The trial was stopped prematurely due to the COVID-19 pandemic

The present randomized crossover clinical trial aims to evaluate the influence of different body postures on pulmonary aeration among mechanically ventilated critically ill patients. Patients admitted to the intensive care unit receiving invasive mechanical ventilation >24 hours, and without contraindications to mobilization, will be randomly assigned to one of two sequences of interventions at a single day: arm 1: bedside sitting posture followed by orthostatic board at 45º and 60º; arm 2: orthostatic board at 45º, 60º and 80º followed by bedside sitting posture. Each postural protocol (bedside sitting posture protocol or orthostatic board posture protocol) will last 30 minutes. A washout window period between 1,5h and 2,5h will be applied between the two postural interventions. The primary outcome is the lung aeration assessed using the Lung Ultrasound Score (LUS) performed by trained evaluators at the end of postural protocol. Secondary outcomes include ventilatory mechanics (static compliance, airway resistance and respiratory work), PaO2/FiO2 ratio, Level of consciousness according to the Richmond Agitation-Sedation Scale (RASS), and adverse events (hypertension, hypotension, tachicardia, bradycardia, tachypnea, bradypnea, decreased level of consciousness, patient distress, fall to knees, invasive device traction or loss, filter hemodialysis clotting or disruption).

Inclusion Criteria: 18 years or older; Invasive Mechanical Ventilation > 24 hours; no weaning expectation on screening day for study eligibility; Signature of Informed Consent.

Exclusion Criteria:

• Patients using vasoative drugs (noradrenaline > 0.2mcg/kg/min or sodium nitroprosside > 1mcg/kg/min);
• Increase > 50% in noradrenaline dose in the last 2 hours; since exceeds 0,1 mcg / kg / min in that period;
• Inclusion of norepinephrine in the last 2 hours, with the dose > 0.1mcg/kg/min;
• Heart rate less than 40 beats per min or more than 130 beats per min
• Active myocardial ischaemia;
• Systolic blood pressure more than 200 mmHg,
• Mean arterial blood pressure less than 65 mm Hg or more than 110 mm Hg;
• Arrhythmia
• Intra-aortic balloon
• RASS <-4 ou > +1;
• Intracranial hypertension;
• Patient agitation
• External ventricular drain;
• Neurologic and/or orthopedic conditions that prevented orthostatism
• spinal cord injury) or
• Spinal cord injury and/or risk od instabilitity
• Acute stroke;
• orthopedic fractures in the lower limf
• Inability to walk with- out assistance before acute ICU illness (use of a cane or walkers its not exclusions;
• MRC > 3 MMII;
• Major pressure ulcers in the calcaneal region;
• FiO2 > 60%
• Positive end-epiratory pressure > 10cmH2O;
• Pulse oximetry less than 88%
• Respiratory rate less than 5 breaths per min or more than 40 breaths per min
• Neuromuscular blocking;
• Reserved Prognosis;
• Peritoneostomy;
• Temperature> 38.5 °C;
• Active gastrointestinal blood loss
• Intra-abdominal Hypertension;
• Thrombocytopenia (platelet count <50 000);
• Diarrhea;
• Hyperglycemia, with HGT < 70mg/g
• Intermittent haemodialysis
• Large abdominal surgery
• Continuous Epidural infusion

The evaluations took place in a single moment/day. Possible adverse events were evaluated from randomization to the last assessment of the outcome.

• First, just over 50% of the sample target was met; however, the early interruption of the study was necessary due to the health reality imposed by the COVID-19 pandemic.
• Second, due to the nature of the interventions, it is not possible to blind the assessments, which may have led to measurement bias and the Hawthorn effect.
• Third, in addition to the small sample, the study was limited to 2 hospitals, which may limit the external validity in other contexts.