The mortality of patients with acute respiratory distress syndrome (ARDS) remains high despite recent advances in lung-protective strategies and even after the overall improvement in intensive care (management of sepsis, hemodynamics, organ failure, and control of nosocomial infections). The use of mechanical ventilation (MV) plays a fundamental therapeutic role in this scenario. It allows for respiratory muscle rest, maintenance of oxygen transport to tissues, elimination of CO2 production, and finally, lung rest and protection in patients with excessive ventilatory demand.

On the other hand, recent studies have also shown that MV can cause iatrogenic injury and inflammation in the lung parenchyma, imposing a significant mechanical energy load and dissipation in the lung parenchyma (mechanotransduction). This effect is more pronounced in patients with low lung compliance or in those receiving inadvertently high tidal volumes, resulting in high distending pressure. Thus, despite being life-saving in the short term, MV may perpetuate or exacerbate pre-existing lung injury.

Various strategies have been proposed to aid in the ventilatory management of patients with ARDS. Among them, the use of higher PEEP values and the prone position have proven beneficial, especially when resulting in the stabilization of diseased alveoli or even promoting the recruitment of new alveolar units, associated with improved gas exchange. Both maneuvers, however, involve considerable risks: PEEP often causes impairments to venous return, and the prone position presents technical/logistical limitations for its widespread use, or even severe adverse effects during its implementation (ocular injury, accidental extubation, arrhythmias, catheter disconnection, etc.).

The hypothesis of this study is that automated lateral decubitus positioning (performed by a rotational bed with proper patient support), guided by monitoring through Electrical Impedance Tomography (EIT), could replace or minimize the need for prone positioning or the need for higher PEEPs in critical patients, resulting in effective alveolar recruitment and improvements in gas exchange, compliance, and lung aeration without affecting the hemodynamic condition.

The objective will be to estimate the efficacy and validate the feasibility of this alveolar recruitment protocol through the automated rotation of the patient, without the need for high airway pressures.Also the aim to demonstrate that this protocol is safe, with fewer repercussions on the hemodynamics of critically ill patients. To achieve this, a prospective, randomized study were conduct in two populations of critically ill patients: Sample-1) patients in the postoperative period of cardiac surgery, with a PF ratio of less than 250 (N=50 patients) admitted to the post-anesthesia care unit of Incor for extubation, and Sample-2) patients with ARDS or acute hypoxemic respiratory failure, with a PF ratio of less than 250, requiring mechanical ventilation (N=30 additional patients), and necessarily presenting an asymmetric (>65%/35%) distribution of ventilation on the functional map of Electrical Impedance Tomography (EIT) while in the supine position. A stratified randomization (1:1) within each of these samples of 30 patients will be done by computer.

For Sample 1 - the control group will undergo an ARDSNet-type ventilatory strategy, with PEEP adjustment according to BMI, based on previous studies that evaluated PEEP titrated by EIT in relation to BMI; and for Sample 2 - the ARDSNet-type ventilatory strategy, with PEEP adjustment according to the "low PEEP/FIO2" oxygenation table. All patients will remain on mechanical ventilation for at least 4 hours and will be monitored with EIT throughout the study. In postoperative patients, the rotation of the treatment group will follow the sequence "supine - lateral - supine - lateral - supine," with 10 minutes in each supine position and 20 minutes in each lateral position, and the first rotated side is defined as the lung with less ventilation being placed in a non-dependent position with a maximum PEEP of 24 cmH2O. In patients with asymmetric injury (acute hypoxemic respiratory failure), the lateralization sequence will be "supine-lateral with the better lung dependent-supine," meaning that the rotation will be unilateral, with 20-minute lateral position times alternated with another 10 minutes in the supine position. Recruitment maneuvers routinely used by the institution may be used as a rescue for any patient and will be mandatory at the end of the 4-hour study period in all postoperative patients (Sample 1, both treatment arms). The maneuvers will be performed with controlled pressure ventilation, a maximum PEEP of 30 cmH2O, with maximum inspiratory pressures of 50 cmH2O, for a maximum time of 30 seconds. These maneuvers will not be applied to patients with asymmetric injury (Sample 2, acute hypoxemic respiratory failure).

The main variables for comparison between the arms of each population sample will be: a) lung collapse and hyperdistension, b) shunt and PF ratio, c) ventilatory ratio (as a "surrogate" for dead space), d) global lung mechanics, e) regional mechanics by EIT, and f) continuous measurements of cardiac output (Volume-View, Baxter), frequency, and mean arterial pressure. These variables will be collected during the baseline period and after the recruitment maneuver for Sample 1, and after 24 hours of intervention for Sample 2.

The main hypothesis is that rotational therapy can increase regional transpulmonary pressure (in the non-dependent region after rotation), resulting in effective alveolar recruitment, evidenced by an improvement in PF ratio, global compliance, and regional compliance after returning to the supine position in both patient populations. In the case of patients with asymmetric lung injury (Sample 2), a effect is expecting within the following 24 hours compared to the control therapy. In the case of patients with symmetric injury, these effects can also be compared with the effects obtained by the more aggressive and traditional recruitment maneuver to be performed at the end of the observation period. As a secondary hypothesis, it was to intend to demonstrate that the therapy will cause minimal hemodynamic impairment compared to the control arm, and also less hemodynamic impairment when compared to the traditional recruitment maneuver at the end of the study (for postoperative patients).

Inclusion Criteria:

Sample 1-

• Patients under mechanical ventilation
• Immediate postoperative period of open-heart valve surgery and myocardial revascularization
• PaO2/FiO2 ratio ≤ 250 mmHg (calculated from values obtained in arterial blood gas analysis)
• Values collected with:

FiO2 ≥ 0.6 PEEP ≥ 8 cmH2O

Sample 2 -

• Patients under controlled/assisted mechanical ventilation, not yet eligible for weaning
• PaO2/FiO2 ratio < 250 mmHg (calculated using arterial blood gas values)
• Values collected with:

FiO2 = 0.6 PEEP > 5 cmH2O

• Acute condition onset less than 2 weeks ago
• Mechanical ventilation duration of less than 1 week
• Asymmetric ventilation distribution (65%/35%) on the functional map from Electrical Impedance Tomography (EIT) in the supine position

Both Samples:

Exclusion Criteria:

• Need for norepinephrine ≥ 1 mcg/kg/min or mean arterial pressure ≤ 65 mmHg;
• Cardiac arrhythmias or bleeding leading to hemodynamic instability;
• Need for surgical revision and/or mechanical circulatory assistance;
• Contraindication to hypercapnia, such as intracranial hypertension or acute coronary syndrome;
• Neurological diseases or symptoms, such as a history of seizures;
• Dependence on a cardiac pacemaker;
• Air leakage through chest drains, undrained pneumothorax, or subcutaneous emphysema;
• Previous lung disease or surgery, or use of home oxygen therapy;
• Comorbidities with a life expectancy &lt; 6 months;
• Pulmonary artery systolic pressure &gt; 45 mmHg;
• Myocardial revascularization using the mammary artery;
• Medical refusal for the patient&#39;s participation in the study.