibility Criteria:
Inclusion Criteria:

* Immediate postoperative period of myocardial revascularization and/or heart valve surgery (aortic and/or mitral)
* Acute respiratory distress syndrome with ratio of partial pressure of arterial oxygen over fraction of inspired oxygen (PaO2:FiO2) no \>200 mmHg and bilateral pulmonary infiltrates on XRay consistent with edema, and no clinical evidence of left atrial hypertension (pulmonary capillary wedge pressure \<18 mmHg, when available).
* Age \> 18 and \< 70 years old
* Absence previous pulmonary disease
* Left ventricular ejection fraction \> 35%
* Absence of previous cardiac surgery and / or lung disease;
* Not requiring adjusted volume expansion (pulse pressure delta \<13% or legs raising test without hemodynamic changes in cardiac index or mean arterial pressure).
* Body mass index \< 40 kg/m2
* Written inform consent

Exclusion Criteria:

* MAP \< 70 mmHg
* Noradrenaline \> 1 micrograms/Kg/min
* Acute arrhythmias
* Blooding associated to hemodynamic instability
* Need of re-surgery and/or mechanical circulatory assistance
* Suspicion of neurological alteration
* Chest tube with persistent air leak